MOLECULAR GENETICS

Ch. 12.1 – DNA: The Genetic MaterialYou will be doing this section in small groups. Each group will read Section 12.1.

You will divide up the section so that everyone is reading equal amounts.

As you read your section you will put down some important information, such as:Year for the discoveryPerson(s) who did the discoveryWhat was discovered &/or how they made discovery

Next, you will put together all of your information into a timeline for the discoveries

Section 12.1 Key Points ContinuedPurines are double ringed bases such as:

Guanine and AdeninePyrimidine are single ringed bases such as:

Thymine, cytosine, and uracilChargaff’s Rule:

C = GT = A

Watson (IU graduate) & Crick built the double helix model for DNAUnique feature of the DNA molecule is the

direction the 2 strands run which is opposite of each other or antiparallel.

Section 12.1 Key Points ContinuedChromosome Structure

A human chromosome length ranges from 51 million to 245 million base pairs long.A DNA strand that is 140 million

nucleotides long would measure approximately 5 cm. long (2 in.)

To fit all of this into the nucleus of the cell the DNA tightly coils around a beadlike protein called a histoneThe histone & the DNA together creates a

nucleosome.The nucleosomes group together into

chromatin fibers, which supercoil to create the DNA structure called a chromosome. biology.kenyon.edu

SECTION 12.2 – REPLICATION OF DNAMAIN IDEA – DNA replicates by making a

strand that is complementary to each original strand.

REVIEW:What nitrogen bases pair together?What is contained in the nucleotide for DNA?What nitrogen bases would you find in DNA?What is contained in the nucleotide for RNA?What bases would you find in RNA?

SEMICONSERVATIVE REPLICATIONSemiconservative replication is where parental

strands of DNA separate and serve as the template to produce DNA molecules that have one strand of parental DNA and one strand of new DNA.

csls-text2.c.u-tokyo.ac.jp

Where does DNA replication take place?During what phase does DNA replication take place?Will DNA replication take place in mitosis, meiosis, or

both?

UNWINDING AND BASE PAIRINGDNA helicase, an enzyme, will unwinding &

unzip the double helix leaving single strands of DNA.

DNA polymerase, an enzyme, helps in adding the correct nucleotides to the new DNA strand.Adenine (A) pairs with thymine (T)Guanine (G) pairs with cytosine (C)

Base pairing:Template: A T C C A G G T GDNA copy:

Produces identical copies to the original double stranded DNA

DNA replication will begin at many places along the chromosome

SECTION 12.3 – DNA, RNA, AND PROTEINMAIN IDEA – DNA codes for RNA, which

guides protein synthesis.

QUESTION: How does DNA replication relate to mitosis?

How does DNA replication relate to meiosis?

How does DNA replication relate to reproduction?

CENTRAL DOGMARemember – proteins function as structural building blocks for the cells and as enzymes.

Central Dogma of biology: DNA codes for RNA, which controls the synthesis of proteins.DNA → RNA → PROTEIN

RNA is a nucleic acid that is similar to DNA, except:RNA contains the sugar ribose, uracil

replaces thymine, and is single stranded.

TRANSCRIPTIONTranscription is the step in the central dogma –

synthesis of the mRNA from the DNATranscription = DNA → RNA

Transfers the DNA code to mRNA in the nucleus.

mRNA takes the code into the cytoplasm for protein synthesis

To create mRNA the DNA is unzipped in the nucleus and RNA polymerase binds to a specific section and creates the mRNA The strand of DNA that is read by the RNA

polymerase is called the template strand.The strand of DNA not read by is called the

nontemplate strand.Uracil is used instead of thymine in mRNANew mRNA strand leaves the nucleus

through the nuclear pores into the cytoplasm

CENTRAL DOGMA CONTINUED3 main types of RNA:

Messenger RNA (mRNA)Long strands of RNA nucleotides that are

formed complementary to one strand of DNALeave the nucleus and go to the ribosomes to

direct the synthesis of a specific proteinRibosomal RNA (rRNA) faculty.southwest.tn.edu

Type of RNA that combine with proteins to form ribosomes in the cytoplasm . legacy.hopkinsville.edu

Transfer RNA (tRNA)Small segments of RNA nucleotides that

transport amino acids to the ribosome.

RNA PROCESSINGScientists noticed that mRNA was shorter than the coding region of DNA

Found that the DNA is interrupted by sequences, called INTRONS, that are not in the final mRNA

Coding sequences that remain to make up the mRNA are called EXONS.

