unit 3 unit 3 -- transmission and transmission and unit 3 ... · 3e. dna structure and replication...

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Unit 3 Unit 3 -- Transmission and Transmission and Molecular GeneticsMolecular Genetics

GeneticsGenetics is the scientific study of is the scientific study of inheritance and the hereditary material:inheritance and the hereditary material:

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Transmission geneticsTransmission genetics deals with how deals with how the genetic material is passed on from the genetic material is passed on from one cell to another during the cell one cell to another during the cell cycle, and from one organism to cycle, and from one organism to another during the life cycle.another during the life cycle.

Unit 3 Transmission and Unit 3 Transmission and Molecular GeneticsMolecular Genetics

Molecular geneticsMolecular genetics deals with the deals with the structure and function of the genetic structure and function of the genetic

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material at the molecular level.material at the molecular level.

Unit 3 Unit 3 -- Transmission and Transmission and Molecular GeneticsMolecular Genetics

3A. How Cells Divide3A. How Cells Divide

3B. Meiosis and Sexual Life Cycles3B. Meiosis and Sexual Life Cycles

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3C. Patterns of Inheritance3C. Patterns of Inheritance

3D. Chromosomes and Inheritance3D. Chromosomes and Inheritance

3E. DNA Structure and Replication3E. DNA Structure and Replication

3F. Protein Synthesis3F. Protein Synthesis

Module 3A Module 3A –– Cell ReproductionCell Reproduction

In this module, we will examine the In this module, we will examine the cell cyclecell cycle, the series of changes that a , the series of changes that a cell goes through from one generation cell goes through from one generation to the nextto the next

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to the next.to the next.

We will pay particular attention to how We will pay particular attention to how the genetic material is passed on from the genetic material is passed on from parent cell to daughter cells during the parent cell to daughter cells during the cell cycle.cell cycle.

Objective # 1Objective # 1

Compare the amount and Compare the amount and organization of genetic material in organization of genetic material in prokaryotic cells with the amountprokaryotic cells with the amount

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prokaryotic cells with the amount prokaryotic cells with the amount and organization of genetic and organization of genetic material in eukaryotic cells.material in eukaryotic cells.

Objective 1Objective 1

An average eukaryotic cell has about An average eukaryotic cell has about 1,000 times more DNA then an 1,000 times more DNA then an average prokaryotic cell.average prokaryotic cell.

The DNA in a eukaryotic cell is The DNA in a eukaryotic cell is

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organized into several linear organized into several linear chromosomes, whose organization is chromosomes, whose organization is much more complex than the single, much more complex than the single, circular DNA molecule found in a circular DNA molecule found in a prokaryotic cell:prokaryotic cell:

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DNADNA ProkaryotesProkaryotes EukaryotesEukaryotesstructurestructure single, naked, single, naked,

circular DNA circular DNA molecule; attached molecule; attached to 1 point on theto 1 point on the

many linear many linear chromosomes, chromosomes, each made of 1 each made of 1 DNA moleculeDNA molecule

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to 1 point on the to 1 point on the inner surface of inner surface of plasma membraneplasma membrane

DNA molecule DNA molecule joined with joined with proteinprotein

locationlocation in an area of the in an area of the cytoplasm called cytoplasm called the nucleoidthe nucleoid

inside a inside a membranemembrane--bound nucleusbound nucleus


If the DNA of either a prokaryotic or If the DNA of either a prokaryotic or eukaryotic cell were completely eukaryotic cell were completely stretched out, it would thousands of stretched out, it would thousands of times longer than the cell itself.times longer than the cell itself.

Therefore, the DNA must be folded Therefore, the DNA must be folded and coiled so it will fit into the cell.and coiled so it will fit into the cell.

On the next slide, you can see how this On the next slide, you can see how this is done in a prokaryotic cell:is done in a prokaryotic cell:

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Describe the process of cell Describe the process of cell division in prokaryotic cells.division in prokaryotic cells.

