CHAPTER 10

MOLECULAR GENETICSNUCLEIC ACIDS to

PROTEINS: •STRUCTURE

•REPLICATION

•PROTEIN SYNTHESIS

DNA is the unit of heredity.it is transmitted fromparents to offspring in reproductive cells calledgametes. (meiosis)

CHROMOSOMES are…DNA coiled around HISTONEproteins then supercoiled into a compact shape. This is important for cell division.

FRANKLIN, WATSON & CRICK discovered the structure of DNA

1953

X-ray diffraction crystallography is a technique that was usedto help scientists learn the structure of DNA. (Rosiland Franklin)

(NOT ON TEST… just thought you’d like to know)

DNA STRUCTURE

Double stranded– 2 polymer chains of

nucleotide monomers– Covalent bonds

joining amino acid monomers “sugar phosphate backbone”

– Hydrogen bonds joining the two strands through nitrogen-containing-bases “A”, “T”, “G” or “C

FUNCTION

Unit of Heredity– Easily copied

(Sphase)– 2 template strands– Gene copied into

mRNA is instructions to assemble protein.

base-pairsare the “rungs” of the ladder

sugar-phosphatebackbone or “uprights” of theladder

THE DOUBLE HELIX

DNA NUCLEOTIDES

DeoxyriboNucleic Acids

are made of 3 parts:

1. Phosphate Group

2. Sugar = deoxyribose

3. Nitrogen-containing base:

• A (adenine)• T (thymine)• G (guanine)• C (cytosine)

RNA NUCLEOTIDES

RiboNucleic Acid

are made of 3 parts:

1. Phosphate Group

2. Sugar = RIBOSE

3. Nitrogen-containing base:

• A (adenine)• U (uracil) instead of

T• G (guanine)• C (cytosine)

The nucleotide is the chemical building block of NUCLEIC ACIDS

sugar

phosphategroup

NitrogenContainingbase

There is no THYMINE base in RNA

URACIL takes it’s place

URACIL is a molecular mimic of THYMINE and does it’s same

job

Base-Pair Rules or Chargaff’s LAWS:

1. purine-pyrimidine2. Adenine-Thymine Thymine-Adenine3. Guanine-Cytosine Cytosine-GuanineRNAUracil-AdenineAdenine-Uracil

purines(A & G)pyrimidines

(T & C)

Each nucleotide’s partner is called it’sCOMPLEMENT

•A

•T

•G

•C

•A

•T

•C

•C

•A

•G

•C

•T

•T

Tell me the complements to this nucleotide sequence….

Each nucleotide’s partner is called it’sCOMPLEMENT

•A

•T

•G

•C

•A

•T

•C

•C

•A

•G

•C

•T

•T

A A G C T G G A T G C A T (DNA)

A A G C U C C A U C G A U (RNA)

if the DNA is 35% A, then…What are the values for T, C, G?

Chargaff’s Rule… The amounts of A & T match, so do the Amounts of C & G (where the base-pair rules came from).

• If A = 35% and A = T… then T=35%• Since 35+35=70 and 100-70=30, G+C=30• If G=C… then G = 15% and C = 15%• ANSWER:A= 35%, T= 35%, G = 15%, C= 15%

• QUESTION: What are the values of A,T,G, and C if the DNA is 20% G?

• ANSWER: A=30%, T=30%, G=20%, C=20%

• QUESTION: What are the values of ATC&G if the DNA IS 10% T?

• ANSWER: A=10%, T=10%, G=40%, C=40%

DNA REPLICATION- copying the DNA.ENZYMES USED:•HELICASE-open DNA•DNA POLYMERASE-build polymer•DNA LIGASE-connect fragments

NUCLEOTIDES USED:•DNA NUCLEOTIDES base-pair rule

SEMICONSERVATIVEREPLICATION:•2 strands: each is 1/2 old & 1/2 new•Leading strand- continuous•Lagging strand- okazaki fragments•Polymerase moves along the template strand in a 3’ to 5’ direction.•New strand is built 5’ to 3’

The 5’ end has the phosphate

Notice, the two strands runanti-parallel (opposite).

