Cell Cycle

Question 1

what is the cell cycle?

Answer 1

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

Question 2

how many main phases does the cell cycle have in eukaryotic cells?

Answer 2

two.

Question 3

what are the 2 main phases in the cell cycle?

Answer 3

• interphase
• mitotic phase.

Question 4

what is interphase?

Answer 4

the long periods of growth and normal working between division of cells.

Question 5

which stage does a cell spend most of its time in?

Answer 5

interphase.

Question 6

why is it not accurate to describe interphase as ‘the resting stage’ ?

Answer 6

interphase is actually a very active phase of the cell cycle, when the cell is carrying out all of its major functions such as producing enzymes, or actively preparing for cell division.

Question 7

what happens during interphase?

Answer 7

• DNA is replicated and checked for errors
• protein synthesis occurs in the cytoplasm
• chloroplasts grow and divide
• normal metabolic reactions occur.
• mitochondria grow and divide, increasing in number in the cytoplasm.

Question 8

what are the three stages of interphase?

Answer 8

• G1 (first growth phase)
• S (synthesis stage)

G2 (growth stage 2)

Question 9

what happens during G1 in interphase?

Answer 9

proteins from which organelles are synthesised and produced and organelles replicate. the cell increases in size.

Question 10

what happens during S in interphase?

Answer 10

DNA is replicated in the nucleus.

Question 11

what happens during G2 in interphase?

Answer 11

the cell continues to increase in size, energy stores are increased and the duplicated DNA is checked for errors.

Question 12

What is the mitotic phase split into ?

Answer 12

• mitosis
• cytokinesis

Question 13

what happens during mitosis?

Answer 13

the nucleus divides.

Question 14

what happens during cytokinesis?

Answer 14

the cytoplasm divides and two cells are produced.

Question 15

what Is G0?

Answer 15

the name of the phase where a cell leaves the cycle, either temporarily or permananently.

Question 16

why might cells enter G0 phase?

Answer 16

• differentiation
• damaged DNA
• aging

Question 17

why might differentiation cause a cell to enter G0?

Answer 17

a cell that becomes specialised to carry out a specific function is no longer able to divide; it will carry out the function indefinitely and not enter the cell cycle again.

Question 18

why might damaged DNA cause a cell to enter G0?

Answer 18

a damaged cell can no longer divide ad enters G0.

Question 19

why might aging cause a cell to enter G0?

Answer 19

the number of senescent cell increases as you age. this is related to arthitis, or other age related diseases.

Question 20

what is vital for the fidelity of cell division?

Answer 20

• ensuring a cell only divides when it has grown to the right size
• the replicated DNA is error free
• chromosomes are in correct positions

Question 21

what are checkpoints ?

Answer 21

the control of mechanisms of the cell cycle. they 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 22

where do the checkpoints occur in the cell cycle?

Answer 22

• G1 checkpoint
• G2 checkpoint
• spincle assembly point (metaphase checkpoint)

Question 23

what happens at the G1 checkpoint

Answer 23

• end of the G1 phase before entry into the S phase.
• if the cell satisfies the requirements of this chempoint, it is triggered to begin DNA replication
• if it does not satisfy the requirements of this checkpoint, it enters G0.

Question 24

what happens at the G2 checkpoint?

Answer 24

• it is at the end of the G2 checkpoint, before mitotic phase.
• if the cell passes this checkpoint, it initiates molecular processes that signal the beginning of mitosis.

Question 25

what happens at the spindle assembly checkpoint?

Answer 25

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

Question 26

what is checked at the G1 checkpoint?

Answer 26

• cell size
• nutrients
• growth factors
• DNA damage.

Question 27

what is checked at the G2 checkpoint?

Answer 27

• cell size
• DNA replication
• DNA damage

Question 28

what is checked at the spindle assembly checkpoint?

Answer 28

• chromosome attachment to spindle.

Question 29

what brings about the passing of a cell-cycle checkpoint?

Answer 29

kinases.

Question 30

what are kinases?

Answer 30

a class of enzyme that catalyses the addition of a phosphate group to a protein (phosphorylation.)

Question 31

what does phosphoylation do for cell cycle regulation?

Answer 31

changes the teriary structure of checkpoint proteins, activating them at certain points in the cell cycle.

Question 32

how are kinases activated?

Answer 32

by binding to a variety of checkpoint proteins called cyclins. binding of the correct cyclin to the appropriate kinase forms cyclin-dependent kinase complex. these are activated by enzymes.

Question 33

what is the role of cyclin dependent kinase complexes?

Answer 33

catalyses the activation of key cell-cycle proteins by phosphorylation. this ensures a cell progresses through the different phases of the cycle at the appropriate times. different enzymes break down cyclins when they are not needed, signalling a cell to move into the next phase of the cycle.

Question 34

what is cancer?

Answer 34

a group of diseases caused by the uncontrolled division of cells.

Question 35

what causes tumours?

Answer 35

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