Honors Biology Study Guide PDF

# Unit 6 Cell Division Notes ## Mitosis: ### Why do cells need to grow and divide? 1. Cells need to stay small so nutrients can be diffused quickly. 2. Living organisms grow by producing more cells through the process of cell division. 3. To replace worn out or damaged cells. 4. A form of asexual...

# Unit 6 Cell Division Notes ## Mitosis: ### Why do cells need to grow and divide? 1. Cells need to stay small so nutrients can be diffused quickly. 2. Living organisms grow by producing more cells through the process of cell division. 3. To replace worn out or damaged cells. 4. A form of asexual reproduction in unicellular organisms. ## Cell Division The process in which a cell divides into two new daughter cells. Before a cell can divide DNA must be replicated so that each new cell has a copy ## Chromosomes DNA is packaged into chromosomes, held together by a centromere. Every somatic cell (body cell) in an organism has the same amount of chromosomes. (Humans = 46 chromosomes) Somatic cells are diploid-have two copies of each chromosome (one from each parent). Chromosomes make it possible to separate DNA during cell division. ## The Cell Cycle As the cells grow and divide, they go through a series of events known as the cell cycle. During the cell cycle, a cell grows, prepares for division, and divides to form two daughter cells. ## Interphase The "inbetween" period of growth. A cell spends most of its time here. Cells grow, DNA replication occurs, perform cell functions. Interphase is broken up into three phases (G1, S, and G2). G1 is the first phase of interphase in which cell growth occurs, proteins are synthesized, and organelles are produced. In the S phase, the DNA is replicated. Finally, in the G2 phase, the cell is preparing for cell division as well as more organelles are produced. After interphase is completed, the cell division (M phase) occurs. ## M Phase The M phase is broken into Mitosis and Cytokinesis. Mitosis consists of Prophase, Metaphase, Anaphase, and Telophase. ### Mitosis Continued The M phase is the shortest phase in the cell cycle. Mitosis is made up of four phases and divides the nucleus. Mitosis is the first phase of cell division. Produces two identical daughter cells that are diploid. Takes place in somatic cells. In prophase, the chromosomes inside the nucleus and the duplicated chromosomes become visible and condense. Outside the nucleus, spindle fibers form from the centrosomes (which contains centrioles). In Metaphase, the centromeres of the chromosomes line up along the metaphase plate. The spindle fibers connect the centromere of each chromosome to the poles of the spindle. In Anaphase, the chromosomes separate and move along spindle fibers to opposite ends of the cell. In Telophase, the chromosomes which were condensed, begin to spread out into a touge of chromatin. The nuclear envelope reforms around each cluster of chromosomes. ## Cytokinesis Completes the process of cell division and forms two identical daughter cells. Cytokinesis is the division of the cytoplasm. In animal cells, a cleavage furrow forms, eventually leading to the cell to be pinched in half. In plant cells, a cell plate forms between the two separate cells, dividing them. ## Differentiation During the development of an organism, cells differentiate into many types of cells. Cells stop dividing to specialize in structure and function, a process called differentiation. Once differentiated, some cells may divide again under certain conditions. The cell cycle contains regulators which determines if cells are ready to pass through. If a cell doesn't pass through the checkpoint it will either undergo apoptosis or be sent back to be more developed. The G1 checkpoint, the regulators check for nutrients, growth factors, and DNA damage. The G2 Checkpoint, the regulators check for cell size and DNA replication. The Metaphase Checkpoint, the regulators check for Chromosome spindle attachment. ## Cell Cycle Regulation Proto-oncogenes code for stimulating proteins such as Cyclins, which increase the cell cycle. Tumor suppressor genes code for inhibitory proteins such as p53, which stop/slow the cell cycle. ### Mitosis continued Mutations to either of these genes can lead to unregulated cell division or cancer. #### Cancer and the Cell Cycle Mutations to some genes cause cell division to be uncontrolled. Uncontrolled cancer growth leads to a tumor = cancer. Cancerous cells do not respond to signals that normally regulate growth. ## Meiosis A form of cell division in the nucleus. Produces gameetes (sex cells) that are haploid. Results in four daughter cells that are genetically different. Takes place in two divisions (Meiosis I and Meiosis II). ### Gametes (Sex cells) The sex cell for males is sperm and the sex cell for women is an egg. Gametes are haploid, meaning they have one copy of each chromosome. Their haploid number of chromosomes in their gamete cells is 23. The fertilization of gametes creates a diploid organism. When an egg and sperm are combined together a zygote is formed. ### Meiosis Before Meiosis occurs, interphase happens in which the 46 chromosomes duplicate creating 46 chromosomes, but now 92 chromatids. In addition, the cell grows, replicates DNA, and does general cell processes. In Prophase I, the chromosomes condense and line up with their homologous pairs. Homologous chromosomes are chromosomes that are similar in size and shape and have the same type of gene in the same location. The chromosomes cross-over and they exchange genetic information. (This produces recombinant chromosomes) In Metaphase I, the chromosomes are ligned up along the metaphase plate in pairs. In Anaphase I, the chromosomes are pulled away from each other by the spindle fibers. In Telophase I, where you have two newly formed nuclei. Meiosis I results in two new cells. Cytokinesis then comes in, separates the cytoplasm and creates two separated cells. Each of these cells contains 23 Chromosomes and 46 Chromatids after Meiosis I. ### Meiosis II In Prophase II, the chromosomes condense and the spindles are beginning to form. In Metaphase II, the chromosomes are lined up on the metaphase plate individually. In Anaphase II, the chromatids are pulled away from each other by the spindle fibers. In Telophase II, the nuclei reforms and you have four newly formed nuclei. In cytokinesis, the two cells are split in half creating four cells. Each of these cells contain 23 chromosomes and 23 chromatids. ## Genetic Variability Every person is genetically different due to three factors; 1. Independent Assortment: random arrangement of homologous chromosomes pair during Metaphase I. 2. Crossing over: pieces of homologous chromosomes swap during prophase (alleles exchange). 3. Random Fertilizations: each fertilization combination of egg and sperm would create different outcomes. (Every gamete is different). ## Comparing Mitosis and Meiosis | | Mitosis | Both | Meiosis | |--------------|----------------|-----------------------------------------|-------------------| | **Occurs in** | All organisms | Plants, animals, and fungi | Plants, animals, and fungi | | **Creates** | All somatic cells | Parent cell and its daughter cells | Only sex cells | | **Involves** | One cell division | Undergo DNA Replication | Two successive cell divisions | | **Produces** | Two diploid daughter cells | Same basic steps | Four haploid daughter cells | | **Daughter cells** | Genetically identical | N/A | Genetically different | | **Creates human cell with** | 46 chromosomes | N/A | 23 chromosomes | **Note:** Pairing occurs in Prophase I and exchange of alleles. **Note:** Interphase doesn't happen after cytokinesis in Meiosis II.