Topic 2 - Cell Life Cycle

Question 1

Why do cells need to divide/reproduce?

Answer 1

To allow for the continuity of life, cells grow and repair. Cells reproduce to replace damaged cells.

Question 2

Define Cell Cycle

Answer 2

the life cycle of a cell

Question 3

2 Main stages of the cell cycle

Answer 3

1. Mitosis (1-2hrs)
2. Interphase (23 hrs)

Question 4

What is mitosis?

Answer 4

• the division of the nucleus (the separation of chromosomes into two new cells)
• all somatic cells reproduce mitosis, not neurons and muscle cells OR GAMETES (sex-cells)
• happens every 24 hours

Question 5

What is interphase?

Answer 5

the phase in which the cell spends 23 out of the 24 hrs - the cell grows, duplicates its DNA and gets ready for the next cell division by mitosis

Question 6

What is cytokinesis?

Answer 6

• the cytoplasm pinches in half, and each new cell formed has an identical set of duplicated chromosomes.

Question 7

3 parts of Interphase

Answer 7

• G1 Phase
• S Phase
• G2 Phase

Question 8

What occurs in the G1 Phase

Answer 8

The cell prepares for cell division by:
- making proteins
- the cell getting bigger in mass/size
- growing in size.
It is the growth period before the replication of DNA

Question 9

What occurs during the S Phase?

Answer 9

The period after G1 where all genetic material (DNA) is synthesized/replicated. The chromosomes are doubled.

Question 10

What occurs during the G2 Phase?

Answer 10

The period after DNA synthesis has occurred but prior to the start of mitosis.
- The cell continues to grow by making more organelles (ribosomes and mitochondria)

Question 11

What is a karyotype?

Answer 11

shows a complete set of chromosomes found in a body cell - organised in pairs and according to size

Question 12

What is a duplicated chromosome?

Answer 12

when each chromosome is made up of two sister chromatids that are held together by a centromere.

Question 13

What happens in Prophase?

Answer 13

The nuclear membrane starts to disappear and the centrioles start to move to different poles of the cell.
- Chromosomes coil up and are seen as strands.

Question 14

What happens in Metaphase?

Answer 14

• The chromosomes line up in the middle and are attached to a fibre in the spindle (web).
• They attach across the middle called the equator and get ready to divide.

Question 15

What happens in anaphase?

Answer 15

• The chromosomes pull apart, the centromeres split and each sister chromatid moves to the opposite end of the cell.

Question 16

What happens in Telophase?

Answer 16

The nuclear membrane starts to form around the separate chromosomes, creating 2 new daughter cells.
- Cytokinesis pinches cytoplasm

Question 17

What is checked at Checkpoint G1/S

Answer 17

• Checks the cell for any DNA damage before being duplicated in the S Phase.
• Makes sure cell is of a proper size and has enough energy to prepare for mitosis
• Cannot progress if damaged or too small

Question 18

What is checked at Checkpoint G2/M

Answer 18

• Makes sure DNA is duplicated correctly before mitosis
• There should be no mistakes or damages to progress into mitosis

Question 19

What is checked at Checkpoint M (metaphase)

Answer 19

Ensures that chromosomes are separating correctly in mitosis and that they divide evenly into the two new cells.

Question 20

What is the G0 phase in the life cycle

Answer 20

• Cells that are sent to G0 after G1 as they do not get the signal to continue further in the cell cycle. They stay there resting, and functioning but do not divide any further.
• Quiscence

Question 21

Why do cells need to balance cell reproduction and cell apoptosis?

Answer 21

to maintain healthy tissues and overall organism functioning. If too much cell reproduction without undergoing apoptosis, may lead to uncontrolled growth = cancer.
If too much apoptosis, can result in tissue damage or degenerative diseases

Question 22

Why don’t all cells go through the cell-cycle at the same rate?

Answer 22

Because some cells receive more wear and tear than others and are more active than other cells. Eg Skin cells are constantly replaced, whereas neurons are not replaced at all.

Question 23

What is being monitored at each stage?

Answer 23

Check if they are abnormal in any way:
- DNA Damage, extra chromosome, grown to correct size