MITOSIS AND MEIOSIS Flashcards
what is growth and cell division ?
cells duplicate its contents
parent cell divide into two daughter cells
why cells divide ?
unicellular : reproduction
multicellular : growth and repair of tisuus
key events for cell division
reproductive signal : initiate cell division
replication : DNA is duplicated
Segregation : distribution of DNA into two new cells
Cytokinesis : separation of two new cells
what are reproductive signals ?
growth factors : external chemical factors that stimulate these cells to divide
e.g : platelet derived growth factor that initiate blood clotting, stimulate skin cells to divide and heal wounds
what are important reproductive signal ?
nutrients conc. and environmental conditions
what is the special thing about meiosis ?
provides diversity among us individual organisms
what are somatic cells?
body cells that are not specialised for reproduction , contains homologous pairs of chromosomes (diploid)
what are gamete cells?
cells that only contain one set of chromosomes (haploid)
what are the three stages of interphase and what Is the key point
G1, S Phase, G2
DNA has replicated but x form condense structure of chromosome - remain as loosely coiled chromatin
what happens in G1
decision to divide/not to divide
doubling of organelles
accumulation of materials for DNA synthesis
what happens in the S phase
DNA replication occurs
-each chromosome being composed of two sister chromatids
what happens in G2
synthesis of proteins needed for cell division
what is centrosomes
microtubules organizing center of the cell which is replicated in the S phase
-composed of two centrioles surrounded by pericentriolar material
what are two ways a cell can die ?
NECROSIS : accidental death - inflammation, loss of ATP
APOPTOSIS : programmed cell death - renewing RBC every other month
what signals control cell death ?
- lack of mitotic signal (growth factor)
- recognition of damaged DNA
- external signals cause membrane proteins to change shape and activate enzymes called CASPASES which hydrolyze proteins of membranes
what is G1 checkpoint ?
main checkpoint (restriction point)
determines whether all conditions are favourable for cell division to proceed
check for growth factors and damaged DNA
check the integrity of DNA
what is G2 checkpoint ?
mitosis checkpoint
verifying of DNA replication - chromosomes must be duplicated
mitosis will occur only if DNA has been replicated correctly
check for damaged DNA and unreplicated DNA
what is M checkpoint ?
spindle assembly checkpoint
occurs between metaphase and anaphase
ensure the chromosomes are properly attached to the spindle so it can be distributed accurately to the daughter cells
spindle checkpoint - kinetochore attachment
mitosis will not occur if chromosomes are not properly aligned
what is cell maintenance ?
cell division > cell death = growth
cell division < cell death = atrophy - wasting away part of a body
cell division»_space;> cell death = cancer - lose control over cell division, evade apoptosis, can migrate to other parts of body (METASTASIS)
whar happens during mitosis ?
cell duplicates all of its contents including its chromosomes & split to form 2 identical daughter cells
why does mitosis occurs ?
- Asexual reproduction to replace & repair body cells
- increase in the no. of cells during growth
- must be regulated correctly or cancer will occur
name all the stages and phases
6 stages and 4 phase Interphase Prophase Metaphase Telophase Cytokinesis
what happens during interphase
- DNA replication
- go through all the chekpoints
- two centrosomes are already present (key to cell division)
what happens during prophase
- DNA molecules are shortened and condense by coiling to form chromosomes (sister chromatids)
- one pair of centrioles (1 chromosome) have migrated to the opp pole
- nuclear membrane and nucleolus starts to break down
- mitotic spindle is formed and attaches itself to the kinetochore of sister chromatidss
what happens during metaphase
- chromosomes are moved to the central/metaphase plate by the mitotic spindle
- sister chromatids line up in the middle of the cell
- each chromatid is attached to one spindle fibre which comes from opp poles
what happens during anaphase
microtubules attached to kinetochores of each sister chromatids shortens, hence sister chromatids are split and move to opp end of poles
the unattached microtubules elongates to stretch the cells
what happens during telophase
begins when chromosomes arrive at the poles of the cell
chromosomes become indsitinct chromatin again
spindle disappears and nuclear envelope reforms
what happens during telophase in plant cells
- a cell plate forms across the cell in the location of the old metaphase plate where chromatids line up
- vesicles from the Golgi apparatus migrate to the plane of the metaphase plate and fuse to form a new plasma membrane
what happens during cytokinesis
- cleavage furrow passes around the circumference of the cell
- actin filaments form a contractile ring which will cause the cleavage furrow to be pinched in half when the ring becomes smaller
what happens during meiosis
2 nuclear divisions but DNA is replicated once only during the interphase
name all the stages and phases
interphase prophase I metaphase I anaphase I telophase I Cytokinesis I prophase II metaphase II anaphase II telophase II Cytokinesis II
what happens in meiosis I
reduction division - reduces the no. of chromosomes in half making haploid daughter cells
when does genetic recombination occur in meiosis
- synapsis and crossing over happen during prophase I
- crossing over occurs as chromosomes condense
what happens to the kinetochores of sister chromatids in Meiosis I
it fuses and functions as one so microtubules can attach to only one side of each centromere
where are homologous pairs of chromosomes held at
chiasmata
