The Cell Cycle

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 how should daughter cells compare to parent cell?In replacement and growth cell divisions how should daughter cells compare to parent cell? The daughter cells should be identical copies of the parent cell.The daughter cells should be identical copies of the parent cell.

How can identical daughter cells form? The genome must be copied and then divided such that each daughter cell gets one of the copies.The genome must be copied and then divided such that each daughter cell gets one of the copies. Genome = all the genes in an organismGenome = all the genes in an organism

Bacterial Reproduction

TERMS ChromosomeChromosome – threadlike structures that are composed of DNA + protein ReplicationReplication –process whereby DNA is identically copied (before cell division) MitosisMitosis –division of the nucleus CytokinesisCytokinesis –division of the cytoplasm ChromatinChromatin –DNA + protein complex that is thin and fibrous; it will condense into distinct chromosomes during cell division

ChromatidChromatid –after replication the chromosome consists of 2 sister chromatids joined at the centromere. CentromereCentromere –specialized region of the chromosome, where chromatids are joined. Each chromosome has one centromere.

The Cell Cycle

Interphase 90% of cell cycle is spent in this phase90% of cell cycle is spent in this phase G 1 = first growth phaseG 1 = first growth phase S = synthesis phase, DNA synthesis (replication) occurs hereS = synthesis phase, DNA synthesis (replication) occurs here G 2 = second growth phaseG 2 = second growth phase

G 2 phase of Interphase in animal cells: Nuclear envelope visibleNuclear envelope visible Centrioles replicated and 2 pairs near nucleusCentrioles replicated and 2 pairs near nucleus Aster formsAster forms Chromatin fiberChromatin fiber

Prophase (early, late)/Prometaphase Nucleoli disappearNucleoli disappear Chromosomes - pullChromosomes - pull MTOC at centriolesMTOC at centrioles Sister chromatids joined at centromereSister chromatids joined at centromere

Metaphase 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?

Anaphase Chromosomes - awayChromosomes - away Centromeres divideCentromeres divide Cell elongation (oval shape)Cell elongation (oval shape) How do kinetochores work to pull chromosomes apart?How do kinetochores work to pull chromosomes apart?

Telophase Cell – twoCell – two New nuclear envelopesNew nuclear envelopes Chromatin fiberChromatin fiber Nonkinetochore microtubules continue to elongate the cellNonkinetochore microtubules continue to elongate the cell

Cytokinesis Begins before telophase has completedBegins before telophase has completed Cleavage furrowCleavage furrow Cell plateCell plate

Mitochondrial Division

Cytoplasmic Cell Signals in Regulation of Cell Cycle:

Checkpoints in the cell cycle: If it passes the G 1 checkpoint cell divides if not enters G 0 phase and does not divide

Cyclin protein levels fluctuate. Cyclin protein levels fluctuate. Cyclin high, Cdk attaches & phsophorylation breaks nuclear envelope Cyclin high, Cdk attaches & phsophorylation breaks nuclear envelope Later MPF initiates cyclin breakdown Later MPF initiates cyclin breakdown

Cancer cells How does abnormal cell division of cancer cells differ from normal cell division?How does abnormal cell division of cancer cells differ from normal cell division? Cancer cells are not under density dependent inhibitionCancer cells are not under density dependent inhibition Continue to grow until all nutrients are used upContinue to grow until all nutrients are used up Cancer cells are immortal, do not shorten telomeres.Cancer cells are immortal, do not shorten telomeres.