Cell Cycle
The Cell Division
•Cells are constantly trying to keep up with changes in the
environment.
•Cells must go through these changes to maintain
homeostasis.
Cell Cycle
• Broken down into interphase and cell division
• Interphase
– Period of the cell cycle between cell divisions
– G1, S, and G2 phase
• Cell division
– Mitosis
– Cytokinesis
• *
Interphase
• G1- Cell growth
– Cells do most of their growing
– Increase in size
– Synthesize new proteins and organelles
• S phase- Synthesis
– Chromosomes synthesized forming sister chromatids
– Usually once cell enters S phase it completes the
rest of the cell cycle
• G 2 – More growth
– Cell synthesizes proteins needed during mitosis and
cytokinesis
– Preparation for mitosis
Interphase
Cell Regulation
• Cyclin – a protein responsible for advancing a
cell through the phases of the cell cycle.
• Tells the cell when it is time to divide
– Internal regulators- regulates what is going on
inside the cell i.e.- make sure all chromosomes
have been replicated before entering mitosis
– external regulators- regulates what is going on
outside the cell- speed up or slow down the cell
cycle i.e. – growth factors – embryonic
development and wound healing
Cell Regulation
Checkpoints3 critical regulation points or CHECKPOINTS in eukaryotic cells
 G1- checkpoint (restriction pt)
 G2- checkpoint
 Metaphase- checkpoint
Checkpoint proteins act as sensors to determine if the cell is in proper
condition to divide.
Cell cycle will be delayed or until problems are fixed
or prevents division entirely
Loss of checkpoint function can lead to mutation
and cancer
Cell Regulation
• Cancer
– These cells don’t respond to the signals that
regulate the growth of most cells
– Some causes: smoking tobacco, radiation
exposure, sun damage.
– Defect in a gene called p53- normally halts the cell
cycle until all chromosomes have been replicated
Disease of the cell cycle
Cell Cycle
Interphase
Mitosis
• Four phases
– Prophase
– Metaphase
– Anaphase
– Telophase
 Cytokinesis – cell completes cell division - two
cells are formed
• Mitosis can last anywhere from a few minutes
to several days depending upon cell type.
Prophase
• Longest phase 50-60 %
of total time
• Chromatin condenses
into chromosomes
• The centrioles separate
• A spindle begins to form
• Nuclear envelope
begins to break down
Prophase
Metaphase
• Chromosomes line up
across the center of the
cell
• Each chromosome is
connected to a spindle
fiber at its centromere
Metaphase
Anaphase
• The sister chromatids
separate into individual
chromosomes and are
moved apart
• Continue to move until they
have separated into two
groups near the poles of the
spindle
Anaphase
Telophase
• The chromosomes
gather at opposite ends
of the cell
• Lose their distinct
shapes
• Two new nuclear
envelopes will form
Telophase
Cytokinesis
• Usually occurs at the
same time as telophase
• Cytoplasm pinches in
half- taking organelles
and proteins with it
• Each daughter cell has
an identical set of
duplicate chromosomes
– Animal cell- cleavage
furrow
– Plant cell- cell wall grows
between
Cytokinesis
MITOSIS
• http://highered.mcgrawhill.com/olc/dl/120073/bio14.swf
• Mitosis process