MITOSIS!!!!!!!! Cell Growth and Division. Limits to Cell Growth As the cell becomes larger, there are more demands placed on the cell. It can cause a.

MITOSIS!!!!!!!!

Cell Growth and Division

Limits to Cell GrowthAs the cell becomes larger, there are

more demands placed on the cell.It can cause a DNA overload. The overload of DNA happens because

as a cell increases in size, it doesn’t make extra copies of DNA.

If the cell was to continue to grow, it would run into an information crisis.

The DNA would not be able to support the cell!

Limits to Cell GrowthIt can also cause a problem with

exchanging material.If a cell grows too large, it is more difficult

to get oxygen and nutrients.

Mitosis and Unicellular OrganismsMitosis in single celled organisms

helps to make new individuals.This is asexual reproduction.Ex – Paramecia and Amoeba

Mitosis and Multicellular Organisms Mitosis in multicellular organisms

helps with growth and repair.Ex- plants and animal cells.

Cell DivisionGrowing cells divide into 2 daughter cells

DNA must be copied firstMitosis – division of the nucleus

Cytokinesis – division of the cytoplasm

Overview of MitosisThere are three major processes to mitosisReplication of genetic material

Separation of genetic material

Formation of two daughter cells

The Nucleus and Cell DivisionChanges have to happen here before

mitosisDNA has to be copied to be passed onIn nondividing cells =

Chromosomes are not visible because the DNA and proteins are spread throughout the nucleus

Chromatin – the DNA as a mass of thin twisted threads DNA is wrapped around histones

(proteins)

The Nucleus and Cell DivisionIn dividing cells =

Chromatin shortens and thickens forming chromosomes

Can be seenBefore cell division the chromosome has

to be copied. When the chromosomes are copied,

there are two sister chromatids made.The chromatids are attached in the

middle at the centromere.

The Cell CycleAre the events a cell goes through

as it grows and divides.A cell grows, prepares for division

and divides to form two daughter cells, each of which will begin the cell cycle again.

includes

is divided into is divided into

Concept MapSection 10-2

Cell Cycle

M phase (Mitosis)

Interphase

G1 phase

S phase Prophase

G2 phase Metaphase Telophase

Anaphase

InterphaseCan be very longG1 phase – cells grow, increase in

size and make new organelles and proteins

S phase – chromosomes are replicated

G2 phase – shortest phase; organelles and molecules are made

MitosisDivided into phase –

Prophase MetaphaseAnaphaseTelophase

M phase

G2 phase

S phase

G1 phase

Section 10-2

ProphaseLongest phase of mitosisTakes up about 50-60% of timeChromosomes are visibleCentrioles move to opposite sides of the

nucleusCentrioles are in the centrosome region

which helps to organize the spindleSpindle – fanlike microtubule structure that

helps separate the chromosomes

ProphaseChromosomes become attached to

fibers in the spindle at a point near the centromere of each chromatid

Plant cells don’t have centrioles but still organize their spindles

At the end of prophase, the chromosomes are soiled tightly, nucleolus disappears, and the nuclear envelope breaks down.

MetaphaseChromosomes line up at the center of the

cell

Anaphase Centromeres that join the sister

chromatids splitThe sister chromatids become

separated and now again have individual chromosomes for each cell

TelophaseChromosomes disperse into a

tangle of dense materialNuclear envelope returnsSpindle breaks apartNucleolus is again visible

CytokinesisThe cytoplasm divides to form the

two cellsUsually happens at the same time

as telophaseIn animals – the cell membrane is

pulled inward and is pinchedIn plants – a cell plate forms and

then the cell wall replaces it

Control of Cell DivisionThe cell cycle can be turned on and offCyclin – protein that regulates the cell cycle

Amount increases during cell division Regulate timing of cell cycle

Internal regulators Proteins that respond to events inside the

cellAllows to proceed only when the inside of

the cell is readyFor example, the chromosomes are copied

A sample of cytoplasm is removed from a cell in mitosis.

The sample is injected into a second cell in G2 of interphase.

As a result, the second cell enters mitosis.

Figure 10–8 Effect of Cyclins

Section 10-3

Control of Cell DivisionExternal regulators

Proteins that respond to events outside of the cell

Tells the division to speed up or slow down

Growth factorsMolecules on neighboring cells cause

the cycle to slow down or stop

Uncontrolled Cell GrowthCancer – body’s own cells lose the

ability to control growthDon’t respond to signals that regulate the growth of most cells

Cells divide uncontrollably and form tumors which can affect tissues

Cancer cells can break loose and spread throughout the body

Control over the cycle is broken

Uncontrolled Cell GrowthCancer cont’d

The cells don’t respond to external or internal regulators

Scientists found lots of cancer cells with a defect in the gene p53 which normally stops the cell cycle until all chromosomes have been properly replicated.