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The Cell CycleChapter 12
Mitosis
Cell division Produce 2 daughter cells Same genetic information
Mitosis
Asexual reproduction Growth Repair
Genome
Genetic information Prokayotes Nucleoid Circular DNA No nucleus
Genome
Eukaryotes Chromosomes: DNA Associated proteins Chromatin: Complex of DNA & proteins Makes up chromosomes Humans 46 chromosomes Dogs 78 chromosomes
Eukaryotes
Somatic cells: Body cells 46 chromosomes Gametes: Sex cells Sperm & eggs 23 chromosomes
Eukaryotes
Chromatid: Duplicated chromosome Centromere: Attachment to another chromatid Prior to cell division chromosomes
replicates
Fig. 12-4 0.5 µm Chromosomes
Chromosomeduplication(including DNAsynthesis)
Chromo-some arm
Centromere
Sisterchromatids
DNA molecules
Separation ofsister chromatids
Centromere
Sister chromatids
Fig. 12-5
S(DNA synthesis)
MITOTIC(M) PHASE
Mito
sis
Cytokinesis
G1
G2
Cell cycle
Cell cycle: Events that occur to produce two
cells 1. Interphase (G1, S, G2) 2. Mitosis 3. Cytokinesis
Interphase
Growth phase of the cell G1, S, G2
Interphase
Where most of cycle is spent Rate of division depends on job of cell. Liver cells may divide rapidly Mature muscle cells do not divide at all Few cells will be in mitosis at a time Most are in interphase
Interphase
G1 or Gap 1 phase Cell is doing its job Preparing for the S phase. Chromosomes are single Can last weeks to years or happen
very quickly
Interphase
S phase DNA replication happens 2 sister chromatids G2 or Gap 2 phase cell prepares for
division Mitochondria & other organelles replicate Microtubules begin to form Chromosomes condense
Interphase
Mitosis
Nucleus & its contents divide Distributed equally Forming two daughter cells Prophase, metaphase, anaphase
and telophase
Prophase
Beginning of mitosis Chromosomes continues to
condense Mitotic spindle forms Begins to move chromosomes to
center Nuclear membrane disintegrates Nucleolus disappears
Prophase
Metaphase
Chromosomes line up in center of cell
Centromeres become aligned along the cells center
Metaphase
Anaphase
Microtubules shorten Separates the sister chromatids Chromosomes move towards the
poles
Anaphase
Telophase
Chromosomes are at the poles Nuclear envelope reforms Nucleolus reappears Chromosomes uncoil or de-
condense
Telophase
Cytokinesis
Cytoplasm separates Animal cells: cleavage furrow pinches the cells
in two Plant cells: cell plate is formed between the
cells Grows until a new cell wall is formed
Cytokinesis
Fig. 12-9
Cleavage furrow100 µm
Contractile ring ofmicrofilaments
Daughter cells
(a) Cleavage of an animal cell (SEM) (b) Cell plate formation in a plant cell (TEM)
Vesiclesformingcell plate
Wall ofparent cell
Cell plate
Daughter cells
New cell wall
1 µm
Binary fission
Prokaryotes produce 2 daughter cells by binary fission
Binary fission
1. Replication of the DNA Origin of replication: Specific location on the DNA 2. Two DNA molecules move to the
ends of the cell 3. Septation Formation of a new cell membrane
& a septum.
Binary fission
4. Septum begins to grow inward 5. Cell pinches into two cells.
Cell cycle control system
Check points Control point with stop & go signals G1, G2 and M phases
Fig. 12-14
SG1
M checkpoint
G2M
Controlsystem
G1 checkpoint
G2 checkpoint
Cell cycle control system
Special proteins Protein kinases & cyclins Cdks – cycle dependent kinases MPF-cyclin-Cdk complex “M-phase promoting factor” Regulate if cell stops or proceeds in
the cycle
Fig. 12-17b
Cyclin isdegraded
Cdk
MPF
Cdk
MS
G 1G2
checkpoint
Degradedcyclin
Cyclin
(b) Molecular mechanisms that help regulate the cell cycle
G2
Cyclin
accum
ulatio
n
Figure 12.16a
M M M G1G2G2G1 G1S S
MPF activity
(a) Fluctuation of MPF activity and cyclinconcentration during the cell cycle
Time
Cyclinconcentration
Cell cycle control system
Go-ahead signal at G1 Divides No signal G0 phase Does not divide
Figure 12.17G1 checkpoint
G0
G1
Without go-ahead signal,cell enters G0.
(a) G1 checkpoint
G1
G1
G2
S
M
M checkpoint
(b) M checkpoint
Without full chromosomeattachment, stop signal isreceived.
PrometaphaseAnaphase
M G2
G1
M G2
G1
With go-ahead signal,cell continues cell cycle.
G2 checkpoint
Metaphase
With full chromosomeattachment, go-ahead signalis received.
Cell cycle control system
Receives signals The environment Other cells Growth factors Density-dependent inhibition Anchorage dependence
Tumor
Abnormal growth of cells Malfunction in control system Abnormal cells grow uncontrollably Benign: Non-cancerous growth
Tumor
Malignant: Cancerous growth Metastasis: Spread of cancer to distant
locations
p53
Protein Works at a checkpoint at G1 p53 determines if DNA is damaged If so stimulates enzymes to fix it Cell division continues Unable to repair damage Cell suicide occurs
p53
Helps keep damaged cells from dividing Cancer cells p53 is absent or damaged p53 protein is found on the p53 gene Considered a tumor-suppressor gene Cigarette smoking causes mutations in
this gene
Henrietta Lacks
1951 developed cervical cancer Before cancer treatment Cells were removed First cells to grow in vitro Outside of the body Cell line is now known as HeLa cell
line Helped in biomedical research
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