week 4 molecular biology and genetics

7/29/2019 Week 4 Molecular Biology and Genetics

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Week 4

SYCPA Regents Prep - LivingEnvironment

Molecular Biology & Genetics


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Week 4 Molecular Biology & Genetics

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This packet provides a review of concepts that may be tested in the NYS Living

Environment Regents and is based on the NYS Core Curriculum. This course will cover individual

topics over 6 weeks as listed below:

Week 1 - Scientific Method

Week 2 - EcologyWeek 3 - Human Body SystemsWeek 4 Molecular Biology & Genetics

Week 5 - LabsWeek 6 - Evolution & Human Impact

The order of these topics is chosen based on their average weight in past Living

Environment Regents.

The individual packets will consist of a review for the specific topic followed by past

regents questions.

Good Luck!

SYCPA Say Yes Collegiate Prep Academy


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Molecular Biology Review

Cell Basics

Vocabulary: axon, ATP, cell, cell membrane, cell theory, cell wall, chloroplast, circulation, contractile

vacuole, coordination, cyton, digestion, dendrite, DNA, dynamic equilibrium, endoplasmic reticulum,enzymes, eukaryotic, excretion, food vacuole, homeostasis, hormones, immunity, life processes,locomotion, mitochondrion, movement, nucleus, neurotransmitter, organ system, organs,organelles, progesterone, prokaryotic, receptor molecules, reproduction, respiration, ribosome,synthesis, system, target cell, target organs, terminal branches, tissue

Living VS. Non-LivingComplex organisms, such as humans, require many systems for their life processes. Lesscomplex living things may lack the complex systems of more complex organisms, but theystill carry on the basic life activities. While non-living things may carry on some of these lifeprocesses, they do not carry on all of them, or these activities do not interact in a manner

allowing the non-living thing to reproduce itself.

Living things carry out almost all the life processes or activities. These life processesinclude digestion, respiration, circulation, excretion, locomotion, immunity, coordination,and synthesis. Non-living things are incapable of carrying out at least one or more of thelife processes. The sum of the energy used in all the life processes representsthe metabolism of the organism.

HomeostasisThe ability to carry on the life processes allow a living thing to maintain dynamicequilibrium orhomeostasis with their surroundings. Homeostasis is a state of balance or

steady state between a living thing and its environment. Homeostasis in an organism isconstantly threatened. Failure to respond effectively to a failure of homeostasis can resultin disease or death.

The components of living things in humans and other organisms, from organ systems tocell organelles, interact to maintain a balanced internal environment. This balanced internalenvironment is called dynamic equilibrium orhomeostasis. To successfully accomplish this,organisms possess many control mechanisms that detect internal changes and correctthem to restore the internal balance of the organism. If an organism fails to maintainhomeostasis, this may result in disease or death. Non-living things possess few controlmechanisms to maintain homeostasis.

Organizational LevelsImportant levels of organization for structure and function of living things include cells,tissues, organs, organ systems, and whole organisms. The organs and systems of the bodyhelp to provide all the cells with their basic needs to carry on the life functions. The cells ofthe body are of different kinds and are grouped in ways that help their function.

All living things are composed of one or more cells, each capable of carrying out the lifefunctions. The organelles present in single-celled organisms often act in the same manner


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as the tissues and systems found in many celled organisms. Single-celled organismsperform all of the life processes needed to maintain homeostasis, by using specializedcell organelles.

Living things have different levels of organization. The simplest level of organization is that

of the cell. A group of cells with a similar function is called a tissue. Groups of tissuesworking together to perform a common function are called organs. An example of thiswould include the nervous, muscle, and other tissues which make up the heart. Groups oforgans working together to perform a common function are referred to asa system ororgan system. The blood vessels, blood, and the heart are organs which worktogether to form the circulatory system. Many different systems function together toallow a complex organism to function.

Cell StructureCells have particular structures ororganelles that perform specific jobs. These structuresperform the life activities within the cell. Just as body systems are coordinated and worktogether in complex organisms, the cells making up those systems must also becoordinated and organized in a cooperative manner so they can function efficientlytogether.

Inside the cell a variety of cell organelles, formed from many different molecules, carry outthe transport of materials, energy capture and release, protein building, waste disposal,and information storage. Each cell is covered by a membrane that performs a number ofimportant functions for the cell as well.

Cell TheoryAll organisms contain one or more cells which are capable of carrying on the life activitiesneeded by the organism. This idea is often referred to as the cell theory.

Parts of the Cell Theory

The cell is the unit of structure in all living things. The cell is the unit of function in all living things. All cells come from preexisting cells.

A few exceptions to this theory exist. Viruses lack typical cellular structure. There also issome question as to how the the first cell arose. In general, the cell theory holds true formost living things, however.

Cell TypesThere are two distinct types of cells. Prokaryotic cells lack a nucleus and other organelles.Two domains of organisms have this type of cell - Archaebacteria and Eubacteria, thesimplist of all organisms. They still perform life functions but all activities must beaccomplished in the cytoplasm. Eukarotic cells are found in organisms from the domainEukarya, which includes all protists (Ameoba and Paramecium are examples), Fungi (yeastand mushrooms are examples), Plants (mosses, ferns, gymnosperm pines and angiosperm


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flowering plants are examples), and Animals (humans are examples).

