Transcript Chapter 12 powerpoint

Chapter 12: The Cell Cycle
Cell
cycle: life of a cell from its
formation from a dividing parent cell
until its own division into 2 cells
Cell division- results in genetically
identical daughter cells
Mitosis:
division of the nucleus
Cytokinesis: division of the cytoplasm
Meiosis: non-identical daughter cells
produced with only one set of chromosomes
Concept Check
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Starting with a zygote, how many cell
would result following five cell divisions?
A chicken has 78 chromosomes in its
somatic cells.
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How many chromosomes are in the chicken’s
egg?
How many cells in the chicken zygote?
How many chromosome pairs are there in a
chicken?
Phases of the cell cycle
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Interphase
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G1 phase (first gap)- (5-6 hours)
S phase (DNA synthesis)- (10-12 hours)
G2 phase (second gap)- (4-6 hours)
M phase (<1 hour)
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Mitosis
Cytokinesis
Mitosis
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Phases:
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Prophase
Prometaphase
Metaphase
Anaphase
Telophase & Cytokinesis
Mitotic Spindle: fibers of microtubules &
associated proteins; assembly starts at the
centrosome
G2 of Interphase
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2 centrosomes have formed by replication
In animal cells centrosomes have 2
centrioles
Prophase
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Chromatin condenses into chromosomes
Nucleoli disappear
Duplicated chromosomes appear as 2
identical sister chromatids
Mitotic spindle begins to form
Centrosomes move away from each other
toward opposite poles as spindle
lengthens
Prometaphase
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Nuclear envelope fragments
Spindle invades nuclear area
Kinetochores of sister chromatids attach to
spindle at the centromere
Metaphase
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Longest phase
(~20 minutes)
Chromosomes
arrange on
metaphase
plate
Anaphase
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Shortest
phase
Sister
chromatids
separate &
move
opposite
poles as
microtubules
shorten
Telophase
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Daughter cell nuclei begin to form
Nuclear envelope arises
Chromosomes de-condense
Cytokinesis
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Occurs simultaneously with telophase
Animals- cleavage furrow pinches the cell
in 2
Plants- cell plate forms to separate cells in
2 (cell plate will become cell wall)
Cell division in Prokaryotes: Binary
Fission
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Circular DNA replicates beginning at the
origin of replication
As DNA replicates cell elongates
When replication is complete plasma
membrane grows inward separating the
parent cell into 2 daughter cells
Evolution of the mitotic process
Concept Check
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In which stages of the cell cycle would a
chromosome consist of two identical
chromatids?
What are the similarities & differences in
the cytokinesis of plant & animal cells?
Why would it be a disadvantage for a cell
to divide first then replicate its DNA?
Cell Cycle Control
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Each stage is triggered by specific
molecular signals present in the cytoplasm
Checkpoints
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3 major checkpoints at G1, G2, & M phases
G1 checkpoint (restriction point)- appears
to be most important
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If a cell is given go-ahead it completes S, G2,
& M phases
If not given go-ahead, cell enters G0 (nondividing state)
Regulating proteins for cell cycle
control: kinases & cyclins
Kinases
 enzymes that activate/inactivate other
proteins through phosphorylation
 Cause go-ahead signals at G1 & G2
checkpoints
Cyclins
 Attach to & activate kinases (cyclin
dependant kinases (Cdks))
Regulating proteins for cell cycle
control: kinases & cyclins
Cdk Example: Maturation promoting factor
(MPF)
 Rises during G2 to initiate mitosis
 Actions include- nuclear envelope
fragmentation, chromosome condensation,
spindle formation
 Destroys own cyclin during anaphase to
initiate end of mitosis
Cell Cycle Control: internal signals
at checkpoints
Growth factors
 Proteins that cells release to cause other cells to
divide- (promote mitosis= mitogen)
 Over 50 different growth factors that trigger cell
division have been identified
Example: platelet-derived growth factor (PDGF)
 Release by platelets to cause fibroblast
(connective tissue cell) division to repair wound
Cell Cycle Control: external signals
at checkpoints
Density-dependant inhibition
 Crowded cells stop dividing
 Determined by the amount of nutrients &
growth factors available to cells
Anchorage dependance
 Cells must be attached to a substratum
(culture dish or tissue matrix) in order to
divide
Loss of cell cycle control: Cancer
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Cancer cells do not respond to regulating signals
of cell cycle
Divide as long as nutrients available while
normal cells divide only 20-50 times before
death
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Transformation: normal cells convert to cancer
cells
Tumor: transformed cell mass that evaded
destruction by immune system
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Ex. “immortal cells” – HeLa cells from Henrietta Lacks
tumor removed in 1951 still dividing in culture
Benign tumor: remain at original site; easier to
remove
Malignant tumor: invades nearby tissues & organs
Metastasis: spread of cancer cells to locations in
the body distant from original site
Henrietta Lacks
 Source of
HeLa cells
Cancer Treatments
Radiation
 cause more damage to cancer cells than
normal cells
 Cancer cells lack repair mechanisms
Chemotherapy
 Chemicals interrupt steps in cell division
process of cancer cells
Concept Check
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If a drug is administered that prevents DNA
synthesis of a cancer cell which phase of the cell
cycle is the cell trapped in?
What is the purpose of Cdks?
What features distinguish cancer cells & normal
cells?
Distinguish between a benign & malignant
tumor.
Why do you believe more money is invested in
researching cancer treatments rather than
researching cancer prevention?