The Cell CycleThe Cell Cycle

When do cells divide?When do cells divide?

• ReproductionReproduction

• Replacement of damaged cellsReplacement of damaged cells

• Growth of new cellsGrowth of new cells

• In replacement and growth cell divisions In replacement and growth cell divisions how should daughter cells compare to how should daughter cells compare to parent cell?parent cell?

• The daughter cells should be identical The daughter cells should be identical copies of the parent cell.copies of the parent cell.

How can identical daughter How can identical daughter cells form?cells form?

• The genome must be copied and then The genome must be copied and then divided such that each daughter cell gets divided such that each daughter cell gets one of the copies.one of the copies.

• Genome = all the genes in an organismGenome = all the genes in an organism

Bacterial ReproductionBacterial Reproduction

TERMSTERMS• ChromosomeChromosome

– threadlike structures that are composed of DNA + proteinthreadlike structures that are composed of DNA + protein

• ReplicationReplication – process whereby DNA is identically copied (before cell process whereby DNA is identically copied (before cell

division)division)

• MitosisMitosis – division of the nucleusdivision of the nucleus

• Cytokinesis Cytokinesis – division of the cytoplasmdivision of the cytoplasm

• Chromatin Chromatin – DNA + protein complex that is thin and fibrous; it will DNA + protein complex that is thin and fibrous; it will

condense into distinct chromosomes during cell divisioncondense into distinct chromosomes during cell division

• Chromatid Chromatid – after replication the chromosome consists of 2 after replication the chromosome consists of 2

sister chromatids joined at the centromere.sister chromatids joined at the centromere.

• CentromereCentromere – specialized region of the chromosome, where specialized region of the chromosome, where

chromatids are joined. Each chromosome has chromatids are joined. Each chromosome has one centromere.one centromere.

The Cell CycleThe Cell Cycle

InterphaseInterphase

• 90% of cell cycle is spent in this phase90% of cell cycle is spent in this phase

• GG11 = first growth phase = first growth phase

• S = synthesis phase, DNA synthesis S = synthesis phase, DNA synthesis (replication) occurs here(replication) occurs here

• GG22 = second growth phase = second growth phase

GG22 phase of Interphase in phase of Interphase in

animal cells:animal cells:• Nuclear envelope visibleNuclear envelope visible

• Centrioles replicated and 2 pairs near Centrioles replicated and 2 pairs near nucleusnucleus

• Aster forms Aster forms

• Chromatin fiberChromatin fiber

Prophase (early, Prophase (early, late)/Prometaphaselate)/Prometaphase

• Nucleoli disappearNucleoli disappear

• Chromosomes - pullChromosomes - pull

• MTOC at centriolesMTOC at centrioles

• Sister chromatids joined at centromereSister chromatids joined at centromere

MetaphaseMetaphase

• Chromosomes - middleChromosomes - middle

• Centromeres aligned at metaphase plateCentromeres aligned at metaphase plate

• Kinetochore microtubule – what is it?Kinetochore microtubule – what is it?

• Spindle fiber – what is it?Spindle fiber – what is it?

AnaphaseAnaphase

• Chromosomes - awayChromosomes - away

• Centromeres divide Centromeres divide

• Cell elongation (oval shape)Cell elongation (oval shape)

• How do kinetochores work to pull How do kinetochores work to pull chromosomes apart?chromosomes apart?

TelophaseTelophase

• Cell – two Cell – two

• New nuclear envelopes New nuclear envelopes

• Chromatin fiberChromatin fiber

• Nonkinetochore microtubules continue to Nonkinetochore microtubules continue to elongate the cellelongate the cell

CytokinesisCytokinesis

• Begins before telophase has completedBegins before telophase has completed

• Cleavage furrow Cleavage furrow

• Cell plate Cell plate

Mitochondrial DivisionMitochondrial Division

Cytoplasmic Cell Signals in Cytoplasmic Cell Signals in Regulation of Cell Cycle:Regulation of Cell Cycle:

Checkpoints Checkpoints in the cell in the cell cycle: If it cycle: If it passes the passes the

GG11

checkpoint checkpoint cell divides if cell divides if not enters Gnot enters G00

phase and phase and does not does not

dividedivide

• Cyclin protein Cyclin protein levels fluctuate.levels fluctuate.

• Cyclin high, Cyclin high, Cdk attaches & Cdk attaches & phsophorylation phsophorylation breaks nuclear breaks nuclear envelope envelope

• Later MPF Later MPF initiates cyclin initiates cyclin breakdownbreakdown

Cancer cellsCancer cells

• How does abnormal cell division of cancer How does abnormal cell division of cancer cells differ from normal cell division?cells differ from normal cell division?

• Cancer cells are not under density Cancer cells are not under density dependent inhibitiondependent inhibition

• Continue to grow until all nutrients are used Continue to grow until all nutrients are used upup

• Cancer cells are immortal, do not shorten Cancer cells are immortal, do not shorten telomeres.telomeres.