7.1: N

UCLEIC

ACIDS

1. HERSHEY-CHASE EXPERIMENTS

Alfred Hershey and Martha Chase researched the genetic material of viruses. They used the T2 bacteriophage (simple structure).

They knew that:

DNA contains phosphorous but not sulphur

Protein contains sulphur but not phosphorous

2. ROSALIND FRANKLIN’S X-RAY DIFFRACTION

1950: Franklin made improvements to the equipment (camera) and procedure for isolating DNA. Until she was able to calculate the dimensions of the double helix.

VIEWING NUCLEOSOMES

- What do you remember about nucleosomes?

- What is the function of a nucleosome?

Go to: http://www.rcsb.org/pdb/home/home.do

Follow the instructions on page 348, purple box.

ENZYMES OF REPLICATION

Enzyme FunctionHelicase Separates the strands

(breaks H-bonds)Topoisomerase Released before helicase,

ahead of the replication forkSingle stranded binding proteins

Separate the strands

RNA primer Initiates activity of DNA polymerase

DNA primase Creates RNA primerDNA polymerase Attaches new nucleotidesDNA ligase Connects fragments of

replicated DNA

NON CODING REGIONS OF DNA

The majority of the genome for eukaryotes is non-

coding.

There are many repetitive sequences – in humans almost 60% of the total

genome is repetitive.

Telomeres contain a large amount of repetitive code (they ‘protect’ the genes

near the end of the chromosome)

PROMOTER

The promoter is an example of a non-coding region of DNA that has a function.

The promoter is the binding site for RNA polymerase, the promoter is not transcribed but proteins would not be produced without it.