Cell Organelles

Cells have particular structures that perform specific jobs. These cell structures arecalled organelles and perform the actual work of the cell. These organelles are formedfrom many different molecules. Some functions carried out by organelles include thetransport of materials, energy capture and release, protein building, waste disposal, andinformation storage. Single celled organisms also have organelles similar to those in moreadvanced organisms to complete their life processes. Many enzymes are needed for thechemical reactions involved in cellular life processes to occur.

A Typical Animal Cell

Some Cell Organelles


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Cell Organelle Function

nucleus

control center of the cell

contains DNA which directs the synthesis of

proteins by the cell

mitochondrioncarries on the process of cell respiration convertingglucose to ATP energy the cell can use

endoplasmic reticulum transport channels within the cell

ribosome

found on the endoplasmic reticulum and free withinthe cell

responsible for the synthesis of proteins for the cell

cell membraneselectively regulates the materials moving to andfrom the cell

food vacuole stores and digests food

contractile vacuole

found in many single celled aquatic organisms

pumps out wastes and excess water from the cell

chloroplastfound in plant cells and algae

carries on the process of photosynthesis

cell wall surrounds and supports plant cells

Life FunctionsHumans and many other organisms require multiple systems fordigestion, respiration,reproduction, circulation, excretion, movement, coordination, and immunity. The systemscollectively perform thelife processes.

Once nutrients enter a cell, the cell will use those raw materials for energy or as buildingblocks in the synthesis of compounds necessary for life. The energy we initially obtainmust must be changed into a form cells can use. A type of protein called an enzyme allowsfor these changes to occur within the cell.

Humans and other complex organisms require many different organ systems to carry on

the activities required for life. These life activities or processes include digestion,respiration, reproduction, circulation, excretion, movement, coordination, and immunity.

Life Processes

Digestionbreakdown of food to simpler molecules which can enterthe cells


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Circulation the movement of materials within an organism or its cells

Movement (locomotion) change in position by a living thing

Excretion

removal of cellular waste products by an organism(wastes may include carbon dioxide, water, salt, and ureaand are released during exhalation, perspiration, andurine formation.)

Respirationprocess which converts the energy in food toATP (theform of energy which can be used by the cells)

Reproductionthe making of more organisms of one's own kind -- notneeded by an individual living thing but is needed by itsspecies

Immunitythe ability of an organism to resist disease causingorganisms (pathogens) and foreign invaders

Coordinationthe control of the various activities of an organism(mostly involves the nervous system and endocrine glandsin complex animals)

Synthesisthe production of more complex substances by combiningtwo or more simpler substances

It is important to realize that cell organelles are involved in many of these life processes, aswell as the organ systems of complex organisms.

Cellular CommunicationNeurotransmitters and hormones allow communication between nerve cells and otherbody cells as well. If nerve or hormone signals are changed, this disrupts communicationbetween cells and will adversely effect organism homeostasis. Additionally,the DNA molecule contains the instructions that direct the cells behavior through thesynthesis of proteins.

Cell Membrane Receptors

Cell Membrane Receptors


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Many cell membraneshavereceptormolecules on theirsurface. Thesereceptor sites play animportant role inallowing cells andorgans tocommunicate withone another.

Hormonal RegulationHormones provide a primary way for cells to communicate with each other. A hormone is achemical messenger with a specific shape that travels through the bloodstream influencinganothertarget cell ortarget organ. Upon reaching the cell the hormone is targeted for, the

hormone often activates a gene within a cell to make another necessary compound. Oneexample of this is provided by the pituitary gland. This gland at the base of the brain makesa hormone called LH (luteinizing hormone). This hormone travels through the bloodstreamand stimulates the ovary to produce yellow tissue that produces thehormone progesterone, which maintains the thickness of the uterus lining. The graphicbelow illustrates how this kind of hormonal regulation can work in a plant cell. Animal cellhormonal regulation involves a similar mechanism.

A Hormonal Feedback Mechanism

The diagram at theright illustrates how ahormone can bind toreceptors on a cellmembrane andtrigger that cell toproduce a neededcompound.

Nervous Regulation

Nerve cells or neurons also allow cells to communicate with each other. Neuroncommunications are one way organism can detect and respond to stimuli at both thecellular and organism level. This detection and response to stimuli helps to maintainhomeostasis in the cell or organism. Neurons may stimulate other nerve cells or musclecells, thus causing the later to contract and produce movement.

Structure and Function of a (Neuron) Nerve Cell


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Structures and their Functions

1. dendrite -- neuron branch which detects stimuli (changes in theenvironment)

2. cyton -- cell body of the neuron where normal metabolic activitiesoccur

3. axon -- longest dendrite covered by a myelin sheath whichprovides electrical insulation -- carries nerve message or impulse tothe terminal branches

4. terminal branches -- release nerve chemicalscalledneurotransmitters which stimulate adjacent dendrites on thenext neuron or a muscle cell

Any change in nerve or hormone signals will change the communication between cells andorgans in an organism and thus may cause problems for organisms stability and ability to

maintain homeostasis.

