DNA 3 Flashcards
Define replication
Making a copy of a DNA strand
Define semi conservative replication
New DNA double helix is made of one original “parent” strand, and one new “daughter” strand of nucleotides
Scientists who verified semiconservative replication.
Meselson and Stahl
Explain how the data collected from equilibrium density gradient centrifugation verifies semiconservative replication.
HELP
They found ratios of 1:1/2:1/4 for hybrids and 0:1/2:3/4 for light
Describe replication bubbles and their location
HELP
Occurs simultaneously at many sites a long a chromosome. The site where replication begins
Describe origin of replication, the organisms identified with them, and if they’re identified in complex life
Sites where replication begins, found in bacteria and simple eukaryotes, not identified in multicellular eukaryotes yet
Identify dominant bp found in an origin of replication and why these pairs are found
AT rich sequences, HELP
Direction replication proceeds from an origin of replication within a replication bubble
Proceeds bidirectionally until bubbles meet
Rate at which DNA must unwind and the number of nucleotides replicated each minute
About 3000 nucleotides replicated per min, must unwind at a rate of 3000 RPMs
Error rate during replication and what this means for progeny
About one mistake per billion nucleotides
About 3 mutations in a set of chromosomes per replication
About 200 new mutations in a child from parents
Identify organism used to study replication and why it’s used
E. Coli. Most aspects of replication are similar in prokaryotes and eukaryotes and easier to study in E. coli.
Phase in cell cycle where replication occurs
S phase, (interphase)
Define replicons, state the number of them in mammals, and how far apart each is
Replicon is a segment with origin and two termini. Mammals have about 10,000 separated by 30,000-300,000 bp
Replicon must occur in the __________ for the new stand, and the strand is read _________
5’-3’ direction
Read 3’-5’
Explain the steps of replication for the leading strand
- ) dnaA protein binds to origin
- ) dnaA and dnaB form replication bubble
- ) DNA helicase (dnaB) breaks H bonds between bases to unwind DNA
- ) Single strand DNA binding proteins keep separate DNA strands apart
- ) new strand is started by attachment of DNA primase which forms the DNA primer attached to template by H bonds
- ) DNA polymerase 3 adds nucleotides to rna primer
- ) DNA polymerase 1 removes RNA primer and replaces it with DNA nucleotides
- ) continuous across replication bubble for leading strand (repeat)
DNA Polymerase 1 has 3 distinct enzyme activities
5’-3’ polymerase adds nucleotides
5’-3’ exonuclease removes primer
3’-5’ exonuclease proofreads and repairs
Another word for new strand
Nascent
Explain difference in direction of nascent strand building between leading strand and lagging strand
Leading strand starts at the origin and lagging starts at the fork, but both still go in the same direction
Explain the steps of lagging strand replication
Steps 1-4 same as leading strand
- ) formation of primosome- DNA primase and DNA helicase (primase creates rna primer and helicase unwinds fork for Okazaki fragment)
- ) DNA poly 3 bonds to primer and synthesizes new strand, based on H bonds (poly 3 stops when it bumps into rna primer of preceding Okazaki fragment)
- ) DNA poly 1: 5’-3’ exonuclease primer and adds DNA nucleotides
- ) nicks remain between Okazaki fragments (DNA ligase catalyzes phosphodiester bond 2 sides of nick)
Length of Okazaki fragment
100-200 bp fragments
Components of a primosome
DNA primase and DNA helicase
Function of a primosome
To create the rna primer (primase) and unwind the fork for Okazaki fragment (helicase)
How does DNA polymerase 3 know when to stop adding nucleotides to lagging strand
It stops when it bumps into rna primer of preceding Okazaki fragment
Number of primases in prokaryotes and eukaryotes
Prokaryotes have 5 (I, II, III, IV, V)
Eukaryotes have at least 15
