Week 5 - Cell Cycle

Question 1

What is mitosis?

Answer 1

process by which the chromosones in the cell are separated into two identical sets of chromosones each in its own nucleus

Question 2

What is cytokinesis?

Answer 2

process in which the cytoplasm divides to form two idential daughter cells

Question 3

What occurs during the M phase of the cell cycle?

Answer 3

mitosis and cytokinesis

Question 4

What phases of the cell cycle make up interphase?

Answer 4

G1, S and G2

Question 5

What occurs during the gap phases (G1 and G2) of interphase?

Answer 5

cell continues to grow and moniters both its external state and the external environment

ensures that conditions are stable to move onto to S phase and mitosis (checkpoints)

G1 - synthesises mRNA and proteins

Question 6

What occurs during S phase?

Answer 6

DNA replication

Question 7

What are the three main checkpoints of the cell cycle control system?

Answer 7

transition from G1 to S phase (G1 checkpoint)

transition from G2 to M phase (G2 checkpoint)

just before end of M phase (M checkpoint)

Question 8

What is the cell checking for at the end of G1 before it can proceed into S phase?

Answer 8

Is the enrvironment favourable for proliferation before comitting to DNA replication?

Question 9

What is G0?

Answer 9

a resting phase that cells can enter if contitions are not favourable to progress to S phase

Question 10

What does the cell check for in the transition from G2 to M phase?

Answer 10

Has all the DNA replicated?

Is the environment favourable?

Question 11

What does the cell check for during M phase?

Answer 11

Are the duplicated chromosones properly attached to the mitotic spindle?

Question 12

What is the purpose of cyclin-dependent kinases (Cdk’s)?

Answer 12

they regulate DNA regulation, mitosis and cytokinesis

binds to cyclin to become enzymatically active

once activated a cyclin - Cdk complex phosphorylates key proteins in the cell that are required to initiate particular steps in the cell cycle

CDKs are continually expressed in cells while cyclins are synthesised at specific points of the cell cycle as a response to other signalling pathways

Question 13

What state are most of the cells of your body in?

Answer 13

G0, because they are non-dividing

Question 14

What cyclin triggers entry into M phase?

Answer 14

M cyclin

Question 15

What cyclin-Cdk complexes help to launch S phase?

Answer 15

S-Cdk and G1/S-Cdk

Question 16

What are the possible options for a cell at the G1 checkpoint?

Answer 16

proceed to S phase

withdraw to G0

pause temporarily in G1 until the conditions are right

permanently withdraw from the cycle in the case of terminally differentiated cells

Question 17

What happens to Cdk’s during G1?

Answer 17

they are inactivated which creates a stable environment for the cell to grow

Cdk inhibitor proteins are deployed to muffle the activity of cyclin-Cdk complexes and synthesis of new cyclins is stopped

Question 18

What is the role of p53 in the cell cycle?

Answer 18

DNA damage in G1 causes an increase in both the concentration and activity of p53

p53 can induce the cell to undergo programmed cell death (apoptosis) if the DNA damage is too severe to be repaired

Question 19

What happens if there is a mutation in the p53 gene?

Answer 19

there will be unrestrained replication of damaged DNA leading to a high rate of mutation and cells that tend to become cancerous

Question 20

What is a kinetochore?

Answer 20

protein complexes that assemble on the centromere of each condensed chromosone during late prophase

they attach chromosones to the mitotic spindle

Question 21

What are the main events of prophase?

Answer 21

chromosones condense

mitotic spindle assembles between the two centrosomes which have begun to move apart

Question 22

What are the main events of prometaphase?

Answer 22

breakdown of the nuclear envelope

chromosones attach to spindle microtubules via their kinetochores

Question 23

What are the 5 stages of mitosis?

Answer 23

prophase

prometaphase

metaphase

anaphase

telophase

Question 24

What are the main events of metaphase?

Answer 24

chromosones are aligned at the equator of the spindle midway between the spindle poles

Question 25

What are the main events of anaphase?

Answer 25

sister chromatids separate and are slowly pulled towards spindle pole kinetochore microtubules get shorter and the spindle poles move apart

Question 26

What cells undergo mitosis?

Answer 26

all somatic cells (occurs only in eukaryotic cells)

Question 27

What is the purpose of meiosis?

Answer 27

to provide genetic variety to produce gametes

Question 28

What are the main events of telophase?

Answer 28

nuclear membranes form division of cytoplasm begins with the assembly of the contractile ring

Question 29

How does a cell divide during cytokinesis?

Answer 29

contractile ring of actin and myosin pinches the cell into two daughter cells

Question 30

What are the main differences between **mitosis** and **meiosis**?

Answer 30

**MITOSIS** * preserves chromosone number * diploid * clonal * genetic conformity **MEIOSIS** * reduction division * chromosone number halved * haploid * genetic variation * inter-chromosonal crossing over

Question 31

What is the purpose of apoptosis?

Answer 31

to get rid of cells that are no longer needed important for development and cellular defense

Question 32

What is *cell necrosis*?

Answer 32

when cells die as a result of acute injury

Question 33

What is the difference between **necrosis** and **apoptosis**?

Answer 33

**necrosis -** a comprimised cell membrane as a result of acute injury leads to cell swelling, the cell bursts and releases intracellular components triggering an inflammatory response *(messy death)* **apoptosis -** cell shrinks and nuclear DNA breaks up into fragments, the cell develops irregular bulges (blebs) on surface, macrophage phagocytoses cell before it spills its contents *(clean death)*

Question 34

Outiline the process of meiosis

Answer 34

* chromosones replicate * chromosones condense * chromosones pair with homologous partner * crossover occurs (genetic variation) * homologous pairs separate * cytokinesis * chromosones condense * chromosones line up individually at equator * chromatids separate * cytokinesis

Question 35

Give an example of a 'post-mitotic' cell?

Answer 35

differentiated neurons and muscle cells that comprise the brain, heart and skeletal muscle

Question 36

What is a 'post-mitotic' cell?

Answer 36

cells that are incapable of proliferation and are irreversible blocked from re-entering the cell cycle

Question 37

DNA damage can cause arrest at which two stages of the cell cycle?

Answer 37

G1 (if damage to DNA is already present) and G2 (if damage has occured during S phase)

Question 38

What are gametes that receive and incorrect number of chromosones called?

Answer 38

aneuploid