6.1. CELL CYCLE

Question 1

What is the cell cycle?

Answer 1

highly ordered sequence of events that takes place in a cell, resulting in division of the cell, and the formation of two genetically identically daughter cells

Question 2

What are the main phases of the cell cycle?

Answer 2

interphase
mitotic phase (mitosis and cytokinesis)

Question 3

Why do cells spend the majority of their time in interphase?

Answer 3

cells do not divide continuously, long periods of growth and normal working separate divisions.

Question 4

What is interphase often referred to as and why is this inaccurate?

Answer 4

Resting phase as cells are not actively dividing, however interphase is actually very active
- cell is carrying out all of its major functions such as producing enzymes/ hormones, whilst also preparing for cell division

Question 5

What happens during interphase?

Answer 5

• DNA is replicated and checked for errors in the nucleus
• protein synthesis occurs in the cytoplasm
• mitochondria grow and divide, increasing in number in the cytoplasm
• chloroplasts grow and divide in plant and algal cell cytoplasm, increasing in number
• normal metabolic processes of cells occur

Question 6

What are the three stages of interphase?

Answer 6

G1
S
G2

Question 7

What happens in G1 phase?

Answer 7

• first growth phase
• proteins from which organelles are synthesised are produced and organelles replicate
• cell increases in size

Question 8

What happens in S phase?

Answer 8

• sythesis phase
• DNA is replicated in the nucleus

Question 9

What happens in G2 phase?

Answer 9

• second growth phase
• cell continues to increase in size, energy stores are increased and duplicated DNA is checked for errors

Question 10

Summarise what happens in mitosis:

Answer 10

• nucleus divides

Question 11

Summarise what happens in cytokinesis:

Answer 11

• cytoplasm divides and two cells are produced

Question 12

What is G0 phase in interphase?

Answer 12

• name given to the phase when the cell leaves the cycle, either temporarily or permanently

Question 13

Why would cells enter G0 phase?

Answer 13

• differentiation
• DNA may be damaged
• too many cells in your body (could lead to age related diseases such as cancer/ arthritis)

Question 14

What types of cells that enter G0 phase can re-enter the cell cycle?

Answer 14

• e.g. lymphocytes (white blood cells) in an immune response

Question 15

What are checkpoints in the cell cycle?

Answer 15

• controls mechanisms
• monitor and verify whether the processes at each phase of the cell cycle have been accurately completed before the cell is allowed to progress into the next phase.

Question 16

What are the checkpoints in the cell cycle?

Answer 16

• G1 checkpoint
• G2 checkpoint
• spindle assembly checkpoint

Question 17

What does the G1 checkpoint check for?

Answer 17

• cell size
• nutrients
• growth factors
• DNA damage

Question 18

Where is the G1 checkpoint?

Answer 18

• end of G1 phase, before entry to S phase
• if cell does not meet requirements, enters G0 phase

Question 19

What does the G2 checkpoint check for?

Answer 19

• cell size
• DNA replication
• DNA damage

Question 20

Where is the G2 checkpoint?

Answer 20

• end of G2 phase, before start of mitotic phase.
• if checkpoint is passed, cell initiates molecular processes that signal the beginning of mitosis

Question 21

What does the spindle assembly checkpoint check for?

Answer 21

• chromosome attachment to spindle

Question 22

Where is the spindle assembly checkpoint?

Answer 22

• point in mitosis where all chromosomes should be attached to spindles and have aligned
• mitosis cannot proceed unless this checkpoint is passed

Question 23

What is the spindle assembly checkpoint also called?

Answer 23

• metaphase chackpoint

Question 24

What brings about the passing of a cell cycle checkpoint?

Answer 24

kinases

Question 25

What are kinases?

Answer 25

enzymes that catalyse the addition of a phosphate group to a protein
- this is called PHOSPHORYLATION

Question 26

What does phosphorylation do?

Answer 26

• changes the tertiary structure of checkpoint proteins, activating them at certain points in the cell cycle

Question 27

How are kinases activated?

Answer 27

• by binding to a variety of checkpoint proteins called cyclins

Question 28

What does binding of the correct cyclin to the appropriate kinase form?

Answer 28

• cyclin-dependent kinase (CDK) complex
• these complexes are activated by enzymes

Question 29

What happens to cyclins when they are not needed?

Answer 29

enzymes break them down
- this signals a cell to move on to the next stage of the cell cycle

Question 30

What is cancer?

Answer 30

• group of many different diseases caused by uncontrolled division of cells

Question 31

What is a tumour?

Answer 31

• abnormal mass of cells

Question 32

What are the two types of tumours?

Answer 32

• benign (stop growing, don’t travel to different places in the body)
• malignant (grows uncontrolled/ unchecked, leads to cancer)

Question 33

What are tumours the result of?

Answer 33

• damage or spontaneous mutation of genes that encode proteins that are involved in regulating the cell cycle
• including the checkpoint proteins

Question 34

What is an example of a tumour in the cell cycle?

Answer 34

• if overexpression of a cyclin gene results from mutation, abnormally large quantity of cyclins would disrupt the regulation of the cell cycle
• resulting in uncontrolled cell division and tumour formation
• possibly leading to cancer

Question 35

How can cyclin-dependent kinases be used in the treatment of cancer?

Answer 35

• used as a possible target for chemical inhibitors
• if activity of CDK’s can be reduced, may reduce/ stop cell division and therefore cancer formation