Cell Transport

Cell MembraneThe cell membrane or plasma membrane performs a number of important functions for the cell.These functions include the separation of the cell from its outside environment, controlling whichmolecules enter and leave the cell, and recognition of chemical signals. The cell membrane consistsof two layers of phospholipids with proteins embedded within these layers. The surface of the cell

contains molecules which recognize other molecules which may attach to or enter the cell.

Cell Membrane Structure


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Membrane ProcessesThe processes of diffusion and active transport are important in the movement of materials in andout of cells.

Diffusion

Diffusion orpassive transport isthe movement of materials from aregion of higher to a region oflower substanceconcentration. The diagram at theright shows the movement ofmolecules from higherconcentration on side A to a lowerconcentration on side B.

Active Transport

In active transport, molecules move from a regionof lower concentration to a region of higherconcentration. As this process does not naturallyoccur, the cell has to use energy in the form ofATP to make active transport occur.

Cell ChemistryMany organic and inorganic substances dissolved in cells allow necessary chemical reactions to take


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place in order to maintain life. Large organic food molecules such as proteins and starches mustinitially be broken down through the life process of digestion in order to enter cells.

Organic Molecules and Digestive End Products

Organic Molecule Digestive End Product(s)

carbohydrates simple sugars (glucose)

proteins amino acids

lipids (fats) fatty acids and glycerol

Photosynthesis

Vocabulary: chloroplasts, chlorophylls, chromotography, enzymes, guard cells, photosynthesis,stomate

Biochemical ProcessesAlmost all life on Earth ultimately depends upon the Sun for its energy. The processof photosynthesis converts the Sun's energy to sugars which living things may use as an energysource. These sugars are converted to a form living things can use by a process called respiration.

Thousands of chemical reactions occur in living things. These reactions are aided by compoundscalled enzymes. Enzymes and some other kinds of molecules have specific shapes which allow themto function.

PhotosynthesisThe energy for life comes primarily from the Sun. Photosynthesis is the major way the energy of theSun is converted to sugars which provide for the energy needs of living systems.

Plants and many microorganisms use solar energy to combine the inorganic molecules carbondioxide and water into energy-rich organic compounds such as glucose sugar and release oxygen tothe environment.

A Representation of Photosynthesis

The overall process of photosynthesis in a plant or algal cell is shown inthe graphic below. Plants use use water and the energy provided bysunlight to combine carbon dioxide into glucose sugar with oxygen beingreleased as a waste product.


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Equation for Photosynthesis

carbon dioxide + water glucose + oxygen(sunlight) (enzymes)


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chloroplasts: organelles that carry on photosynthesis ingreen plant cells

chlorophylls: the variety of green pigments within the

chloroplasts

ChromatographyWhile chlorophyll is the chief pigment responsible forphotosynthesis in green plants, many plants contain othercolored pigments as well. These chlorophyll and coloredpigments may be separated according to their variouschemical charges by a technique knownas chromatography. In this technique, a mixture of plantpigments is separated by placing a drop or two of pigmenton a special paper called chromatography paper which isdipped in a chemical allowing the different plant pigmentsto move based on their charges. A picture of a completedchromatography may be viewed in the graphic at the right.

Homeostasis by Plants

Maintenance of Water

plants need to regulate water loss and carbon dioxide intake for photosynthesis and otherlife activities

when plants do not keep enough water in their cells, they wilt and diestomate: a microscopic hole in a plant leaf which allows gases to enter and leave and water vaporto leave as well. Stomata is the plural of stomate.


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guard cells: open and close the stomate.

the ability of the guard cell to close during periods of limited water availability for the plantallows the plant to maintain water homeostasis

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Cell Respiration

Vocabulary: active site, antibodies, ATP, catalyst, cellular respiration, denatured, enzymes,hormones, hydrolysis, pH, specific, substrate, synthesis, temperature

RespirationIn all organisms, organic compounds such as glucose can be used to make other molecules. Thesemolecules include proteins, DNA, starch, and fats. The chemical energy stored in bonds can be usedas a source of energy for life processes.

Stored energy is released when chemical bonds are broken during cellular respiration and newcompounds with lower energy bonds are formed. Cells usually transfer this energy temporarily inphosphate bonds of a high-energy compound called ATP. (adenosine triphosphate)

In all organisms, the energy stored in organic molecules may be released during cellular respiration.This energy is temporarily stored in ATP molecules. In many organisms, the process of cellularrespiration is concluded in mitochondria, in which ATP is produced more efficiently, oxygen is used,and carbon dioxide and water are released as wastes.

The energy from ATP is used by the organism to obtain, transform, and transport materials, and to

eliminate wastes.


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Equations for Cell Respiration

glucose + oxygen carbon dioxide + water + 36 ATP

The energy from ATP is then used by the organism to obtain, transform, and transport

materials, and to eliminate wastes.

water + ATP ADP + P + Energy

(ATP-ase)

Note: ADP is adenosine diphosphate.

This reaction is reversible and ADP can be converted back to ATP in cellular respiration.

