Cell Cycle Regulator Molecules

When Rb is bound to E2F

production of proteins necessary for the G1 /S transition is blocked.

Retinoblastoma protein (Rb), p53, and p21are

negative regulatory molecules

As a cell is exposed to more stress,

higher levels of p53 and p21 accumulate, making it less likely that the cell will move into the S phase.

In the active, dephosphorylated state, Rb binds to

proteins called transcription factors, most commonly, E2F.

Rb exerts its regulatory influence on

other positive regulator proteins.

If damaged DNA is detected, p53

halts the cell cycle and recruits enzymes to repair the DNA.

Cyclins regulate the cell cycle only when

they are tightly bound to Cdks.

Regulator molecules may act

individually, or they can influence the activity or production of other regulatory proteins.

Transcription factors

:"turn on "specific genes, allowing the production of proteins encoded by that gene.

As the cell increases in size

Rb is slowly phosphorylated until it becomes inactivated.

If the DNA can't be repaired

p53 can trigger apoptosis, or cell death, to prevent the duplication of damaged chromosomes.

P21

enforces the halt in the cycle dictated by p53 by binding to and inhibiting the activity of the Cdk /cyclin complexes.

Retinoblastoma proteins

a group of tumor-suppressor proteins common in many cells

Transcription factors

"turn on" specific genes, allowing the production of proteins encoded by that gene

Regulatory molecules either

promote progress of the cell to the next phase (positive regulation) or halt the cycle (negative regulation)

What two groups of proteins are responsible for the progress of the cell through the various checkpoints?

cyclins and cyclin-dependent kinases (Cdks),

Increases in the concentration of cyclin proteins are triggered by

both external and internal signals.