This is a comprehensive and detailed note on Chapter 11; cell cycle and cell division for Biol 105.
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Chapter 11:
Cell cycle and cell division
Why do Cells Divide?
● Unicellular organisms use cell division for
reproduction.
● In multicellular organisms, cell division is
also important in growth and repair of
tissues.
→ Cell division
How Do Prokaryotic and Eukaryotic Cells Divide?
● Four events must occur for cell division to occur:
1. Reproductive Signal: to initiate cell division
2. Replication: of DNA
3. Segregation: distribution of the DNA into the two new cells
4. Cytokinesis: separation of the two new cells
● DNA replication and segregation are perhaps the most complicated processes
in cell division, especially in eukaryotes. • Most prokaryotes have one
chromosome: a single, usually circular, molecule of DNA.
● Eukaryotes have multiple chromosomes, all of which are replicated before cell
division.
● Ensuring that each daughter cell contains a
complete set of chromosomes is a critical
part of cell division
Prokaryotic Cell Division
● In prokaryotes, binary fission results in two
new cells.
● External factors such as nutrient
concentration and environmental conditions
are the reproductive signals that initiate cell
division.
● For many bacteria, abundant food supplies
speed up the division cycle.
, → The Cell Cycle
The Eukaryotic Cell Cycle
● If a cell is not destined to divide further, it usually leaves the cell cycle at this
point --- before DNA replication. Cells are arrested in what is sometimes called
the G0 phase.
How Is Eukaryotic Cell Division Controlled?
● Interphase has three subphases: G1, S,
and G2
● G1: between cytokinesis and S phase;
chromosomes are single, unreplicated
structures. Duration of G1 is variable.
Some cells enter a resting phase (G0).
● At the G1-to-S transition the commitment
is made to DNA replication and
subsequent cell division. Sometimes
called the restriction (R) point.
● S phase: DNA replicates; sister chromatids
remain together.
● G2: cell prepares for mitosis (e.g., by
synthesizing structures to move the
chromatids).
● Regulation of the Cell Cycle
○ Specific signals trigger the transition from one phase
to another.
○ Identification of these signals came from cell fusion
experiments.
○ For example, cells in the S phase produce a
substance that activates DNA
replication.
● The signals for cell cycle progression act
through cyclin-dependent kinases (Cdks).
● Protein kinases catalyze transfer of a
phosphate group from ATP to a protein
(phosphorylation). The shape and function of
the protein changes.
● Cdks play important roles in the cell cycle.
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