Cell Division Flashcards
Mitosis
Interphase Prophase Metaphase Anaphase Telophase Cytokinesis
Interphase
Semi-Conservative DNA Replication
Prophase
DNA becomes condensed
Chromosomes becomes more distinct
Nuclear Envelope breaks down and dissolves
Centrioles migrate to the poles
Metaphase
Spindles have fully formed
Chromosomes line up along the equator of the cell (mataphase plate)
Anaphase
Spindles contract
Centimere divide
spindle pulls 1 chromatid from each pair to opposite poles of the cell
Telophase
Chromatids reach poles
spindles break down
2 new nuclear envelopes are formed
chromosomes decondese again
Cytokinesis
cell divides into 2 identical diploid daughter cells
genetically identical
chromosomes are indistinct
nucleolus is now present
Why do cells divide by mitosis?
growth and repair of damaged cells or tissues
Meiosis
Meisosi 1 and Meiois 2
Meiosis 1
Interphase Prophase 1 Metapahse 1 Anapahse 1 Telophase 1
Interphase
Semi Conservative DNA Replication
Prophase 1
Chromosmes condense becoming visible
nuclear membrane breaks down
spindles start to form
Mataphase 1
Bivalents line up along the equator in homologous pairs (metaphase plate)
Anaphase 1
Spindles contract Bivalents are pulled apart Homologous chromosomes are pulled apart Separated randomly 2 chromatids are pulled towards the poles
Telophase 1
Chromosomes reach the poles
Nuclear envelope starts to reform
Cells do NOT divide
Meiosis 2
Prophase 2 Metaphase 2 Anaphase 2 Telophase 2 Cytokinesis
Prophase 2
Spindles form around both sets of chromosomes
nuclear membrane breaks down
Metaphase 2
Chromosmes line up along the equator (metaphase plate)
Anaphase 2
Spindle fibres contract causing
centomeres divide
chromatids separate to opposite poles
Telophase 2
Chromosomes reach poles and disperse
spindles break down
nuclear membrane reforms
Cytokinesis
Cytoplasm divides membranes form around new cells producing 4 haploid daughter cells 23 chromosomes NOT genetically identical
Why do cells divide by mitosis
produce gametes
sex cells
Cell Cycle
cells spend 90% of thir time in interphase and the rest in mitosis
G1 phase
after mitosis the 2 small cells enter this phase
here they grow up to normal cell size
S1 phase
after G1 if the cells get the message to divide they move into tis phase where DNA replication occurs
GO phase
resting phase
after G1 if they do not move into the S1 phase they move here
it can be temporary or for the rest of its life
this is where stem cells wait until they are needed for replcaement
G2 phase
after the S1 phase is complete cells move into this phase
preparation for division and undergo more growth
Variation is increased in
Crossing over in prophase 1
Independent segregation in anaphase 1
Random Combinations
4 daughter cells have completely different combinations of chromosomes
due to random segregation in meiosis 1 and 2
Independent Segregataion
Either copy of a chromosme can go towards the gamete
the other copy can move to the same side or other side
Both have the same genes just different alleles
2^n
number of unique gametes that could be formed
n = number of homologous pairs in the organism
(2^n)^2
Number of combinations
Crossing Over
each pair of homologous chromosomes become twisted around each other
tension causes part of the chromosome to break off
these broken portions join the the other partner of the homologous pair
equivalent portions of the chromosmes are exchanged
Bacterial Cell Division
Binary Fission
circular DNA replication
attachment to cell membrane
plasmid replication
cell membrane grows between the 2 DNA molecules
seperating them
new cell wall forms between the 2 DNA molecules
Viral Replication
Virus attachment proteins attach to the receptor proteins on cell surface membrane
virus injects its genetic material into the cell
cell produces new viral proteins and genetic material
assembling new virus particles