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p yp y

Objective 2Objective 2Prokaryotes use a type of cell division Prokaryotes use a type of cell division called called binary fissionbinary fission::

1)1) First, the single, circular DNA First, the single, circular DNA molecule replicates, producing two molecule replicates, producing two id i l i f h i i lid i l i f h i i l

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identical copies of the original. identical copies of the original. Replication begins at a specific site Replication begins at a specific site called the called the origin of replicationorigin of replication and and proceeds bidirectionally around the proceeds bidirectionally around the circle to a specific circle to a specific site of terminationsite of termination::

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3


2)2) As the DNA replicates, growth of the As the DNA replicates, growth of the cell results in elongation. After cell results in elongation. After replication is complete, the DNA replication is complete, the DNA molecules are actively partitioned to molecules are actively partitioned to

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¼ and ¾ of the cell length. During ¼ and ¾ of the cell length. During this process, specific DNA sequences this process, specific DNA sequences near the origin of replication are near the origin of replication are attached to the plasma membrane.attached to the plasma membrane.


3)3) Finally, the cytoplasm is divided in Finally, the cytoplasm is divided in half by the growth of a new half by the growth of a new membrane and septum in the middle membrane and septum in the middle of the cell. This produces 2 daughter of the cell. This produces 2 daughter

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cells which are cells which are genetically identicalgenetically identical(unless a mutation occurred) to each (unless a mutation occurred) to each other and to the original cell:other and to the original cell:

Bacterial cell

Origin ofreplicationBacterial DNA

Prior to cell division, the bacterial DNA molecule replicates. The replication of the double-stranded, circular DNA molecule that constitutes the genome of a bacterium begins at a specific site, called the origin of replication (green area).

The replication enzymes move out in both directions from that site and make copies of each strand in the DNA duplex. The

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2.

Binary Fission – part 1

penzymes continue until they meet at another specific site, the terminus of replication (red area).

As the DNA is replicated, the cell elongates, and the DNA is partitioned in the cell such that the origins are at the ¼ and ¾ positions in the cell and the termini are oriented toward the middle of the cell.

3.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Septum

Septation begins, in which new cell membrane and cell wallmaterial begins to grow and form a septum at approximately themidpoint of the cell. A protein molecule called FtsZ (orange dots)f ilit t thi

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Binary Fission – part 2

facilitates this process.

When the septum is complete, the cell pinchesin two, and two daughter cells are formed, each containing a bacterial DNA molecule.

5.


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Describe the structure of both Describe the structure of both duplicated and unduplicated duplicated and unduplicated eukaryotic chromosomes; and eukaryotic chromosomes; and distinguish betweendistinguish between

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distinguish between distinguish between chromosome, chromatid, chromosome, chromatid, centromere, and chromatin.centromere, and chromatin.

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Eukaryotic chromosomes are made Eukaryotic chromosomes are made of of chromatinchromatin, a complex of DNA , a complex of DNA and protein.and protein.

Each unduplicated chromosomeEach unduplicated chromosome

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Each unduplicated chromosome Each unduplicated chromosome contains one DNA molecule, which contains one DNA molecule, which may be several inches long.may be several inches long.


How can such long molecules fit inside How can such long molecules fit inside a microscopic nucleus?a microscopic nucleus?

Every 200 nucleotide pairs, the DNA Every 200 nucleotide pairs, the DNA wraps twice around a group of 8wraps twice around a group of 8 histonehistone

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wraps twice around a group of 8 wraps twice around a group of 8 histonehistoneproteins to form a proteins to form a nucleosomenucleosome..

Higher order coiling and supercoiling Higher order coiling and supercoiling also help condense and package the also help condense and package the chromatin inside the nucleus:chromatin inside the nucleus:

ChromosomeRosettes of

Chromatin LoopsChromatin

Loop SolenoidScaffold protein


Levels of DNA Coiling in a Chromosome

NucleosomeDNA Double Helix

DNAHistone core

Chromatin loop


The degree of coiling can vary in The degree of coiling can vary in different regions of the chromatin:different regions of the chromatin:

Heterochromatin Heterochromatin refers to highly refers to highly coiled regions where genes aren’tcoiled regions where genes aren’t

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coiled regions where genes aren t coiled regions where genes aren t expressed.expressed.

EuchromatinEuchromatin refers to loosely refers to loosely coiled regions where genes can be coiled regions where genes can be expressed.expressed.


For much of the cell cycle, most For much of the cell cycle, most chromatin is loosely coiled. chromatin is loosely coiled.

