Chapter 15: DNA Replication and Repair

Gene history: two experiments

Hershey-Chase: what are genes made of
Meselson-Stahl: DNA replication?

Hershy-Chase Experiment

1952
Grow T2 bacteriophage viruses w/ radioisotopes of P (DNA) and S (protein)

Meselson-Stahl
experiment and theories

1958
Grew E.coli in radioactive N
semiconservative, conservative, and dispersive

origin of replication

a specific sequence of bases where a new strand of DNA is built

the origin of replication creates a ____________

bubble in the double helix where the strands are separated from each other

replication fork

located at both ends of the bubble where daughter strands are elongated

dNTPs

Deoxyribonucleoside triphosphates
Nitrogenous bases w/ 2 xtra phosphates
Provide energy for polymerization

What end are dNTPs added to?

ONLY the 3' end

7 enzymes for repliosome

helicase, topoisomerase, RNA primase, DNA polymerase, SSBPs, sliding clamp, DNA Ligase

helicase

DNA strands are separated
(unzipped)

topoisomerase

cuts and re-ligates parent DNA to relieve twisting forces

RNA primase

attaches a short RNA segment (primer) to the unwound DNA strands

DNA polymerase

uses primer to bind to parent DNA strand and begin synthesis

What end does DNA polymerase attach nucleotides to?
Thus, which direction are the strands created in?

add to the 3' carbon
added in 5' to 3' direction

What are the two strands called?

leading (continuous)
lagging (Okazaki)

SSBPs

single strand DNA-binding proteins:
keeps single-stranded DNA from re-associating into double helix

sliding clamp

Keep DNA polymerase "on task"
Keeps replication speedy

DNA ligase

creates phosphodiester bond between Okazaki fragments

why is the end of replication not an issue for bacteria?

they're a circle!!

Telemerase

enzyme that uses its own RNA template to extend the unreplicated end of the lagging strand

All chromosomes have telomeres, which contain _______________

no coding DNA

What's the deal with telomeres in somatic cells?

most somatic cells in eukaryotes, telomerase is not present/weakly active: limit to # of somatic replication

What about telomeres in other cells?

Telomeres are active in stem cells and germ cells

Proofreading

DNA polymerase checks base pairs: recognizes mistake, goes back and fixes it

Mismatch repair

proteins that remove mismatched nucleotides from the newer DNA stand, allowing DNA polymerase to repair it

Mismatch repair reduces error to

1 per billion base pairs

What happens to mutations that aren't corrected?

Propagated in the daughter cell

What does DNA polymerase do

removes the RNA primer and replaces it w/ DNA

What are okazaki fragments

short DNA sequences that are created during DNA replication of the lagging strand

What is the Replisome

complex machine made of proteins responsible for replicating DNA

What are telomeres?

a new section of the DNA segment that is a buffer region that prevents DNA shorting