Types of Reactions

hydrolysis: reaction in which large molecules are broken down into smaller molecules. Chemicaldigestion is an example of a hydrolysis reaction

synthesis: the combining of simpler molecules to form a more complex molecule

Biochemical processes, both breakdown (hydrolysis) and synthesis, are made possibleby enzymes. Enzymes and other molecules, such as hormones and antibodies, have specificshapes that influence both how they function and how they interact with other molecules.

Enzyme Structure and Functioncatalyst: inorganic or organic substance which speeds up the rate of a chemical reaction withoutentering the reaction itself.

enzymes: organic catalysts made of protein.

most enzyme names end in -ase enzymes lower the energy needed to start a chemical reaction (activation energy), thus

speeding the reaction

How do enzymes work?substrate: molecules upon which an enzyme acts. The enzyme is shaped so that it can only lock

up with a specific substrate molecule.enzyme

substrate -------------> product


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Lock and Key Theory

Each enzyme is specific for one and ONLY one substrate (one lock - one key)

active site: part of the enzyme that fits with the substrate

Note that the active site has a specific fit for this particular substrate and no other.

This theory has some weaknesses, but it explains many basic things about enzyme function.

Since the enzyme may unhook from the substrate, it may be reused many times.

Factors Influencing Enzyme ActivitypH: the optimum (best) in most living things is close to 7 (neutral). High or low pH levels usuallyslow enzyme activity

Temperature: strongly influences enzyme activity

optimum (best) temperature for maximum enzyme function is usually about 35-40 C. reactions proceed slowly below optimal temperatures


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above 45 C. most enzymes are denatured (change in their shape so the enzyme active siteno longer fits with the substrate and the enzyme can't function)

Concentrations of Enzyme and Substrate

When there is a fixed amount of enzyme and an excess of substrate molecules, the rate ofreaction will increase to a point and then level off.

This leveling off occurs because all of the enzyme is used up and the excess substrate has nothingto combine with.

If more enzyme is available than substrate, a similar reaction rate increase and leveling off willoccur. The excess enzyme will eventually run out of substrate molecules to react with.

Enzymes and other molecules, such as hormones, receptor molecules, and antibodies, havespecific shapes that influence both how they function and how they interact with othermolecules.__________________________________________________________________________

Cell Division

Vocabulary: anaphase, asexual reproduction, binary fission, budding, cell cycle,chromatids,chromatin, chromosomes, clones, cloning, cytokinesis, DNA, DNA replication, heredity,interphase, metaphase, mitosis, prophase, replication, sporulation, synthesis, telophase

Asexual ReproductionSpecies are maintained in existence through the life spans process of reproduction. Asexualreproduction produces genetically identical offspring from a single parent cell. The processof mitosis is associated with asexual reproduction and the growth and repair of cells insexually reproducing organisms.

Reproduction and development are necessary for the continuation of any species. Asexualreproduction is a method of reproduction with all the genetic information coming from one paren


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Some Methods of Asexual Reproduction

1. binary fission -- involves an equal

division of both the organismcytoplasm and nucleus to form twoidentical organisms

-- the diagram of the protist at theright is example of this

2. budding -- involves one parent

dividing its nucleus (genetic material)equally, but cytoplasm unequally

-- the diagram of a yeast at the rightis an example of this

3. sporulation (spore formation) -- isreproduction involving specializedsingle cells coming from one parent

-- the diagram of mold spores beingformed at the right is an example ofthis

Asexual reproduction is sometimes called cloning. Cloning is the production of identical geneticcopies. All forms of asexual reproduction are variations of the cell division process ofmitosis. Mitosis is associated with asexual reproduction, as well as growth and repair in sexuallyreproducing organisms.


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MitosisMitosis is the method used for cell division and reproduction in cells not involved in sexual

reproduction. This process starts with one replication (copying of the chromosome material) andone division of the chromosome material. This results in the chromosome numbers in the two cellsproduced being the same as in the parent cell. This process is represented in the graphic whichfollows.

An Overview of the Process of Mitosis

The Cell CycleThe cell cycle is the lifespan of a cell. It is divided into three parts: Interphase, Mitosis, andCytokinesis. Interphase is divided into three parts. G1 - or the first growth phase, is the stage in acells life when normal cell functioning is occurring. A cell will remain in this stage unless it receives asignal to reproduce. Cells can receive signals from neighboring cells during development of a multi-cellular organism, or it may receive a signal for repair of neighboring cells or a cell may receive a


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signal to divide if the cell becomes too large for intracellular transport to occur effectively. When acell receives the signal to divide, it moves into the second stage of interphase called synthesis.Synthesis is the longest part of the cell cycle because this is the stage when a cells DNAreplicates. DNA replication involves separating the double helix, complimentary nucleotides finding

their match (Adenine joins with Thymine, Cytosine joins with Guanine) and two identical strands ofDNA forming. Once this is accomplished, and proteins have confirmed its success, a cell moves intothe third phase of interphase called G2, or the second growth phase. Here, organelles replicate andthe cell grows in anticipation of dividing into two smaller cells.

