the cell cycle “mitosis”

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The Cell Cycle“Mitosis”

Packet #33Chapter #13

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IntroductionCell Cycle

An ordered sequence of events in the life of a dividing eukaryotic cell and is a type of asexual reproduction.

The contents of the parent’s cell nucleus is duplicated and an orderly separation of the cell’s contents is separated into two new, identical nuclei.

Two daughter cells are produced the parent cell.

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Cell CycleThree General Stages

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Interphase

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Interphase Interphase

Accounts for about 90%** of the cell cycle

G1 Phase Gap Phase I

Cell grows in size S Phase

Synthesis Phase Copies of

chromosomes and DNA are made DNA Replication

G2 Phase Gap Phase II

Cell grows in size

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Mitotic Phase

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Mitotic Phase (Mitosis)—ProphaseProphase

Longest of mitotic phase Chromosomes condense

and become visible Chromosomes, once

duplicated, are called two sister chromatids Two chromatids (sister

chromatids) are formed by one chromosome

Mitotic spindle assembles

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Mitotic Phase (Mitosis)—MetaphaseChromosomes align

along the middle (equatorial plane) of the cell

Microtubules attach chromosomes to opposite ends of the spindle

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Mitotic Phase (Mitosis)—AnaphaseAnaphase

Chromosomes are pulled to the poles of the cell

Sister chromatids are separated

Centromeres divide

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Mitotic Phase (Mitosis)—TelophaseTelophase

Nuclei (nucleus) and, nuclear envelope, reforms in daughter cells

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Cell Cycle—Cytokinesis

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Cell Cycle—CytokinesisCytokinesis

Both daughter cells are separated and two distinctive cells are formed. Daughter cells are

pinched off from each other

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Review

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Review I

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Review II

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Review IIIInterphase

DNA is duplicatedProphase

Chromosomes condenseAnaphase

Sister chromatids separateTelophase

Nuclei and nuclear envelope reformCyctokinesis

Separation of two daughter cells

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Review IVOne cell division resulting in two daughter cellsChromosome number, per nucleus, remains the

sameHaploid results in haploidDiploid results in diploid

No crossing overMore on this in meiosis

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Control of the Cell Cycle

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Control IThe steps of the cell cycle must occur in sequence and

before the process can proceed to the next step, a checkpoint must be passed. There are checkpoints for

Cell size Determination of whether DNA replication is complete

These checkpoints are also regulated by various means Growth factors

MPF M phase promoting factor

Signals from other cells Protein kinases

Cyclin-dependent protein kinases (Cdks)

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p53 GeneDuring the S phase, if the DNA is damaged, the p53

gene becomes activated and produces the p53 protein.

The p53 gene protein stimulates transcription of the gene (p21 gene) that codes for a Cdk inhibitor protein.The p53 gene protein behaves as a transcription factor.

The Cdk inhibitor protein (p21 inhibitor protein) binds onto the S phase cyclin-Cdk complex and inactivates them.Stopping the cell cycle.

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Signals from Other CellsUnicellular organisms, such as bacteria and

yeasts, grow and divide as fast as they can.Depends on the amount of nutrients available

Specialized eukaryotic cells, of a multicellular organism, must have their proliferation controlled so that individual cells only divide when necessary.They divide to allow growth or to replace

damaged/old cells.

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Signals from Other Cells IIRetinoblastoma protein (Rb protein) is ONE

example of a protein that keeps these cells from dividing however they want.Binds onto a gene and prevents transcription.

Growth factors are used to override the “brakes.”Once they have bound to the enzyme linked

receptors, tyrosine kinase receptors, a pathway is initiated to allow the cells to replicateAllowing the removal of the Rb protein.

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Survival Factors Survival factors allow cells to

“survive” and if cells are deprived of them, cells will then activate intracellular suicide programs. Programmed cell death Apoptosis

How may programmed cell death be useful? Fetal development

The spade-like structure of the hand/foot leads to the development of hand and feet structure due to the death cells in particular areas.

Metamorphosis Tadpolefrog

Prevents necrosis

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ApoptosisApoptosis occurs because of a series of enzymatic

reactions carried out by proteases.

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Cancer Cells

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Cancer CellsCancer cells develop because of mutations that

directly/indirectly impact the “proliferation control system.”Faulty control system

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Cancer Cells IIProliferation genes code for proteins that promote

cell division.Anti-proliferation genes, such as the p53 gene, code

for proteins that stop cell division.CdkMPF

Mutation in the proliferation genes, the genes that promote cell division, causes the cell to divide “non-stop”--hence a cancer growth or tumor is formedMutant proliferation genes are called oncogenes

Cancer promoting genes.

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