cell cycle

Question 1

what are 2 main phases of cell cycle?

Answer 1

• interphase and mitotic phase

Question 2

what are the phases of interphase?

Answer 2

G1, (G0), S, G2,

Question 3

what are the phases of mitotic phase?

Answer 3

prophase
(prometaphase)
metaphase
anaphase
telophase

(cytokinesis)

Question 4

what are cyclins? and examples in cell cycle?

Answer 4

a family of proteins whose concentration increases and decreases throughout cell cycle

• cyclin A (S phase)
• cyclin B (G2 phase)
• cyclin E (G1 phase)

Question 5

what do cyclins do in cell cycle?

Answer 5

they activate cyclin dependant kinases (CDK’s) which act in conjunction with with cyclins

Question 6

what happens with cyclins & CDK’s after completion of cell cycle?

Answer 6

they are degraded - the residues pf used up molecules taken up by cytoplasmic care taker protein = ubiquitin

Question 7

what happens in G1 phase?

Answer 7

gap in cell cycle before S phase (first phase of interphase)
- period where cells respond to growth factors directing initiation of new cycle
(phase that needs most molecular machinery is required to complete another cycle)

Question 8

what is G1 phase controlled by?

Answer 8

cyclin E (for entry) and CDK’s

Question 9

what is Go pahse?

Answer 9

cells enter G0 phase when:
cells remain capacity for proliferation and in process of differentiation (still have potential for being involved) but no longer dividing
- described as quiescent (like dormant)

Question 10

how can cells leave G0 phase?

Answer 10

by cells in G0 being stimulated by growth factors

Question 11

what blocks the cell cycle in G1?

Answer 11

proteins encoded by certain tumour suppressor genes like retinoblastoma protein (regulates transition form G1 to S phase)

Question 12

how long does each phase of cell cycle take to complete?

Answer 12

G1 = varies from 2- more than 100 hours
S = 7/8 hours
G2= 2-4 hours

prophase = 1.5 hours
metaphase = 20 mins
anaphase & telophase = don’t know?

Question 13

what is S phase?

Answer 13

DNA replication phase = new DNA synthesised and relation of genes to DNA established

Question 14

what controls S phase?

Answer 14

cyclin A and CDK’s

Question 15

how can DNA replication/DNA synthesis not work in S phase?

Answer 15

certain anti-cancer drugs can exert their cytotoxic effect by intercalating into narrow groove of DNA double helix
(DNA has 2 chains coiled around helical axis and paired in antiparallel menner, hydrophilic deoxy ribose- phosphate on outside and hydrophobic on inside - arrangement makes major (wide) groove and minor (narrow) groove)

Question 16

how can DNA be damaged during replication?

Answer 16

= deoxynucleotide (amino acid monomer) incorporation error
= spontaneous deamination (removal of amino group) of bases
= x-radiation causing nicks to DNA
= UV radiation
= various chemicals

Question 17

what is G2 phase?

Answer 17

second growth phase
when the cell prepares for division; this period ends with the breakdown of the nuclear membrane and the onset of chromosome condensation

Question 18

what is G2 phase controlled by?

Answer 18

cyclin B and CDK’s

Question 19

when are chromosome first individually visable?

Answer 19

in prophase
(in interphase they’re just long, narrow structures)

Question 20

what happens in prophase?

Answer 20

= individual chromosomes visualised as thin threads and are tightly coiled along entire length
= each chromosome splits longitudinally into 2 chromatids joined at centromere
= 2 paired centriole (that were outside nuclear envelope in interphase) separate by elongation of continuous microtubules of achromatic spindle & go to opposite poles of nucleus

Question 21

what happens in prometaphase?

Answer 21

nuclear membrane & nucelolus disappears
- chromosomes entangles in meshwork of continuous microtubules

Question 22

what happens in metaphase?

Answer 22

= centromere region of each chromosome presents bilateral disc called kinetochores
= from kinetechores, set of chromosomal microtubules are organised and extend bilaterallly towards opposite centrioles
= growth of chromosomal microtubules allow centromere of individual chromosomes with their paired chromatid to occupy equatorial plane of spindle (they line up along equator)

Question 23

what is function of colchicine?

Answer 23

arrests cell cycle at metaphase
= prevents formation of microtubule of spindle

Question 24

why is colchicine used in cell culture and what result is found?

Answer 24

it’s important tool in karyotyping
- when used in metaphase, chromosomes assemble around centriole

underpins rationale for cytotoxic drugs used in cancer therapy (something to use to stop replication)

Question 25

what happens in anaphase?

Answer 25

= centromeres split longitudinally and chromatids seperate to form 2 new chromosomes = spindle fibres contract and exert centrifugal force in centromere region and newly formed chromosome pulled apart to opposite poles

Question 26

what is non- disjunction?

Answer 26

when in anaphase, the chromosomes fail to migrate properly - tends to lead to one daughter cells having extra chromosome and one having less

Question 27

what are isochromosomes?

Answer 27

centromere splits transversely instead of longitudinally in anaphase = forms 2 daughter chromosomes of unequal length

Question 28

what happens in telophase?

Answer 28

= recognisation period = daughter chromosome enveloped by new nuclear membrane & nucleolus appears = chromosome becomes uncoiled and individual identity lost

Question 29

what happens in cytokinesis?

Answer 29

cytoplasm divides and cleavage furrow develops (the pinching shape of plasma membrane) around the equator region of achromatic spindle = contraction of fibrillar component of cytoplasm help in hour glass constriction of cleavage (actin-myosin at cleavage furrow)