During this time, only the During this time, only the heterochromatin is visible as denseheterochromatin is visible as dense

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heterochromatin is visible, as dense heterochromatin is visible, as dense granules inside the nucleus. granules inside the nucleus.

There is also a dense area of RNA There is also a dense area of RNA production called the nucleolus:production called the nucleolus:

Nucleus

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Chromatin

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Prior to cell division each Prior to cell division each chromosome duplicates itself. chromosome duplicates itself.

All the duplicated chromosomes All the duplicated chromosomes then condense into short rodthen condense into short rod--likelike

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then condense into short rodthen condense into short rod--like like structures that can be seen and structures that can be seen and counted under the microscope:counted under the microscope:

Fully Condensed Human ChromosomesFully Condensed Human Chromosomes

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Because of duplication, each Because of duplication, each condensed chromosome consists of 2 condensed chromosome consists of 2 identical identical chromatidschromatids held together by a held together by a complex of proteins called complex of proteins called cohesinscohesins..

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Each duplicated chromosome contains Each duplicated chromosome contains 2 identical DNA molecules (unless a 2 identical DNA molecules (unless a mistake occurred during replication), mistake occurred during replication), one in each chromatid.one in each chromatid.

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The The centromerecentromere is a constricted region is a constricted region of the chromosome where the 2 of the chromosome where the 2 chromatids remain connected from the chromatids remain connected from the middle of prophase to the start of middle of prophase to the start of anaphaseanaphase

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anaphase. anaphase. It contains repeated DNA sequences It contains repeated DNA sequences

that bind specific proteins. These that bind specific proteins. These proteins make up a diskproteins make up a disk--like structure like structure called the called the kinetochorekinetochore..

Two UnduplicatedHomologous chromosomes

Two DuplicatedHomologous chromosomes

Replication

Kinetochore

Sister chromatids

Non- sister chromatids

Centromere

Replication

Kinetochores

Cohesinproteins


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Kinetochores serve as points of Kinetochores serve as points of attachment for a network of attachment for a network of microtubules that move the microtubules that move the

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chromosomes during cell division:chromosomes during cell division:

Chromatid

Centromerei f

Metaphase Chromosome

Cohesinproteins

Kinetochoremicrotubules

region ofchromosome

Kinetochore



Explain what karyotypes are Explain what karyotypes are and how they are useful.and how they are useful.

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yy


The particular array of chromosomes in The particular array of chromosomes in a eukaryotic cell is called its a eukaryotic cell is called its karyotypekaryotype..

To examine a karyotype, the To examine a karyotype, the chromosomes are photographed when chromosomes are photographed when

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p g pp g pthey are highly condensed, then photos they are highly condensed, then photos of the individual chromosomes are cut of the individual chromosomes are cut out and arranged in order of decreasing out and arranged in order of decreasing size:size:

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Karyotypes are used to study the Karyotypes are used to study the number and structure of the number and structure of the chromosomes present in a cell.chromosomes present in a cell.

Th l b d dTh l b d d

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They can also be used to detect They can also be used to detect chromosomal abnormalities that may chromosomal abnormalities that may be associated with specific genetic be associated with specific genetic traits or defects.traits or defects.

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Distinguish between a haploid Distinguish between a haploid cell and a diploid cell. cell and a diploid cell. Distinguish between identicalDistinguish between identical

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Distinguish between identical Distinguish between identical chromosomes, homologous chromosomes, homologous chromosomes, and nonchromosomes, and non--homologous chromosomes.homologous chromosomes.


In eukaryotes, every species requires a In eukaryotes, every species requires a specific number of chromosomes to specific number of chromosomes to code for all the polypeptides produced code for all the polypeptides produced by the organism. These chromosomes by the organism. These chromosomes

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make up 1 complete set.make up 1 complete set.

Each chromosome in a set controls Each chromosome in a set controls the production of a different group of the production of a different group of polypeptides.polypeptides.


Cells that contain 1 complete set of Cells that contain 1 complete set of chromosomes are called chromosomes are called haploidhaploid..

n or N = number of chromosomes in n or N = number of chromosomes in a haploid cell.a haploid cell.

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pp

Cells that contain 2 complete sets of Cells that contain 2 complete sets of chromosomes are called chromosomes are called diploiddiploid..

2n or 2N = number of chromosomes 2n or 2N = number of chromosomes in a diploid cell.in a diploid cell.


