DNA AND RNAChapter 12

HISTORICAL DEVELOPMENT

1928 – Griffith Discovered

bacteria transferred something between them that changed them into a new strain.

Called this “bacterial transformation”.

Disease-causing bacteria (smooth

colonies)

Harmless bacteria (rough colonies) Heat-killed,

disease-causing bacteria (smooth colonies)

Control(no growth)

Heat-killed, disease-causing bacteria (smooth colonies)

Harmless bacteria (rough colonies)

Dies of pneumonia Lives Lives Live, disease-causingbacteria (smooth colonies)

Dies of pneumonia

Section 12-1

GRIFFITH’S EXPERIMENT

HISTORICAL DEVELOPMENT 1944 – Avery

Determined the transforming factor was DNA.

He destroyed different parts of the bacteria, and only when the DNA was destroyed did transformation not

occur.

HISTORICAL DEVELOPMENT 1952 – Hershey and Chase

Using a blender and bacteriophage, determined that DNA, not protein, was the genetic material.

Bacteriophage with phosphorus-32 in DNA

Phage infectsbacterium

Radioactivity inside bacterium

Bacteriophage with sulfur-35 in protein coat

Phage infectsbacterium

No radioactivity inside bacterium

HERSHEY-CHASE EXPERIMENT

Section 12-1

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 12-1

HERSHEY-CHASE EXPERIMENT

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 12-1

HERSHEY-CHASE EXPERIMENT

HISTORICAL DEVELOPMENT 1952 – Rosalind

Franklin Used x-ray

crystallography to show the structure of DNA was a helix.

HISTORICAL DEVELOPMENT

1953 – Watson and Crick Determined the

structure of DNA was a double helix, and proposed a model for DNA replication.

DNA STRUCTURE DNA is a chain (polymer) of

nucleotides. A nucleotide consists of a sugar, phosphate

and nitrogenous base.

Purines PyrimidinesAdenine Guanine Cytosine Thymine

Phosphate group Deoxyribose

DNA NUCLEOTIDESSection 12-1

DNA STRUCTURE DNA is a double helix (twisted ladder).

Two nucleotide polymers are held together by weak hydrogen bonds.

Nitrogen bases always pair up this way: Adenine with thymine A-T Cytosine with guanine C-G

The backbone of the ladder is alternating sugars and phosphates.

The steps of the ladder are the base pairs.

Hydrogen bonds

Nucleotide

Sugar-phosphate backbone Key

Adenine (A)Thymine (T)Cytosine (C)Guanine (G)

STRUCTURE OF DNASection 12-1

CHROMOSOMES AND DNA REPLICATION

12-2

DNA AND CHROMOSOMES Prokaryotic cells (bacteria)

No nucleus Single circular chromosome Bacterial DNA is about 1.6mm long

Eukaryotic cells (all else) 1000X more DNA than bacteria DNA in nucleus (protected) Multiple chromosomes Human DNA (combined) is over 1 meter long

Chromosome

E. coli bacteriumBases on the chromosome

PROKARYOTIC CHROMOSOME STRUCTURE

DNA AND CHROMOSOMES Eukaryotic DNA is tightly packed and

folded. It is wound about proteins called

histones.

Chromosome Structure of Eukaryotes

Chromosome

Supercoils

Coils

Nucleosome

Histones

DNAdoublehelix

Section 12-2

DNA Packing

DNA REPLICATION A cell copies its DNA before dividing.

The DNA uncoils. Then it “unzips” – the two strands separate

along the weak hydrogen bonds. Complimentary nucleotides are added with

the help of the enzyme DNA Polymerase. The result: two identical molecules of DNA.

DNA REPLICATIONSection 12-2

Growth

Growth

Replication fork

DNA polymerase

New strandOriginal strand DNA

polymerase

Nitrogenous bases

Replication fork

Original strand

New strand

DNA REPLICATION C:\Users\Carolyn\Videos\RealPlayer Do

wnloads\How DNA Copies Itself.mp4

RNA AND PROTEIN SYNTHESIS12-3

BIG IDEA DNA makes RNA makes Proteins makes

You.

RNA STRUCTURE Single-stranded chain of nucleotides No thymine - its replaced by uracil Sugar is ribose, not deoxyribose

TYPES OF RNA Messenger RNA (mRNA)

Carries a copy of the genetic code (gene) for a protein into the cytoplasm.

Ribosomal RNA (rRNA) A component of ribosomes where proteins

are made. Transfer RNA (tRNA)

Carries amino acids to the ribosome for assembly into proteins.

TRANSCRIPTION The process of DNA making mRNA in the

nucleus is called transcription. A section of DNA (gene) unwinds and separates Enzymes add complimentary RNA nucleotides

to make mRNA. mRNA leaves the nucleus and goes to a

ribosome in the cytoplasm. What is the complimentary nucleotide sequence for

this DNA sequence? DNA = A-T-T-C-G-C-G

RNADNA

RNApolymerase

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

TRANSCRIPTION C:\Users\Carolyn\Videos\RealPlayer Do

wnloads\Transcription.flv

TRANSLATION The process of mRNA being read on a ribosome

to make a protein is called translation. mRNA attaches to a ribosome. tRNA carries amino acids to the ribosome. The mRNA codon (3 nucleotide sequence) matches

up with a complimentary tRNA anticodon (complimentary sequence).

The amino acid is dropped off and added the growing polypeptide chain.

What is the amino acid sequence for the following mRNA sequence? See the universal genetic code chart…

mRNA = AUAAGCGCU

THE GENETIC CODE

TRANSLATION

FIGURE 12–18 TRANSLATION (CONTINUED)

TRANSLATION C:\Users\Carolyn\Videos\RealPlayer Do

wnloads\Translation.flv

TRANSCRIPTION AND TRANSLATION C:\Users\Carolyn\Videos\RealPlayer Do

wnloads\From DNA to Protein.mp4

TRANSCRIPTION AND TRANSLATION C:\Users\Carolyn\Videos\RealPlayer Do

wnloads\DNA Transcription and Protein Assembly.mp4

GENES AND PROTEINS Proteins are made of several

polypeptide chains folded together. The shape is important to how the protein

functions. One gene codes for the production of

one polypeptide. Therefore, several genes are needed to

make one protein.

GENE MUTATIONS12-4

KINDS OF MUTATIONS Mistakes made when DNA is copied are

called mutations. Two kinds: gene and chromosome

mutations

GENE MUTATIONS Gene mutations affect only one gene.

There is a change in the sequence of bases in DNA.

This causes the protein made by that gene to be incorrect. (sometimes)

Ex: lactose intolerance

CHROMOSOME MUTATIONS Changes in the number or structure of

chromosomes are called chromosome mutations. Ex: An extra chromosome causes Down

Syndrome.

MUTAGENS Substances that can cause mutations

are called mutagenic agents. UV light, chemicals, radiation

SIGNIFICANCE OF MUTATIONS• Inherited only if the mutation occurs in a sex

cell. Harmful mutations – cause many genetic

disorders. Ex: cystic fibrosis

Neutral mutations – have no effect on gene expression or protein function (most).

Beneficial mutations – source of genetic variability. Breeders artificially select for these traits