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Control of cell cycle and cancer - Coggle Diagram
Control of cell cycle and cancer
The cell cycle is the ordered sequence of events that occur in a parent cell in prep for cell division
External factors controlling the cell cycle
These factors may initiate or inhibit cell division
Nutrient dependence: cells need particular nutrients in the extracellular fluid to divide
Anchorage dependence: many cells only divide if they are attached to a substrate or surface
Density dependence: cells that are in close contact with one another will usually not divide but stop after forming one layer of cells
Large cell size: large cells have low SA:V ratio and this acts to stimulate cell division to give 2 smaller cells each with a higher SA:V
Growth Factor:
The G1 checkpoint
Growth factors are chem factors external to the eukaryotic cell that initiate cell division
A growth factor binds to its specific receptor usually imbedded in the membrane of the cell. However lipid soluble growth factors diffuse through the lipid bilayer and bind to receptors inside the cell. Binding of the growth factor to it initiates a metabolic pathway inside the cell that concludes with synthesis of proteins that initiate cell division. Hormones are examples of GF that regulate cell division
GH travels in blood to target cell in the liver and muscles where it binds to specific regions and initiates cell division and break down of glycogen into glucose. HG makes people grow taller
Cell cycle in Eukaryotes
Interphase
Sub phases: G1, S, G2
The cell increases in size. Metabolic reaction including DNA replication, transcription and translation occur in prep for cell divsi
G1
Fist gap phase. Duration: 10 h
The cell grows in size and carries our metabolic reactions including protein synthesis and respiration
The cell accumulates DNA nucleotides and ATP in prep for DNA replication in S phase
S
Synthesis of DNA. The chromosome is replicated and the copies, the sister chromatids are joined by a centromere. The cytoskeleton is dismantled and the centrioles are replicated in prep for mitosis
G2
protein synthesis continues, some organelles are replicated, ATP is synthesised and the cell grows in size in pre for M phase. In addition the DNA is checked and any damage is repaired before the cell enters M phase
Mitosis
Sub phases: prophase, metaphase, anaphase, telophase
The parent nucleus is broken down and the chromosomes are separated into daughter nuclei. The parent cell then divides into two daughter cells
Cytokinesis
The parent cell divides into 2 daughter cells that are genetically identical with equal amount of cytoplasm distributed into each daughter cell.
G0
Cells are removed from the cell cycle to function and do not divide
Checkpoints
Where the cycle is stopped and the cell is prevented from entering the next stage is one or more conditions are unfavourable
G1: The chromosomes are checked for mutations and other forms of damage at the G1 checkpoint. The availability of DNA nucleotides, DNA polymerase enzymes and ATP is assessed. The cell is prevented from entering the S phase if one or more condition unfavourable for DNA replic
G2: The genome is checked to ensure that all chromosomes have been replicated and that each chromosome is free from mutation and damage before the cell enters mitosis
M: The sister chromatids are checked to ensure that the centromere is attached to spindle fibres before the chromatids are separated in anaphase.
Internal signals
The most common internal signal are families of proteins called cyclin and cyclin-dependent kinases (Cdks).
Cdks are enzymes that transfer a phosphate group to target molecules when activated and this process called phosphorylation is used to signal the cell to enter the next stage of cell cycle. The activity of Cdks are controlled by proteins called cyclins.
Cyclin is a protein that is synthesised during the cell cycle and its concentration changed throughout the cycle. Cyclin bind to Cdks to form a complex called MPF ( mitosis promoting factor). The concentration of MPF increases as the cyclin concentration increases and more cyclin bind to Cdk. A higher level of MPF triggers mitosis to start and stop at metaphase. A lower level of MPF triggered mitosis to continue past metaphase to completion
Cyclins and Cdks and other proteins that regulate the cell cycle are synthesised from proto-oncogenes and tumour suppressor gene
Mutation in proto-oncogenes and tumour sup genes can initiate unregulated cell division