Mitosis

Recap…

• The cell goes through growth phases.• G1• S• G2• M phase and Cytokinesis

• Let’s talk about the M phase and Cytokinesis

Interphase

• Cell growth occurs in interphase• During that time, DNA is

loosely organized- it looks a bit like spaghetti.

• Remember: DNA is a double-stranded molecule made of four different subunits called nucleotides.

• A chromosome is one long continuous thread of DNA that consists of numerous genes

centrioles

nuclear envelope

chromatin

How does all the DNA fit inside the nucleus of a cell?

• DNA wraps around proteins called histones that help organize and condense it.• This process looks similar to beads on a string.

• Parts of the histones interact with each other, further compacting the DNA. At this stage – the “spaghetti” stage – the combination of DNA and proteins is called Chromatin.

• Recall that a chromosome is a strand of DNA, we have 23

• During the S phase each chromosome is copied, so we end up with 46 for the Mitosis phase

Continued….•**DNA during the M-phase**

• As the cell progresses, chromatin further condenses, it coils more and more tightly around organizing proteins, finally forming small thick rods.

• Since the chromosome has already been copied during the S phase, the chromosome looks similar to an “X” in which the left and

right halves are two identical DNA double helixes

Continued……• One half of a duplicated chromosome is called a

chromatid.• Together, two identical chromatids are called

sister chromatids.• Sister chromatids are held together at the

centromere, a region of condensed chromosome that looks pinched.

• Lastly, at the ends of DNA molecules form structures called telomeres, which are made of repeating nucleotides that do not form genes.• This prevents the ends of chromosomes from

accidentally attaching to each other or the loss of genes.

Chromosomes

• The cells of every organism have a certain number of chromosomes:•Fruit flies: 8•Humans: 46•Carrots: 18

Cell Division

• Once the cell is completely prepped for division, it enters the M phase.

• The M Phase is divided into 2 major stages:•Mitosis•Cytokinesis

Mitosis

• Biologists have further divided mitosis into four phases known as PMAT:•Prophase•Metaphase•Anaphase•Telophase

Prophase• The nucleolus and nuclear membrane “break up” and temporarily disappear.• Chromatin (spaghetti) condenses into

tightly coiled chromosomes, each consists of two identical sister chromatids

• Centrosomes and Centrioles migrate to opposite sides of the cell

• Organized microtubules called spindle fibers grow from the centrioles and radiate toward the center of the cell.

spindle

chromosomes

Prophase

Metaphase• Only a few minutes long.• Spindle fibers attach to the

centromere and align the chromosomes (sister chromatids)

along the cell equator

Metaphase

Anaphase• Sister chromatids separate from each

other.• The spindle fibers begin to shorten,

which pulls sister chromatids away from each other and toward opposite sides of the cell.

Anaphase

Telophase• A complete set of identical chromosomes

are positioned at each pole of the cell.• The nuclear envelope reforms around the

chromosomes• Chromosomes begin to uncoil back to

chromatin and the spindle fibers fall apart

Telophase

Cytokinesis• This phase divides the cytoplasm into two cells

and completes a full stage of the cell cycle.• Each cell is identical to each other

Cytokinesis• In animal cells, the cell membrane is

pinched inward until the cytoplasm is separated into nearly equal halves.• The pinching creates a furrow or

trench.• In plants, a cell plate is formed in the

center of the cell and grows outward to separate the two cells.• A cell wall will eventually form on

each side of the cell plate.

Cytokinesis

Review – The Whole Process

Major Function of Mitosis

• In unicellular organisms, mitosis is asexual reproduction. A new organism is created.

• In multicellular organisms, mitosis increases the number of cells to help the organism grow and/or replace dying cells.

Cell Cycle

is divided into

includes

is divided into

G1 phase S phase ProphaseG2 phase Metaphase TelophaseAnaphase

M phase (Mitosis)Interphase

Why do cells divide rather than continuing to grow indefinitely?

