The Cell Cycle

G1 checkpoint - cell size and nutrient levels are checked, and p53, a tumor suppressor gene, checks for and mistakes in DNA. If cells can’t pass the checkpoint, apoptosis occurs.

S- DNA is copied (replicated) so that two copies of each chromosome exist

G2- organelles needed for replication (microtubules, centrosomes, centrioles) are created

G1- cells grow and make proteins needed. Organelles are created too.

Copying DNA is known as replication and occurs during the S phase of interphase


Cells use cyclins and CD kinases to move from one phase to the next.

M- mitosis with its phases of PMAT occur here
G0 is for dead/ non dividing cells

G2 checkpoint - DNA is checked for mistakes, and proteins and organelles needed for mitosis are checked.

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Insertion occurs when an extra base (or more) are added to a gene • Mistakes in tumor suppressor genes/ proto -oncogenes can result in cancer

Substitution occurs when one base is substituted for another base • Deletion occurs when a base (or more) is missing f rom a gene

1.Helicase unwinds the DNA by breaking the hydrogen bonds between the bases

  1. Strands of DNA separate
  1. D NA polymerase adds bases to the growing strand that base pair with the original strand
  1. Hydrogen bonds reform between the bases of the original strand and the new strand 5. Ligase seals the bonds between the sugar-phosphate backbone

6.

Proto-oncogenes are genes that control the rate of the cell cycle and when mutated act like an accelerator that is stuck on. One mutation in these causes cell to go through the cell cycle faster.

• Tumor suppressor genes work to slow down the cell cycle and when normal, they act as a brake to the cell cycle. When mutated , they act like a brake that doesn’t work - you step on the pedal to slow down and nothing happens.

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CD kinase levels are always the same; cyclin levels rise to push the cell into the next phase

• Cancer cells either ignore cell signals, or receive wrong signals

• Certain genes, when mutated, can lead to cancer because their function affects the cell cycle

CDK and Cyclins bind to the phosphate group