The Cell Cycle Cells divide by Mitosis or Meiosis. Mitosis allows the organism to replace cells that have died or aren't working, and is how living things grow. It makes an exact copy of the parent cell. Meiosis makes sex cells (eggs or sperm). These cells are different from the parent cell, and from each other. The Cell Cycle Asexual reproduction is when cells of a single parent divide to form offspring identical to themselves, through mitosis. Amoebas, bacteria, and a few animals (the hydra) reproduce this way. Some plants can reproduce asexually by growing new plants from parts of themselves, like stems or roots. 1
Terms to know... A chromosome is an organized structure of DNA and Protein found in cells that contain your genes A gene is a tiny part of a chromosome that helps give a living thing a certain trait or characteristic. Genes tell cells how to grow and develop, and are made of DNA. DNA, or deoxyribonucleic acid, is the "code" that makes up your genes. DNA "codes" for amino acids, which link together to make proteins. The Cell Cycle Mitosis Phases Overview Interphase (beginning stage) Prophase (1st main stage) Metaphase (2nd main stage) Anaphase (3rd main stage) Telophase (4th main stage) Cytokinesis These 4 stages actually make up Mitosis 2
Mitosis: 1) Interphase Interphase is when the cell is actually doing its job. (The cell spends most of its "life" in interphase.) Before cell division starts, chromosomes (made of DNA) in the nucleus begin to copy themselves, resulting in 2 chromatids. 2) Mitosis: A) Prophase the chromosomes condense and become visible. Chromatid Chromatid } Chromosome Interphase Prophase Mitosis: 2) Mitosis: B) Metaphase the chromosomes line up along the equator (middle) of the cell. Homologous chromosomes match up. (Homologous chromosomes are pairs of similar chromosomes, and are made of 2 chromatids). C) Anaphase the chromatids separate and move toward opposite sides of the cell. Metaphase Anaphase 3
D) Telophase the chromatids reach opposite sides of the cell, a nuclear membrane begins to form around each set of chromosomes, and the chromosomes begin to unwind. 3) Cytokinesis the cell pinches in to form 2 cells identical to the original cell. Telophase Cytokinesis Cytokinesis, cont. In cells that lack a cell wall (Human), the cell pinches in two. In cells that have a cell wall (Plants), a cell plate forms between the two new cells. Question? Which cell on the right is the animal cell, and which is the plant? 4
**Mitosis creates 2 body cells. Each new cell is identical to, and has the same number of chromosomes as the original cell. A cell can go through Mitosis many times.** Which part of the cell cycle lasts the longest? Why is the cell cycle drawn in a circle? Ways to help you remember the order of steps in Mitosis: IPMAT C Mitosis "live" Meiosis Many multi celled organisms produce offspring through sexual reproduction. During sexual reproduction, gametes (sperm or eggs) from a male and a female parent combine during fertilization. Gametes are different from ordinary cells because they have half the number of chromosomes found in the organism's body cells. If gametes had the same number of chromosomes as body cells, the organism formed from those cells would have twice as many chromosomes as it should. Since gametes only have half, when they combine, the new organism has the correct number of chromosomes. Humans have 46 chromosomes in their body cells, so... If... Then... 46 + 46 = 92 sperm egg new organism WRONG Since... Then... 23 + 23 = 46 sperm egg new organism RIGHT Feb 11 9:17 AM 5
Meiosis: During meiosis, each new cell has half the number of chromosomes as the original cell. The parents DNA also gets recombined randomly, so the offspring are different than the parents, and from each other. Original Cell Crossing over (Prophase) Results: 4 sex cells Stages of Meiosis: Meosis goes through stages like in Mitosis (Interphase, Prophase, Metaphase, Anaphase, etc.) BUT, Meiosis goes through each set of stages twice. **Meiosis creates 4 sex cells (eggs and sperm). Each new cell is different from the original and from each other, because of crossing over. Each new cell also has half the number of chromosomes as the original cell. A cell goes through the two sets of Meiosis stages only once.** Meiosis "live" Mitosis vs. Meiosis 6
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