For example, 23 different For example, 23 different chromosomes are needed to code for chromosomes are needed to code for all the polypeptides produced by all the polypeptides produced by humans.humans.

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Therefore, in humans:Therefore, in humans:N=23 N=23 2N = 462N = 46


We will use different We will use different shapesshapes to to represent the different chromosomes represent the different chromosomes that make up a set, and different that make up a set, and different colorscolorsto represent different sets of to represent different sets of

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chromosomes.chromosomes.


Unduplicated Chromosomes

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Haploid Cell, N = 3 Diploid Cell, 2N = 6

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Duplicated Chromosomes

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Haploid Cell, N = 3 Diploid Cell, 2N = 6


In a diploid cell, the chromosomes In a diploid cell, the chromosomes occur in pairs. The 2 members of each occur in pairs. The 2 members of each pair are called pair are called homologous homologous chromosomeschromosomes or or homologueshomologues..

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Under the microscope, homologous Under the microscope, homologous chromosomes chromosomes looklook identical. identical.

In addition, because they code for the In addition, because they code for the same polypeptides, they control the same polypeptides, they control the same traits.same traits.

Objective 5Objective 5 However, homologous chromosomes are However, homologous chromosomes are

not identical because they may code for not identical because they may code for different forms of each trait. Therefore we different forms of each trait. Therefore we will represent them using 2 different colors:will represent them using 2 different colors:

Short wings Tan bodyRed eyes

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White eyes Long wings Tan body


Identical chromosomes:Identical chromosomes:Look the sameLook the sameControl the same traitsControl the same traitsCode for the same form of each traitCode for the same form of each trait

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Common origin Common origin –– they have both they have both descended from the same original descended from the same original chromosome. (When the 2 halves of a chromosome. (When the 2 halves of a duplicated chromosome separate, we duplicated chromosome separate, we get 2 identical chromosomes.)get 2 identical chromosomes.)


Homologous chromosomes:Homologous chromosomes:Look the sameLook the same

Control the same traitsControl the same traits

May code for different forms of each traitMay code for different forms of each trait

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yy

Independent origin Independent origin -- each one was inherited each one was inherited from a different parentfrom a different parent

NonNon--homologous chromosomes:homologous chromosomes:Look different Look different

Control different traitsControl different traits


Homologous Chromosomes

Non-homologous Chromosomes

48Diploid Cell, 2N = 6

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Define and be able to use the Define and be able to use the following terms correctly: gene, following terms correctly: gene,

l d ll ll d ll l

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gene locus, and allele.gene locus, and allele.


GeneGene –– a section of a DNA molecule a section of a DNA molecule that contains the code for making one that contains the code for making one polypeptide.polypeptide.

Gene locusGene locus ––the location of a gene the location of a gene

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ggalong the length of a chromosomealong the length of a chromosome

AllelesAlleles –– genes that can occupy the genes that can occupy the same gene locus (on different same gene locus (on different chromosomes)chromosomes)



Homologous Chromosomes

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White eyes Long wings Tan body


Identify the stages of the Identify the stages of the eukaryotic cell cycle, and eukaryotic cell cycle, and

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y y ,y y ,describe the events of each describe the events of each stage.stage.


The The cell cyclecell cycle refers to the sequence of refers to the sequence of events that occur as a cell grows and events that occur as a cell grows and divides. It is divided into 2 main stages:divides. It is divided into 2 main stages:

InterphaseInterphase –– chromosomes are not chromosomes are not

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ppvisible. Involves cell growth and visible. Involves cell growth and duplication of the genetic material.duplication of the genetic material.

Cell divisionCell division –– includes division of the includes division of the duplicated chromosomes (duplicated chromosomes (mitosismitosis) and ) and division of the cytoplasm (division of the cytoplasm (cytokinesiscytokinesis).).


Interphase is subdivided into 3 stages:Interphase is subdivided into 3 stages:

GG11 is the primary is the primary growthgrowth phase of the phase of the cell cyclecell cycle

SS is when the cell is when the cell synthesizessynthesizes a copy of a copy of

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SS s w e t e ces w e t e ce sy t es essy t es es a copy oa copy oits chromosomes (DNA duplication).its chromosomes (DNA duplication).