SEMICONSERVATIVE REPLICATION…

each strand of the DNA double helix acts as the “template” or instructions to build the matching strand

Mutations dooccur but arefixed by enzymes.

1/100,000 nucleotides are incorrectly placed

Enzymes fix mostmistakes reducingthe number to

1/ billion base pairs

Mutations (changes in the DNAsequence) can mean changes in phenotypes. They are the fuel forevolution.

What is the connection between your genes (genotype) and how

you look (phenotype)???

PROTEIN

PROTEIN SYNTHESIS

Central dogma = DNA --> RNA --> protein

DNA (instructions) REMAIN IN THE NUCLEUS

PROTEINS ARE ASSEMBLED OUTSIDE THE NUCLEUS on RIBSOMES

DNA… the instructions• double stranded• twisted shape

RNA… the workersmRNA- single strandedrRNA- globular form

w/ proteinstRNA- single stranded,

hairpin loop

PROTEIN… the productAmino acids strung together

molecularmodel oftRNA I made while working at my oldJob.

TRANSCRIPTION

making mRNA, tRNA, and rRNA

The promoter has the sequence TAC which causes the RNA polymeraseto attach to the beginning of the template chain and mRNA to be made.

The terminator sequence causes the RNA polymerase to release boththe DNA and the newly formed mRNA. There are 3 different terminator signals: ACT, ATT, and ATC.

TRANSCRIPTION

TRANSLATION

•3 types of RNA work together to produce proteins

• proteins are chains of amino acids bonded together by peptide bonds

TRANSLATION • Ribosome attaches to start codon on mRNA (AUG).

• 1st tRNA w/ anticodon (UAC) binds to start codon w/in ribosome.

• 2nd tRNA w/ matching anticodon to 2nd codon binds.

• Peptide bond is formed between amino acid #1 and amino acid #2.

• First tRNA leaves. • Ribosome moves to next codon

on mRNA and tRNA #3 moves in…. Peptide bond.REPEAT

• When stop codon is reached (UAA, UGA, UAG) release factor breaks binds instead of tRNA.

• All parts separate.

How can 4 nucleotides code for 20 different

proteins??????????????read the nucleotides as sets of three

3 (4)

4 x 4 x 4 = 64 combinations

anticodon

codon

Nucleotides have meaning in sets of THREE.

The CODE can be cracked using this table. Use it to determine whichof the 20 amino acids each mRNA codon- codes for.

Don’t Betricked

WHICH AMINO ACID?1) DNA Triplet is TTT 2) Codon is AUG3) Anticodon is CCC4) ACT

WHICH AMINO ACID?1) DNA Triplet is TTT 2) Codon is AUG3) Anticodon is CCC4) ACT

OK… I will!ANSWERS:1) Lys2) Met3) Gly4) STOP

…G A T T A C A T A……C T A A T G T A T…

DNA TRIPLET

mRNA CODON

tRNA ANTICOD

ON

Amino Acid

GAT

TAC

ATA

…G A T T A C A T A…

DNA TRIPLET

mRNA CODON

tRNA ANTICOD

ON

Amino Acid

GAT

TAC

ATA

RNA polymeraseU

U

UA

A

A

AG C RNAnucleotides

…G A T T A C A T A…

DNA TRIPLET

mRNA CODON

tRNA ANTICOD

ON

Amino Acid

GAT CUA

TAC AUG

ATA UAU

RNA polymeraseU

U

UA

A

A

AG C RNAnucleotides

…G A T T A C A T A…

DNA TRIPLET

mRNA CODON

tRNA ANTICOD

ON

Amino Acid

GAT CUA GAU

TAC AUG UAC

ATA UAU AUA

RNA polymeraseU

U

UA

A

A

AG C RNAnucleotides

1. WRITE THE CORRECT LETTER BELOW EACH SYMBOL.

2. USE “BASE PAIR” RULES TO WRITE THE mRNA

3. TRANSFER THE CODONS BELOW.

4. USE “BASE PAIR RULES” TO WRITE THE ANTICODONS.

5. USE CODONS & THE CHART TO FIND AMINO ACIDS.

CHECK YOUR WORK.

HOW DID YOU DO?

ANY QUESTIONS?

YOUR Classwork/ homework… plus the Other sheets.