cell cycle
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vegetative and reproductive cell division
vegetative: identical parent and daughter cells (mitosis) reproductive: the number of chromosomes in the daughter cells is reduced by half to produce haploid gametes (meiosis)
terminally differentiated cells
cells that can withdraw permanently from the cell cycle, permanently stopping cell division
four phases of cell cycle (followed by)
G1, S, G2 and M (followed by cytokinesis)
what are cell phases G1, S and G2 together called
interphase
cyclins
proteins that control the cell cycle by deciding whether to allow the cell to proceed to the next stage
what enzyme do cyclins activate and explain the function of that enzyme
kinases - enzymes that attach phosphate groups to substrates in phosphorylation
protein phosphorylation/dephosphorylation and its catalysts
transfers a phosphate group from ATP to an amino acid side chain of the target protein, which is catalysed by a protein kinase dephosphorylation is catalysed by the protein phosphatase
a common way by which cells switch the activity of a protein on and off
phosphorylation/dephosphorylation
Example of apoptosis: during embryonic development in tadpoles
Tail disappears when a tadpole becomes a frog Induction of apoptosis in the tail which is stimulated by an increase in thyroid hormone in the blood
function of p53
detection of DNA damage and stops the cell cycle
how p53 detects DNA damage and stops the cell cycle
• protein kinases are recruited to the site of damage and initiate a signalling pathway that results in the phosphorylation of p53 • p53 is now free to bind to a cyclin-inhibiting gene and stimulate its transcription
compare mitosis and meiosis
mitosis - produces a pair of daughter cells - identical daughter cells meiosis - involved in sexual reproduction - one round of DNA replication followed by two rounds of cell division - genetically varied daughter cells - organisms undergo meiosis generally have diploid cells
gametes
specialised haploid cells (eg. sperm and egg) important to the reproductive cycle in meiosis
diploid zygote
forms when a sperm and egg fuse
Function of mitogens
stimulate cell division via cyclins
prokaryotic cell division - binary fission
genetic material is segregated equally into two identical daughter cells
three major classes of signalling molecule in controlling cell division and growth
mitogens - stimulate cell division growth factors - promote cell growth by biosynthesis survival factors - promote cell survival by suppressing apoptosis
what is apoptosis can it be signalled inside/outside of cell?
programmed cell death (suicide) by shrinking and forming membrane blebs both inside/outside the cell
process of apoptosis
The cell breaks into apoptotic bodies and is phagocytosed, avoiding bursting and the release of toxic compounds to the neighbour cells prevents inflammation
caspases
a family of protease enzymes that execute apoptosis
mechanism of how caspases are involved in apoptosis signalling
a cysteine in its active site nucleophilically attacks the target protein and only cleaves the fragment following an aspartic acid residue
intercellular signalling - endocrine signalling
hormones produced in endocrine glands are secreted in to the bloodstream and are distributed widely throughout the body
intercellular signalling - paracrine signalling
molecules are released by cells into the extracellular fluid in their neighbourhood which act locally (short-range)
intercellular signalling - neuronal signalling
signals are transmitted electrically along a nerve cell axon. neurotransmitters are related onto adjacent target cells when the signal reaches the nerve terminal