Cell Replication

Question 1

what is the cell cycle?

Answer 1

orderly sequence of events in which a cel duplicates its contents and divides in 2

Question 2

give a brief overview of the stages of the cell cycle

Answer 2

1. cell growth and chromosome replication
2. chromosome separation
3. cell division (cytokinesis)

Question 3

what factors affect the rate of cell division?

Answer 3

age, complexity of system, need for renewal, state of differentiation, tumour cellss

Question 4

which cells never divide?

Answer 4

neuron and cardiac myocytes

Question 5

which stages make up interphase?

Answer 5

G1, S, G2

Question 6

what happens in S phase?

Answer 6

DNA replication

Question 7

what happens in M phase?

Answer 7

mitosis (nuclear division)
cytokinesis (cytoplasmic division)

Question 8

what is G0?

Answer 8

quiescent phase

in the absence of a stimulus, cells go into G0

Question 9

give example of cells which stay in G0 for long periods

Answer 9

neurons, skeletal muscle, hepatocytes

Question 10

what do checkpoints in G1 do?

Answer 10

check if environment’s favourable to enter S phase

Question 11

what do checkpoints in G2 do?

Answer 11

check all DNA is replicated
check all damaged dna is repaired

Question 12

what do checkpoints in mitosis do?

Answer 12

check all chromosomes are properly attached to the mitotic spindle

Question 13

what does c-Myc do?

Answer 13

a transcription factor which stimulates the expression of cell cycle genes and promotes G0 to G1 transition

its an oncogene that’s over expressed in many tumours

Question 14

when is c-Myc produced?

Answer 14

in response to the detection of a growth factor

Question 15

How do we get cell growth? (Leaving G0 to G1)

Answer 15

Growth factors bind to tyrosine kinase receptors, which triggers an intracellular signalling pathway which ultimately leads to protein synthesis increasing and protein degradation decreasing, stimulating cell growth

Question 16

what two things can occur if something goes wrong with cel replication?

Answer 16

1. Cell cycle arrest - can be temporary while damage is being fixed
2. Programmed cell death = apoptosis

Question 17

What happens to the cell when the DNA damage is too great and cannot be repaired?

Answer 17

Programmed cell death = apoptosis

Question 18

In the absence of a stimuli to progress into the next stage of replication, what happens to the cell?

Answer 18

Cells go into G0 phase (quiscent phase)

Question 19

What does the exit from G0 phase require?

Answer 19

Growth factors and intracellular signalling cascades

Question 20

What forms when cyclins bind to cyclin dependant kinases?

Answer 20

They form an activated cyclin-CDK complex

Question 21

does the concentration of cyclins in the cell fluctuate?

Answer 21

yes

Question 22

when is the Cdk active?

Answer 22

only during mitsois
as soon as cyclin has basically disappeared, no activity of cyclin dependant kinase

Question 23

b

Answer 23

cell detects growth factor
production of c-Myc
target gene for c-Myc = cyclin D (first cyclin needed to get into S phase)

Question 24

what do protein kinases cascades lead to?

Answer 24

signal amplification- kinases activate many others, have targets, can phosphorylate lots of things

regulation: dephosphorylate to stop the cycle

intracellular signalling cascade
kinase phosphorylates

Question 25

what is cell cycle control based on?

Answer 25

cyclically activated and expressed proteins

Question 26

where are cyclin-dependent kinases present?

Answer 26

in proliferating cells throughout the cell cycle

Question 27

what is the activity of cyclin-dependent kinases regulated by?

Answer 27

interaction with cyclins
phosphorylation

Question 28

when are cyclins expressed, regulated and synthesised?

Answer 28

transiently expressed at specific points in the cell cycle
regulated at level of expression
synthesised then degraded