Cell Division

Cell Continuity Aristotle: Spontaneous Generation Continuity of Life – living things arise from other living things of the same type. (1800s)

Cell Structure Nucleus consists of strands called DNA DNA = Deoxyribonucleic acid DNA arranged in structures called chromosomes

Chromosomes Every organism has a definite number of chromosomes E.g. Humans (46), Worms (2)

Chromosomes Cells NOT dividing – Chromosomes are elongated and interwoven (Chromatin) 2. Cells ARE dividing – chromosomes shortened and distinguishable.

Genes Located randomly along chromosomes. May be thousands on a gene Have the information to make particular proteins. E.g. Protein = Enzyme Units of Inheritance E.g. Eye Colour, skin colour, shape of face etc… All Genes in an organism = genome

Human Genome Project June 2000 – all positions of the genes in human cell found. About 25,000 genes Store Information in a database 13 year project Ongoing work – structures & functions

Reproduction Asexual – bacteria Sexual – plants, humans Organisms that reproduce sexually produce sex cells called gametes.

Gametes Each gamete has a single set of chromosomes…..why? Each normal (somatic) cell has a double set of chromosomes.

Haploid & Diploid Cells Haploid – single set of chromosomes, i.e. one of each type of chromosome Represented by ‘n’ E.g. Eggs & Sperm = 23 chromosomes (n=23)

Haploid & Diploid Cells Diploid – two sets of chromosomes, i.e. two of each type of chromosome Represented by ‘2n’ E.g. somatic cells = 46 chromosomes (n=46)

Cell Cycle

Interphase Cell is not dividing 90% of cycle Chromosomes = chromatin New organelles being developed (mitochondria / chloroplasts) Chromosomes making identical copies of themselves….

Chromosome

Mitosis

Mitosis Produces 2 identical daughter cells Number & Structure of chromosomes identical to parent cell. Uses: Growth and Repair, asexual reproduction

Stages of Mitosis Interphase Prophase Metaphase Anaphase Telophase

Interphase Chromosomes = chromatin New organelles being developed (mitochondria / chloroplasts) Chromosomes making identical copies of themselves….

Prophase (Early) Chromatin shorten and appear as two chromatids, joined by a centromere. Nuclear membrane starts to disappear Centrioles go to opposite sides of cell

Prophase (Late) Nuclear membrane completely gone. Spindle fibres (protein) form out of the centrioles at opposite poles

Metaphase Chromosomes line up along equator of the cell. Attach to spindle fibres

Anaphase Spindle fibres contract. Pull apart chromosomes by centromeres Occurs rapidly Recognised by U and V shapes of chromosomes

Telophase Membranes start to reform Spindle fibre breaks down into cytoplasm Cell begins to split in two….

Telophase – Animal Cells Plasma membrane divides cytoplasm in two - cytokenisis

Telophase – Plants Cell plate divides the cytoplasam in half. Cell wall starts to form on both sides of it.

Interphase Chromosomes return to chromatin Each cell starts to produce new organelles A store of energy is gathered.

Definition and two causes Cancer Definition and two causes

What is Cancer? A large group of almost 100 diseases Two main characteristics: Uncontrolled growth of cells in the body Ability of these cells to migrate to distant sites

What Causes Cancer? A mistake in the genetic code of the cell Causes the cell to grow without control In 90% of cases, the mistake is not inherited. Often caused by exposure to carcinogens.

Carcinogens Factors that cause the DNA inside a cell to alter Mutation of DNA Mutations causes cells to become immortal

Carcinogens Physical – radiation, e.g. X-Rays, Sunlight and asbestos Chemical – Cigarette smoke, Vinyl Chloride Biological – Viral or bacterial, e.g. Hepatitis B.

Meiosis Reduction – Division

Meiosis Produces 4 un-identical daughter cells Number of chromosomes halved Diploid→ Haploid Produces gametes Genetically varied daughter cells Uses: Sexual reproduction, Genetic Variation