Mitosis and The Cell Cycle

Question 1

How are cells made?

Answer 1

Through cell division

Question 2

How do prokaryotic cells divide?

Answer 2

Binary Fission

Question 3

Types of eukaryotic cell division (2)

Answer 3

• Mitosis
• Meiosis

Question 4

Mitosis definition

Answer 4

When a parent cell divides into 2 daughter cells with identical copies of DNA and the same number of chromosomes as the parent

Question 5

Meiosis definition

Answer 5

When a parent cell divides into 4 daughter cells that each contain half the number of chromosomes in the parent cell

Question 6

TRUE/FALSE: All multicellular organisms can divide

Answer 6

False e.g. neurones

Question 7

Why shouldn’t cells divide continuously?

Answer 7

It may lead to uncontrolled cell division which can lead to cancer and brain tumours

Question 8

Stages of the cell cycle

Answer 8

1. Interphase
2. Nuclear division (Mitosis)
3. Cell division

Question 9

Interphase

Answer 9

• Occupies most of the cycle in a 3-step process:

1. Gap Phase 1: Proteins required for organelles are synthesised
2. Synthesis Phase 1: DNA replication which doubles the mass
3. Gap Phase 2: Organelles grow and divide, ATP levels increase

Question 10

Nuclear division (Mitosis)

Answer 10

The nucleus divides into two or four, where each cell contains half the chromosomes of a complete nucleus

Question 11

Cell division

Answer 11

Cytokinesis AKA division of cytoplasm where the cell divides into two or four daughter cells

Question 12

How long does the cell cycle typically take?

Answer 12

24 hours

Question 13

Stages of mitosis

Answer 13

1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

Question 14

Prophase

Answer 14

The chromosomes thicken and shorten by supercoiling.
The nuclear envelope disappears.
The centrioles form a spindle network, separate and move to opposite poles of the cell

Question 15

Metaphase

Answer 15

The chromosomes move to the equator of the cell.
The spindle fibres attach to the centromeres.

Question 16

Anaphase

Answer 16

The spindle fibres contract, separating the sister chromatids.
The individual chromatids are pulled towards the poles - they are now chromosomes.

Question 17

Telophase

Answer 17

A nuclear envelope appears around each set of chromatids to form two new nuclei
The chromatids uncoil and the spindle fibres disintegrate
The cell surface membrane starts to invaginate at the equator of the cell

Question 18

Mitotic index

Answer 18

The proportion of cells in a population undergoing mitosis

Question 19

Formula for mitotic index

Answer 19

Number of cells undergoing mitosis/Total number of cells observed

Question 20

How do cancer treatments control cell division?

Answer 20

Many treatments prevent DNA replication or interfere with metaphase by inhibiting spindle formation

Question 21

How does chemotherapy stop uncontrolled cell division?

Answer 21

They disrupt the cell cycle in all dividing cells but have a greater effect on rapidly dividing cells

Question 22

How does a virus replicate?

Answer 22

They do not divide but inject their nucleic acid into a host cell which synthesises viral nucleic acid and proteins and assembles virus particles

Question 23

How does Binary Fission happen?

Answer 23

• Replication of the circular DNA and of plasmids in the cytoplasm
• Division of the cytoplasm to produce two daughter cells, each with a single copy of the circular DNA and a variable number of copies of any plasmid