-The larger the cell becomes, the more demands it places on the DNA-The cell has trouble moving enough nutrients and wastes across the cell membrane

What are the three limits to cell growth?

1. Diffusion

2. DNA

3. Surface area to volume ratio

What is cell division? The process by which 2 new cells are produced from one cell.

What are the 4 phases of the cell

cycle?

1. G1 Phase

2. S Phase

3. G2 Phase

4. M Phase

What happens during the G1 Phase?

Cell Growth – the cell increases in size and synthesizes new proteins and organelles.

What happens during the S Phase?

DNA Replication – a new set of DNA is created from the original and proteins associated with DNA are synthesized.

What happens during the G2 phase?

Prep for Mitosis – Organelles and molecules required for cell division are produced.

What happens during the M phase?

Mitosis and Cytokinesis

- Cell division occurs

In what form does genetic information take

in eukaryotes?

DNA –

deoxyribonucleic acid

During what phase does cell growth occur?

Interphase

What is chromatin? The granular material made up of DNA bound to protein.

What are the three parts of Interphase?

G1, S, and G2 phases

What are sister chromatids?

The original chromosome joining with the copied

chromosome.

How are the two sides of the chromatids joined

together?

centromere

What are the two parts of the M Phase?

Mitosis and Cytokinesis

What are the four phases of Mitosis?

- Prophase- Metaphase- Anaphase- Telophase

What happens during Prophase?

-The nucleolus and nuclear membrane “break up” and temporarily disappear.

- Centrioles duplicate and separate to opposite sides of the cell.

-The mitotic spindle begin to form near

the centrioles.

What happens during Metaphase?

-The chromosomes line up across the center of the cell on an imaginary line called the metaphase plate.

- Microtubules attach to the centromere of each chromosome from both poles of the spindle.

How are plants cells different in prophase?

Plant cells do not have centrioles but still form a spindle to organize cell division.

What happens during Anaphase?

-The centromeres are broken and the sister chromatids separate.

- Each sister chromatid is now called a chromosome. - The chromosomes continue to move until they have separated into two groups near the poles of the spindle.

What happens during Telophase?

-Chromosomes begin to unwind back to chromatin. -The nuclear envelope reforms around the chromosomes.- a nucleolus becomes visible in each daughter nucleus-The spindle breaks apart.

What happens during cytokinesis for animal

cells?

- The cell membrane is pinched inward until the cytoplasm is separated into nearly equal halves.

What happens during cytokinesis for plant

cells?

- A cell plate is formed in the center of the cell and grows outward to separate the two cells.

What is the major function of mitosis for

unicellular organisms?

- mitosis is asexual reproduction so a new organism is created.

What is the major function of mitosis for

multi-cellular organisms?

Mitosis increases the number of cells to help the organism grow and/or replace dying cells.

What is this

phase and

what is

happening?

Interphase - G1, S, G2, Cell growth, and replication of DNA and organelles.

What is this

phase and

what is

happening?

Prophase -The nucleolus and nuclear membrane “break up” and temporarily disappear.

- Centrioles duplicate and separate to opposite sides of the cell.

-The mitotic spindle begin to form near the centrioles.

What is this

phase and

what is

happening?

Metaphase-The chromosomes line up across the center of the cell on an imaginary line called the metaphase plate.- Microtubules attach to the centromere of each chromosome from both poles of the spindle.

What is this

phase and

what is

happening?

Anaphase-The centromeres are broken and the sister chromatids separate. - Each sister chromatid is now called a chromosome. - The chromosomes continue to move until they have separated into two groups near the poles of the spindle.

What is this

phase and

what is

happening?

Telophase-Chromosomes begin to unwind back to chromatin. -The nuclear envelope reforms around the chromosomes.- a nucleolus becomes visible in each daughter nucleus-The spindle breaks apart.

What are

stages of the

cell cycle?

1. G1 Phase

2. S Phase

3. G2 Phase

4. M Phase – Prophase, Metaphase, Anaphase, Telophase