DNA and RNA

Chapter 12

Hereditary MaterialHereditary Material

• Genes are protein codes.

• Our genes are on our chromosomes.

• Chromosomes are made up of DNA.

• Genes are composed DNA!

Chromosome StructureChromosome Structure

• Chromatin is tightly coiled around proteins called histones.

• DNA and histone molecules form a beadlike structure: nucleosome

• Nucleosomes create the supercoils

of DNA in a chromosome.

Chromosome Structure of Eukaryotes

Chromosome

Supercoils

Coils

Nucleosome

Histones

DNA

double

helix

Structure of DNA• In eukaryotes, DNA is found in the

NUCLEUS of cells.• DNA is made up of a series of monomers

called nucleotides.Nucleotide structure:

1. 5–carbon sugar: Deoxyribose2. Phosphate group3. Nitrogenous base

• DNA is a twisted-ladder called a

DOUBLE HELIX!

DNA NucleotideDNA Nucleotide

OO=P-O O

PhosphatePhosphate GroupGroup

NNitrogenous baseNitrogenous base (A, G, C, or T)(A, G, C, or T)

CH2

O

C1C4

C3 C2

5

SugarSugar(deoxyribose)(deoxyribose)

Nitrogenous BasesNitrogenous Bases

• Double ring Double ring PURINESPURINESAdenine (A)Adenine (A)Guanine (G)Guanine (G)

• Single ring Single ring PYRIMIDINESPYRIMIDINES

Thymine (T)Thymine (T)Cytosine (C)Cytosine (C) T or C

A or G

Chargaff’s (Base Pairing) Chargaff’s (Base Pairing) RuleRule

• AdenineAdenine must pair with ThymineThymine

• GuanineGuanine must pair with CytosineCytosine

• The bases form weak hydrogen bonds

G CT A

Why do they pair together

this way?

DNA Double HelixDNA Double Helix

NitrogenousNitrogenousBase (A,T,G or C)Base (A,T,G or C)

““Rungs of ladder”Rungs of ladder”

““Legs of ladder”Legs of ladder”

Phosphate &Phosphate &Sugar BackboneSugar Backbone

Hydrogen bonds

Nucleotide

Sugar-phosphate backbone

Key

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

DNA Structure

DNA Replication

• Occurs during cell division.

• Helicase enzyme “unzips” the molecule of DNA, breaking the hydrogen bonds.

• Free-nucleotides in the nucleus will be bonded with its complementary base.

• DNA polymerase helps to bond the nucleotides together and check for errors.

DNA ReplicationSection 12-2

Growth

Growth

Replication fork

DNA polymerase

New strand

Original strand DNA

polymerase

Nitrogenous bases

Replication fork

Original strand

New strand

DNA Replication

The Scientists

• Griffith – one strain of bacteria was “transformed” into another strain.

• Avery – found that DNA was the transforming factor.

• Hershey and Chase – DNA is the genetic material.

• Watson and Crick – discovered the molecular structure of DNA.

Griffith’s “Transformation” Experiment

Avery’s experiment isolated the element that caused the bacterial to become lethal…DNA

Bacteriophage with phosphorus-32 in DNA

Phage infectsbacterium

Radioactivity inside bacterium

Bacteriophage with sulfur-35 in protein coat

Phage infectsbacterium

No radioactivity inside bacterium

Section 12-1Hershey-Chase Experiment

Chargaff and Franklin• Chargaff

Percentages of guanine and cytosine bases are almost equal in any sample of DNA

Same is true of adenine and thymine

DNA in all instances and from all organisms followed this rule

• Rosalind FranklinX-Ray diffraction showed that

DNA was twisted into a

double helix.

RNA and Protein Synthesis

Section 12-3

RNARNA

• Long, single strand of nucleotides.

• Nitrogen bases: A,U,G,C no Thymine!

• Sugar: Ribose

• Found in cytoplasm and nucleus

• Types: messenger, transfer, ribosomal

• Function: Involved in the synthesis of protein molecules.

Protein Synthesis occurs in two phases:

TRANSCRIPTIONTRANSLATION

TranscriptionTranscription• Location where it occurs: Nucleus

• RNA polymerase will unwind DNA at the region to be transcribed.

• It locates and binds at the promoter.

• mRNA is then made by base-pairing:

A-U, G-C, T-A, C-G If DNA sequence is: GATTACA

Then mRNA sequence is: CUAAUGU

• When finished, mRNA leaves the nucleus and goes to the cytoplasm.

RNADNA

RNApolymerase

TranscriptionSection 12-3

Adenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)

TranslationTranslation

Location: Cytoplasm mRNA finds a ribosome

Ribosome reads strand for the start “codon”A codon is a mRNA triplet. Ex: AUG, UUC, etc

Start codon is: AUG

Transfer RNA’s bring

amino acids to

ribosome.

• tRNA’s anticodon bonds with mRNA codon.

mRNA codons AUG UAA CGC

tRNA anticodons UAC AUU GCG

• Amino acids connected with peptide bonds.

• When a “Stop” codon is reached. Protein is released from ribosome.

Translation continued…Translation continued…

TranslationSection 12-3

Animation

How to Interpret m-RNA’s Code:

• Each 3 nitrogen base sequence is called a CODON.

• Each codon specifies for a particular amino acid.

• AUG codon starts the initiation of the protein and codes for the amino acid methionine.

• Stop codons do not code for any amino acids ending the protein chain.

• A polypeptide is a chain of amino acids joined with peptide bonds – aka a PROTEIN!

Codon Chart #1Section 12-3

Codon Chart #2

Let’s Practice!Let’s Practice!

DNA: TACTTGGAT

mRNA: AUGAACCUA

tRNA: UACUUGGAUAmino Acid squence:

Methionine, Asparagine, Leucine

Mutations

Section 12-4

MutationsMutations

• Changes that occur in the DNA

• Two types:

1. Gene mutations

2. Chromosomal mutations

• Many mutations are harmless

• Pros: increase adaptation or survival

• Cons: some can be lethal or debilitating

Gene MutationsGene Mutations

• Changes that occur in a single gene.

• Point mutations: one nucleotide that affects one amino acid.

(substitutions produce point mutations)

• Frameshift mutations: involve the reading of the DNA or m-RNA strand; many amino acids are affected. (insertion or deletions produce frameshift mutations)

Point mutation:

Substitution Insertion

Deletion

Gene MutationsGene Mutations

Frameshift mutations

Chromosomal MutationsChromosomal Mutations

• Whole chromosome is affected.

• Four types:

1. Deletion – loss of material

2. Duplication – addition of material

3. Inversion – rearrangement of material

4. Translocation – switching material with another chromosome

Deletion

Duplication

Inversion

Translocation

Chromosomal MutationsChromosomal Mutations