cell division and death

Question 1

name the two types of cell division

Answer 1

vegetative division = mitosis
reproductive cell division = meiosis

Question 2

define mitosis

Answer 2

each daughter cell is genetically identical to parent cell

Question 3

define meiosis

Answer 3

the number of chromosomes in the daughter cells is reduced by half to produce haploid gametes

Question 4

name the four phases of the eukaryotic cell cycle

Answer 4

G1, S, G2, M

two gap phases for growth
S for DNA Synthesis
M for Mitosis

Question 5

what occurs in the S-phase of the cell cycle?

Answer 5

DNA synthesis = chromosome duplication occurs
10-12 hrs in humans

Question 6

what occurs in the M-phase of the cell cycle?

Answer 6

mitosis = nuclear division with copied chromosomes being distributed into two daughter nuclei
about 1 hr in humans

followed by cytokinesis (cytoplasmic division, cell divides into two)

Question 7

key events in mitosis

Answer 7

PMAT (pro/meta/ana/telophase)
chromosomes condense, nucleolus disappears
mitotic spindle captures/orders chromosomes
metaphase=chromosomes line up
pulled apart
two nuclei form

probably more detail than we really need

Question 8

what is the interphase?

Answer 8

G1, S and G2 phases together

Question 9

main checkpoints in cell cycle

Answer 9

Start checkpoint: before entering S, check favourable environment
G2/M: check all DNA is replicated
meta-anaphase transition: checks all chromosomes are attached to spindle

Question 10

what controls the cell cycle?

Answer 10

cyclins - a class of proteins
bind to kinases (enzymes that attach phosphate groups in phosphorylation)

controls cell checkpoints and hence whether the cycle progresses

Question 11

define CDKs

Answer 11

Cyclin-dependent kinases

Question 12

what is phosphorylation?

Answer 12

a common mechanism for regulating protein activity
generally, a phosphate group from ATP is transferred to an amino side chain of the target protein by a protein kinases

Question 13

role of phosphatase

Answer 13

dephosphorylation - enzyme catalyses the removal of a phosphate group from a protein

opposite role to kinases

Question 14

how is DNA damage detected in the cell cycle?

Answer 14

at two checkpoints: late G1 or G2/M checkpoint
regulated by protein P53 (halts cell cycle when DNA damage detected by binding to and inactivating a cyclin)

P53 found to be mutated in many cancers

Question 15

define fertilisation

Answer 15

haploid egg + haploid sperm fuze to form a diploid zygote

Question 16

general processes occurring in meiosis

Answer 16

one round of DNA replication (meiotic S phase) followed by TWO rounds of cell division (meiosis I and II) resulting in four haploid gametes

Question 17

three fundamental processes that control cell number (and hence organ size)

Answer 17

cell growth
cell division
cell death

Question 18

three major classes of signalling molecule controlling cell growth/division/death

Answer 18

mitogens: stimulate cell division via cyclins
growth factors
survival factors (promotes survival by suppressing apoptosis)

Question 19

what is density dependent inhibition of cell division?

Answer 19

normal cells stop proliferating once they have formed a confluent monolater (ie no more space to grow)
mechanically disrupted

Question 20

prokaryotic cell division

Answer 20

undergoes BINARY FISSION
= vegetative cell division

can take 20-25 mins for some bacteria in ideal conditions to replicate

Question 21

main stages of binary fission

Answer 21

DNA replication
chromosome segregation
cytokinesis

basically just like mitosis

Question 22

apoptosis vs necrosis

Answer 22

apoptosis is programmed cell death
necrosis is not planned (swells and bursts, often eliciting inflammation response)

Question 23

function of apoptosis

Answer 23

controls cell numbers and eliminates unwanted cells (including faulty immune cells)

very useful in developing / embryonic systems

Question 24

role of apoptosis in developing nervous systems

Answer 24

adjusts the number of nerve cells to match the size of the target that nerve cells connect to, allowing plasticity of the nervous system

Question 25

steps in apoptosis signalling

Answer 25

apoptotic stimulus –> cytochrome C released from mitochondria (due to change in membrane potential by flipped phosphatidyl serine, now on outer leaflet of PM)
triggers the assembly of the apoptosome
recruits caspases (enzymes) that lead to cascades resulting in cell death