L01 Mitosis, DNA & Chromosomes.pdf

Mitosis Section 4.2 Why do we do mitosis? Essential for growth and repair Occurs in all somatic (body) cells Results in the production of two daughter cells that are genetically identical.  se ha op Pr Cell Cycle...

Mitosis Section 4.2 Why do we do mitosis? Essential for growth and repair Occurs in all somatic (body) cells Results in the production of two daughter cells that are genetically identical.  se ha op Pr Cell Cycle ase aph Met Anaphase Telo p h ase Key Stages of Interphase (G1, S, G2) Interphase (G1, S, G2) Longest stage of the cell cycle Preparation for cell division Cells grows in size and duplicates organelles Genetic material (DNA) is duplicated so that there are 2 identical copies → formation of the “doubled chromosome” in the shape of an X Mitosis (M) Process of dividing the content of the nucleus (genetic information) Involves 4 stages Prophase Metaphase Anaphase Telophase Prophase Chromosomes visible The nuclear membrane is dissolved, releasing the chromosomes into the cytoplasm Nuclear Membrane Metaphase Chromosomes align in the middle of the cell Replicated chromosomes are held together in the middle by a centromere Each copy of a chromosome is called a chromatid Remember…. Meta = Middle This is 1 chromosome, but 2 chromatid (since the chromosome has been copied)  Anaphase Spindle Fibres begin to pull the chromatids to opposite ends of the cell which gives each new cell a copy of every chromosome. Remember…. Ana = Apart Telophase Chromosomes reach the opposite ends of the cell New nuclear membranes begin to form at each end of the cell around the chromosomes The cell has NOT yet split Mitosis Video Recap: Cytokinesis The final stage of the cell cycle The remaining contents (organelles, cytoplasm etc.) are split This step is sometimes called “cytoplasm splitting” By the end of this stage, 2 identical cells will have been produced.  Animal Cell Plant Cell Centrosomes (pair of centrioles) help No Centrosomes, but contain a different organize spindle fibers structure for organizing spindle fibers Microfilaments align in middle to help Carbohydrate Vesicles align in middle to form cleavage furrow help form cell plate. Cleavage furrow form is formed Cell Plate is formed between cells Cells completely separate to form two A new cell wall is formed between the two separate cells cells Occurs in tissues throughout the body Occurs only in meristem (cell division) zone of plant.  Prokaryotic Cells Eukaryotic Cells (single cellular organisms such as bacteria) (animal & plant cells) No Nucleus Nucleus No membrane enclosed organelles Membrane enclosed organelles Divide without mitosis Cell Division by Mitosis Messy single stranded DNA Double stranded DNA No Histone Proteins bound to histone proteins DNA & Chromosomes What is DNA? (deoxyribonucleic acid) A biological molecule Made up of repeated units called “nucleotides” (or base pairs) The specific sequence of nucleotides is what determine the genetic code DNA is double stranded and forms a double helix structure Background of DNA….. Each cell contains 3 meters of DNA! Our cells package this into a nucleus that is only 10–15 m 0.0000000000000001 m Purpose of Chromosomes Chromosomes allow cells to organize all of their DNA (genome) so that it can fit inside the nucleus. Keeping the DNA organized in chromosomes ensures that each new cell will receive the correct amount of DNA during mitosis Chromosomes Human cells have 46 chromosomes (23 pairs) All 23 chromosome pairs must be duplicated during interphase of mitosis. Once a chromosome is duplicated it is held together by a centromere. More on this to come later! 22 pairs of autosomal chromosomes Each pair is identical in size, shape & gene sequence 1 pair of sex chromosomes (XX female, XY Male)  (a section of DNA) How are chromosomes formed? (double helix) (long string of nucleosomes that condense into a chromosome) Nucleosome (histone protein with DNA wrapped around it) Another representation of how chromosomes are formed…  Genes A segment of DNA is called a gene These are units of information about heritable traits Each chromosome contains MANY Drosophila (fruit fly) different genes Alleles These are the two different Genes exit in many alleles for the same gene different versions called alleles. We inherit two alleles for every gene - one from the egg and one from the sperm. The combination of alleles we inherit determines the trait we express. One of these chromosomes came from the egg and the other from the sperm Chromosomes Homologous chromosomes - they have the same size,shape and genes (BUT the alleles might be different). 1 from egg, 1 from sperm) (occurs during which interphase)