13346 CellCycle&Mitosis

8/6/2019 13346 CellCycle&Mitosis

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Cell Cycle&

Mitosis


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Cell Reproduction

Cell Theory Cells come from preexisting cells

Cell division - process which ends with newcells formed from an old cell.

All organisms grow and change; worn outtissues are repaired or replaced by new cells


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CHROMwords

Chromatin uncoiledDNA + proteins

Chromosome coiledDNA + proteins (Looks likean X)

Chromatid only half of a chromosome

Sister chromatids Two chromatids joinedtogether, by a centromere,to form a chromosome


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Chromosomes

Contain DNA

Becomes dark when stained

Carriers of genetic material that is copiedand passed from generation to generation

Identity of cell


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Chromatin


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Cell CycleThe sequence of growth and divisionof the cellTwo general periods

Growth(interphase)

Division (mitosis)Majority of time isspent in the growthperiod known asInterphase


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The entire sequence of events happening fromThe end of one nuclear division to the beginningof the next.Involves following cycles:-1. Chromosome cycle:- In it, DNA synth. Alternateswith mitosis.2. Cytoplasmic cycle:- In it, cell growth alternates with

Cytokinesis.3. Centrosome cycle:- Both the above cycles require

proper inheritance of centrosome and its distributionon poles.


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Cell Cycle

Four stages to the cellcycle (by Howard &

Pelc, 1953) Growth period -

Interphase includes:G1S StageG2

Division period -Includes:

Mitosis


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Interphase:

Known as thegrowth period

Majority of cellslifeThree stageswithin Interphase

G1 S Stage G2


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G1Stage #1

Chromosomes are notvisible under a

microscope - becausethey are uncoiled,therefore calledchromatin

Proteins are quicklymade


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S Stage

Stage #2Chromatin isreplicated in the

nucleus

Chromatin divides toform sister

chromatids whichare connected bycentromeres


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G2Stage #3

Chromatin shortens and coils

Organelles are made

Most proteins made are for mitosis

Animals - centriole pair replicates and prepares toform spindle fibers.


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Interphase InformationBusiest phase of cell cycleReplication of chromosomesMost protein production

Organelles madeCell parts madePackaging of chromatins atthe latter part of interphase


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Mitosis

Four Phases of mitosis

Prophase Metaphase Anaphase Telophase


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Prophasefirst phase of mitosis

Longest PhaseChromatin coils up intovisible chromosomes

Chromosomes lookhairyEach chromosome nowhas two halves


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Chromosomes are also called sister chromatids Two sister chromatids can be

called a diploid chromosome One sister chromatid can also be

called a haploid chromosome DNA in sister chromatids are

alike Sister chromatids are held

together by a centromere


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Prophase

first phase of mitosisNucleus disappears

Nuclear envelopedisintigrates

Nucleolus disintigrates

Completely absent by theend of prophase


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ANIMAL CELLS Centrioles begin to go to

opposite ends of the cell Centrioles are small dark and

cylinder like Centrioles help to separatesister chromatids

ANIMAL AND PLANT CELLS Spindles begin to appear -

look like footballs Spindles have fibers in them

which help to separate sister chromatids


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Metaphase

second stage of mitosisShort stageSister chromatidsline up at theequator Sister chromatidsare attached by their centromeres to thespindle fibers


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Anaphasethird stage of mitosis

SC are pulled apart atthe centromere toopposite ends of thecell

This ensures that eachnew cell gets one set of the information needed

SC are pulled apartbecause the spindlefiber shortens


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Telophase

fourth stage of mitosisChromatids reach opposite polesof cellChromosomes unwindSpindle breaks downNucleolus reappearsNew nuclear envelope formsaround each set of chromosomesNew double membrane begins toform between the two newnuclei.


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Cytokinesis

end of telophaseThe dividing of thecytoplasm

ANIMALS Plasma membrane

pinches along theequator

Two new cells areseparated


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Cytokinesisend of telophase

PLANTS B/c rigid cell wall:

Cell plate is laid across the equator Cell membrane forms around each cellNew cell walls fom on each side of the cellplate until separation is complete


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P rophase

Metaphase

Anaphase


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Mitosis: Significance

Guarantees genetic continuity

Results in two new cells, daughter cells

Daughter cells carry out samefunction and cellular process as theparent cell


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Cells

Cells can function on their own or together as a group.

One-celled organisms remain one-celled

Multicellular organisms use mitosis toreplace and replenish their existing cells


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13346 CellCycle&Mitosis

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