Part 1 Mitosis Slides 1-35

The larger a cell becomes, the …….

…. more demands the cell places on its DNA.

If the cell grows too large, it will have trouble moving enough nutrients and wastes across the cell membrane.

There are two main reasons why cells divide rather than continuing to grow larger and larger:

• All of the information that a cell needs to

function is stored in the DNA of the cell.

• DNA is packaged into chromosomes. A

chromosome consists of one very long linear

DNA molecule consisting of 1000's of genes.

• Each gene is the instructions for making a

particular protein that the cell needs.

• The cell is constantly making copies of these

genes and sending the copies (in the form of

RNA) out to the ribosomes.

• When the cell is small, the information stored

in the cell’s DNA is adequate to meet the

needs of the cell.

• As the cell grows too large, there is an

“information crisis”. The DNA cannot keep

up with the demands of running a larger cell.

A cell must take in a constant inflow of food, oxygen and water across the membrane.

Waste products must constantly be crossing the membrane in order to leave the cell.

A larger cell will require much more food, oxygen and water. A larger cell will generate much more waste.

As the cell grows, the volume of the cell increases much more rapidly than the surface area of the cell membrane.

When the cell gets too large, the membrane surface area is not adequate enough to transport the large quantities of food and water in and waste products out.

Cell division is the process by which cellular material is divided between two new daughter cells.

1 Mother Cell 2 Daughter cells.

The two daughter cells will be….

…identical to each other and to the mother cell.

Each daughter is half the size of the parent cell, but immediately begins growing.

A typical human cell has about 2 meters of DNA. Before the cell can divide, all of this DNA must be copied and then the two copies separated so that each daughter cell ends up with a complete set of DNA.

Each species has a characteristic number of chromosomes in each cell nucleus; humans have 23 pairs or 46.

Each cell must first __________________before cell division occurs.

copy its chromosomes

Each daughter cell gets a complete copy of that information.

Cell division occurs in two main stages:Mitosis – The division of the nucleus

Cytokinesis – The division of the cytoplasm

The chromosomes are not visible except during cell division. At the beginning of cell division, the chromosomes condense into compact, visible structures that are easily seen with a microscope.

Replicated chromosome

consisting of 2 sister chromatids.

centromere

Well before cell division takes

place, each chromosome is

replicated or copied.

At the beginning of cell division, each chromosome consists of two identical “_______________”. These chromatids are connected at an area called a __________.

sister chromatids

centromere

The Cell Cycle

The cell cycle is:The series of events that cells go through as they grow and divide.

The cell cycle is the life of the cell from the time it is first formed from a dividing parent cell until its own division into two cells.

During the cell cycle: 1. A cell grows.

2. The cell prepares for division.

3. The cell divides to form two daughter cells.

The cell cycle consists of five major phases:

G1 (first gap)

S (synthesis)

G2 (second gap)

Mitosis

Cytokinesis

G2

SG1

Mitosis is the division of the nucleus.

Cytokinesis is the division of the cytoplasm.

Two new cells are produced.

Before a cell can begin mitosis and actually divide, it

must do two things:

a) It must form duplicates of its chromosomes.

b) It must produce a supply of organelles for the two daughter cells.

These preparations occur during the G1, S, and G2

phases of the cell cycle.

These three (G1, S, and G2) are collectively known as interphase.

interphase

G1 phase

S phase

G2 Phase

a) The cell doubles in size.b) The enzymes, cytoplasmic

organelles and other molecules double in number.

Replication of DNA occurs.

The cell assembles the special structures needed for cell division

When interphase (G1, S, G2) is complete, the cell

is ready to begin the process of cell division.

“Let’s break

mitosis down

into its

individual

stages and see

what is going

on in each

stage.”

centrioles

nuclear membrane

nucleolus

chromosomes

Nucleus is ___________ and bounded by the ________________.well defined nuclear membrane

Outside of the nucleus are two __________. Their function is to:centrioles

organize the microtubules into a spindle.

They will begin to move apart as spindle microtubules grow out of them.

centrioles

nuclear membrane

nucleolus

chromosomes

G1 phase is a period of intense biochemical activity:

The cell doubles in size and the enzymes, cytoplasmic organelles and other molecules double in number.

The chromosomes have duplicated during the S phase and they appear as a jumbled mass of fibers. They have not yet condensed.

G2 Phase: The cell assembles the special structures needed for cell division

Remember!Interphase includes the

G1 phase, the S phase,

and the G2 phase. It is

the period of time

preceding mitosis.

Mitosis has 4 stages:

1. Prophase

2. Metaphase

3. Anaphase

4. Telophase

Prophase Early prophase

The chromosomes coil and thicken and become distinctfrom one another. The chromosomes are now visible.

The nucleolus __________.disappears

The chromosomes are doubled throughout their length.

