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?????