Chapter 12-13 –DNA and How Genes Work

• What is transforming agent? DNA or protein?

Avery, MacLeod and McCarty

Avery, MacLeod and McCarty

• DNA carries the heritable information

Avery, MacLeod and McCarty conclusion

1944

Hershey and Chase

Martha Cowles Chase

Alfred Day Hershey

Hershey and Chase

Bacteriophage: viruses that infect bacterial cells

Hershey and Chase

• Genetic material in virus was DNA• DNA is agent of heredity

Hershey and Chase conclusion

INDEPENDENT FUNCTIONS OF VIRAL PROTEIN AND NUCLEICACID IN GROWTH OF BACTERIOPHAGE*

B~ A. D. HERSHEY AND MARTHA CHASE(From the Department of Genetics, Carnegie Institution of Washington, Cold Spring

Harbor, Long Island)(Received for publication, April 9, 1952)

The work of Doermaml (1948), Doermann and Dissosway (1949), and Anderson and Doermann (1952) has shown that bacteriophages T2, T3, and T4 multiply in the bacterial cell in a non-infective form. The same is true of the phage carried by certain lysogenic bacteria (Lwoff and Gutmann, 1950). Little else is known about the vegetative phase of these viruses. The experimentsreported in this paper show that one of the first steps in the growth of T2 is the release from its protein coat of the nucleic acid of the virus particle, after which the bulk of the sulfur-containing protein has no further function.

DNA – just what is it?

Nucleic AcidsMonomers =

nucleotides

Polymer = DNA, RNA

DNANucleotide

(monomer)

4 bases

DNA

“double helix”

DNA

A - TG - C

DNA

“double helix”

A - T G - C

Rosalind Franklin (1920-1958)

X-ray crystalography

Structure of DNA

Watson and Crick

1953

Watson and Crick (1953)

Replication

Expression

DNA

DNA Replication

DNA Replication

DNA Replication

DNA Replication

DNA Replication

DNA Replication

DNA

Information stored in order of the bases

+/- 1200 copies

Central Dogma of Cell Biology

DNA (gene)Protein

GENETICS: TA TUM AND BEADLEGENETIC CONTROL OF BIOCHEMICAL REACTIONS IN NEUROSPORA:

AN "AMINOBENZOICLESS" MUTANT*By E. L. TATUM AND G. W. BEADLE

DEPARTMENT OF BIOLOGY, STANFORD UNIVERSITYCommunicated April 17, 1942

Para-aminobenzoic acid has recently been recognized as a factor required for the growth of a number of micro6rganisms' and as a member of the vitamin B group.2 One of the number of x-ray induced mutants of Neurospora crassa, obtained as described elsewhere,' is characterized by the loss of ability to synthesize p-aminobenzoic acid. This "aminobenzoicless“ mutant is differentiated from normal by a single gene, is unable to grow on unsupplemented synthetic medium, but its growth is indistinguishable from normal when p-aminobenzoic acid is supplied.

Each gene codes for a specific and unique protein

1958 – Nobel Prize

One-Gene/One-Polypeptide Hypothesis

Central dogma of molecular biology

Extracting and using the information

Two Steps:

1. 2.

Extracting and using the information

The information

Extracting and using the information

An intermediate

Extracting and using the information

The product

Translation – constructing a protein

DNA mRNA

proteintranscrip

tion

translatio

n

Transcription

DNA copied into mRNA

mRNAsingle-stranded

U instead of T

Translation – constructing a protein

DNA mRNA

proteintranscrip

tion

translatio

n

Instructions are coded in the order of the bases

20 amino acids

Protein is a polymer of amino acids

Instructions are an ordered list of amino acids in protein

Each ‘word’ in the DNA-RNA vocabulary is 3 ‘letters’ long

One “word”

Each ‘word’ in the DNA-RNA vocabulary is 3 ‘letters’ long

A ‘word’ is called a codon

Triplet Codon: group of 3 bases that specifies an amino acid

The Genetic Code

-Redundant -Not ambiguous-Stop codons-AUG - start-Universal (nearly)

Marshal W. Nirenberg

The Dictionary

Punch tape

Ribosome

mRNAtRNA

tRNA brings in the amino acides

Translation

Translation

Translation

Translation

Translation

Translation

Universal (nearly)

Reading frames

the red dog ate the bug

Reading frames

her edd oga tet heb ug