DNA Replication, the cell cycle and mitosis

Question 1

DNA replication is semi-conservative

Answer 1

Each daughter cell inherits 1 old and 1 new strand

Question 2

Topoisomerase

Answer 2

Unwinds DNA

Question 3

DNA polymerase

Answer 3

Synthesises the new strand

Adds nucleotides to the 3’ end

Question 4

DNA polymerases require

Answer 4

Template strand
Oligonucleotide primer
Supply of deoxynucleotide triphosphates (dNTPs)

Question 5

DNA (and RNA) synthesis occurs in a … direction

Answer 5

5’ to 3’

Question 6

Replication begins at specific points on the DNA molecule called …

Answer 6

Origin of replication

Question 7

What is the site of DNA synthesis is called?

Answer 7

Replication fork

Question 8

What do the templates for the 2 new daughter strands have?

Answer 8

opposite orientations: 3’ to 5’ and 5’ to 3’

Question 9

How is the leading strand synthesised?

Answer 9

synthesised continuously

has its 3’ end closest to replication fork

Question 10

How is the lagging strand synthesised?

Answer 10

synthesised in short pieces- Okazaki fragments

has its 3’ end away from the replication fork

Question 11

RNA primes the synthesis of new DNA

Answer 11

DNA primase (an RNA polymerase) synthesises a short RNA fragment
-only transient, removed at a later stage of replication

Question 12

DNA polymerase adds to 3’ end of RNA primer and continues to synthesise the Okazaki fragment…

Answer 12

Until it reaches the end of the previous Okazaki fragment
Old RNA primer erased and replaced by DNA
DNA ligase joins new Okazaki fragment to growing chain

Question 13

Ribonuclease

Answer 13

removes RNA primer using a 5’ to 3’ exonuclease activity

Question 14

Repair DNA polymerase

Answer 14

replaces RNA with DNA

Question 15

DNA Ligase

Answer 15

joins 2 Okazaki fragments together

Question 16

Single strand DNA binding protein

Answer 16

Prevents the single stranded DNA from locally folding

Question 17

Sliding clamp

Answer 17

Ensures DNA polymerase is in the right place

Question 18

Lagging strand forms a loop

Answer 18

So both daughter strands can be synthesised in a coordinated manner

Question 19

What does the proofreading mechanism do?

Answer 19

Ensures no mistakes are made because mutations can be dangerous

Question 20

Proofreading mechanism

Answer 20

Before a new nucleotide is added, DNA polymerase checks the previous nucleotide for correct base-pairing
Incorrect bases are removed by 3’ to 5’ exonuclease activity

Question 21

In E.coli, replication starts at a unique origin, OriC

Answer 21

2 replication forks proceed simultaneously in opposite directions.
2 forks meet at the other side of the circular chromosome

Question 22

Eukaryotes have large, linear DNA so there are multiple origins of replication

Answer 22

Each replication origin gives bi-directional replication forks.
Replication is finished when all the forks have met

Question 23

M phase: Mitosis

Answer 23

2 chromatids separate to the daughter cells

Question 24

G1 phase: Gap 1

Answer 24

DNA of each chromosome present as a single linear double helix of DNA

Question 25

S phase: Synthesis

Answer 25

DNA is replicated

Question 26

G2 phase: Gap 2

Answer 26

each chromosome has 2 identical sister chromatids

Question 27

G0 phase

Answer 27

cells have stopped dividing

Question 28

Late prophase

Answer 28

Condensed chromosomes, | each contains 2 sister chromatids

Question 29

Metaphase

Answer 29

Condensed chromosomes, | aligned on central plane of spindle

Question 30

Anaphase

Answer 30

Sister chromatids separate and are pulled to spindle poles

Question 31

Telophase

Answer 31

Sister chromatids move to opposite poles of spindle

Question 32

Cytokinesis

Answer 32

Division of cytoplasm

Question 33

Interphase (G1)

Answer 33

Condensation process reversed

Question 34

Flow of genetic information

Answer 34

DNA replication Transcription Translation

Question 35

DNA helicase

Answer 35

separates DNA strands by using ATP as a source of energy to break hydrogen bonds

Question 36

Deoxynucleotide triphosphates (dNTPs)

Answer 36

nucleotide with 3 phosphates attached

Question 37

Oligonucleotide primer

Answer 37

made of RNA by specialised RNA polymerase: DNA primase

Question 38

What drives the DNA synthesis? (Energy)

Answer 38

Hydrolysis of triphosphate releases energy

Question 39

Exonuclease activity

Answer 39

ability of an enzyme to remove 1 nucleotide at a time from the end of a polynucleotide chain