If everything goes according to plan, a cell is ready to move into the mitotic stage of the cellcycle. Mitosis is the division of the nucleus stage. It is a choreographed mechanism to efficiently andaccurately divide the two identical copies of DNA into the newly forming cells and it is done thesame way in every living cell. The four parts of this cycle are prophase, metaphase, anaphase andtelophase (PMAT). In prophase, the DNA which is in long, stringy chromatin form condenses andcoils up intochromosomes. The identical pieces of DNA are joined together with a centromere.During this phase, the nuclear membrane in eukaryotes begins to disintegrate. Inmetaphase, the

paired chromatids line up (chromosomes) single file down the equator of the cell. In anaphase, thesister chromatids separate and identical chromatids each move to opposite poles. Telophase iswhen the chromosomes begin to uncoil again back into chromatin and new nuclear membranesbegin to form in eukaryotes.

The final stage of the cell cycle begins in telophase when the cells cytoplasm begins to divide. Inanimal cells, the cell membrane pinches in during this stage calledcytokinesis. In plant cells, a cellplate forms between the newly forming nuclei as the cell wall can't pinch in. This continues until twonew cells are formed with identical DNA.


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2 Key Results of Mitosis

1. The same chromosome number is retained from generation to generation.2. Each daughter cell receives an exact copy of the chromosomes of the parent cell. (clones)

Asexual HeredityEvery organism requires a set of coded instructions for specifying its traits. For offspring toresemble their parents, there must be a reliable way to transfer information from one generation tothe next. Heredity is the passage of these instructions from one generation toanother. The DNA molecule provides the mechanism for transferring these instructions.

In asexually reproducing organisms, all the genes come from a single parent. As asexually producedoffspring are produced by the cell division process of mitosis, all offspring are normally geneticallyidentical to the parent.

Genetics ReviewIntro to Genetics

Vocabulary: sexual reproduction, gamete, egg/ovum, sperm, gonads, fertilization, differentiation,meiosis, replication, crossing over, variations, natural selection, recombination, external fertilization,

external development, internal fertilization, internal development

Sexual Reproduction ProcessThe process of sexual reproduction involves two parents. Both parents normally contributeone gamete or sex cell to the process. This process assures that the genetic information given to theoffspring will be obtained equally from each parent. The female gamete is called the egg orthe ovum and the male gamete is called a sperm. These gametes are formed in specializedreproductive structures called gonads. The sperm is much smaller than the egg, but is capable ofmoving on its own power using a whip-like tail called a flagellum.

Sperm and Egg(fertilization)


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The sperm and egg unite in a process called fertilization.This process forms a single celled structure called azygote which contains the complete genetic information todevelop into a complete new organism havingcharacteristics of both parents.

Process of Fertilization

This zygote will then divide by mitosis and form the specialized cells, tissues, and organs of theorganism. This development of specialized structures from the zygote is called differentiation.

MeiosisThe process of meiosis produces gametes or sex cells. While some parts of this cell division processare similar to the asexual cell division process of mitosis, there are several key differences. Meiosisproduces gametes, while mitosis produces other cell types. The process of meiosis halves thechromosome number from the original parent cell in the four cells it forms. It does this by having

two cell divisions forming four cells, where mitosis has only one cell division forming two cells. Bothprocesses start out with one doubling orreplication of the chromosome material. Thegraphic below will help to visually illustrate some of the key events of meiosis.


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Process of Meiosis

Another important way that meiosis differs from mitosis is the exchange of chromosome pieceswhich occurs in the first division of this process. This exchange of chromosome pieces is

called crossing over. Crossing over assures that the cells produced as a result of meiosis will bedifferent from and exhibit variations from the parent cell that produced them. This process is chieflyresponsible for the variations seen in members of the same species of sexually reproducingorganisms. These variations are the driving force for the process of natural selection.

The process of crossing over and how it produces variation when these chromosomesare recombined in the process of fertilization is illustrated in the graphic below.


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Crossing Over and Genetic Recombination

Comparative Reproduction and DevelopmentDifferent organisms possess different adaptations for reproduction and development. Organismswhich spend their lives or a large proportion of their lives in the water tend to lay their eggs in greatnumbers (thousands) in the water and wait for the male of the species to release sperm near themto fertilize them. The fertilization which occurs in the water in this case outside the body of theorganism is called external fertilization. These young organisms then develop outside the mother inthe water once this has occurred, which is called external development. A disadvantage of this


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process is that the eggs and developing young have little or no parental protection. Many fish andamphibians like frogs undergo fertilization and development in this manner.

Reptiles and birds engage use the process of internal fertilization to fertilize their eggs. In this

situation, the male of the species inserts his sperm inside the female, who then lays her fertilizedeggs outside her body. The process of development is then external. Reptiles and especially birdstend to lay fewer eggs and provide much more parental protection for their developing young.Organisms (with some exceptions) which use the process of internal fertilization tend to spendmuch of their lives on land. Mammals like humans have both their fertilization and initial stages ofdevelopment occur within the female organism. This is referred to as internalfertilization and internal development. These organisms tend to release very few eggs, but thoseeggs and the developing organism are very well protected by one or both parents.

