Mitosis and the cell cycle

Question 1

What are the two ways that eukaryotic cells can divide

Answer 1

Mitosis and meiosis

Question 2

What does mitosis produce

Answer 2

Two genetically identical daughter cells that have the same number of chromosomes as the parent cell and each other.

Question 3

What does meiosis produce

Answer 3

Meiosis produces four genetically different daughter cells, each with half the number of chromosomes as the parent cell.

Question 4

What are the four stages in mitosis

Answer 4

Prophase
Metaphase
Anaphase
Telophase

Question 5

What is the name of the stage preceding mitosis where the cell is not dividing

Answer 5

Interphase

Question 6

What are the three stages within the interphase of the cell cycle

Answer 6

G1 phase
S phase
G2 phase

Question 7

Describe what occurs during the G1 phase of interphase

Answer 7

During G1, the cell is preparing to replicate its DNA by synthesising the mRNAs and proteins required to execute further steps. The cell usually grows larger and some organelles are copied.

Question 8

Describe what occurs during the S phase of interphase

Answer 8

• During the S phase, all of the genetic information in the cell is replicated.
• This process of DNA replication generates sister chromatids, which are identical pairs of chromosomes.
• These sister chromatids are attached to each other by a centromere which is a specialised sequence of DNA.

Question 9

Describe what happens during the G2 phase of interphase

Answer 9

The G2 phase is the final phase of interphase. During it, the cell undergoes additional growth, replenishes energy stores and prepares and reorganises the cytoplasmic components for division, including duplicating some organelles and dismantling the cytoskeleton. G2 ends when mitosis begins.

Question 10

Describe what happens during the prophase of mitosis

Answer 10

• The chromosomes become visible-initially as long threads which later shorten and thicken.
• The centrioles move to opposite poles of the cell and form spindle fibres which span from pole to pole.
• The nucleolus disappears and the nuclear envelope breaks down, leaving the chromosomes free in the cytoplasm of the cell.
• These chromosomes are drawn to the centre of the cell by the spindle fibres attached to the centromere.

Question 11

What is the spindle apparatus formed in the prophase of mitosis

Answer 11

The collective name for all of the spindle fibres that span from pole to pole in the cell.

Question 12

What is different about the formation of spindle fibres in plant cells during the prophase of mitosis

Answer 12

Plant cells do not contain centrioles so the spindle fibres form differently. Plants still develop a spindle apparatus.

Question 13

Describe what occurs during the metaphase of mitosis

Answer 13

• Each chromosome is seen to be made up of two chromatids.
• Each chromatid is an identical copy of DNA from the parent cell and they are joined by the centromere.
• It is to this centromere that some microtubules from the poles are attached and the chromosomes are pulled along the spindle apparatus and arrange themselves across the equator of the cell.

Question 14

Describe what occurs during the anaphase of mitosis

Answer 14

The centromeres divide into two and the spindle fibres pull the chromatids apart.
The chromatids are pulled rapidly to their respective, opposite poles of the cell and are now referred to as chromosomes.

Question 15

How does the cell get the energy needed for the anaphase of mitosis

Answer 15

The energy is provided by the mitochondria, which gather around the spindle fibres.

Question 16

What happens if cells are treated with chemicals that destroy the spindle during the anaphase of mitosis

Answer 16

The chromosomes remain at the equator,unable to reach the poles.

Question 17

Describe what happens during the telophase and cytokinesis stage of mitosis

Answer 17

• The chromosomes reach their respective poles, become longer and thinner and disappear altogether, leaving chromatin behind.
• The spindle fibres disintegrate and the nuclear envelope and nucleolus re-form.
• Finally the cytoplasm divides in a process called cytokinesis.

Question 18

By what process do prokaryotic cells divide

Answer 18

Binary fission

Question 19

Describe the process of binary fission

Answer 19

1) The circular DNA molecule replicates and both copies attach to the cell membrane
2) the plasmids also replicate
3) the cell membrane begins to grow between the two DNA molecules and begins to pinch inward, dividing the cytoplasm into two.
4) A new cell wall forms between the two molecules of DNA, dividing the original cell into two daughter cells, each with a singular copy of the circular DNA and a variable number of copies of the plasmids.

Question 20

Describe how viruses replicate

Answer 20

They attach to the host cell with the attachment proteins on their surface. They then inject their nucleic acid into the host cell. The genetic information on the injected viral nucleic acid the provides the ‘instructions’ for the host cells metabolic processes to start producing the viral components, nucleic acid, enzymes and structural proteins that are then assembled into new viruses.

Question 21

What are the three stages in the cell cycle

Answer 21

1) Interphase
2) Nuclear division (mitosis or meiosis)
3) Cytokinesis (division of the cytoplasm)

Question 22

How long does a typical mammalian cell cycle take

Answer 22

24 hours, of which 90% is interphase.

Question 23

When does a tumour become cancerous

Answer 23

When it changes from benign to malignant.

Question 24

What is a mutation

Answer 24

A change in the base sequence of an organisms DNA

Question 25

What stage of the cell cycle does chemotherapy affect and how does this treat cancer

Answer 25

Chemotherapy affects the G1 phase of interphase which is responsible for cell growth and protein production. It prevents the synthesis of enzymes needed for DNA replication and if these aren’t produced, the cell is unable to enter the S phase, which disrupts the cell cycle and causes the cell to die.

Question 26

What stage of the cell cycle does radiation affect and how does this help it to treat cancer

Answer 26

Radiation affects the S phase of the cell cycle that is responsible for DNA replication. Radiation damages the replication of DNA and when the cell checks for damages to DNA during various points in the cell cycle, and finds it, it kills itself, thus preventing further tumour growth.

Question 27

What is a tumour

Answer 27

A group of abnormal, mutated cells that rapidly grow and divide

Question 28

How do the drugs used to treat cancer usually affect the cell cycle

Answer 28

By preventing DNA from replicating
By inhibiting the metaphase stage of mitosis by interfering with spindle formation.

Question 29

What is the main problem with drugs used to treat cancer

Answer 29

They affect the cell cycle of normal cells as well as cancerous ones, causing the patient to feel ill.

Question 30

Which cells are affected by cancer drugs

Answer 30

All of them. However, fast dividing cells such as cancer cells and hair producing cells are damaged more by the drugs.