the cell cycle and cell divison
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- Created on: 14-04-16 19:02
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- the cell cycle and cell divison
- cells and chromosomes
- chromsome structure
- are made of DNA and a protein called HISTONE
- chromsomes only become visable when chromatin condenses before cell division
- two exsacts copies of a chromsome are called sister chromatids
- there joined and cenromere
- plodidy level and chromsome number
- differnt species have a different number of chromosomes
- human has 46, whilst a fly has 8
- the number of chromsomes in a complete set in the hapliod number
- get one set from mother and one set from father and they match called a homologous pair
- humans have 23 hamologous pairs
- 2N
- chromsome structure
- Mistosis and the cell cycle
- mistosis produces 2 daugter cells which are genetically identical
- all cells divide in a regular patternt called the cell cycle
- there are different phases interpahse, prophase metaphase anaphase telophase
- inerphase
- is the longest phase of the cell cycle
- lots of metabolic activity
- cells grow and oranelles replicate
- chromosomes are no longer visable in a microscope as the nuclear material, chromatin, disappears
- prophase
- the chromosome condenses. they coil getting shorter and thicker
- centriols are present in animal cells, the pairs separate and move to different ends called poles
- spindle fibers extend from pole to pole
- the nucleoulos disaperes
- pairs of chromatids can clearly be seen lying free in cytoplasm
- metaphase
- chromosomes attach to the spindle fibers at their centromeres and aline on the equator
- anaphase
- is a very rapid stage
- the centromere sperate and the spindle fibers shorten pullin the now spenrated chromatids to the poles
- telophase
- this is the final stage of mitosis
- chromsomes uncoil and lengthen
- the spindle fribers break down
- the nuclear envelpoe re forms
- the nucleus reapers
- shape
- animal cells become round befpre mitosis
- plant cells no shape change
- cnetrioles
- animal cells present
- plant cells absent
- cytokinesis
- animal cells cleavage frrow
- plant cells cell plate
- spindle
- animal cells degenerates at telophase
- plant cells remains throughout new cll wall formation
- occureence
- aniaml cells bone marrow
- plant cells in metristems
- inerphase
- there are different phases interpahse, prophase metaphase anaphase telophase
- chromosme number
- mitosis produces the same numberof chromosomes in the daughter nuceli as in the parent nuclei
- the daugter nuclei is an exstact repulica of parent
- growth
- by producing new cells an organisms increases its cells number and can grow and repair tissues
- asexual reproduction
- produces offspring that are genetically identical to the parent
- it takes place in unicelluar organisms such saw yeast and bacteria
- damage and disease
- if the genes that control the cell cycle are damaged cells may fail to divide or divde too frequently or at the wrong time
- ratiation and certain chemicals and some viruses mutate DNA
- if genes are damaged they could repucate too fast. if this happens in solid tissue a tummor is formed
- if this happens in somewhere like bone marrow. the blood cells spill into blood circulation and can cause cancer
- meiosis
- takes place in the reproductive organs of plants animals and some protocactistans
- it results in 4 geneticall distinct gametes
- the number of chromosomes
- in miosis the diploid number is halved to hpoliod number
- when two hapliod gametes fuse at fertilisation the zygote that is formed has two complete sets of chromosomes
- the significance of miosis
- keeps the chromosme number constant throughout generations
- meiosis genrates genetic variation in the gametes n
- cells and chromosomes
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