Cell Division Flashcards
Functions of cell division
Growth, reproduction, tissue renewal and repair
Karykinesis
Nuclear division typically followed by whole cell division (mitosis)
Cytokinesis
Division of the cytoplasm
Somatic cells
Body cells, not reproductive, diploid, 46 chromosomes
Gametes
Reproductive, haploid cells 23 chromosomes
Sister chromatids
Pairs of chromosomes formed at the start of cell division, seen together when single chromatid chromosomes have been replicated
Cohesins
Protein complexes that attach two sister chromosomes all along the sister chromatids (split by seperase)
Kinetochore
Protein complex at the centromere that spindle apparatus attaches to
Centromere
Where two chromatids are most tightly held together
Consists of repeating sequences of DNA (centromeric DNA) contains the kinetochore
Cell cycle steps
G0, G1, S, G2, M
Checkpoints
Control points where stop and go signals can regulate the cell cycle
Occurs at G1, G2, and M
Cell cycle control system
Cyclically operating set of molecules (kinases and cyclins) in the cell that triggers and coordinates key events in the cell cycle
Cyclins
Appear in the cell in cyclical patterns/rhythmic fluctuations
CDK
Cyclin dependent kinases are kinases that must attach to a cyclin to be active and thus are dependent on the fluctuations of cyclin
MPF
M-phase promoting factor
go-ahead for G2 checkpoint
CDK complex acts as a kinase and activates other kinases by phosphorylation
Several cyclin
CDK complexes involved with G1 checkpoint
Stop and go signals
Internal or external signals for cell cycle
Internal stop/go signals
Kinetochore fibers attached to each sister chromatid
DNA replicated without errors
External stop/go factors
Presence of essential nutrients and growth factors
Density dependent factors
Anchorage dependence
Growth factor
Proteins released by certain cells that stimulate other cells to divide
Density Dependent Factors
External factor of density inhibits cell division
Anchorage dependence
Cells that must be attached to something in order to divide
Gap 0
Resting, non-dividing
Gap 1 phase
Proteins made, organelles replicated
S phase
DNA is replicated, proteins made and organelles replicated
G2 phase
Proteins made, organelles replicated, cell readies for division
Cell enlarged
DNA replication is checked with repair enzymes
M phase
Division of genetic material in the nucleus
Interphase
Preparing for cell division
DNA replicated and checked
Organelles replicated
G2 checkpoint
Checkpoint requiring the cyclin dependent kinase (CDK) MFP (maturation promoting factor) to phosphorylate proteins and other CDK’s
Prophase
Chromosomes condensed and visible inside nucleus
Centrosomes move towards the poles
Asters and spindle apparatus formed
Late prophase
Chromosomes further condensed
Nuclear envelope broken
Centrosomes at the poles
Organelles pushed to the sides
Kinetochore and non-kinetochore fibers formed
Kinetochore fibers
Microtubules of the spindle apparatus that attach to the kinetochores at the centromeres of sister chromatids and pull them apart
Non-kinetochore fibers
Microtubules that grow from one centrosome and push the other away allowing the cell to elongate
Asters
The centrosome and extending microtubules, holding the centrioles in position at the poles
Metaphase
Sister chromatids arranged along the metaphase plate
Centrosomes at the poles of the cell
Complete spindle apparatus
Kinetochore fibers attached to the kinetochore of each of the sister chromosomes
Equator/metaphase plate
Line along which chromosomes arrange themselves during metaphase
Anaphase
Seperase splits the cohesions and sister chromatids are pulled apart
Daughter chromosomes move toward pulls
Cell elongated by non-kinetochore fibers
Quick phase
Telophase
Two new nuclei forming around the daughter chromones at the poles
Cytokinesis begins
Cytokinesis
Division of the membrane
Contractile ring closes in forming cleavage furrow and pinching the cell in two
Cell plate
Cell wall formed in plant cell cytokinesis
Formed in the middle of two cells by material deposited from Golgi Apparatus that grows outward towards existing walls
Coenocyte
Cell that undergoes mitosis and not cytokinesis resulting in multiple nuclei in one cell
Binary fission
Simple division in half without mitosis
DNA replicated, cell doubles in size, new membrane grows/pinches in, new cell wall deposited
Autosomes
Non sex chromosomes
22 in human haploid cells
Homologous chromosomes
Chromosomes of the same size and shape same genes at the same loci, one from each parent
Meiosis
Involves two nuclear divisions to create 4 cells
Meiosis I
A diploid nucleus to two haploid nuclei
Meiosis II
Similar to mitosis but starting with haploid nuclei
Prophase I
Nuclear envelope breaks
Chromosomes condense
Synapsis occurs joining homologous chromosomes
Crossing over occurs at chiasmata (1-3 per homologous chromosome)
Synapsis
Homologous chromosomes pair up using synaptonemal complexes along their lengths
Chiasmata
Loci where crossing over occurs
Metaphase I
Homologous chromosome pairs line up (tetrads)
Nuclear envelope fully dissolved
Centrosomes have reached the pulls w/ complete spindle apparatus
Anaphase I
Cohesions separated by seperase and homologs are pulled apart
Telophase I
Nuclei may reform
2 haploid cells
Cytokinesis may occur
Prophase II
Spindle apparatus begins to form
Metaphase II
Sister chromatids line up along the metaphase plate
Centrosomes at the poles
Complete spindle apparatus
Anaphase II
Seperase cleaves cohesions and non-identical sister chromatids pulled to the poles
Telophase II
Nuclei reform
4 distinct haploid cells form
Cytokinesis starts
Variation of individuals
Independent assortment
Crossing over
Sexual reproduction (union of gametes)
Independent assortment
Each pair of homologs line up independently of each other