Each half of the double chromosome is a __________.chromatid

The chromatids are connected by a ___________.centromere

The __________ separate and start moving to opposite ends of the cell. A ________ made of ____________ begins to form.

centriolesspindle microtubules

Chromatids connected by a centromere.

centrioles

Spindle made of microtubules

Prophase Late prophase

The _________________ fragments and the microtubules invade the nuclear area. The spindle is completely formed.

nuclear membrane

The spindle is a structure that will help to _______________________. During prophase the pairs of __________ become attached to the fibers of the spindle.

separate the chromosomes

chromatidsThe centrioles have moved to the opposite poles, forming the spindle as they go.

centrioles

Microtubulesform a complete spindle.

chromatids

centrioles

MetaphaseThe centrioles are now at opposite sides of the cell.

The spindle fibers will push and pull the chromosomes.

The chromosomes line up at the center of the cell.

Each chromosome is connected to a spindle fiber at its centromere.

centrioles

chromatids

Spindle composed of microtubules

centrioles

Anaphase

The centromeres divide and the chromatids move to opposite sides of the cell.

The microtubules begin to shorten and this pulls the chromatids apart to opposite sides of the cell.

By the end of anaphase, the two ends of the cell have equivalent and complete sets of chromosomes.

Chromatids are being pulled to opposite sides of the cell.

Shortening of the microtubules

Telophase

cleavage furrow

Nuclear membrane is returning.

Nuclear membrane begins to form.

Nucleolus returns.

The cell begins to pinch in. This is called a cleavage furrow.

The end result is two cells that are exact

copies of each other.

Can you name these phases?

1 - Prophase 2 - Metaphase 3 - Anaphase

4 - Telophase 5 - Interphase

metaphase

anaphase

anaphase

Telophase

Prophase

Metaphase

At the end of mitosis, __________ have been formed. Each nucleus has an identical set of _____________.

two nuclei

Cytokinesis is: the division of the cytoplasm.

Cytokinesis usually occurs at the same time as telophase.

chromosomes

In animal cells, a ______________ pinches the cell membrane inward until the cell is pinched into two separate cells. Each new cell contains its own nucleus, cytoplasm, and organelles.

cleavage furrow

In plants, it is __________ for the cell to pinch inward because of the rigid _______.

not possible

In plants, a ________ forms midway between the two nuclei. The cell plate continues to form across the cell until two separate cells have been formed.

cell plate

cell wall

Takes between 30 minutes and 2

hours.

One Mother Cell = Two Daughter

cells.

The two daughter cells are identical

to the mother cell.

M

I

T

O

S

I

S

• In unicellular plants and animals, it results in new offspring by asexual reproduction.

• In multicellular organisms, it results in the growth and repair of the organism.

Results of Mitosis

• The two new cells are exact duplicates.

• Insures that the new cells will be able to carry on the same functions as the mother cell.

Importance of Mitosis

The frequency of cell division varies with the type of cell.

_________ divide frequently throughout our lives.

Skin cells

_________ maintain the ability to divide but only do so on rare occasion - say to repair a wound.

Liver cells

The most specialized cells, such as muscle cells and nerve cells, do not divide at all.

When cells come into contact with other cells, they respond by not growing.

When an injury, like a cut in the skin occurs, the cells at the edge of the injury begin to divide rapidly.

When the healing process nears completion, the rate of cell

division slows down.

There are many proteins found on the inside and the outside

of the cell that regulate cell division.

Some of these proteins are

responsible for starting and stopping

cell division.

Other proteins seem to speed up or slow

down the cell division process.

These proteins send out signals that prevent

excessive cell growth. This keeps the tissues of the body from disrupting

one another.

Cell Cycle Regulators

Uncontrolled Cell Growth

If the cells in a tissue grow uncontrollably,

the consequences may be severe.

Cancer cells do not respond to the signals that regulate the growth of cells.

Cancer cells divide uncontrollably and form masses of cells called tumors.

These tumors can damage the surrounding healthy tissues.

All cancers have one thing in common:

The protein regulators that control the cell cycle have failed to do their job.

Part 2 Meiosis

Slides 35-57

Asexual Reproduction

Each parent passes ALL of

its genes to the offspring.

Offspring are produced by only

one parent.

Sexual reproduction requires two parents. Each parent passes on HALF its genes to its offspring.

Must have male and female: male to produce sperm and female to produce eggs.

Sexual Reproduction involves:Gametes: Sex cells (egg and

sperm)Fertilization: The union of sperm

and egg.Zygote: A fertilized egg.

If an organism is the result of sexual reproduction, it will have ____ sets of chromosomes. two

One set comes from the mother and one set comes from the father.

These two sets are called homologous chromosomes.

Homologous chromosomes are the two copies of each chromosome, one coming from the mother and one coming from the father.

Homologous chromosomes carry the same genes, but they may have different expressions of that gene.

You are a “diploid”organism.

