Cell cycle 1

Why do cells divide?

Repair, reproduction and growth

Cannot just grow as decrease SA:V

What triggers cell division?

Mitogens like VEGF, ATP and hormones

What is the function of telomeres?

Every time cell divides not all of the telomere is copied

Causes the telomere to shorten which is cell senescence (limits amount cell can divide)

What can the interphase be separated into?

G1 phase (growth)

S phase (DNA synthesis)

G2 phase (prepares for mitosis)

What is the G0 phase?

A resting phase where cells are quiescent

Mitogenic signalling causes cells to exit G0

Some cells reach quiescent when mature and remain so to perform function (nerve cells)

What do cells need to pass the G1 checkpoint?

Inactivate the retinoblastoma tumour suppressor protein(Rb)

Usually blocks function of E2F

which stimulates expression of genes for cell cycle

What controls Rb activity?

Cyclins which fluctuate through cycle

How do cyclins function?

Bind to cyclin dependent kinases (CDKs), only active with cyclin

cyclin-CDK complexes

What occurs during early G1?

Cyclin D-CDK4/D-CDK6 partially inactivate Rb

E2F is now partially active

What occurs during late G1?

Cyclin E-CDK2 phosphorylates Rb again

Rb is now fully inactive and cannot bind to E2F

E2F allows expression of all S-phase needed genes

How does the G1 checkpoint work?

If DNA is damaged p53 is stabilised

prevents entry to S-phase until DNA repaired

When DNA repaired its degraded

What is DNA helicase function in S-phase?

Unwinds the double helix

DNA is tightly packed during mitosis

What is DNA polymerase function?

Semi-conservative replication

Reads from 5 prime to 3 prime

Produces a complementary strand

What is Ori?

Ori is the origin of replication, binding site for proteins

Eukaryotic cells have multiple

How is DNA polymerase and DNA helicase regulated by cyclin-CDK complexes?

cyclin E-CDK2 for helicase

cyclin A-CDK2 for polymerase