Exam 4: 503 - Roberts - Cell Cycle And Apoptosis - Study Questions

Front 1

Draw the cell cycle with its stages, main checkpoints and expressed cyclins.

Back 1

See Slides 4, 7, and 24.

Front 2

What does CDK stand for and how is it activated?

Back 2

Cyclin dependent kinase – activated by cyclin-binding.

Front 3

Which proteins are degraded at specific stages of the cell cycle?

Back 3

a. Cyclins – are degraded after mitosis and DNA synthesis via ubiquitination.
b. CDKs – Are inactivated, not degraded.

Front 4

What does G0 mean?

Back 4

G0 is the “G1” equivalent in terminally differentiated cells (like neurons, muscles, etc.) where the cell in always stuck in the G0 phase.

Front 5

What is the main difference between apoptosis and necrosis?

Back 5

• Apoptosis - Programmed cell death, where the cell is engulfed by a macrophage. Also, it does not cause an inflammatory response.
• Necrosis – Accidental cell death. Also, it causes an inflammatory response.

Front 6

Rb stands for retinoblastoma. Describe how this protein can contribute to cell proliferation and cancer.

Back 6

- Retinoblastoma protein binds to E2F protein to sequester it away (keeps it inactive).
- Active G1-Cdk comes in to phosphorylate Rb to make it inactive.
- Rb disassociates from E2F protein to cause E2F to become active.
- E2F can now progress through S-phase (start transcription).
- END RESULT is UNREGULATED CELL PROLIFERATION.

Front 7

What happens with apoptotic cells?

Back 7

They are engulfed by macrophages.

Front 8

What is a caspase and how does it act?

Back 8

- Is part of a family of proteases with a cysteine at the active site that cleaves target proteins at specific aspartic acid residues. Caspases also activate other caspases. Acts through either extrinsic pathway or Intrinsic pathway.

Front 9

Briefly define the intrinsic and extrinsic pathways for apoptosis.

Back 9

• Extrinsic pathway – Death receptors become triggered by a signal and activate the caspase cascade.
• Intrinsic pathway – Due to too much DNA damage, mitochondria release cytochrome c, which interacts with an adaptor and together they activate the caspase cascade.