Mitosis

Cell division

Agenda

Cell cycle Mitosis Overview When things go wrong

The Expectations

2.5.1 Outline the stages in the cell cycle, including interphase (G1, S, G2), mitosis and cytokinesis

The Cell Cycle…

• • Cells have a life cycle, called the cell cycle The cell cycle consists of 3 stages: – Interphase (growth and replication) – Mitosis (Nuclear(DNA) division) – Cytokinesis (cytoplasm division)

The Cell Cycle

M G 1 Phase of rapid cell growth Synthesis of DNA for Duplication of chromosomes S Growth and preparation for cell division G 2

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. This is doubled to 92 strands (still considered 46 chrom) during the S stage of interphase.

Mitosis and Cytokinesis

• Mitosis(M phase) –refers to the process of nuclear division. Results in two identical nuclei.

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

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 Basics: Genetic Material

DNA

• • • •

Deoxyribonucleic Acid (DNA): Double helix strand containing genetic code that acts as instructions for the cell Chromatin structurally loose DNA in the cell during interphase.

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

Histone: Proteins that DNA wraps around to become condensed chromosomes

Chromosomes

Chromosome: a long piece of supercoiled 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

one chromosome (unduplicated) one chromosome (duplicated) Centromere Sister Chromatids

Mitosis Structures

• • •

Centromeres: A centromere is a region on a

chromosome that joins two sister chromatids .

Centrioles: a cylindrical cell structure

composed mainly of a protein called tubulin. Produce spindle fibres.

Mitotic spindle: microtubule-based bipolar

strands that segregate the chromosomes in mitosis

Cyclins

• • Cyclins are involved in the control of the cell cycle Cyclins bind to enzymes called cyclin dependent kinases. These kinases become active and attach phosphate groups to the proteins in the cell. The attachment then triggers other proteins to become active and carry out their various functions.

• • • •

Cyclin D triggers cells to move from G phase to S phase Cyclin E prepares the cell for DNA replication in S phase Cyclin A activates DNA replication inside the nucleus Cyclin B promotes the assembly of the mitotic spindle

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.

Mitotic Index

• Mitotic index= number of cells in mitosis total number of cells Useful prognostic tool for predicting response of cancer cells to chemotherapy

The Expectations

Describe the events that occur in the four phases of mitosis -PMAT-

Prophase

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

* Centrioles move

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

present

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

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

Metaphase

*Each chromosome becomes completely condensed. The chromosomes line up at the centre of the cell. Line up at the

metaphase plate

*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 becomes 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

Metaphase Anaphase Late Prophase Early Prophase

Chromosomes continue to condense.

and spindle The chromosomes condense, completely dissolves.

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

becoming shorter and thicker.

The centrioles move to opposite nuclear membrane fibres start to form.

Interphase

DNA replicated and cell prepares for division. In humans, 46 chromosomes

Interphase

nuclear membrane forms around the chromosomes. In humans, each new nucleus contains 46 unique chromosomes http://www.youtube.com/watch?v=AhgRhXl7 w_g

Telophase

Mitosis Summary

Two divisions occur during cell division

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

During interphase genetic material is replicated 2 Identical daughter cells produced

Embryonic growth is a result of repeated mitotic divisions • A zygote is one cell after fertilization. As divisions occur, specialization

occurs.

Cancer

• • • There is a strong correlation between smoking and cancer Women smokers are 25.7 times more likely than women who never smoked to develop lung cancer. For men smokers, it’s 25 times the risk of men who never smoked. (Source: US Surgeon General Report 2014) Besides lung cancer, tobacco use also increases the risk for cancers of the mouth, lips, nose and sinuses, larynx (voice box), pharynx (throat), esophagus (swallowing tube), stomach, pancreas, kidney, bladder, uterus, cervix, colon/rectum, ovary (mucinous), and acute myeloid leukemia. (Source: Cancer Facts & Figures 2014)

Cancer

• • • • Mitosis and cell division are under strict control. Only producing cells when needed for growth and repair Mutagens, oncogenes and metastasis are involved in the development of primary and secondary tumors Tumour repressive genes- inhibit cell division Prot-oncogenes- stimulate growth/division

Cancer

• •

Cancer: Disorder in which some of the body's

cells lose the ability to control their growth.

Tumour -

cancer.

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 –

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

Make exact copies of themselves during mitosis

Normal Cells

Make exact copies of themselves during mitosis Do not stop reproducing Behave independently Metstacize, no controlled death Reproduce 50-60 cells Work dependently/stick together Self destruct “apoptosis” when old

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

Any Questions?