Lecture 1B: Introduction to the Cell Cycle

Question 1

What does quiescent mean?

Answer 1

In a state of inactivity or dormancy

Question 2

Which state are most of the cells in the body at?

Answer 2

• G0 - quiescent state
• cell replication is only required to replenish lost cells
• only very small fraction of cells are dividing
• ## cells must be recruited to cell cycle (via growth signals/factors)

Question 3

What is a restriction point in cell cycle?

Answer 3

point in cycle where cells commit - either proceed towards S or move out of cycle to G0

Question 4

When are cells responsive to extracellular signals?

Answer 4

Responsive in G1 up to R point

Question 5

What are the molecular drivers of progression in the cell cycle?

Answer 5

• activation of signaling cascades - often via phosphorylation – promote recruitment into and progression through cell cycle
• phosphate groups are added onto substrates by enzymes called kinases
• cyclins and cyclin-dependent kinases are key components of the cell cycle clock

Question 6

What are the cell cycle checkpoints?

Answer 6

Checkpoints are places in the cell cycle where a cell is stopped and checked for mistakes

Question 7

Where are the cell cycle checkpoints located?

Answer 7

• end of G1 - DNA damage checkpoint - entrance into S is blocked if genome is damaged
• S phase - DNA damage checkpoint - DNA replication halted if genome is damaged
• end of G2 - entrance into M is blocked if DNA replication is not completed
• M phase - anaphase blocked if chromatids are not properly assembled on mitotic spindle