The Cell Cycle
Molecular Biology
Sumner HS
Cell
Reproduction/Division
The ability of organisms to reproduce their kind
is the one characteristic that best distinguishes
living things from nonliving.
The continuity of life is based on the
reproduction of cells, or cell division.
Cell Division Importance
Multicellular organisms depend on cell division
for
Development from a fertilized cell
Growth
Repair or replacement of “bad” cells
Big Growth
We start as one cell
We end up being made of trillions of cells
They don’t magically appear **Poof!**
The result of countless cycles of growth and
division of cells.
Question to ponder...
What tasks does a cell need to do in order to
divide?
Have a 2nd copy of DNA
Have enough cytoplasm and organelles for a
second cell
The Cell Cycle
Cells go through predictable, controlled patterns
of growth or development and division.
Called the cell cycle
The Cell Cycle
Big Picture
Cell 1
Cell 1
Interpha
se/
Mitosis
Cell 2
Cell 1
Big Picture Cont’d
Interpha
se/
Mitosis
Cell 1
Cell 3
Cell 2
Cell 2
Interpha
se/
Mitosis
Cell 4
Cell Cycle Major Phases
Interphase = period of
growth, DNA replication
and protein synthesis
Mitosis = cell division
Interphase
Interphase can be
divided into
subphases
G1 phase
S phase
G2 phase
G1 Phase
Rapid growth
High
metabolic
activity
Making lots
of proteins
S Phase
DNA is copied
(replicated)
Cell has twice the
number of
normal
chromosomes.
Cell keeps
growing
G2 Phase
More proteins made
Mitochondria & other
organelles replicate
Cell keeps growing
Summarize
In your own words, summarize each of the
phases of interphase.
Mitotic Phase
The Mitotic Phase has two major phases
Mitosis has four sub-phases
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
New Note Instructions
For each of the phases of cell division...
....don’t write down the details I put up
Instead, prepare to summarize the main events
in about 10 words.
Prophase
Chromosomes coil up and
become visible (twisted rubber
band)
Centriole begins to form spindle,
made from same material as
cytoskeleton.
Nuclear envelope and nucleolus
begin to disappear
Summarize!
Metaphase
Chromosomes move to “equator” of
the cell
Each half of the chromosome is
attached to a spindle fiber at the
centromere.
Centromere is a protein that joins
the two “sister” chromatids, or
replicated chromosome pairs
Summarize!
Anaphase
Sister chromatids are
pulled apart to opposite
ends of the cell.
Each chromatid is now a
separate chromosome.
Summarize!
Telophase
Genetically identical
daughter nuclei form at
opposite ends of the cell
Nuclear envelope begins
to reappear.
Summarize!
Cytokinesis
In animal cells,
cytokinesis occurs by a
process known as
cleavage, forming a
cleavage furrow.
A “string” of
cytoskeleton pinches
the cell in two
Summarize!
Cytokinesis cont.
In plant cells, a cell plate
forms between the cells
after telophase.
Mitosis
results in
two identical cells called
daughter cells
Real Pictures: Early
Prophase
Real Pictures: Late
Prophase
Real Pictures: Metaphase
Real Pictures: Anaphase
Real Pictures: Early
Telophase
Real Pictures: Late
Telophase
Test Yourself
Check Your Knowledge
 Identify
prophase, metaphase, anaphase and
telophase in these cells.