cell division Flashcards
what are the 3 stages of interphase ?
G1G0) s G2
what happens in G1
cells grow, transcription of genes, organelles duplicate, bio synthesis
what happens at S in interphase?
DNA replicates so that each chroma zone has 2 identical sister chromatids (a pair), genes replicate housekeeping then one in all cells
why is the S phase quick?
exposed DNA pairs are susceptible to mutation
what happens at G2 in interphase?
chemicals stimulate proteins that make chroma zones condense and will make the spindle form, cells grow
what happens during G0 phase of interphase?
a resting phase, apoptosis, differentiation, senescence
what are 4 purposes of a restriction points?
to prevent uncontrolled division, detect and repair damage to uv light, that the cycle cant be reversed and DNA is only replicated once
what is senesence?
when an aging cell has lost the ability to divide
what is apoptosis?
a programmed cell death
how is cell division helped to be regulated?
proto-oncogenes help regulate cell division by coding for proteins that help regulate cell growth and differentiation
how does a prokaryotic cell divide?
by binary fission, dna is replicated, 2 new loops of DNA are pulled to opposite ends of the cell and a cell wall forms, plasmids replicate
what is mitosis and what products does it make?
nuclear division that maintains the chromazone number the same. it produces genetically identical daughter cells which are diploid
what is mitosis used for in the body?
asexual reproduction, growth, tissue repair
what happens within cells in prophase?
chromazones condense (get shorter and thicker) as DNA supercoils,
nuclear envelope breaks down,
in animal cells only, centrioles separate to opposite ends of the cell,
tubulin threads form spindle fibres between centrioles
what happens during metaphase?
pairs of chromatids align along equator of cell and
spindle fibres are released and attach to the centromere of the chromazone
what is the centromere?
the point at which the 2 chromatids attach in a chromazone
what happens during anaphase?
spindle fibres retract and pull chromatids apart to the to poles, centromere goes first so it assumes a V shape
how do the spindle fibres get to the poles of the cell?
motor proteins walk along tubulin, hydrolysing ATP with every step taken
what happens during telophase?
chromazones at each pole lengthen and get thinner
spindle fibres disintergrate and nucleus reforms but are all still in 1 cell
what happens during cytokynesis?
cytoplasm splits in two because myosin and actin filament ring contact to cleave cell in two
describe what happens in plant cells during cytokynesis?
an end plate forms where equator of spindle was, new plasma membrane and cellulose cell wall are laid down either side of the end plate
what does meiosis produce?
4 haploid daugther cells that are geneticaly different to each other
state 2 mportantces of meiosis
increases genetic variation, produces haploid gametes which allow for sexual reproduction
state 4 ways meiosis increases genetic variation?
crossing over of non sister chromazones- in prophase 1
independant assortment= metaphase 1
mutations
random fusion of gametes
how does crossing over increase genetic variation?
non sister chramazones wrap around each other and swap sections so genes and alleles get shuffled
when does crossing over occur ?
prophase 1 initially
what is indpendant assortment?
when homologous pairs are arragnged randomly along equator of the cell
when does independant assortment happen ?
metaphase 1 and anaphase 2
how does independant assortment increase genetic variation?
homologous pairs get separated so one of each pair ends up in each daughter cell which creates a large number of possible combinations and therefore increases genetic variation
how does a haploid gamete create a diploid cell?
undergo fission with another haploid gamete and creates a further genetically different diploid cell which undergos mitosis to form and embryo
what are homologous chromazones?
one maternal and one paternal, they carry same genes
what is a non-sister chromatid?
when two different pairs chromazones cross their chromatids so the crossing is between 2 chromazones that are not the same as each other
why do multicellular organisms need differenciation in cells?
they have a small sa/vol ratio so most cells arnt in contact with external environment so oxygen and carbon dioxide cant diffuse in therefore a diverse range of cells are needed to do specific functions
state how cells differentiate ?
genes that are needed to carry out specific functions are switched on and genes that are not needed are switched off
what 3 things will happen to cell as a result of differentiation?
proportions of the organelles will differ from other cells,
shape of cell will change,
contents of cell will change
what is the function of erythrocytes?
to carry oxygen from the lungs to repiring cells
how does the stucture of erythrocytes link to the function? 3 points
they are very small, therefore have a high sa/v meaning oxygen can diffuse across all regions of cell.
they have a well developed cytoskeleton therefore is very flexible, this allows them to change shape and travel through narrow cappilarys.
most organells were lost at differenciation therefore allows room for haemoglobin to carry oxygen
what is the function of a neutrophil?
ingest invading pathogens by phagocytosis
how does structure of a neutrophil relate to its function?
has a multilobed nucleas due to flexibility, therefore it can get through capilaries and form cytoplasmic projections to engulf pathogens
large number of lysomomes, in order to digest invading pathogens by phagocytosis
what is the function of spermatozoa?
to fuse with ovum in reproduction, initiate development of the embryo, pass on paternal genes
how does the sructure of spermatozoa relate to its function?
head contains haploid nucleas to pass on genes.
acrosome contains digestive enzymes to digest the ovum outer layer.
mid-peice is packed with mitochrondria to release energy to propel the undulipodim
what is the scientific name of the sperms tail?
undulipodium