Wk2- DNA Replication

Question 1

What are the 5 phases of the cell cycle?

Answer 1

-G1
-S
-G2
-Mitosis
-Cytokinesis

Question 2

What occurs during G1?

Answer 2

-Cell growth
-Organelles replicate

Question 3

What occurs during S phase?

Answer 3

-DNA replication

Question 4

What occurs during G2?

Answer 4

-Protein production
-Checking cell is ready to divide

Question 5

What occurs during mitosis?

Answer 5

Cell divides (prophase, metaphase, anaphase, telophase)

Question 6

What occurs during cytokinesis?

Answer 6

Cytoplasm splits to create 2 new daughter cells

Question 7

Where is the origin of replication in eukaryotes?

Answer 7

Multiple points along chromosomes due to their length

Question 8

Where is the origin of replication in prokaryotes?

Answer 8

On a single point, e.g. a sequence of 245 bp in E. coli

Question 8

What are the 5 polymerases in prokaryotes?

Answer 8

I, II, III, IV, V

Question 9

What does polymerase I do?

Answer 9

Synthesis, proofreading, repair, removal of primers

Question 10

What does polymerase II do?

Answer 10

Repair

Question 11

What does polymerase III do?

Answer 11

Main polymerising enzyme

Question 12

What do polymerase IV and V do?

Answer 12

Repair in unusual circumstances

Question 13

What are the 5 polymerases in eukaryotes?

Answer 13

α, β, γ, δ, ε

Question 14

What does polymerase α do?

Answer 14

Polymerising

Question 15

What does polymerase β do?

Answer 15

Repair

Question 16

What does polymerase γ do?

Answer 16

Mitochondrial DNA synthesis

Question 17

What does polymerase δ do?

Answer 17

Main polymerising enzyme

Question 18

What does polymerase ε do?

Answer 18

Unknown

Question 19

How long are Okazaki fragments in prokaryotes?

Answer 19

1000-2000 bp

Question 20

How long are Okazaki fragments in eukaryotes?

Answer 20

150-200 bp

Question 21

What are the 7 main enzymes required in DNA replication?

Answer 21

-Helicase
-Single-stranded binding proteins
-Topoisomerase I
-DNA primase
-DNA polymerase III
-DNA polymerase I
-DNA ligase

Question 22

What is the 1st step in DNA replication?

Answer 22

DNA helicase unwinds the 2 strands by breaking H-bonds using ATP

Question 23

What is the 2nd step in DNA replication?

Answer 23

SSBs bind to each strand to prevent self-complementarity and secondary structures which would inhibit DNA polymerase

Question 24

What is the 3rd step in DNA replication?

Answer 24

Topoisomerase I unwinds the supercoils that form in front of the replication forks

Question 25

How does topoisomerase unwind the supercoils?

Answer 25

1. It binds to a phosphate group and breaks the phosphodiester bons b/n nucleotides so that the strands unwind 2. Energy of bond stored in phosphotyrosine 3. Topoisomerase reforms the bone using this energy

Question 26

What is the 4th step of DNA replication?

Answer 26

RNA primase make complementary RNA primers to show DNA polymerase where to start

Question 27

How long are primers?

Answer 27

10-12 bp

Question 28

How many primers are on each strand?

Answer 28

-One on leading strand -Multiple on lagging

Question 29

Why is it not an issue that RNA primase makes so many mistakes?

Answer 29

Because they will be replaced anyway

Question 30

What is the 5th step in DNA synthesis?

Answer 30

DNA polymerase II adds complementary nucleotides to the 3' OH of primers, going in both directions

Question 31

What are the fragments in which nucleotides are added on the lagging strand (away from replication fork) called?

Answer 31

Okazaki fragments

Question 32

What are the 4 things required for DNA polymerases?

Answer 32

-Primer w/ free OH -Template DNA -dNTPs (nucleotides) -Mg2+

Question 33

What is the 6th step in DNA replication?

Answer 33

-DNA polymerase I detects and fixes mistakes by cleaving phosphodiester bonds and removing incorrect nucleotides -Simultaneously, it removes primers (exonuclease activity) and replaces them w/ DNA dNTPs

Question 34

In what direction does DNA polymerase I work?

Answer 34

From 3' to 5'

Question 35

In what direction does DNA polymerase III work?

Answer 35

From 5' to 3'

Question 36

What is the 7th (and final) step of DNA replication?

Answer 36

DNA ligase joins gaps by phosphodiester bonds

Question 37

Why does DNA become shorter w/ each replication?

Answer 37

Because once the final primer on the lagging strand in removed, there is no 3' OH to add nucleotides to

Question 38

How is the issue of DNA shortening overcome?

Answer 38

Telomeres: Repeated sequences of DNA that don't code for anything

Question 39

What are telomere sequences made of?

Answer 39

1000s of repeats of TTAGGG

Question 40

What happens if telomeres get too short?

Answer 40

-Since they are added as an embryo and most cells don't have telomerase, they cannot be replaced -Short telomeres are associated w/ senescence and death

Question 41

What is a mutation?

Answer 41

Change in nucleotide sequence of a DNA or a gene

Question 42

Can a mutation be passed to offspring if in a somatic cell?

Answer 42

No

Question 43

Can a mutation be passed to offspring if in a gamete?

Answer 43

Yes

Question 44

What are the 4 types of mutations?

Answer 44

-Silent -Missense -Nonsense -Readthrough

Question 45

What is a silent mutation?

Answer 45

Where a base change does not change an aa as multiple codons may code for one aa

Question 46

What is a missense mutation?

Answer 46

One aa change that may effect entire protein

Question 47

What is a nonsense mutation?

Answer 47

Codes for stop codon, prematurely ending protein and potentially severely affecting length and function

Question 48

What is a readthrough mutation?

Answer 48

A stop codon is replaced with one for an aa, potentially lengthening the protein and changing function

Question 49

What is the mutation in sickle cell anaemia?

Answer 49

CTC for glutamic acid is replaced w/ CAC for valine in haemoglobin

Question 50

What is the effect of the mutation in sickle cell anaemia?

Answer 50

Makes haemoglobin more crystalline, changing the shape of RBCs so they get stuck in BVs and are less effective at carrying O2