•CELL

DIVISION

Objectives

Students will learn what causes a cell

to divide and how it happens.

They will explore all parts of the cell

cycle and mitosis.

They will discuss what happens when

this process malfunctions causing

mutations or cancer

Today you need: notebook, pen

or pencil, textbook, colors to

share, colored paper foldable

later •Bellwork: • Carefully copy, label and color

the cell cycle diagram on page

130

Cell Growth

Does an animal get larger because each cell

increases in size or because it produces more

of them?

Cell Growth • As you might have guessed, living things grow

by producing more cells.

• The koalas have the same size cells, just one

has more then the other.

Limits to Cell growth • The larger a cell becomes, the more

demands the cell places on its DNA. In addition, the cell has more trouble moving enough nutrients and wastes across the cell membrane.

• The cell can’t grow. It must reproduce!

Ratio of surface area to volume:

Cell Division • The process by which a cell divides into

two new daughter cells is called cell

division.

• Before cell division occurs, the cell

replicates, or copies, all of its DNA. This

replication solves the info. problem.

Cell Division • What do you think would happen if a cell

were simply to split into two without any

advance preparation?

Chromosomes • In eukaryotic cells, the genetic

information that is passed on from one generation of cells to the next is carried by chromosomes.

• The cells of every organism have a specific number of chromosomes.

• Each chromosome consists of two identical “sister” chromatids. When the cell divides, the “sister” chromatids separate and go to each of the new cells.

Chromosome

• Each pair of chromatids is attached at an

area called a centromere.

• Centromeres are usually located near the

middle of the chromatids, although sometimes

can be found at each end.

The Cell Cycle

• The cell cycle is the series

of events that cells go

through as they grow and

divide.

• During the cell cycle:

- A cell grows

- Prepares for division

- And divides to form to

daughter cells

Events of the Cell Cycle

• There are four phases of the Cell Cycle.

• G1 phase – period where cell does most of

their growing

• S phase – chromosomes are copied and the

synthesis of DNA molecules takes place.

(DNA Replication)

• G2 phase – usually the shortest of the

phases. The phase where essential

organelles are constructed. More growth

• and M phase – Cell Division.Mitosis

I P on a MAT © *preparation between split

Interphase

*mitosis

Prophase

Metaphase

Anaphase

Telophase

*cells split

Cytokenesis

Steps of Cell Division

Interphase

• Stage between cellular

division.

• Also known as the G1, S,

and G2 stages of the cell

cycle.

• In Interphase the cell is

allowed to grow, copy its

DNA and check for crucial

genetic mistakes.

Mitosis • Mitosis (M phase) steps which include the

process for asexual cell division.

• Biologists divide the events of mitosis into

four phases:

- Prophase

- Metaphase

- Anaphase

- Telophase

Depending on the type of cell, the four phases

may last anywhere from a few minutes to

several days.

Mitosis

• Let’s look at each of the

parts of mitosis..

and practice our hand

symbols as we go.

Prophase - The first and the longest phase of mitosis, prophase can take as much

as 50 to 60 percent of the total time required to complete mitosis.

- During prophase in animal cells, the centrioles

separate and take up positions on opposite

sides of the nucleus.

- The centrioles help organize the spindle,

fanlike microtubule structure that helps

separate the chromosomes.

Prophase

• chromosomes

appear-chromatin

condenses to form

chromosomes

• the nucleolus

disappears

• the cell membrane

begins to break

down

Metaphase

• chromosomes align

along the equator of

the cell pulled by the

spindle fibers

• Spindle fiber that

are attached to the

poles connect to the

centromeres

• Short Phase

Early Anaphase

• chromosomes are

pulled to the poles

by the contraction of

the spindle fibers

chromatids are

separated at the

centromere

Late Anaphase

• chromosomes begin

to move to the

opposite poles

• Karyokinesis

• the energy for this

process is provided

by the mitochondria

Early Telophase

• the new cell wall

begins to form to

separate the new

cell the

chromosomes begin

to form a nucleus

Late Telophase

• the chromosomes

start to uncoil and

become less dense

• Nuclear membrane

reassembles

• Nucelolus reappears

• Plasma membrane

begins to separate

• Cell plate forms

• two new identical

cells are formed

• Cytokinesis is the

division of the

cytoplasm of a

parent cell.

• Microfilaments form

a ring around the

equator. When the

microfilaments

contract-pinches

makes a furrow

Cytokinesis

• You may either consider it the end of Mitosis or the beginning of Interphase.

• While each daughter cells gets identical sets of DNA, the cytoplasm and organelles are only roughly divided equally between the two cells.

• Parent chromosome #= Daughter chromosome#

Cytokinesis

Mitosis

• all four

stages of

mitosis can

be seen in

this picture.

note the

process by

which the

red and blue

chromosome

s separate.

MITOSIS

What time is it Mrs. Weatherall????

• It’s foldable time!!!!!!!!!

://www.youtube.com/watch?v=

VlN7K1-9QB0

Regulating the Cell Cycle

• If we grow by cell division, then why do we stop

growing?

• Multi-cellular organisms cell growth is

controlled.

• For example, in the human body, most muscle

and nerve cells don’t divide at all once they

have developed, whereas skin cells and blood

cells divide rapidly.

What time is it Mrs. Weatherall????

• It’s foldable time!!!!!!!!!

Today you need: textbook,

notebook, pen or pencil,

worksheet, question packet

• Bell work: copy & answer 1. What happens during

cytokinesis?(136)

2. Why do we need to make new

cells? (4 reasons)

•

Today you need: worksheet,

pen or pencil, 4 hi-liters to

share, • Bell work: copy and answer:

• 1. If an animal has 60 chromosomes,

how many cells does it produce in one

cell cycle?

• 2. How many chromosomes would be

in each cell?

• 3. If those cells were for that animal’s

sperm or egg how many chromosomes

would they have and why?

Controls on Cell Division

• What would happen if the cells continued to

divide?

• When cells come into contact with other

cells, they respond by not growing.

• How does this relate to how your body

responds to a cut or a bone fracture?

Cell Cycle Regulators • Scientists discovered

that cells in mitosis

contain a protein called

cyclin when injected in

a non-dividing cell,

would cause a miotic

spindle to form.

• Cyclins regulate the

timing of the cell

cycle in eukaryotic

cells.

Other Cell Cycle Regulators

• Internal regulators- proteins that respond to

events inside the cell.

For example: several regulatory proteins make

sure that a cell does not enter mitosis until all

its chromosomes have been replicated.

- External regulators- proteins that respond to

events outside the cell.

For example: external regulators direct cells to

either speed up or slow down the cell cycle.

Uncontrolled Cell Growth

• Why is cell growth regulated so carefully?

• Cancer- a disorder in which some of the

body’s own cells lose the ability to control

division. Cancer cells do not respond to the

signals that regulate the division of most cells.

Skin Cells

Practice Hand Signs IPMAT

worksheet

• Let’s do the mitosis

worksheet together…

EOC questions

Put away everything except

your notebook.

Everyone will need a dry erase

board, marker and some paper

towel.