DNA 3

Question 1

Define replication

Answer 1

Making a copy of a DNA strand

Question 2

Define semi conservative replication

Answer 2

New DNA double helix is made of one original “parent” strand, and one new “daughter” strand of nucleotides

Question 3

Scientists who verified semiconservative replication.

Answer 3

Meselson and Stahl

Question 4

Explain how the data collected from equilibrium density gradient centrifugation verifies semiconservative replication.
HELP

Answer 4

They found ratios of 1:1/2:1/4 for hybrids and 0:1/2:3/4 for light

Question 5

Describe replication bubbles and their location

HELP

Answer 5

Occurs simultaneously at many sites a long a chromosome. The site where replication begins

Question 6

Describe origin of replication, the organisms identified with them, and if they’re identified in complex life

Answer 6

Sites where replication begins, found in bacteria and simple eukaryotes, not identified in multicellular eukaryotes yet

Question 7

Identify dominant bp found in an origin of replication and why these pairs are found

Answer 7

AT rich sequences, HELP

Question 8

Direction replication proceeds from an origin of replication within a replication bubble

Answer 8

Proceeds bidirectionally until bubbles meet

Question 9

Rate at which DNA must unwind and the number of nucleotides replicated each minute

Answer 9

About 3000 nucleotides replicated per min, must unwind at a rate of 3000 RPMs

Question 10

Error rate during replication and what this means for progeny

Answer 10

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

Question 11

Identify organism used to study replication and why it’s used

Answer 11

E. Coli. Most aspects of replication are similar in prokaryotes and eukaryotes and easier to study in E. coli.

Question 12

Phase in cell cycle where replication occurs

Answer 12

S phase, (interphase)

Question 13

Define replicons, state the number of them in mammals, and how far apart each is

Answer 13

Replicon is a segment with origin and two termini. Mammals have about 10,000 separated by 30,000-300,000 bp

Question 14

Replicon must occur in the __________ for the new stand, and the strand is read _________

Answer 14

5’-3’ direction

Read 3’-5’

Question 15

Explain the steps of replication for the leading strand

Answer 15

1. ) dnaA protein binds to origin
2. ) dnaA and dnaB form replication bubble
3. ) DNA helicase (dnaB) breaks H bonds between bases to unwind DNA
4. ) Single strand DNA binding proteins keep separate DNA strands apart
5. ) new strand is started by attachment of DNA primase which forms the DNA primer attached to template by H bonds
6. ) DNA polymerase 3 adds nucleotides to rna primer
7. ) DNA polymerase 1 removes RNA primer and replaces it with DNA nucleotides
8. ) continuous across replication bubble for leading strand (repeat)

Question 16

DNA Polymerase 1 has 3 distinct enzyme activities

Answer 16

5’-3’ polymerase adds nucleotides
5’-3’ exonuclease removes primer
3’-5’ exonuclease proofreads and repairs

Question 17

Another word for new strand

Answer 17

Nascent

Question 18

Explain difference in direction of nascent strand building between leading strand and lagging strand

Answer 18

Leading strand starts at the origin and lagging starts at the fork, but both still go in the same direction

Question 19

Explain the steps of lagging strand replication

Answer 19

Steps 1-4 same as leading strand

5. ) formation of primosome- DNA primase and DNA helicase (primase creates rna primer and helicase unwinds fork for Okazaki fragment)
6. ) 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)
7. ) DNA poly 1: 5’-3’ exonuclease primer and adds DNA nucleotides
8. ) nicks remain between Okazaki fragments (DNA ligase catalyzes phosphodiester bond 2 sides of nick)

Question 20

Length of Okazaki fragment

Answer 20

100-200 bp fragments

Question 21

Components of a primosome

Answer 21

DNA primase and DNA helicase

Question 22

Function of a primosome

Answer 22

To create the rna primer (primase) and unwind the fork for Okazaki fragment (helicase)

Question 23

How does DNA polymerase 3 know when to stop adding nucleotides to lagging strand

Answer 23

It stops when it bumps into rna primer of preceding Okazaki fragment

Question 24

Number of primases in prokaryotes and eukaryotes

Answer 24

Prokaryotes have 5 (I, II, III, IV, V)

Eukaryotes have at least 15