CELL DIVISION Mitosis Complete Notes

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CELL DIVISION:

MITOSIS

Unit 9

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MITOSIS is

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What is Mitosis?

• _{Cells divide to make more cells. While all the}

other organelles can be randomly separated into

the daughter cells, the chromosomes must be

precisely divided so that each daughter cell gets

exactly the same DNA.

• _{Mitosis is normal cell division, which goes on}

throughout life in all parts of the body.

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Genes and Proteins

• Proteins do the work of the cell: growth,

maintenance, response to the

environment, reproduction, etc.

• Proteins are chains of amino acids. The

sequence of amino acids in each protein is

coded in the DNA as a specific sequence

of A, C, G and T bases: a gene.

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Key Points about genes

• _{All cells within an organism have the same genes.} • _{What makes cells different from each other is that}

different genes are turned on and turned off in different cells.

• _{The DNA must be copied and then divided exactly so}

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All the cell’s

DNA is found in

the

cell

nucleus

in

structures called

chromosomes

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Chromosomes

• _{Humans have 46 chromosomes, 23 from}

each parent.

• _{Every cell has the same 46 chromosomes}

• _{Each species has a characteristic number}

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Mitosis

When cells

divide, the

chromosomes

appear, divide

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What is a chromosome?

• _{The essential part of a chromosome is a}

single very long strand of DNA. This DNA contains all the genetic information for

creating and running the organism.

• _{The DNA is supported and neatly}

packaged by proteins bound to it. At

different times, these proteins cause the DNA to be spread out like spaghetti in a bowl, or tightly condensed into the

X-shaped chromosomes we can see in a microscope.

• _{Each chromosome has a central}

constricted region called a centromere

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Mitosis

Two new cells

form with

identical

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And more on chromosomes!

• _{Chromosomes exist in 2}

different states, before and after they replicate their DNA.

• _{Before replication,}

chromosomes have one chromatid.

• _{After replication,}

chromosomes have 2 sister chromatids, held together at the

centromere.

• _{Each chromatid is one}

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What happens during mitosis

to a chromosome?

• _{In mitosis, the two chromatids of each}

chromosome separate, with each

chromatid going into a daughter cell.

• _{Remember that diploid cells have two}

copies of each chromosome, one from

each parent.

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Here are the main cell parts

involved in mitosis

-Centrioles

Cell Membrane

Nucleolus

Nuclear

Envelope

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Looking at what

happens to the

chromosomes when

the cell divides by

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MITOSIS can be divided into

FIVE different stages:

• Interphase

• Prophase

• Metaphase

• Anaphase

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• Interphase

• Prophase

• Metaphase

• Anaphase

• Telophase

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The cycle of the cell

• _{Some cells divide constantly:}

cells in the embryo, skin cells, gut lining cells, etc. Other cells divide rarely or never: only to replace themselves.

• _{Actively dividing cells go through}

a cycle of events that results in mitosis. Most of the cycle was called “interphase” by the

scientists who first studied cell division. During interphase the cell increases in size, but the chromosomes are invisible.

• _{The 3 stages of interphase are}

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What are the 3 stages of

interphase?

• _{The S phase (“Synthesis”) is the time when the DNA is}

replicated, when the chromosome goes from having one chromatid to having 2 chromatids held together at the centromere.

• _{G1 (“Gap”) is the period between mitosis and S, when}

each chromosome has 1 chromatid. Cells spend most of their time in G1: it is the time when the cell grows and

performs its normal function. Control of cell division occurs in G1: a cell that isn’t destined to divide stays in G1, while a cell that is to divide enters the S phase.

• _{G2 is the period between S and mitosis. The}

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Interphase

This is the

phase in

between the cell

dividing. DNA

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Prophase

In prophase, the cell begins the process of division.

1. The chromosomes condense. The proteins attached to the DNA cause the chromosomes to go from long thin

structures to short fat one, which makes them easier to pull apart.

2. The nuclear envelope disappears. The double

membrane that surround the nucleus dissolves into a collection of small vesicles, freeing the chromosomes to use the whole cell for division

3. The centrosomes move to opposite poles. During interphase, the pair of centrosomes were together just

outside the nucleus. In prophase they separate and move to opposite ends of the cell.

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Metaphase

• _{Metaphase is a short resting period where}

the chromosomes are lined up on the

equator of the cell, with the centrosomes

at opposite ends and the spindle fibers

attached to the centromeres.

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Metaphase

Chromosomes

line up

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Anaphase

• _{In anaphase, the centromeres divide.}

• _{At this point, each individual chromosome goes}

from 1 chromosome with 2 chromatids to 2

chromosomes with one chromatid each.

• _{Then the spindle fibers contract, and the}

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Anaphase

Double

stranded

Chromosomes

split to form

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Anaphase

Single

stranded

chromosomes

move to

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Telophase

• _{In telophase the cell actually divides.}

• The chromosomes are at the poles of the

spindle.

• _{The spindle disintegrates}

• The nuclear envelope re-forms around the

two sets of chromosomes.

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MITOSIS

Original Cell

Divides to form

TWO new cells

with the SAME

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Summary of Mitosis

• _Prophase:

• _{Chromosomes condense} • _{Nuclear envelope disappears}

• _{centrosomes move to opposite sides of the cell} • _{Spindle forms and attaches to centromeres on the}

chromosomes

• _Metaphase

• _{Chromosomes lined up on equator of spindle} • _{centrosomes at opposite ends of cell}

• _Anaphase

• _{Centromeres divide: each 2-chromatid chromosome}

becomes two 1-chromatid chromosomes

• _{Chromosomes pulled to opposite poles by the spindle} • _Telophase

• _{Chromosomes de-condense} • _{Nuclear envelope reappears}

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