Cell Division and The Cell Cycle Flashcards
(12 cards)
What is the cell division cycle?
The process from a cell’s “birth” (parental division) to its own division into two daughter cells.
How long does the cell cycle take in different organisms?
Yeast: 2-3 hours.
Human cell in culture: 24 hours.
What two major processes must happen only once per cycle?
1️ DNA replication (S phase).
2️ Genome segregation (M phase).
What are the four phases of the cell cycle?
S phase – DNA replication (DNA synthesis).
M phase – Cell division (mitosis + cytokinesis).
G1 phase – Gap 1 (preparation for S phase).
G2 phase – Gap 2 (preparation for mitosis).
What is G0 phase?
A quiescent (non-dividing) state where cells do not actively proceed through the cycle.
Why are G1 and G2 important?
They act as control checkpoints ensuring the cycle progresses correctly.
G1/S checkpoint:
Is the cell big enough to divide?
What do the neighboring cells signal?
G2/M checkpoint:
Has the DNA been replicated correctly?
Are there any errors or damage before entering mitosis?
Why are the checkpoints important?
Uncontrolled cell division leads to cancer—cells must pass control points to prevent mutations.
How were yeast cell cycle mutants discovered?
Hartwell & Nurse used temperature-sensitive yeast mutants to study cycle progression
Permissive temperature (25°C) → Normal cell growth.
Restrictive temperature (36°C) → Cell cycle arrest.
What is the execution point of a cell cycle mutant?
The point after which the gene product is no longer required—cells continue dividing normally until reaching the blocked phase.
What happens with loss of cdc2 function?
No division occurs.
What happens with gain of cdc2 function?
Division is accelerated.
What does cdc2 control in all species?
Commitment to cell division:
Low cdc2 activity → Interphase (No Division).
High cdc2 activity → Mitosis (Division).
