Mitosis Cell division

AgendaCell cycle

Mitosis Overview

When things go wrong

The Basics: Genetic Material

Chromatin in the cell during interphase is structurally loose

DNA

• Chromosome: DNA and associated proteins (nucleosomes/histones) that help condense chromosome into a smaller area during mitosis.

Chromosomes

one chromosome(unduplicated)

one chromosome(duplicated)

Centromere

Sister Chromatids

Chromosome: a long piece of coiled DNA and proteins. The number of chromosome in each organism differs. 46 in humans. Seen only when the cell divides.Sister chromatids: 2 identical copies of the same chromosome

Cell theory

• All living things are made of cells• Cells are the basic unit of life• All cells come from pre-existing cells– Cell division is how life is perpetuated– Humans start out a s a single cell

Why Divide?

It is because the Surface area of a cell to its cytoplasm volume ratio affects the exchange of

materials and wastes through the cell.

Why do cells divide?

1. If cells got too large, they would not be able to carry out their functions to survive

2. Growth: allow organisms to grow from a single cell to a multi-celled organism

3. Maintenance: allows new cells to replace worn-out or dead cells

4. Repair: regenerates damaged tissues

The Cell Cycle…

• Cells have a life cycle, called the cell cycle• The sequence of events from one division to

the next.• Cell division is a very small part of a cells life.• The cell cycle consists of 3 stages:– Interphase (growth and replication)– Mitosis (Nuclear(DNA) division)– Cytokinesis (cytoplasm division)

Stages of Cell Cycle

• Mitosis(M phase) –refers to the process of nuclear division

• Cytokinesis (C phase)- occurs after mitosis and is the actual physical division of the cell. Not included in mitosis

• Interphase: (G1, S, G2)

The Cell Cycle

Phase of rapid cell growth

Synthesis of DNA for Duplication of chromosomes

Growth and preparation for

cell division

G1

S

G2

M

Interphase

• Most of the time of a cell’s life• The stage between mitotic divisions• Made of G1, S and G2 phase• The cell grows takes in nutrients and produce proteins

which are used for energy, growth and repair• After a period of rapid growth (G1), the cell prepares

for division by duplicating its chromosomes within the nucleus (S phase)

• After duplication there is another growth period. The cell ensures there is enough of everything for the division.

Interphase

• 1. Stage G1: primary growth phase. Increase in proteins and in the number of cell organelles.

• 2. Stage S: indicates the synthesis of DNA. A.k.a- DNA replication

• 3. Stage G2: Chromosome condensation, preparation for mitosis.

• Longest stage of cell cycle (The part where it does not divide). (G1, S, G2). Human cells contain 46 chromosomes during the G1 stage of interphase.

The Expectations

Describe the events that occur in the four phases of mitosis

-PMAT-

Prophase

* Sister chromatids present

* Centrioles move to poles

* During late prophase the nuclear envelope breaks down and each chromosome is connected to a spindle fibre by its centromere

*chromatin condenses into chromosomes that contains 2 sister chromatids attached by a centromere

*the nuclear envelope and nucleolus disintegrate

*Mitotic spindle forms from microtubules*the pair of sister chromatids attach to the spindle at their centromeres.

*in animal cells, a pair of centrioles move to each end, called the poles

Metaphase

*Each chromosome becomes completely condensed. The chromosomes line up at the centre of the cell. Line up at the equitorial plate (equator)

*The mitotic spindle (made of tubes) is complete and extend from each pole (centrioles) to the middle of the cell.

Anaphase

• The sister chromatids separate at the centromere. Each is now called a chromosome. The separated chromosome are pulled to opposite poles by the spindle fibres

Telophase

• Chromosomes have arrived at the poles• Spindle disappears• Centrioles replicate (in animals)• Nuclear membrane reappears• Nucleolus beocmes visible• Chromosomes become chromatin

Cytokinesis

• The cell divides the cytoplasm and organelles into two portions (splitting known as cytokinesis)

• The cell membrane cleaves inward and in plant cells a cell plate forms, nuclear membrane reforms and spindle disappears

• 2 identical daughter cells result

Mitosis is an Animal cell

Interphase

Early Prophase

Late ProphaseMetaphase Anaphase

Telophase

Interphase

The chromosomes condense,becoming shorter and thicker.The centrioles move to oppositepoles of the cell and spindlefibres start to form.

Chromosomes continue to condense.The centrioles assemble and spindlefibres attach to the centromeres ofthe chromosomes. The nuclear membranestarts to dissolve.

Chromosomes line upat the equatorial plate.The nuclear membranecompletely dissolves.

The centromeres divide and the resulting chromosomes, move to opposite poles of the cell. An identical set (homologues) of chromosomes moves to each pole.

TelophaseChromosomes lengthen again, the spindle fibres dissolve, and a nuclear membrane forms around the chromosomes. In humans, each new nucleus contains 46 unique chromosomes

DNA replicated and cell prepares for division. In humans, 46 chromosomes are duplicated (46 pairs).

http://www.youtube.com/watch?v=AhgRhXl7w_g

Difference between Plant and Animal Cell Division

Differences in Cell Division Between Animal Cells & Plant Cells

Animal Cells Plant Cells

Late in anaphase, the plasma membrane pulls inward forming a cleavage furrow, which divides the cell in two during telophase.

After anaphase, a new cell wall forms between the two new nuclei to create two cells.

A centriole is found at each pole during mitosis. No centrioles are found in plant cells.

Uses of Mitosis in Eukaryotic Cells: a. during growth of the individual.b. when tissues have been damaged and need to be repaired (as in healing of a cut).c. to reproduce asexually.

Mitosis Summary

Two divisions occur during cell division

• Nuclear division (mitosis) and cytoplasmic division (cytokinesis)

During interphase genetic material is replicated

During G1 there are 46 single stranded chromosomes and then after the S phase there are 46 double stranded chromosomes

2 Identical daughter cells produced

Both daughter cells are diploid 2n=46

Embryonic growth is a result of repeated mitotic divisions

• A zygote is one cell after fertilization. As divisions occur, specialization occurs.

Cell Death

• Apoptosis: regulated or controlled cell death of cells that are no longer useful. This is also used to control cells that have stopped performing properly– E.g your body must produces cells to fight a viral

infection. When the infection is gone the cells are removed by apoptosis

Cancer

• Cancer: Disorder in which some of the body's cells lose the ability to control their growth.

• Tumour - repeated, uncontrolled cell division to form a mass of cells. This can happen in any organ. Some tumours grow large and spread to other parts of the body (metastasis). The diseases caused by the growth of tumours is known as cancer.– Tumours can be benign (harmless) or malignant

(spread)

Causes

• Carcinogens (increase chances of mutation leading to cancer)– Radiation (gamma, UV, x-ray etc.)– Chemicals (textile dyes, paints and inks) – Viruses (hepititis B and C and HPV)

Removal

• Surgical- – physically excise the tumour cells

• Radiation- – using strong ionising or nuclear radiation beam

which can be directed to a point and burn the cells • Chemotherapy-– Uses chemicals to destroy all rapidly dividing cells

by medication. Can destroy other rapidly dividing cells (hair, stomach/intestinal cells, sperm)

Cancer vs. Normal cells

Cancer cells Normal CellsMake exact copies of themselves during mitosis

Make exact copies of themselves during mitosis

Do not stop reproducing Reproduce 50-60 cellsBehave independently Work dependently/stick

togetherMetstacize, no controlled death

Self destruct “apoptosis” when old

Any Questions?