DNA/RNA

Vocabulary:genes, DNA, replication, mutation, gamete, heredity, complementary base pairing,chromosomes, asexual, mitosis, crossing over, genetic recombination, natural selection, cancer,

adenine, guanine, cytosine, thymine, template, RNA, mRNA, rRNA, tRNA, transcription, regulation

DNAAll Organisms have a set of instructions that determine their characteristics. These instructions arecalled genes and contain the instructions for life that are passed from parents to offspring duringreproduction.

The inherited instructions that are passed from parent to offspring exist as a code.The DNA molecule which makes up our genes contains this code.

Asexual v. Sexual HeredityThe DNA molecules must be accurately replicated before being passed on. Asexually reproducingorganisms normally pass on this genetic code identically between the parent and offspring, whilethe offspring of sexual reproduction produce offspring that resemble their parents, but exhibitsome variations from them.

MutationsChanges in DNA ormutations which occur in non sex cells of a sexually reproducing organism willnot be passed on to their offspring.Mutations which occur in sex cells orgametes will be frequentlybe passed on to their offspring.

Protein SynthesisOnce the coded information contained in the DNA molecule is passed on, it is used by a cell to makeproteins. The proteins that are made become cell parts and carry out most functions of the cell. Thesubtle differences in DNA between different human beings and different species results in theproduction of different proteins. This is a major reason why we show individual differences.


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DNA Structure and FunctionDNA provides the set of coded instructions required by every organism for specifying its traits.

The DNA molecule also provides for a reliable way for parents to pass their genetic code from onegeneration to the next. Heredity refers to this passage of these instructions from one generation toanother.

DNA is a double stranded molecule which has the shape of a twisted ladder. This shape is called analpha helix. The sides of this twisted ladder are composed of alternating phosphate and deoxyribosesugar units, while the rungs of the ladder are composed of pairs of nitrogenous bases. These basesare called adenine (A), thymine (T), guanine (G), and cytosine (C). These bases exist in pairs on therungs of the ladder with A always pairing with T and G pairing with C. This principle is sometimescalled complementary base pairing. (The saying G CAT provides a means of remembering this idea.

Structure of the DNA molecule


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Location of DNA

Gene-Chromosome ModelHereditary information is contained in genes, which are composed of DNA, located inthe chromosomes of each cell. Chromosomes are found in the nucleus of each cell.

The Gene Chromosome Model

Each gene carries a separate piece of information. An inherited trait of an individual can bedetermined by one genes, but is usually determined by the interaction of many different genes.


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A single gene can influence more than one trait. A human cell contains many thousands of differentgenes coding for many different traits. Changes in the sequence of the DNA molecule and thereforethe gene are called mutations. A mutation may change the manner in which a trait is expressed byan organism.

Asexual HeredityEvery organism requires a set of coded instructions for specifying its traits. For offspring toresemble their parents, there must be a reliable way to transfer information from one generation tothe next. Heredityis the passage of these instructions from one generation to another.TheDNA molecule provides the mechanism for transferring these instructions.

In asexually reproducing organisms, all the genes come from a single parent. As asexually producedoffspring are produced by the cell division process of mitosis, all offspring are normally geneticallyidentical to the parent.

Sexual HeredityIn sexually reproducing organisms, the new individual receives half of the genetic information fromits mother through the egg and half from its father from his sperm. Sexually produced offspringresemble, but are not identical to, either of their parents. Some reasons for these variationsbetween sexually reproduced offspring and their parents include crossing over when gametes areformed in each parent and genetic recombination, which is the combining of the geneticinstructions of both parents into a new combination in the offspring when fertilization occurs.

Genetic Recombination

Note that two of the four offspring in the punnett square at the righthave a completely different genetic makeup than that of either

parent

The processes of crossing over and genetic recombination will result in offspring exhibiting variationfrom the original parents. The variations shown between different sexually produced offspringprovide the driving force for the process of natural selection.


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Heredity and EnvironmentThe characteristics of an organism can be described in terms of combinations of traits. Traits areinherited, but their expression can be modified by interactions with the environment. Examples ofthis include the lack of color in completely shaded grass, even though it still possesses the genetic

makeup to appear green and the change in fur color of returning fur in a shaven Himalayan hare atcold temperatures.

Effect of Cold on Himalayan Hare Fur Color

The application of an ice pack to a region of shaved hair results inblack hair growing back instead of the original white color.

The many body cells in an individual can be very different from one another, even though they are alldescended from a single cell and thus have identical genetic instructions. This is because differentparts of these instructions are used in different types of cells, influenced by the cells environment

and past history. Poor health habits can have an adverse effect on the development and expressionof many genes in human cells, resulting in sickness or even death.

MutationA mutation is a change in the genetic material of an organism.

Mutations

Mutations which occur in non sex cells of sexually reproducing organisms will not be passed on tothe offspring, although they may result in disease or death for the organism involved. One possibleconsequence of a mutation in a non sex cell is uncontrolled mitotic cell division orcancer.

Mutations which occur in sex cells or gametes may be passed to the offspring. Along with crossingover and genetic recombination, mutation provides for a source of variation in sexually reproducingindividuals.


