cell cycle 1 & 2: mitosis & cell cycle

Question 1

what are the stages of mitosis?

Answer 1

prophase, metaphase, anaphase, telophase

Question 2

what happens during prophase?

Answer 2

condensation of chromatin: double helices wrapped around histones -> wrapped around itself to form 30nm fibres -> form scaffold -> wrapped further to form chromosome
nuclear envelope breaks down -> chromosomes come out into cytoplasm -> centrosomes migrate to opposite sides -> begin to organise spindle

Question 3

what is the structure of a condensed chromosome?

Answer 3

2 sister chromatids each with their own kinetochore (complex of proteins that regulates processes in cell cycle) & centromere (acts like a belt)

Question 4

how does the spindle form?

Answer 4

radial microtubule arrays (ASTERS) form around each centrosome -> radial arrays meet -> polar microtubules form

Question 5

what happens during metaphase?

Answer 5

early prometaphase: breakdown of nuclear membrane, attachment of chromosomes to spindle via kinetochores
late prometaphase: microtubule from opposite pole captured by sister kinetochore -> chromosomes slide towards center along microtubules

Question 6

what are the 3 types of half-spindle?

Answer 6

kinetochore microtubule: bound to kinetochore

polar microtubule: microtubule that has met and connected with microtubule from other centrosome

astral microtubule: microtubule that is originating from the centrosome that doesn’t connect to a kinetochore

Question 7

what happens during anaphase?

Answer 7

anaphase A: cohesin broken down & microtubules get shorter -> daughter chromatids pulled towards opposite spindle poles

anaphase B: daughter chromosomes reach opposite poles -> centrosomes migrate apart

Question 8

what happens during telophase?

Answer 8

daughter chromosomes arrive at pole -> nuclear envelope reassembles at each pole -> centrosomes move apart -> equal distribution of cell material -> assembly of contractile ring of actin & myosin filaments -> ring squeezes cell to divide into daughter cells

Question 9

what happens during cytokinesis?

Answer 9

insertion of new membrane at cleavage furrow (site of cell cleavage)

Question 10

what features of inappropriate regulation of cell division can be seen?

Answer 10

• aneuploidy
• chromosome instability
• altered levels of cell cycle regulator proteins
• contact inhibition of growth
• premature mitosis (-> death)

Question 11

what is the most vulnerable period of the cell cycle?

Answer 11

mitosis

• cells are more easily killed (irradiation, heat shock, chemicals)
• DNA damage cannot be repaired
• gene transcription silenced

Question 12

what are the stages of interphase?

Answer 12

G0: cell cycle machinery dismantled
G1 (gap): decision point
S phase: synthesis of DNA + proteins
G2 (gap): another checkpoint phase

Question 13

what happens during S phase?

Answer 13

• DNA replication
• protein synthesis: initiation of translation & enlongation increased
• organelle replication (centrosomes, mitochondria, golgi etc)

Question 14

what is the structure of a centrosome?

Answer 14

two centrioles (9 triplet microtubules arranged in a hollow cylinder) perpendicular to each other

Question 15

what is the function of a centrosome?

Answer 15

form MTOC and mitotic spindle