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SOME DEFINTIONS Chromatin – DNA-protein complex – uncoiled DNA fiber One double-chromosome has two sister chromatids Chromatids joined at centromere
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Raven & Johnson Chapter 10
Campbell Chapter 12
THE CELL CYCLETHE CELL CYCLE
SOME DEFINITIONSGenome – full set of genetic infoChromosomes – way DNA is packagedGametes – reproductive cells
23 chromosomesSomatic cells – all but reproductive
cells46 chromosomes
SOME DEFINTIONS• Chromatin – DNA-protein complex –
uncoiled DNA fiber• One double-chromosome has two sister
chromatids• Chromatids joined
at centromere
SOME DEFINTIONS• Produce gametes in gonads through
meiosis• Produce somatic cells through mitosis &
cytokinesis
CELL CYCLE - OVERVIEWM phase (mitosis) – 10% of cycleInterphase (non-dividing) – 90%
Divided into G1, S, G2 phasesCell grows (makes proteins &
organelles)Copies chromosomes in S
(synthesis) phaseG1 S G2 MM – 5 phases
THE MITOTIC SPINDLE• Begins assembly in centrosome
(organizes microtubules)• Interphase – centrosomes replicate• Prophase & prometaphase – move
to opposite ends of cell & microtubules grow from them – now spindle poles
THE MITOTIC SPINDLE• Spindle fibers attach to
chromosome’s kinetochore• Complete when chromosomes line
up along metaphase plate
THE MITOTIC SPINDLE• Anaphase – proteins joining
chromatids inactivate kinetochore motor proteins “walk” chromatid to pole microtubules shorten
CYTOKINESISAnimal cells go through cleavage
Starts with cleavage furrow (shallow groove)
Actin & myosin involvedPlant cells make cell plate
Vesicles from Golgi bodies come together and bring together cell wall material
EVOLUTION OF MITOSIS
• Prokaryotes binary fission• Single bacterial chromosome –
circular DNA & proteins• As DNA replicates, copies of
first replicated region (origin of replication) move apart
• Cell grows & splits plasma membrane
Replication of E. coli
CELL CYCLE REGULATION (INTERNAL)
• Critical control points where stop & go signals regulate cycle
• Signal-transduction pathways at G1, G2, and M
• If, at G1, it cannot continue (or does not need to), it exits cycle & moves into G0 (nondividing) phase
• Most cells in G0 phase until need to divide
CELL CYCLE REGULATION
Kinases drive cell cycle when activated – activated when attached to cyclin (protein that fluctuates conc. in cell) called cyclin-dependent kinases (Cdk)Cdk activity rises when cyclin conc. risesCyclin-Cdk complex is called MPF
Maturation Promoting Factor (M-phase PF)
Triggers cell from G2 into M
CELL CYCLE REGULATION
CELL CYCLE REGULATION
• Cdk now stays inactive until joining with new cyclin during next turn of the cycle
• Checkpoints
CELL CYCLE REGULATION• M-phase checkpoint makes sure
chromosomes are attached at metaphase plate before anaphase• Kinetochores not yet attached send
out a delay signal • Keeps anaphase-promoting
complex (APC) inactive until all are attached
CELL CYCLE REGULATION
• Cell Cycle Checkpoints• Video on mitosis and meiosis (we
will view just checkpoints here)
CELL CYCLE INFLUENCES (EXTERNAL)
Growth factors – protein released by body cells to stimulate cell divisionEx: Platelet-derived growth
factor (PDGF)Density-dependent inhibition
Crowded cells stop dividingAnchorage dependence
Must be attached to substrate (tissue, petri dish) to divide
CANCER
• No density-dependent inhibition• Doesn’t stop when growth factors deplete• Divide & stop randomly – don’t adhere to
checkpoints• Divide indefinitely if nutrients present• Transformation: normal cell cancer cell
CANCER• Tumor: mass of abnormal cells
• Benign – remains at original site• Malignant – invasive; impairs functions
of one or more organs• Metastasis – spread of cancer cells to
other distant parts of the body
9:18
WHO OWNS YOUR
CELLS?????