DNA replication and cell cycle

Question 1

What reaction is catalysed by DNA polymerase

Answer 1

The formation of phosphodiester bonds between nucleotides
Add nucleotides to 3’ end of growing chain
need - template strand, oligonucleotide primer, deoxynucleotide triphosphates (dNTP)
energy released by hydrolysis of triphosphate

Question 2

What is the function of components of the reaction complex

Answer 2

helicase breaks hydrogen bond so DNA unzips
RNA primer - identify DNA to be replicated
special RNA polymerase - DNA primase synthesis short RNA fragment - transient
DNA polymerase - catalyse formation of phosphodiester bonds
sliding clamp - ring around DNA - DNA polymerase doesn’t open
nucleotides - complementary

Question 3

explain semi-conservative replication

Answer 3

Replication begins at ‘origin of replication’
site of replication is ‘replication fork’ - asymmetric
each new double strand DNA - one old strand 1 new
DNA unzips - helicase - ATP source to break H bond
old strands are complementary so both act as a template
complementary bases are added to each old strand forming new strand
leading and lagging strand
Nucleotides added 5’ to 3’
lagging forms in Okazaki fragments - need primers at start of each fragment
ribonuclease get rid of primers, repair DNA polymerase replace primer with DNA, and DNA is re-joined by ligase

Question 4

Explain DNA proof reading

Answer 4

Before adding next nucleotide first one is checked

incorrect base removed by 3’-5’ exonuclease activity of DNA polymerase

Question 5

Describe replication of E coli chromosomes

Answer 5

Start at unique origin OriC
2 replication forks because DNA is circular - simultaneous in opposite directions
bi-directional replication

Question 6

describe replication of mammalian chromosomes

Answer 6

multiple replication origins
distributed 100kb pairs
replication finish when all forks meet

Question 7

What are the phases of the cell cycle

Answer 7

gap 1 - grow, organelles develop - 10hours
s phase - DNA replicate 9hours
gap 2 - continue to grow 4 hours
Mitotic phase - cell division 1 hour

Question 8

What are the phases of mitosis

Answer 8

Prophase - chromosome condense, nucleolus disappear, nuclear env disintegrate
Metaphase - chromosomes lie on metaphase plate
Anaphase - microtubule spindle fibres attach to centromere - pull chromosomes to opposite poles - characteristic V shape
Telophase - Nuclear env and nucleolus reform, chromosomes decondense
cytokinesis

Question 9

Describe the state of chromosomes in each phase of the cell cycle

Answer 9

G1 - linear, double helix
S - replicated
G2 - identical sister chromatids
Mitosis - 2 chromatids separate