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DNAIn all organisms, the coded instructions for specifying the characteristics of the organism are carried

in DNA. The genetic code is contained in the four nitrogenous bases ofDNA; adenine, guanine, cytosine, and thymine. These bases are often indicated only by using theirbeginning letters A, G, C, and T. Each individual DNA strand serves as a template or model for theformation of other DNA molecules by replication.

RNADNA codes for the formation of RNA in the nucleus of the cell. RNA is short for another kind ofnucleic acid called ribonucleic acid. RNA is very similar in structure to DNA except for three smalldifferences. These differences include the fact that RNA is a single stranded molecule, lacks the basethymine (T) as it is replaced by the base uracil (U), and its five carbon sugar ribose has one moreoxygen atom than the sugar in DNA. Three different types of RNA exist, mRNA ormessengerRNA, tRNA ortransfer RNA, and rRNA orribosomal RNA.

Protein SynthesisCells store and use coded information. The genetic information stored in DNA is used to direct thesynthesis of the thousands of proteins that each cell requires. The chemical and structuralproperties of DNA are the basis for how the genetic information that underlies heredity. DNA isencoded in the sequence of nitrogenous bases which directs the formation of proteins in the cell.How does this process work? First, the DNA code is copied on to the mRNA (messenger RNA)codon. A codon is a sequence of three nitrogenous bases. This process is calledtranscription. ThismRNA codon is then carried from the nucleus out to the ribosome. Messenger RNA attaches toanother kind of RNA called tRNA (transfer RNA). Transfer RNA attaches to amino acids and carriesthem to the ribosome. This assembly of amino acids due to the code provided to RNA by the original

DNA molecule is what produces proteins for the cell. Remember a protein is a long molecule formedfrom amino acid subunits.

Protein Synthesis


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In summary, the code of DNA directs the synthesis of RNA, which in turn directs the making ofproteins on the ribosomes. This is sometimes referred to as being the central dogma or idea ofbiology. There are 64 possible combinations of triplets (sequences of 3 nitrogenous bases) whichcode for the 20 different possible amino acids. As the DNA of different organisms and mostindividuals (except for identical twins) is different, this means the proteins produced by differenthumans and other organisms exhibit differences. It is these differences which make us uniqueindividuals.

The work of the cell is carried out by the many different types of molecules it assembles, mostlyproteins. Protein molecules are long, usually folded chains made from 20 different kinds of aminoacids in a specific sequence. This sequence influences the shape of the protein. The shape of theprotein, in turn, determines its function.

Offspring resemble their parents because they inherit similar genes (DNA sequences) that code forthe production of proteins that form similar structures and perform similar functions.

Cell RegulationCell functions are regulated. Regulation occurs both through changes in the activity of proteins and

through the selective expression of individual genes, as humans and other organisms have geneswhich direct the expression of other genes. This regulation allows cells to respond to theirenvironment and to control and coordinate cell growth and division.

Genetic Engineering

Vocabulary: selective breeding, recombinant DNA, artificial selection, inbreeding, hybridization,


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genetic engineering, restriction enzyme, cloning, genetic mapping, Human Genome Project

Genetic EngineeringThroughout recorded history, humans have used selective breeding and other methods to produce

organisms with desirable traits. Our current understanding of genetics and heredity allows for themanipulation of genes and the development of new combinations of traits and new varieties oforganisms. This includes various aspects of DNA technology, including recombinantDNA technology. Scientists have also developed many ways of determining the genetic makeup ofdifferent organisms, including humans.

Selective BreedingFor thousands of years new varieties of cultivated plants and domestic animals have resultedfrom selective breeding for particular traits. Some selective breeding techniques include artificialselection, where individuals with desirable traits are mated to produce offspring with those traits. Avariation of this process traditionally used in agriculture isinbreeding, where the offspring producedby artificial selection are mated with one another to reinforce those desirable traits.Hybridization isa special case of selective breeding. This involves crossing two individuals with different desirabletraits to produce offspring with a combination of both desirable traits. An example of this are SantaGertrudis cattle, which were developed by breeding English shorthorn cattle, which provided forgood beef, but lacked heat resistance, with Brahman cattle from India which were highly resistantto heat and humidity. The Santa Gertrudis breed of cattle has excellent beef, and thrives in hot,humid environments.

An Example of Selective Breeding

Brahman cattle:Good resistance to heatbut poor beef.

English shorthorncattle: Good beef butpoor heat resistance.

Santa Gertrudis cattle:Formed by crossingBrahman and Englishshorthorns; has goodheat resistance andbeef.

Genetic EngineeringIn recent years new varieties of farm plants and animals have been engineered by manipulating theirgenetic instructions to produce new characteristics. This technology is known as genetic


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engineering orrecombinant DNA technology. Different enzymes can be used to cut, copy (clone),and move segments of DNA. An important category of enzyme used to cut a section of a gene andits DNA from an organism is known as a restriction enzyme. When this piece of DNA, which hasbeen cut out of one organism, is placed in another organism, that section of gene will express the

characteristics that were expressed by this gene in the organism it was taken from.

An Example of Genetic Engineering

Inserting, deleting, or substituting DNA segments can alter genes. An altered gene may be passedon to every cell that develops from it.

