Transcript Cell Cycle and Mitosis - mvhs

Cell Cycle and Mitosis
AP Biology
Unit 3
Cell Cycle
• Cell Cycle = the entire
cycle of a cell from one
division to the next
– Interphase (G1, S, G2) =
between cell divisions
– M Phase (Mitosis and
Cytokinesis) = cell
division
– Continuous process of
replication  alignment
 separation (of DNA)
Interphase
• Most of the time, a cell is in Interphase
• G1 (Gap1)
– Cell grows, copies organelles
– Protein synthesis and all normal activities of
cell (like cellular respiration) are carried out
Interphase
• S (Synthesis)
– DNA is copied
– Protein synthesis, cellular respiration occur
– Cell continues to grow, copy organelles
• G2 (Gap2)
– Cell growth continues
– Protein synthesis and cellular respiration occur
– Cell prepares to divide
M Phase
• Mitosis = division of the nucleus
• Cytokinesis = division of the rest of cytoplasm
and its contents
• Results in 2 identical daughter cells
• Important for growth, repair, asexual
reproduction
Duplicating Chromosomes
• Before cell division can
occur, all of the DNA must
be copied in S phase
• After duplication, you
have 2 sister chromatids
per chromosome
Sister Chromatids
• Sister Chromatids Chromosome BEFORE duplication
= identical copies
of a chromosome Chromosome
AFTER
• Centromere =
duplication
where sister
chromatids are
attached to one Chromosome
after mitosis
another
Question…
• Why do chromosomes duplicate?
– To have a copy of DNA for each new daughter
cell
Haploid vs. Diploid
• Diploid (2n)
– 2 copies of each chromosome
– All somatic cells are diploid (non-gametes)
• Haploid (n)
– 1 copy of each chromosome
– Sperm and egg are haploid
Mitosis vs. Meiosis
• Mitosis
– Results in 2
identical diploid
daughter cells from
the original diploid
cell
• Meiosis
– Results in 4
nonidentical haploid
cells from one
original diploid cell
Phases of Mitosis
•
•
•
•
•
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
“P P M A T”
Phases of Mitosis
• Prophase (P)
– Chromosomes begin to
condense into
chromatids
– Mitotic spindle forming
• Prometaphase
– Chromosomes
condensed & attached
to spindle fibers,
nuclear envelope in
fragments
Phases of Mitosis
• Metaphase (M)
– Chromosomes line up
in the middle of the cell
• Anaphase (A)
– The spindle fibers pull
the sister chromatids
apart
• Telophase (T)
– Nuclear Envelope
reforms
Overview: Phases of Mitosis
Cytokinesis
• Cytokinesis differs
between Animal and Plant
Cleavage
cells
Furrow
• Animal Cells – forms a
cleavage furrow
– Cells narrow and pinch off
from each other
• Plant Cells- forms a cell
plate
Cell Plate
Control of the Cell Cycle
• Checkpoints
– determine if the cell is able to continue to the
next phase
– Regulated by external and internal signals
(trigger signal transduction pathways)
– ability proceed usually depends on whether
certain processes have been completed
• Ex. Cell cannot start G2 until DNA has been
replicated
Control of Cell Cycle
• Ex. PDGF
– Platelet Derived Growth Factor
– Released by platelet cells in response to an
injury
– Allows fibroblast cells in the damaged area to
pass the G1 checkpoint  divide
– Cell division helps to repair the damaged area
Control of Cell Cycle: G0
• G0
– A nondividing state that cells
go into if they don’t get the
signal to proceed in the cell
cycle
– Most cells in the human body
are in this state
– Cells can also be triggered to
come out of G0 and re-enter the
cell cycle by external signals
Control of Cell Cycle
• Cyclins and Cyclin-dependent
kinases (Cdks)
– Regulatory proteins that
determine if the cell can pass
checkpoints
– Cyclins vary in concentration
throughout the cell cycle
– presence of specific cyclin/Cdks
bound together (MPF)
determines if cell can continue
through cell cycle
Binary Fission
• Bacteria don’t go through
mitosis
• Why not?
– No nucleus, just free floating
DNA
• Steps of Binary Fission
– Cell grows in size
– Copy DNA
– Split cell into 2 new cells
Cancer
• Cancer is uncontrolled cell growth
• Cancer cells do not respond to checkpoint
signals  keep on dividing
• Cancer cells no longer perform their normal
functions, steal nutrients from other cells,
crowd out other cells.