cell division Flashcards
what are the 3 phases interphase is split into
G1, S, G2
what occurs at interphase G1?
- growth phase
- preparations (duplicating organelles, growing in size & making proteins) are made to ensure the cell is ready to go into S phase
what occurs in S and G2 phase
S phase::
-now no going back
-also called the synthesis phase because this is where DNA synthesis occurs
- DNA replicates- more important sequences are replicated first.
-each chromosome consist of a pair of sister chromatids
G2 phase::
-cell grows in prep for mitosis
where does exiting of the cell cycle occur
- occurs early in G1 phase- cells can either continue in the cell cycle or enter the G0 phase (exiting the cell cycle)
what do cells do in the G0 phase
- cells in the G0 phase may differentiate, die or enter senescence (where they stop dividing)
in what part of the cell cycle is DNA replicated
the S phase
… the G2 phase is where the cell is getting prepared to double
what are the 3 things mitosis is used for?
growth, tissue repair, wound repair
why is mitosis relevant for tissue repair?
- mitosis can produce a genetically identical copy.
- the new cell is able to take over the cell that was lost as it contains all the same genes- e.g repair of skin
why is mitosis relevant for wound repair
a wound stimulates the action of white blood cells, platelets and growth factors.
these cause cells to undergo mitosis to repair damaged tissues/ blood vessels
- ensures for fast wound recovery
why is mitosis relevant for growth
- allows for a growth of a foetus, cells duplicate
- all multicellular organisms grow by producing genetically identical cells
what do bacteria reproduce asexually by?
via binary fission
what type of offspring does asexual reproduction result in?
genetically identical offspring
when can damage to DNA occur
during DNA replication in interphase (s phase)
why is the DNA replication phase ( S phase) kept short
since exposed bases are more susceptible to mutation
what do cell cycle checkpoints do?
- when mutation occurs damaged DNA id detected and repaired
- makes sure DNA is replicated once in each cycle
- also checks cell division and that its not going too fast as tumours and cancer can then form
- ensures the cell cycle goes in one direction or sections could occur twice
what are cell checkpoints
-times in the cell cycle where chemical events occur to regulate division
what happens at the G1/S checkpoint (restriction point)
during the G1 phase a chemical can trigger a cell to leave the cell cycle and enter G0- makes sure there are not too many cells or not too few cells
what happens at the G1 checkpoint
checks cell is ready for S phase ( occurs at the end of G1)
what happens at the G2/M checkpoint
- checks and repairs DNA
- makes sure all the DNA has been checked and repaired before the cell enters mitosis
what happens at the mitosis checkpoint
- checkpoint in the middle of mitosis
- checks cell is ready to proceed in mitosis
what can happen when the genes controlling cell division mutate
-cell division can occur uncontrollably
whats a chromosome
a set of genes made from chromatin (genetic material) wrapped around histones
where do spindle fibres attach and what do they do
at the centromere and separate the chromosomes
whats a chromatid
a copy of a chromosome while attached to a duplicate
how many chromosomes does a human (somatic (body)) cell contain
46 chromosomes ( 23 pairs of homologous chromosomes)
what does each pair of chromosomes contain
one chromosome from each parent
what are many body cells ( haploid or diploid)
diploid
what are homologous chromosomes
matching pairs of chromosomes ( 1 paternal 1 maternal) containing the same genes at the same place but may contain different alleles (variants for the gene)
what occurs in meiosis one: prophase 1
- nuclear envelope disappears
- homologous chromosomes pair up and chromatids cross over==-crossing over- random chromatin moves from one pair to another (genes will change)
what occurs in meiosis one: metaphase 1
- spindle fibres form and reach chromosomes
- pairs of chromosomes line up on the equator
- pairs line up in a random order (paternal and maternal each way)
- this is independent assortment
what occurs in meiosis one: anaphase 1
- entire chromosomes=pulled to poles
- homologous pairs= now separated
what occurs in meiosis one: telophase 1
- two nuclei reform
- each is haploid
- chromosomes decondense
- cytokinesis follows
what occurs in meiosis two: prophase 2
- nuclear envelope disappears
- chromosomes condense
- chromosomes move to poles +s.f form
what occurs in meiosis two: metaphase 2
- chromosomes line up in single file at equator
- s.f binds to centromeres
- random arrangement introduces further variation
what occurs in meiosis two: anaphase 2
-chromatids= separated and are pulled to poles
what occurs in meiosis two: telophase 2
- envelope forms
- chromosomes decondense
- cytokinesis splits to produce 4 haploid cells
where is variation introduced in sexual reproduction
-crossing over in prophase 1, independent assortment in metaphase 1, random arrangement in metaphase 2, random selection of gametes that fuse
