Cell cycle

Question 1

What is the cell cycle?

Answer 1

A sequence of events that leads to the reproduction of a cell

Question 2

Before cell division

Answer 2

• Chromosome replication and segregation
• Cell growth
• Separation of organelles
• Gap phases (provides time for cell growth)

Question 3

How does the cell cause cell division?

Answer 3

When cells grow DNA/mass ratio decreases. Then chromosomes and DNA duplicate causing an increase in ratio and so the cell doubles in size for division

Question 4

What are the 4 nitrogenous bases in DNA?

Answer 4

Adenine, guanine, thymine and cytosine

Question 5

What is the basic structure of DNA?

Answer 5

Nitrogenous bases connected together via pentose sugars and phosphate

Question 6

Eukaryotic DNA replication

Answer 6

• Takes place in nucleus
• 4+ types of polymerases
• Slow
• Occurs in S phase

Question 7

Prokaryotic DNA replication

Answer 7

• Takes place in cytosol
• 1-2 types of polymerases
• Fast
• Occurs throughout cell cycle

Question 8

1st step of DNA replication

Answer 8

2 strands of DNA are in a straight bond which is then separated by an initiator protein to form a replication bubble

Question 9

2nd step of DNA replication

Answer 9

DNA becomes untwisted by DNA helicases to form a Y shaped replication fork by breaking hydrogen bonds between bases

Question 10

3rd step of DNA replication (single-stranded DNA-binding (SSB))

Answer 10

2 single-stranded template strands are formed which bind to proteins to prevent re-joining

Question 11

What are DNA topoisomerases?

Answer 11

They are part of SSB and relieve tension

Question 12

4th step of DNA replication

Answer 12

RNA primase synthesises a short RNA primer which attaches to a template strand

Question 13

5th step of DNA replication

Answer 13

DNA polymerase causes the addition of nucleotides to the RNA primer where it forms a base pair with a nucleotide on the template strand of DNA

Question 14

What are Okazaki fragments?

Answer 14

Small fragments of DNA nucleotides

Question 15

What are the 4 periods of the cell cycle?

Answer 15

G1, G2, M and S

Question 16

G1 period

Answer 16

• Cell growth
• Preparation of chromosomes for replication
• Duplication of cell components

Question 17

S period

Answer 17

• When DNA is made
• Each chromosome has many origins of replication

Question 18

G2 period

Answer 18

• Cell prepares for M period
• Genes are expressed

Question 19

M period

Answer 19

• Mitosis or meiosis occurs
• Chromosomes are condensed and separated
• Cell divides

Question 20

Mitosis

Answer 20

• Occurs in somatic or body cells
• Asexual reproduction for healing cells and growth and development of cell body
• One cell division
• 4 stages of cell division
• No independent assortment at metaphase
• Separation of sister chromatids at anaphase

Question 21

Meiosis

Answer 21

• Occurs in reproductive cells
• Only needed for sexual reproduction
• 2 cell divisions
• 8 stages of cell division
• Independent assortment of homologous chromosomes at metaphase
• Separation of homologous chromosomes and sister chromatids at anaphase