DNA Structure and Replication

Central Dogma

DNA → RNA → Proteins

Reverse Transcription

done by reverse transcriptase

turn RNA to cDNA

Frederick Griffith’s experiment

tested on mice w the S strain (violent) and R strain

Boiled S strain when given to the mice together w the R strain killed the mice

→ something in the S strain was able to transfer to the R strain

Avery, Macleod, McCarthy experiment

carried on the Griffith exp to figure out the genetic component.

destructed several component one at a time and only when DNA is destroyed, the mouse lives

→ virulent factor (gene) in the DNA

nucleotide

deoxyribose sugar + base (A/T/C/G) + P

nucleoside

deoxyribose sugar + base (A/T/C/G)+ without P

deoxyribose

1C: base attachment site

3C: -OH, for DNA replication

5C: P attachment site (for DNA replication)

purines

adenine and guanine

2 ring structure

pyramidines

thymine and cytosine

1 ring structure

Chargaff rule

all bases are added to 100%

does not apply to RNA

base pairing

C-G : 3 H-bonds

A-T: 2 H-bonds

structure of DNA

double-stranded alpha helix or double helix

1 full turn = 10bp = 34A (armstrong)

backbone: deoxyribose sugar joined by phosphodiester bonds

ATCG bonds in central core

anti-parallel strands

chromatin

DNA wraps 2.5 times around histone → nucleosomes

chromatin: lots of nucleosomes form together into a string

after replication:

CAF-1: chromatin assembly factor - assembles histone

PCNA proliferating cell nuclear antigen: wrap DNA around histones

DNA Replication

semiconservative

parent strand = template strand

new strand remains paired w template strand until mitosis

elongation

• new nucleotide is added to the 3’ end, requires a 3’-OH

replication fork

the opening of DNA where the DNA Synthesis occurs

DNA rep process

• helicase: unzip the genes

• DNA Pol A: makes primers and makes the first 20bp of lagging strand

• DNA Pol D starts replication and fill in gaps in O fragments

• RNAse H: remove primers

• Ligase: seals the bases, especially on the Okazaki fragments

• topoisomerase: removes supercoiled twists by cutting and rejoining the strands.

Okazaki Fragments

the short strands of DNA being made on the lagging strand.

Prokaryote DNA Rep

• synthesis happens in both direction from multiple origins

• primase: make RNA primer

• DNA Pol 3, helicase and gyrase (a variety of topoisomerase) are involved

• DNA Pol 1: remove primers and fill in the gaps in O fragments

telomeres

the special sequence at the end of gene to prevent shortening pop gene due to unpaired bases

constantly being maintained by telomerase