Before mRNA leaves the nucleus the INTRONS are removed

TRANSCRIPION CONTINUEDRemember: Base pairs in RNA

• Cytosine Guanine GuanineCytosine

• Adenine Uracil Uracil Adenine

• Thymine (from DNA) Adenine • DNA Strand: A T G C T A A

G C RNA Strand: ________

THE CODEThere are 20 amino acids that are used to make proteins.

DNA code is read as a 3 base code.In DNA or mRNA the 3 base code is called a CODON

The codon that will start the reading of the mRNA is the codon AUG, which codes for the amino acid methionine

GENETIC CODE:emc.maricopa.edu

CIRCLE GENETIC CODE: krishnascience.info

The Genetic CodeProteins are made by joining amino acids into long chains called polypeptides amino acids are like puzzle pieces

Proteins would be like the whole puzzle

TRANSLATIONTranslation = RNA → proteinOnce the mRNA is made and the introns are

removed and exons are left mRNA leaves the nucleus and goes and attaches to a ribosome in the cytoplasmThis is where the mRNA is read and translated to

make a protein through a process called translation.

Translation involves:tRNA that acts as the interpreters of the mRNA

codon sequence.tRNA has a cloverleaf shape that has a 3 base

coding sequence called the anticodon.Anticodons are complementary to a codon on the

mRNA.

ROLE OF THE RIBOSOMERibosomes consists of 2 subunits.When mRNA leaves the nucleus the 2 subunits of the ribosome come together and attach to the mRNA.

Now the tRNA will bring in the correct amino acid and attach to the mRNA.

This continues until a stop codon is reached and it is the end of the protein synthesis.

Protein is now released.

TRANSLATION: ajinomoto-eurolysine.com

SECTION 12.4 – GENE REGULATION AND MUTATION

MAIN IDEA – Gene mutation is regulated by the cell, and mutations can affect this expression.

QUESTION: What words and images come to mind when you hear the words mutation or mutant?

HOX GENESGene regulation is crucial during development.

Eukaryotes develop from a single cell called a zygote.

Zygote produces all the different kinds of cells needs by the organism by mitosis.

Hox genes helps control how the body of an organism develops.Mutations in the Hox genes can cause a fruit fly to develop a leg where its antennae should be.

HOX GENE MUTATION: palaeos.com

MUTATIONSMutation is a permanent change in a cell’s

DNA.Types of gene mutations:

Point mutation is a chemical change in one base pair and could cause a genetic disorder.Types of point mutations:

Substitution (missense) – one base is exchanged for anotherEX: C is replaced with G (now codes for the wrong amino acid)

Substitution (nonsense) – changes the codon for an amino acid to a stop codon causing translation to end early resulting in a protein that cannot function normally.

MUTATIONS – CONTINUEDTypes of gene mutations continued:

Frameshift: Insertion – adds a nucleotide to the DNA sequence shifting the reading frame

EX: original strand: A C C G G C C A A amino acids: _________________________________

mutated strand:A C C C G G C C A A amino acids: _________________________________ Frameshift: Deletion – deletes a nucleotide from the DNA sequence shifting the reading frame

EX: original strnad: A C C G G C C A A mutated strand: A C G G C C A A

CHROMOSOMAL MUTATIONSDeletions

Part of chromosome is deleted/gone completelyOriginal: A B C D Deleted: A C D

DuplicationsPart of chromosome is duplicated/repeated Original: A B C D Duplicated: A A B C D

InversionsPart of code is read in a different direction (reverses

the directions of the parts of the chromosome)Original: A B C D, Inverted: A C D B

TranslocationsEntire sections of chromosome are shifted (when

part of one chromosome breaks off and attaches itself to another chromosome) http://staff.tuhsd.k12.az.us/gfoster/standard/bmut.htm

CAUSES OF MUTATIONS:Some mutations, like point mutations, occur spontaneously.Cells proofread so it happens rarely

Mutagens are some types of chemicals and/or radiation

BODY CELL VS. SEX CELL MUTATIONBody cell:

Mutation in a body cell (somatic cell) is in that one cell and the future daughter cells that this cell makes.If these mutations do not cause problems for the

cell it is called a neutral mutation.If these mutation cause problems in the cell the

cell could become cancerous or the cell may die.These mutations are not passed down to offspring

Sex cell:If the mutations occurs in the sex cells it will be

passed down to the offspring and will be present in every cell of the offspring.The mutation may or may not affect the offspring.