Cyclins and cyclin-dependent kinases are regulatory proteins that assist in the cell cycle. Particular protein kinases give the go-ahead signals at G1 and G2 checkpoints. These protein kinases are present at a constant concentration in the cell but are inactive unless in the presence of cyclin, these are cyclin dependent kinases. The activity of a cdk rises and falls with the concentration of cyclin.
Cyclin levels rise during the S and G2 phases then fall abruptly in the M phase.
MPF – maturation-programming factor – cyclin cdk complex that triggers a cells passage past the G2 checkpoint into the M phase (m-phase promoting factor). May assist in the fragmentation of the nuclear envelope during prometaphase. Helps to switch itself off by initiating a process that leads to the destruction of its own cyclin.
Platelet-derived growth factor, stimulates human fibroblast division in culture and in an animal. PDGF is released when injury occurs stimulating fibroblast growth and healing the wound.
Cancer cells – are cells that do not display density-dependent inhibition, they do not stop proliferating even when there is no more space, nor do the display anchorage dependence, they do not need to be attached to a substratum to divide, they also often create their own growth factors, and often don’t even need a growth factor to divide, and normal mitotic checkpoints are not present in a cancer cell, therefore cancer cells may have an abnormal cell cycle control system.
Normal cell becomes cancerous by ‘transformation,’ cancer cells that are not destroyed by the immune system become tumors. Tumors can be either benign or malignant. Malignant tumors often spread and metastasize and can cause serious problems whereas benign tumors can often be removed with no serious complications. Often cancer cells have lost the ability to fix DNA when it becomes damaged which is why localized radiation effects cancer cells more so than it effects normal cells.
Plant Cells – golgi vesicles move along microtubules to the middle of the cell, where the coalesce, producing a cell plate, which eventually fuses with the cell wall and splits the cell in two
Animal Cells – A cleavage furrow forms. On the cytoplasmic side of this cleavage furrow there is a contractile ring of actin filaments associated with molecules of the protein myosin. These two molecules interact causing the cleavage furrow to contract and act as a drawstring until the cell eventually splits in two.
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Punnett Square Calculations:
Multiplication Rule – probability two or more independent events will occur together is the product of their individual probabilities. Probability of a monohybrid cross can be determined this way. Each gamete has a ½ chance of getting the dominant allele and a ½ chance of getting the recessive allele. Example: ½ R ½ r
1:2:1 genotypic, 3:1 phenotypic
In calculating the chances for various genotypes, each character is considered separately, and the individual probabilities are multiplied. Such as in a dihybrid or monohybrid cross.
Addition Rule - probability that any one of two or more mutually exclusive events will occur is calculated by adding their individual probabilities. This can be used to find the probability that an F2 plant from a monohybrid cross will be heterozygous rather than homozygous. E.g. use the probabilities from using multiplication and add them to determine the probability that an F2 plant will be heterozygous.
These rules are used to predict the outcome of crosses with multiple characters. ** A dihybrid, or other multi-character, cross is equivalent to two or more independent monohybrid crosses occurring simultaneously.
Pea Plants, Why?
Many varieties with distinct heritable characters or traits (e.g. flower color) Mating easy to...
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