Chapter 14 - DNA

bacteriophage

A virus that infects bacteria

Chargaff’s rules

A% = T% and G% = C%;

Purine

Adenine and Guanine; Larger, 2 sugars

Pyrimidine

Thyemine and Cytosine; Smaller, 1 sugar

Rules for complimentary strands

Dna runs antiparallel to its complimentary strand, from 5’ to 3’.

Conservative model for DNA replication

When replicating DNA; The two parent strands rejoin

Semiconservative model for DNA replication

When replicating DNA; each daughter strand will match with a new strand; This is the one we actually use

Dispersive model for DNA replication

Each strand is a mix of new and oldWhen replicating DNA;

Experiment 1: griffith

Found that pathogenic bacteria could cause non pathogenic bacteria to become pathogenic

Experiement 2: Avery

Found that DNA is the transforation consist, not Protein

Experiment 3:Hershey-Chase

More evidence for DNA being genetic material, and discovered virus and backeriophages

Experiment 4: Watson-Crick and Photo 51

Discovered the Shape of DNA using a photo from Rosalind Franklin

Experiment 5: Meselson - Stahl

Using heavy nitroen, they where able to prove semiconservative replication of dna

DNA replication Core Idea

RNA polymerase starts, then DNA polymerase binds to and extends the DNA, DNA is replicated from 5’ to 3’

Origins of replication / Replication Bubble

Two DNA strands are separated opening a space for replication, 1 in bacteria; thousands in eukaryotic chromosomes; Begins in both directions

Helicase

Unzips the double helix

Primase

RNA polymerase that makes the RNA primer

Topoisomerase

Cuts the DNA to prevent it from winding up, then rejoins

DNA polymerase

Transcribes the DNA, must have a RNA primer to be able to bond to the DNA strand; uses dATP for energy; must go in the 5’ → 3’ direction

Sliding clamp

Binds dna polymerase to dna

Leading strand

Moves continously towarsd the replication fork

Lagging strand

moves behind the leading strand, replicates towards it; synthesised in a serrises of Okazaki fragments

Okazaki fragments

the lagging strands, joined with DNA ligase

Single stand binding protein

Binds to and stabilized the DNA during replication

DNA proof reading

DNA polymerase proofreads as it goes,

Mismatch repair

Repair enzymes correct the base pair error

nuleotide excision repair

Nuclease cuts out and replaces the damages streach

The End replication problem

Dna gets shorter and shorter each time it is replicated

End replication solution; Telomere

Found at the end of eukaryotic chromosomes; repeating base sequence of TTAGGG; 100-1000 repetitions; extended by Telomerase

Euchromatin

Loosly packed chromatin

Heterochromatin

Highly condensed and prevents expression