The Cell Cycle

Question 1

Why is the model of DNA replication considered to be ‘semi-conservative’?

Answer 1

Each of the new DNA molecules contain 1 of the original strands and 1 new strand

Question 2

What are the 4 requirements of DNA replication?

Answer 2

• 4 types of nucleotides
• DNA helicase and polymerase
• the DNA strand to be replicated (act as a template)
• a source of energy to activate the free nucleotides

Question 3

Outline the process of semi-conservative replication

Answer 3

1. DNA helicase breaks H bonds between the complimentary bases, exposing the bases and creating 2 strands
2. Each polynucleotide strand acts as a template to which complimentary bases are attracted; energy activates these nucleotides.
3. DNA polymerase joins new bases to old strands

Question 4

Describe mitosis

Answer 4

Nuclear division by which 2 daughter cells are produced, each with same number of chromosomes as parent cells

Question 5

Describe meiosis

Answer 5

Nuclear division by which 4 daughter cells are produced, each with half number of chromosomes as parent cell

Question 6

What happens during metaphase?

Answer 6

The chromosomes line up in centre of cell, and spindle fibres form

Question 7

What happens during prophase?

Answer 7

• Chromosomes shorten and condense, becoming visible
• chromosomes pair up,
• nuclear membrane disappears

Question 8

What happens during telophase?

Answer 8

• chromatids reach opposite poles
• spindle fibres disappear
• nuclear membrane disappears

Question 9

What happens during anaphase?

Answer 9

• spindle fibres contract, pulling chromatids to opposite poles of the cell

Question 10

Why is mitosis important?

Answer 10

• allows growth: new organism has all genetic info from parents
• differentiation: different cell types divide to give identical cells which perform a particular function, must be the same structure
• repair: damaged cells are replaced with identical cells

Question 11

How is genetic variation produced in meiosis?

Answer 11

1. Independent Segregation: when chromosomes line up in meiosis 1, they do som randomly. It is also random which pair goes into which daughter cell, and which chromosomes pair up.
2. Crossing Over: In meiosis 1, each chromosomes line up, and chromatids become twisted. Tensions are created and portions of chromatid break off, rejoining other chromatid. New genetic combos are produced

Question 12

What is the purpose of the Interphase stage in the cell cycle?

Answer 12

To enable the cell to prepare its content before division

Question 13

What are the 3 stages of Interphase in the cell cycle?

Answer 13

1. G1: proteins are synthesised to make cell organelles
2. S: DNA replication
3. G2: organelles grow and divide, and energy stores are increased

Question 14

What is cancer?

Answer 14

A disease caused by mutations, that leads to rapid, uncontrolled cell division. Eventually forms a tumour.

Question 15

What does treatment of cancer involve?

Answer 15

• blocking part of cell cycle by;
• inhibiting DNA replication
• inhibiting metaphase stage, spindle fibres are prevented from forming

Question 16

What are the 3 stages of the cell cycle?

Answer 16

1. Interphase; the resting phase, no division takes place
2. Nuclear division; nucleus divides into 2 or 4
3. Cell division; whole cell divides into 2 or 4