GG22 is the second is the second growthgrowth phase, during phase, during which preparations are made for cell which preparations are made for cell division.division.

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Mitosis is subdivided into 5 stages:Mitosis is subdivided into 5 stages:

ProphaseProphase

PrometaphasePrometaphase

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MetaphaseMetaphase

AnaphaseAnaphase

TelophaseTelophase

C

M

G2

Metaphase

ProphaseAnaphase

Telophase

Prometaphase

Stages of the Cell Cycle

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G1

G2

C- CytokinesisM- Mitosis

S Interphase

S G1


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List, describe, diagram, and List, describe, diagram, and identify the stages of mitosis.identify the stages of mitosis.

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y gy g


Mitosis:Mitosis:

some haploid and some diploid cells some haploid and some diploid cells divide by mitosis. divide by mitosis.

each new cell receives one copy of each new cell receives one copy of

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eac ew ce ece ves o e copy oeac ew ce ece ves o e copy oevery chromosome that was present in every chromosome that was present in the original cell. the original cell.

produces 2 new cells that are both produces 2 new cells that are both genetically identical to the original cell.genetically identical to the original cell.

Some diploid cells divide by mitosis:Some diploid cells divide by mitosis:

DNA duplication during interphase

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Mitosis

Diploid Cell

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Some haploid cells can also divide by mitosis:Some haploid cells can also divide by mitosis:

DNA duplication during interphase

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Mitosis

Haploid Cell


Stages of Mitosis in Diploid Cell, 2N = 6Stages of Mitosis in Diploid Cell, 2N = 6

Prophase:Prophase:

duplicated chromosomes condense and duplicated chromosomes condense and become visiblebecome visible

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beco e v s b ebeco e v s b e

cytoskeleton is disassembled; mitotic cytoskeleton is disassembled; mitotic spindle begins to formspindle begins to form

Golgi and ER are dispersedGolgi and ER are dispersed

nuclear envelope disintegratesnuclear envelope disintegrates

Prophase

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PrometaphasePrometaphase::chromosomes attach to microtubules at chromosomes attach to microtubules at

the kinetochoresthe kinetochores

each chromosome is oriented so that the each chromosome is oriented so that the

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kinetochores of sister chromatids are kinetochores of sister chromatids are attached to microtubules from opposite attached to microtubules from opposite polespoles

chromosomes move toward equator of chromosomes move toward equator of cellcell

Prometaphase

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Metaphase:Metaphase:

chromosomes are aligned, in single chromosomes are aligned, in single file, along metaphase plate at the file, along metaphase plate at the equator of cellequator of cell

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equator of cellequator of cell

chromosomes are attached to chromosomes are attached to opposite poles and are under opposite poles and are under tensiontension

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Metaphase

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Anaphase:Anaphase:

centromeres split so that each centromeres split so that each duplicated chromosome becomes 2 duplicated chromosome becomes 2 identical, unduplicated chromosomesidentical, unduplicated chromosomes

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pp

kinetochore microtubules shorten, kinetochore microtubules shorten, pulling identical chromosomes to pulling identical chromosomes to opposite polesopposite poles

polar microtubules elongate preparing polar microtubules elongate preparing cell for cytokinesiscell for cytokinesis

AnaphaseKinetochore Microtubule

69Polar Microtubule

Objective 8Objective 8Telophase:Telophase:

chromosomes cluster at opposite poles chromosomes cluster at opposite poles of the cell and decondenseof the cell and decondense

kinetochores disappearkinetochores disappear

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polar microtubules continue to polar microtubules continue to elongate, preparing cell for cytokinesiselongate, preparing cell for cytokinesis

nuclear envelope reformsnuclear envelope reforms

Golgi complex, ER and cytoskeleton Golgi complex, ER and cytoskeleton reformreform

Telophase

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ProphaseStages of Mitosis in Haploid Cell, N = 3Stages of Mitosis in Haploid Cell, N = 3

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Prometaphase

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Metaphase

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AnaphaseKinetochore Microtubule

75Polar Microtubule

Telophase

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Describe the process of Describe the process of cytokinesis and distinguish cytokinesis and distinguish

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y gy gbetween mitosis and between mitosis and cytokinesis.cytokinesis.

