MitosisQuick Quiz

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MitosisOccurs in autosomes except red blood cells,

and mature neurons, skeletal and cardiac muscle cell

Does NOT occur in gametes (reproductive cells)Needed to:• Grow (make more cells)• Replace cells (50 million die every second!)

Both plants and animalsChromosome number stays the same

Mitosis During mitosis, follow what is happening to the

chromosomes! Chromosomes• One long continuous thread of DNA that consists of

numerous genes along with regulatory information• Humans have 46 chromosomes in every cell of their

body (except sex cells – they only have 23) If these 46 chromosomes were stretched out

straight and laid end to end they would be about 10 feet long!

That means there is 10 feet of DNA in everyone of your body cells

Chromosomes

During cell division (mitosis), the DNA in eukaryotic cells is coiled into very tight compact structures called CHROMOSOMES.

Chromosomes are rod-shaped structures made of DNA and Proteins

The DNA in eukaryotic cells wraps tightly around proteins called HISTONES. They help to maintain the shape of chromosomes and aid in the tight packing of DNA.

Chromatin• Between cell divisions (interphase), DNA IS NOT so

tightly coiled into chromosomes.  The less tightly coiled DNA-Protein complex is called CHROMATIN

Interphase Chromosomes

+ =

Remember, this is what chromosomes are like during interphase – long and stringy.

Interphase Chromosomes• Notice the nuclear membrane is still in tact, and

the DNA is loose, but contained within the nucleus.

ChromosomesWhen preparing for cell division, chromosomes

form copies of themselves, each half of the chromosome is called a CHROMATID or SISTER CHROMATIDS. Chromatids form as the DNA makes copies of itself (during the S phase) before cell division.

The constricted area of each chromatid is called a CENTROMERE . The centromere holds the two chromatids together until they separate during cell division.

Chromosome TerminologyDyad – Chromosome with two parts

Monad – Chromosome with only one part

1 centromere + 1 chromatid = 1 monad = chromosome

1 centromere + 2 chromatids = 1 dyad = 1 chromosome

Human ChromosomeMonads

Human ChromosomeDyads

Chromosome Condensation

MitosisMitosis is an amazing process that carefully

divides two sets of DNA• The process of eukaryotic cell division during which

the cell nucleus divides• During mitosis and cytokinesis each daughter cell

must receive a full set of DNA – no more, no less – to work properly

If chromosomes remained long and stringy during mitosis, they could become entangled. • Therefore part of mitosis involves converting the

chromosomes from a linear strand of DNA (chromatin) to its highly condensed form (chromosomes)

Mitosis TerminologyCentrosome: The major microtubule

organizing center of an animal cell.Centriole: A paired organelle that helps

organize the microtubules in animal and protist cells during nuclear division.• Plant cells do not have centrioles, but still

have organizing centers for microtubules.Spindle fibers: An assemblage of

microtubules that coordinate chromosome movement during mitosis

• Spindle microtubules attach to the centromeres and begin tugging the chromosomes back and forth

Centrosomes and Centrioles

Spindle Fibers

• Parent cell

• centrioles

• spindle fibers

• centrosome

• nucleus with• DNA

Mitosis4 Phases:

ProphaseMetaphaseAnaphaseTelophase

ProphaseNucleolus disappearsNuclear membrane disappearsChromatin condenses (shortens and thickens)

into chromosomes (dyads)Centrioles (in animals) separate and migrate to

polesSpindle fibers grow from centrioles and radiate

toward center of cell

Prophase

Prophase

MetaphaseSpindle fibers attach centrioles to centromere

of each chromosomeChromosomes (dyads) line up across equator of

cell• Most often referred to as the ‘metaphase

plate’oThis is a place, not a structure

Metaphase

AnaphaseSpindle fibers begin to shorten which pulls the

sister chromatids away from each other towards opposite ends of the cell• They separate to form individual chromatids

oDyads separate into monadsoAssures that each resulting cell (“daughter

cell”) gets one of each chromosome

Anaphase

TelophaseChromosomes (monads) reach

poles and unwind into chromatin.Nuclear membrane reforms around chromatinNucleolus reformsSpindle fibers disappearCentrioles (in animals) duplicateCytokinesis may occur

cleavage furrow

Telophase

CytokinesisCytokinesis• Division of the cytoplasm and cell into two

daughter cells• Differs in plant and animal cells

oIn animal cells a ring of filaments forms around the equator of the cell, and then tightens for form a cleavage furrow, which splits the cell in two

Cytokinesis

Animals from the outside in Plants from the inside out

Review Mitosis

Review MitosisA single division

Starts with one nucleus and ends with two

In the end there is no change in the number of chromosomes.

Each resulting nucleus has the same number of chromosomes as the original nucleus.

Review the Cell Cycle Interphase• G1• S• G2

M Phase• Mitosiso Prophaseo Metaphaseo Anaphaseo Telophase

• Cytokinesis