DNA Part 2

Question 1

Define semi conservative replication

Answer 1

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

Question 2

Who verified semiconservative replication

Answer 2

Melselon & Stakl used equilibrium density-gradient centrifugation

Question 3

What is another word for new strand

Answer 3

Nascent

Question 4

What are the three enzyme activities of DNA Polymerase 1?

Answer 4

1) 5’-3’ polymerase 3( adds nucleotides)
2) 5’-3’ exonuclease (removes primer)
3) 3’-5’ exonuclease (proofreads & repairs)

Question 5

What is the location of the replication bubbles

Answer 5

Occurs simultaneously at many sites along a chromosome

Question 6

Explain how the data collected from Equilibrium Density-Gradient Centrifugation verifies Semiconservative Replication.

Answer 6

It found ratios of 1:1/2:1/4 for hybrids and

0:1/2:3/4 for light

Question 7

Describe Origin of Replication, & the organisms identified with the

Answer 7

The sites where replication begins

They are found in bacteria and simple eukaryotes(AT-rich sequences)

Question 8

Is the origin of replication identified in complex life

Answer 8

Not identified in multicellular eukaryotes

Question 9

Identify the dominant base pairs found in an Origin of Replication, and why these pairs are found.

Answer 9

The dominant base pairs are adenine and thymine. These base pairs are found because they have double hydrogen bond between them and they are easier to break than the triple bond between guanine and cytosine

Question 10

How many nucleotides are replicated per minute in humans

How fast must the DNA unwind

Answer 10

3,000

DNA must unwind at 3,000 RPM

Question 11

How many mistakes are per billion nucleotides

And how many mutations are in a set of chromosome per replication

Answer 11

1 mistake per billion nucleotides

3 mutations in a set of chromosomes per replication

Question 12

How many new mutations are in a child from parents ?

Answer 12

200 new mutations

Question 13

State the direction Replication proceeds from an Origin of Replication within a Replication Bubble.

Answer 13

Proceeds bidirectionally(both directions) until bubbles meet

Question 14

What is organism used to study Replication, and why is it used?

Answer 14

E. Coli

Most aspects of replication are similar in prokaryotes and eukaryotes

Question 15

Identify the Phase in the Cell Cycle where Replication occurs

Answer 15

Occurs in S-phase, during Interphase of the cell

Question 16

What are the 8 steps for the leading strand?

Answer 16

1) dnaA protein binds to origin
2) dnaA & other proteins from replication bubble
3) DNA helicase(dnaB protein) breaks H-bonds between bases to unwind DNA
4) Single Strand DNA binding proteins(SSB) keep separate DNA strands apart
5) New Strand(Nascent) is started by attachment of DNA primase which forms the RNA Primer(-10bp long) 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) this is a continuous across replication bubble for leading strand(3’-5’ template)

Question 17

Nucleotides are added based on what

Answer 17

H-Bonds

Question 18

DNA polymerase needs a what and gets it from who

Answer 18

Needs a free 3’-OH and gets it from RNA Primer

Question 19

Definition replicon

Answer 19

Segment with origin and 2 termini

Question 20

State the number of Replicons in mammals & how far apart each is.

Answer 20

10,000 replicons and they are separated by 30,000-300,000 bp

Question 21

Replication occurs in the what direction
Reads template in what direction
New strand is laid out in what direction

Answer 21

Occurs in 5’-3’ direction
Reads template from 3’-5’
New strand is laid down 5’-3’

Question 22

Differentiate the number of Primases between Prokaryotes and Eukaryotes.

Answer 22

Prokaryotes have 5
- 1, 2, 3, 4, 5
Eukaryotes have at least 15

Question 23

Identify the length of an Okazaki fragment

Answer 23

100-200 bp fragements

Question 24

Identify the components of a Primosome

Answer 24

DNA Primase and DNA Helicase

Question 25

Explain the function of a Primosome

Answer 25

Creates RNA Primer and helicase unwinds fork for Okazaki fragments

Question 26

Explain how DNA Polymerase III “knows” when to stop adding new nucleotides to Lagging Strand.

Answer 26

It knows when to stop when it bumps into RNA Primer of preceding Okazaki Fragement

Question 27

Steps for leading lagging strand

Answer 27

• when template is orientated 5’-3’ away from origin
• steps 1-4 occur for any replication-forming replication bubble and forks
• starts towards fork & builds to origin
• must synthesize 5’-3’ (Okazaki fragments)
  5) Formation of primosome
  6) DNA Poly 3 bonds to Primer and synthesizes new strand, based on H-bonds
  7) DNA poly 1: 5’-3’ exonucleases Primer & adds nucleotides
  8) Nicks remain between Okazaki fragements

Question 28

DNA Ligase catalyze what

Answer 28

Phosphdiester bond 2 sides of nick

Question 29

Define replication

Answer 29

process by which a double-stranded DNA molecule is copied to produce two identical DNA molecules

Question 30

Describe Replication Bubbles

Answer 30

Spot where replication happens,

Contains origin and replication forks