BI210 - DNA History and DNA Replication Study Guide

where does each of the main events of the central dogma occur in pro. cells

• cytoplasm

  • replication, transcription, translation

where does each of the main events of the central dogma occur in euk. cells

• nucleus

  • replication and transcription

• cytoplasm

  • translation

what is DNA replication

process of producing two identical replicas of DNA from one original model

when does DNA replication occur in the cell cycle

S phase

3 studies that led DNA to being identified as molecule of heredity

• Griffith

• Avery, Macleod, McCarty

• Hershey-Chase

Griffith

• 1928

• studying two strands of streptococcus pneumonia in mouse

  • found living S cells in blood sample from dead mouse that had been injected w/ heat-killed S cells mixed w/ living R cells

what is a transformation

genetic alteration of a cell

Avery, McCarty, MacLeod

• 1944

• discovered DNA was transforming substance

  • only DNA worked in transforming harmless bacteria into pathogenic bacteria

• treated heat-killed virulent bacteria w/ enzymes

  • only destroying DNA prevented transformation

DNAses

destroy DNA

RNAses

destroy RNA

proteases

destroy proteins

bacteriophages + why they are a great model

viruses that infect bacteria

• only made of DNA and proteins

Hershey-Chase

• 1952

• discovered that T2 DNA enters cell and proteins remain outside

  • labeled bacteriophage DNA w/ radioactive P

  • labeled bacteriophage proteins w/ radioactive S

chargaff’s rules

A=T, C=G

Chargaff

• 1947

• within species, amount of 4 bases was unequal but consistent

• between species, A/T, C/G 1:1

• broke down DNA and used paper chromatography to separate 4 bases
  

Franklin, Watson, and Crick

• 1950s

• Franklin’s X-ray crystal provided helical foundation for structural model proposed by Watson and Crick

conservative replication

all new and all old

semiconservative replication

one parental strand and one synthesized strand

dispersive replication

mix of parental and synthesized

Meselson and Stahl

• proved DNA rep. is semiconservative

  • used E.coli cultured in N and centrifugation to observe shift from heavy to intermediate to light DNA

origin of replication

starting point for DNA rep.

• allows double helix to unwind and form two replication forks

why is origin of replication A/T rich

easier to unwind

• less H-bonds

replication bubble

unwound, open region of DNA helix where replication occurs

replication fork

Y-shaped structure formed when DNA helices separates two strands of helix

how many origins of replication are there in prokaryotes

one

how many origins of replication are there in eukaryotes

many

why is there a big difference between pro. and elk. # origins of replications

euk. are larger, liner, and more complexly packed

replicon

region that autonomously replicates from a single origin of rep.

helicase

untwists double helix ad replication fork

topoisomerase

corrects “overwinding” ahead of replication fork by breaking, swiveling, and rejoining DNA strands

single stranded binding proteins

bind to and stabilize single-stranded DNA until it can be used as a template

what would happen if SSBP were absent

two individual brands would fuse back together

primase

synthesizes RNA primer

primer

provides starting point for DNA pol to synthesize new DNA strand

• made of RNA because they provide 3 OH- group necessary for DNA pol.

DNA polymerases

enzymes that catalyze synthesis of DNA

DNA pol. in pro.

• DNA pol I

• DNA pol II

• DNA pol III

DNA pol I

forms bonds between DNA fragments

DNA pol II

replaces RNA w/ DNA

DNA pol III

synthesizes new DNA strand

which direction is new strand synthesized

5’ → 3’

how does directionality cause differences in formation of leading and lagging strands

two template strands are antiparallel

• leading strand (3’ → 5’) can be synthesized continuously toward rep. fork

• lagging strand (5’ → 3’) synthesizes discontinuously away from rep. fork

Okazaki fragments

short, newly synthesizes DNA fragments formed discontinuously on lagging strand

exonuclease

enzyme that removes primers

DNA ligase

forms bonds between DNA fragments

steps of DNA replication

1. primase makes RNA primer

2. DNA pol III makes Okazaki frag 1

3. DNA pol III detaches

4. DNA pol III makes Okazaki frag 2

5. DNA pol I replaces RNA w/ DNA

6. DNA ligase forms bonds between DNA fragments

nuclease

cuts out and replaces damages stretches of DNA

compare and contrast pro. and euk. DNA rep.

same:

• semi-conservative

• similar enzymes

• same nucleotides

diff:

• # origins of rep

• speed of rep.

• DNA pol

• telomerase activity

DNA pol alpha

starts polymerization off primer

DNA pol beta

DNA repair, proofreading

DNA pol delta

lagging strand synthesis and primer sub

DNA pol epsilon

leading strand synthesis

euk. replication fork vs pro. replication fork

euk.

• slower

• operate multiple origins of rep

pro.

• faster

• one origin of rep

enzymes that play key role in removing primers during euk. replication

RNase, FENI, and pol beta

end replication problem

primer removal results in incomplete and unprotected ends

telomeres

C/G rich nucleotide sequences that postpone erosion of genes

how do telomeres change with age

shortening of telomeres associated w/ age

do telomere sequences differ between species

yes, but all generally C/G rich

telomerase

catalyzes lengthening of telomeres

what type of enzyme is telomerase

reverse transcriptase w/ its own RNA template to add repetitive DNA sequences

what type of cells express telomerase

germ cells, single-celled organisms, and stem cells

hayflick limit

# cell divisions before senescence

hayflick limit + aging

senescence prevents cells from repairing damage → age-related tissue dysfunction

hayflick limit + genetic clones

clones born with already shorted telomeres = shorter life span