cell division and death Flashcards
name the two types of cell division
vegetative division = mitosis
reproductive cell division = meiosis
define mitosis
each daughter cell is genetically identical to parent cell
define meiosis
the number of chromosomes in the daughter cells is reduced by half to produce haploid gametes
name the four phases of the eukaryotic cell cycle
G1, S, G2, M
two gap phases for growth
S for DNA Synthesis
M for Mitosis
what occurs in the S-phase of the cell cycle?
DNA synthesis = chromosome duplication occurs
10-12 hrs in humans
what occurs in the M-phase of the cell cycle?
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)
key events in mitosis
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
what is the interphase?
G1, S and G2 phases together
main checkpoints in cell cycle
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
what controls the cell cycle?
cyclins - a class of proteins
bind to kinases (enzymes that attach phosphate groups in phosphorylation)
controls cell checkpoints and hence whether the cycle progresses
define CDKs
Cyclin-dependent kinases
what is phosphorylation?
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
role of phosphatase
dephosphorylation - enzyme catalyses the removal of a phosphate group from a protein
opposite role to kinases
how is DNA damage detected in the cell cycle?
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
define fertilisation
haploid egg + haploid sperm fuze to form a diploid zygote
general processes occurring in meiosis
one round of DNA replication (meiotic S phase) followed by TWO rounds of cell division (meiosis I and II) resulting in four haploid gametes
three fundamental processes that control cell number (and hence organ size)
cell growth
cell division
cell death
three major classes of signalling molecule controlling cell growth/division/death
mitogens: stimulate cell division via cyclins
growth factors
survival factors (promotes survival by suppressing apoptosis)
what is density dependent inhibition of cell division?
normal cells stop proliferating once they have formed a confluent monolater (ie no more space to grow)
mechanically disrupted
prokaryotic cell division
undergoes BINARY FISSION
= vegetative cell division
can take 20-25 mins for some bacteria in ideal conditions to replicate
main stages of binary fission
DNA replication
chromosome segregation
cytokinesis
basically just like mitosis
apoptosis vs necrosis
apoptosis is programmed cell death
necrosis is not planned (swells and bursts, often eliciting inflammation response)
function of apoptosis
controls cell numbers and eliminates unwanted cells (including faulty immune cells)
very useful in developing / embryonic systems
role of apoptosis in developing nervous systems
adjusts the number of nerve cells to match the size of the target that nerve cells connect to, allowing plasticity of the nervous system
steps in apoptosis signalling
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