Knowledge of genetics, including genetic engineering, is making possible new fields of health care.Genetic engineering is being used to engineer many new types of more efficient plants and animals,as well as provide chemicals needed for human health care. It may be possible to use aspect of

genetic engineering to correct some human health defects. Some examples of chemicals being massproduced by human genes in bacteria include insulin, human growth hormone, and interferon.Substances from genetically engineered organisms have reduced the cost and side effects ofreplacing missing human body chemicals. While genetic engineering technology has many practicalbenefits, its use has also raised many legitimate ethical concerns.

Other Genetic TechnologiesCloning involves producing a group of genetically identical offspring from the cells of an organism.This technique may greatly increase agricultural productivity. Plants and animals with desirablequalities can be rapidly produced from the cells of a single organism.

Genetic mapping, which is the location of specific genes inside the chromosomes of cells makes itpossible to detect, and perhaps in the future correct defective genes that may lead to poor health.Thehuman genome project has involved the mapping of the major genes influencing human traits,thus allowing humans to know the basic framework of their genetic code

Knowledge of genetics is making possible new fields of health care. Genetic mapping in combinationwith genetic engineering and other genetic technologies may make it possible to correct defective


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genes that may lead to poor health.

There are many ethical concerns to these advanced genetic technologies, including possibleproblems associated with the cloning of humans. Another down side to genetic mapping

technologies it is possible that some organizations may use this genetic information againstindividuals.

Human Genome

Vocabulary: karyotype, sex chromosome, autosome, pedigree, sex-linked gene, DNA fingerprinting,gene therapy

Humans are identified by their 46 chromosomes (23 pairs of homologous chromosomes). We receive23 chromosomes via the egg cell from our mother and 23 chromosomes via the sperm cell from our

father. Sperm and egg cells are haploid, meaning that they contain only a single set of chromosomes.When the sperm and egg unite during fertilization, the resulting cell (the zygote) has 46chromosomes. A zygote is diploid because it contains both sets of homologous chromosomes.

KaryotypesA karyotype is a photograph of chromosomes in order from largest to smallest in pairs. By looking ata karyotype, you can decipher whether the person is male or female, and often you can see if there


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are any chromosome abnormalities. For example, if a person has Down's Syndrome, their karyotype

would have an extra 21st chromosome. See the karyotype below.

Sex ChromosomesTwo of our 46 chromosomes are known as sex chromosomes and are identified as the 23rd pair in akaryotype. Females have two large X chromosomes and males have one X and one small Ychromosome. The other 22 pairs of chromosomes are known as autosomes.

PedigreesA pedigree is a chart that scientists use to show the relationships within a family. A genetic counselormay use a pedigree to see how traits are passed from one generation to the next, making inferencesabout the genotypes of the different individuals. Pedigrees are usually used to trace a single-gene

trait through a family (ex: white forelock).

Many traits are either polygenic (controlled by many genes) or are influenced by the environment.This means that the expression of your genes can be affected by the environment you are exposedto (ex: your nutrition plays a large role in what your height and weight will be).

The red circle highlights the extra chromosome. The red arrow is pointing to the sex chromosomes(XX). This karyotype is of a female with Down's Syndrome.


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There are many genetic disorders that humans can inherit. Some of them include PKU, Down'sSyndrome, sickle cell anemia, and Huntington's disease. There are many ways to diagnose geneticdisorders including blood tests, amniocentesis, urine tests, and karyotype analysis.

Sex-Linked GenesGenes that are found on the sex chromosomes (the X and Y) are known as sex-linked genes. Manygenetic disorders are found on the X chromosome. Females would need two recessive copies ontheir X chromosomes for disorders like hemophilia and colorblindness to be expressed. Since malesonly have one X chromosome, all alleles located on the X chromosome are expressed. Due to themale's single X chromosome, disorders like colorblindness are found more commonly in males.

DNA FingerprintingTo identify individuals, scientists use a method called DNA fingerprinting. The DNA that is chosen tobe analyzed serves little to no function to the individual, but these sections can vary greatly fromperson to person. DNA is cut by a restriction enzyme and undergoes gel electrophoresis, whichseparates the DNA by size. The resulting banding pattern is unique to each person, and theinformation is extremely useful in convicting criminals or in overturning wrongful convictions.

Gene TherapySince scientists completed work on the Human Genome Project in 2000, we can use the information

gathered to help treat genetic disorders.Gene therapy is when a faulty gene is replaced with aproper working gene. A similar scenario would be adding a gene in where one is missing. This can beaccomplished with the help of a virus, since they are able to enter the DNA of a cell. First the virus ismodified so it cannot cause disease. Next, a piece of DNA containing the normal functioning gene isinserted into the DNA of the virus. Lastly, the patient is "infected" with the virus (that has themodified DNA), introducing the proper working gene.


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Ethical IssuesAs we develop new technology and are able to alter the human genome, many ethical issuesarise. Should we use the knowledge we have to just cure diseases, or is it alright to startchanging whatever it is we don't like about ourselves? Should we be able to choose thetraits we want for our babies before they are even born? Where do we draw the line?

Review provided by regentsprep.org and The NYS Core Curriculum


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Microbiology & Genetics Regents Questions

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week 4 molecular biology and genetics

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