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CytokinesisCytokinesis refers to division of the refers to division of the cytoplasmcytoplasm during cell division, while during cell division, while mitosismitosis refers to division of the genetic refers to division of the genetic material (chromosomes).material (chromosomes).

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Although cytokinesis generally follows Although cytokinesis generally follows mitosis, this isn’t always the case.mitosis, this isn’t always the case.


In animal cells and other eukaryotic In animal cells and other eukaryotic cells that lack a cell wall, cytokinesis is cells that lack a cell wall, cytokinesis is achieved by means of a constricting achieved by means of a constricting belt of actin filaments.belt of actin filaments.

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As the filaments slide past each other, As the filaments slide past each other, they create a cleavage furrow which they create a cleavage furrow which deepens and eventually pinches the cell deepens and eventually pinches the cell in half:in half:

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Plant cells possess a cell wall which is Plant cells possess a cell wall which is too rigid to be squeezed in half by too rigid to be squeezed in half by actin filaments.actin filaments.

Instead, a new cell membrane, called a Instead, a new cell membrane, called a

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cell platecell plate, is assembled in the middle of , is assembled in the middle of the cell. As this expands outward, it the cell. As this expands outward, it effectively divides the cell in two.effectively divides the cell in two.

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Explain how the eukaryotic Explain how the eukaryotic cell cycle is controlled.cell cycle is controlled.

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yy


The eukaryotic cell cycle is The eukaryotic cell cycle is controlled by a complex interaction controlled by a complex interaction of internal and external regulatory of internal and external regulatory molecules.molecules.

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Some of these molecules act to Some of these molecules act to stimulate cell division while others stimulate cell division while others act to inhibit it.act to inhibit it.


The level of these regulatory molecules The level of these regulatory molecules affects 3 principal checkpoints at which affects 3 principal checkpoints at which the cycle can be delayed or halted.the cycle can be delayed or halted.

The cell uses these checkpoints to both The cell uses these checkpoints to both

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ppassess its internal state and evaluate assess its internal state and evaluate external signals.external signals.

The cell proceeds past each checkpoint The cell proceeds past each checkpoint only if internal and external conditions only if internal and external conditions are favorable.are favorable.


the the GG11/S/S checkpointcheckpoint assess cell growth. assess cell growth. This is the primary point at which the cell This is the primary point at which the cell decides whether or not to divide.decides whether or not to divide.

the the GG22/M checkpoint/M checkpoint ensures DNA ensures DNA integrity At this point the cell assesses theintegrity At this point the cell assesses the

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integrity. At this point the cell assesses the integrity. At this point the cell assesses the accuracy of DNA replication.accuracy of DNA replication.

the the Spindle checkpointSpindle checkpoint ensures that all the ensures that all the chromosomes are attached to spindle chromosomes are attached to spindle fibers, with bipolar orientation, in fibers, with bipolar orientation, in preparation for anaphase.preparation for anaphase.

G2

C

Spindle checkpointG2 / M checkpoint

M

Cell Cycle

90Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

S G1

G1 / S checkpoint(Start or Restriction Point)

Control

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To pass each checkpoint, enzymes called To pass each checkpoint, enzymes called CyclinCyclin--dependent kinasesdependent kinases ((CdksCdks) must be ) must be activated.activated.

Full activation of Cdks requires binding Full activation of Cdks requires binding

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q gq gwith specific regulatory proteins called with specific regulatory proteins called cyclins, cyclins, along with the appropriate along with the appropriate pattern of phosphorylation:pattern of phosphorylation:

Cyclin

PPhosporylation of the red site inactivates Cdk

Activation of CdkActivation of Cdk

Cyclin-dependentKinase (Cdk)

P


Phosporylation of the green site activates Cdk

Objective 10Objective 10The cyclinThe cyclin--Cdk complex, is also called Cdk complex, is also called

MPF or mitosis promoting factor.MPF or mitosis promoting factor.

MPF activates numerous proteins MPF activates numerous proteins needed for the next stage of the cell needed for the next stage of the cell

l b h h l i hl b h h l i h

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cycle by phosphorylating them.cycle by phosphorylating them.

When the level of MPF is high When the level of MPF is high enough, the cell passes through the enough, the cell passes through the checkpoint and enter the next stage of checkpoint and enter the next stage of the cell cycle.the cell cycle.