Diploid means that …

…there are two of each kind of chromosome in each cell.

The symbol for diploid is 2N.

“N” is the number of different chromosomes an

organism has. Humans are 2N because we have

2 of each kind of chromosome.

Diploid cells contain two complete sets of chromosomes.

So in mitosis:1 (2N) cell -------> 2 (2N) cells

Human egg cell

Human sperm cells

_____________ cells must have _____ the number of chromosomes so that when added together, the ______ will have the proper number.

Egg and sperm half

zygote

Example: Gametes of the Human Body

Egg (23) + sperm (23) zygote (46)

1N + 1N 2N

Gametes are said to be haploid or

1N because they contain only one

of each kind of chromosome.

The cells which produce eggs and the cells which

produce sperm are diploid or 2N. So how do the egg

and sperm cells get to be 1N?

Meiosis is a process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes.

Phases of Meiosis

Occurs in the sex

cells only: the egg

and sperm.

Purpose is to reduce the

chromosome number of

the egg and sperm by

half.

Meiosis, like mitosis, is

preceded by the replication of

chromosomes. Unlike mitosis, this replication is then followed by two

divisions: meiosis I and meiosis II.

The stages of meiosis I and II

Interphase Prophase I Metaphase I Anaphase I

Telophase I

Prophase II Metaphase II Anaphase II Telophase II

(and cytokinesis)

(and cytokinesis)

The Stages of Meiosis I

Interphase

The chromosomesreplicate. It is similar to chromosome replication of mitosis. Two identical sister chromatids are held together by a centromere.

Prophase I

Chromosomes shorten and thicken. Each chromosome pairs with its corresponding homologous chromosome to form a tetrad. There are 4 chromatids in a tetrad.

Metaphase I

Tetrads line up at the center of the cell.

Anaphase I

The tetrads break apart and the pairs move to opposite sides of the cell. Sister chromatids remain attached at their centromeres.

The Stages of Meiosis II

Telophase I

Prophase II Metaphase II Anaphase II

(and cytokinesis)

The cell separates into two cells.

Telophase II

(and cytokinesis)

Meiosis I results

in 2 haploid (1N)

daughter cells

Each daughter cell has half the number of chromosomes as the original cell.

The pairs of sister chromatids start toward the center.

Pairs of sister chromatids line up at the center.

The pairs of sister chromatids separate and move to opposite sides of the cell.

Results in 4

new cells

that are 1N.

The chromosome number of the egg and sperm is cut in half to insure that the zygote will have the proper number of chromosomes.

1 (2N) cell -------> 4 (1N) cells

The Importance of Meiosis

“Crossing Over” During Meiosis

During ________, each pair of chromatids lines up next to its _________.

prophase I

homologue homologous chromosomes

This pairing of homologous chromosomes produces _______.tetrads

tetrad

A tetrad consists of ___________.4 chromatids

It is possible for the chromatids within a homologous pair to twist around one another. Portions of the chromatids may break off and attach to adjacent chromatids.

This process is called “___________”crossing over

“Crossing over” is the exchange of genetic information (genes) between segments of homologous chromosomes during meiosis.

Crossing over leads to ______________.

The result is that the offspring will receive a new combination of genetic information. This leads to ________ in the offspring.variation

Variation leads to ____________________. These variations will cause some of the offspring to be ___________ for their particular environment. If they are better suited for their environment, it is _________ that they will _______ to reproductive age and pass these favorable variations on to their offspring.

adaptation and changebetter suited

more likely survive

If the result of crossing over causes the offspring to be less suited for its environment, it may not survive. Or, if the offspring does survive, it may not be reproductively competitive. This means that it may not be able to secure a mate. These “unfavorable” genes are not likely to be passed on to the offspring. Evolution!

Meiosis produces four haploid cells that are different.

In males, meiosis results in 4 sperm cells.

In females, 4 cells are produced, but only one will become an eggcell. All of the cytoplasm and all of the organelles are put into one egg cell. The other three cells will never be functional.

Mitosis occurs in all cells of the _____ except _____________.

Meiosis only occurs in the formation of _____________.

body egg and sperm

egg and sperm

In meiosis, each _______ cell divides ______ to produce a total of ___ cells.

In mitosis each _______ cell divides _____ to form ___ cells.

diploid

diploid

twice

once

4

2

In meiosis, each of the four cells contains _____ the number of chromosomes as the parent cell.

In mitosis, each new cell contains the ______ number of chromosomes as the original cell.

half

same

In mitosis, the homologous pairs do not come together to form _______.

In meiosis, the homologous pairs do come together to form _______. While the chromosomes are in tetrads, _____________ may occur. There will be no crossing over in _______.

tetrads

tetradscrossing over

mitosis

In meiosis, the four haploid cells contain ________ combinations of chromosomes from each other.

In mitosis, the new cells contain ________ copies.

different

identical