- Slides: 33
Mitosis Cell division
Cell division All complex organisms originated from a single fertilized egg (egg + sperm). Every cell in your body came from the first original cell created by your parents; through cell division the numbers were increased. Cells then specialize and change into their various roles as you developed (differentiation).
Why do cells divide? § As the cell grows, its volume increases much more rapidly than the surface area. § The cell might have difficulty supplying nutrients and expelling enough waste products.
REASON 1: Transport of Substances § Substances move by diffusion or by motor proteins. § Diffusion over large distances is slow and inefficient. § Small cells maintain more efficient transport systems.
REASON 2: Cellular Communications § The need for signaling proteins to move throughout the cell also limits cell size. § Cell size affects the ability of the cell to communicate instructions for cellular functions.
REASON 3: Growth and Repair • Mitosis is the process by which new body cells are produced for: – Growth – Replacing damaged or old cells. • This is a complex process requiring different stages.
REASON 4: Reproduction • In order to sexually reproduce, the organism must have a way to reduce the chromosome number in half in sex cells (gametes). • The process that does this is called Meiosis. – Diploid mother cell (2 n) divides to make haploid daughter cells (n).
In humans, the cell division is necessary for A. Making gametes B. Repairing broken bones C. Growing after fertilization D. All of the above
The Stages of the Cell Cycle (division) § The first stage is called Interphase. It consists of three phases. 1. G 1 - The cell is growing and preparing to replicate DNA. 2. S - The cell copies its DNA in preparation for cell division. 3. G 2 - The cell prepares for the division of its nucleus.
Interphase A. Is the same as prophase, metaphase, anaphase and telophase B. Is composed of G 1, S, and G 2 stages C. Requires the presence of spindle fibers D. Is the name of the entire cell cycle
Cell Cycle Regulation Normal Cell Cycle § The cell cycle has built-in checkpoints that monitor the cycle and can stop it if something goes wrong. § Proteins called cyclins along with CDK regulate the cell cycle and stop it if something is wrong (ie. damaged DNA) … most of the time
If a mutation occurs that eliminates the presence of cyclin, A. The cell will continue to divide out of control B. The cell will stop the cycle C. The cell will grow in G 1 until it [Default] bursts [MC Any] [MC All]
Abnormal Cell Cycle: Cancer § Cancer is the uncontrolled growth and division of cells. § Cancer cells can kill an organism by crowding out normal cells, resulting in the loss of tissue function.
When cancer occurs, A. They cell can no longer enter the cell cycle B. Cells cannot pass the G 1 checkpoint C. Control of the cell cycle is lost
Causes of Cancer § The changes that occur in the regulation of cell growth and division of cancer cells are due to mutations. § Various environmental factors can affect the occurrence of cancer cells. § Heredity - oncogenes § Viral infection - oncogenes § Radiation § Chemicals § Carcinogens § Mutagens § Chronic inflammation
Apoptosis § Programmed cell death – the cell’s response to poorly functioning cells or older cells. § Cells going through apoptosis actually shrink and shrivel in a controlled process.
Which of the following would be a characteristic of cancer cells A. They become differentiated/specialized B. They are usually smaller C. They undergo apoptosis
Parent cell Chromosomes are copied and double in number Chromosomes now split 2 daughter cells identical to original
Mitosis • The stage of the cell cycle that actually divides the cell. • All daughter cells contain the same genetic information from the original parent cell. • Every different type cell in your body contains the same genes, but only some are “turned on” to make the cells differentiate/specialize (e. g. into nerve or muscle tissue).
Stages of Mitosis • Prophase: chromosomes condense, nuclear envelope disappears, and the spindle forms • Metaphase: chromosomes are lined up on cell equator, attached to the spindle at the centromeres • Anaphase: centromeres divide & the monad chromosomes (sister chromatids) are pulled to opposite poles by the spindle. • Telophase: chromosomes de-condense, nuclear envelope re-forms, spindle vanishes --cytokinesis: cytoplasm divided into 2 separate cells
Mitosis Visualized • http: //www. youtube. com/watch? v=DD 3 IQk n. CEdc&feature=related
Mitosis – bone cell slides 1 2 Chromosomes copied Parent cell 3 Copies separating Cells split 4 5 2 daughter cells
Plants apical meristem
Rat – epithelial cells
Chromosomes • Key feature of a chromosome: centromere (where spindle attaches) • Chromosomes come in 2 forms, depending on the stage of the cell cycle. The monad form consists of a single chromatid. The dyad form consists of 2 identical chromatids (sister chromatids) attached together at the centromere. • Chromosomes are in the dyad form before mitosis begins, and in the monad form during interphase. • The dyad form is the result of DNA replication: a single piece of DNA (the monad chromosome) replicated to form 2 identical DNA molecules (the 2 chromatids of the dyad chromosome).
More Chromosomes • Diploid organisms have 2 copies of each chromosome, one from each parent. The two members of a pair of chromosomes are called homologues. • Each species has a characteristic number of chromosomes, its haploid number n. Humans have n=23, that is, we have 23 pairs of chromosomes. Drosophila have n=4, 4 pairs of chromosomes.
Meiosis • Purpose – produce gametes (sex cells) for reproduction. • Location – gonads / sex organs only – Meiosis is the special cell division that converts diploid body cells into the haploid gametes. Only occurs in specialized cells. • Takes 2 divisions, Meiosis 1 and M 2 • In humans, cells start with 46 chromosomes (23 pairs) in dyad state. After M 1, there are 2 cells with 23 dyad chromosomes each. After M 2 there are 4 cells with 23 monad chromosomes each.
Genetic Recombination • Purpose: to create chromosomes that are a new combination of paternal and maternal material • Genetic variation is important to the survival of every species.