Different cyclins must bind with Cdk Different cyclins must bind with Cdk to pass each checkpoint.to pass each checkpoint.

The cyclins needed to pass a specific The cyclins needed to pass a specific checkpoint are synthesized during the checkpoint are synthesized during the

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p gp gstage preceding that checkpoint, and stage preceding that checkpoint, and are quickly degraded during the stage are quickly degraded during the stage following that checkpoint:following that checkpoint:

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In multicellular organisms, passage In multicellular organisms, passage through cell cycle check points is through cell cycle check points is stimulated by external signal molecules stimulated by external signal molecules called called growth factorsgrowth factors. .

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gg

Over 50 different growth factors have Over 50 different growth factors have been identified, and each one binds to a been identified, and each one binds to a different cell surface receptor.different cell surface receptor.

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When a growth factor binds to its When a growth factor binds to its surface receptor, this triggers an surface receptor, this triggers an intracellular signaling cascade that intracellular signaling cascade that activates regulatory proteins inside the activates regulatory proteins inside the

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nucleus.nucleus.

The activated nuclear regulatory The activated nuclear regulatory proteins stimulate DNA to produce proteins stimulate DNA to produce proteins (e.g. Cdk or cyclins) needed to proteins (e.g. Cdk or cyclins) needed to pass through cell cycle checkpoints:pass through cell cycle checkpoints:

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While growth factors act to stimulate While growth factors act to stimulate cell division, other regulatory molecules cell division, other regulatory molecules may inhibit it. may inhibit it.

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yy

An example is a protein named p53:An example is a protein named p53:


When When normal p53normal p53 detects damaged detects damaged DNA, it stops cell division by DNA, it stops cell division by preventing cyclins from joining to preventing cyclins from joining to Cdk. Cdk.

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Abnormal p53Abnormal p53 fails to stop division in fails to stop division in cells with damaged DNA. If genetic cells with damaged DNA. If genetic damage accumulates as the cell damage accumulates as the cell continues to divide, the cell can turn continues to divide, the cell can turn cancerous.cancerous.

p53 allows cellswith repairedDNA to divide.

Cell Division and Normal p53

DNA repair enzyme

p53protein

p53protein


DNA damage is caused by heat, radiation, or chemicals.

Step 1 Step 3

p53 triggers the destruction of cells damaged beyond repair.

Cell division stops, and p53 triggers enzymes to repair damaged region.

Step 2

protein

Cell Division and Abnormal p53

Abnormalp53 protein

Cancercell


DNA damage iscaused by heat,radiation, or chemicals.

Step 1 Step 2

Damaged cells continue to divide. If other damage accumulates, the cell can turn cancerous.

cell

Step 3

The p53 protein fails to stop cell division and repair DNA. Cell divides without repair to damaged DNA.

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Explain what cancer is, and Explain what cancer is, and describe how cancer can describe how cancer can result when control of theresult when control of the

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result when control of the result when control of the eukaryotic cell cycle breaks eukaryotic cell cycle breaks down.down.


Cancer is the uncontrolled growth and Cancer is the uncontrolled growth and division of cells.division of cells.

Most cancers result from mutations in Most cancers result from mutations in one of two types of growthone of two types of growth--regulating regulating

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p gp g g gg ggenes:genes:

protoproto--oncogenesoncogenes

tumortumor--suppressor genessuppressor genes


ProtoProto--oncogenesoncogenes code for proteins code for proteins involved in stimulating cell division involved in stimulating cell division (e.g. growth factors, growth factor (e.g. growth factors, growth factor receptors, cyclins)receptors, cyclins)

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Mutated protoMutated proto--oncogenes that oncogenes that stimulate a cell to divide when it stimulate a cell to divide when it shouldn’t are called shouldn’t are called oncogenesoncogenes(cancer(cancer--causing genes).causing genes).


TumorTumor--suppressor genessuppressor genes code for code for proteins involved in inhibiting cell proteins involved in inhibiting cell division (e.g. p53).division (e.g. p53).

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Mutated tumorMutated tumor--suppressor genes that suppressor genes that do not inhibit cell division when they do not inhibit cell division when they should can also cause cancer.should can also cause cancer.

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unit 3 unit 3 -- transmission and transmission and unit 3 ... · 3e. dna structure and replication...

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