Class  Lecture Notes

Objectives:
    1. Define Chromosomes
    2. Describe the structure of the chromosome
    3. Distinguish between diploid and haploid cells
    4. Explain the significance of sex chromosomes
    5. Describe cell reproduction in bacteria and eukaryotes
    6. Summarize the events of mitosis and cytokinesis
    7. Define cell cycle and a cells activity during interphase
    8. Explain how cancer arises
    9. Define gamete, and state its function in sexual reproduction
    10. Explain how meiosis maintains chromosome number throughout generations
    11. Summarize the events of meiosis
    12. Define crossing over and explain its impact on evolution
  1. Chromosomes
    1. Chromosome structure
    1. Chromosomes are strands of DNA tightly wrapped around proteins called histones
    2. DNA in a non dividing cell is long and string like – Chromatin
    3. Typical strnad contains 500 million nucleotides and about 2 inches long
    1. Chromosome number
    1. If the chromosomes were laid out of the cell they could be matched up – Karyotype
    2. There are 23 pairs of chromosomes (46 individual) in a human cell
    3. A diploid cell contains 23 pairs of chromosomes (body cell) 2n
    4. A haploid cell contains 23 individual chromosomes (gamete) (sex cell) n
    5. Sex chromosomes determin male or female gender
    6. If XX is present the individual is female
    7. If XY is present then one is Male
    8. The Presence of a Y allows an individual to develop into the male gender
    9. Y’s are inherited by the father, Xs are inherited from both father and mother
    10. A pre-sex cell has 46 chromosomes, but each parent can only donate 23 to the child
    11. Meiosis allows for a reduction division to take place and the cell will be reduced from 46 chromosomes to 23 chromosomes
  1. Mitosis and Cell Division
    1. Differences in Prokaryotes and Eukaryote division
    1. A cell must divide its genetic information in an orderly way.
    2. A bacteria has a circular strand of DNA that is fairly simple
    3. All it has to do is duplicate the DNA, get a little larger, then divide. This is called fision
    4. Eukaryotic cells must go through a more complicated process called mitosis
    1. How Eukaryotic Nuclei Divide: Mitosis
    1. The division of a nucleus must mean that there must be an exact copy of the information in the nucleus
    2. The first stage of cell division is when the DNA is duplicated. Exactly copied
    3. The cell then has to sort the chromosomes so that none are left out or duplicated in the newly formed cell
    4. Two process have developed to allow the cells to do this efficiently. Mitosis and cytokinesis (cell splitting)
    5. The end result is that the newly formed cells are identicle genetically
    1. The Cell Cycle
    1. The cell cycle has three stages. Interphase, mitosis and cytokinesis
    2. Interphase
    1. there are three phases to interphase, G1, S phase, and G2.
    2. In this phase the cell is growing replicating DNA and preparing for cell division
    3. G1 phase is when the cell will go through intense growth,
    4. S phase occurs as the cell will duplicate the number of chromosomes in its nucleus. The cell after this stage is now diploid and both copies are attached to eachother by a centromere. Each copy is now a chromatid
    5. G2 phase sees the cell growing some more and preparing fof the next stage mitosis (M phase)0
    1. The cell cycle is different for each type of organism.
    2. Cell cycle may take as little as 8 minutes but average around 10-30 hours
    3. Some cells, like our nerve cells, may never replicate once they mature
    4. M Phase
    1. Prophase – Chromatin condense into chromosomes, nuclear membrane breaks down and disappears, spindle apparatus begins to form, centrioles begin migration to the cell poles
    2. Metaphase – Chromosomes line up in the center of the cell, centrioles end their migration
    3. Anaphase – Centromere splits and chromatid pull apart as the spindle fibers shorten
    4. Telophase – chromosomes migrate to opposite ends of the cell, nuclear envelopes form around them, chromosomes decondense

7. Cytokinesis – The cell splits by pinching in two. If plant cell, a cell wall forms between the two nuclei instead of pinching apart.

    1. Controlling the cell cycle
    1. Cancer results if a cell replicates with no controls
    2. DNA makes proteins
    3. Proteins such as S cyclin and M cyclin helps trigger when a cell replicates
    4. If there is a problem with the genes that make the proteins, the cell will not replicate properly.
    5. If a cell divides uncontrollable, it willpass those problem genes down to its daughter cells. Now you have a mass of cells called a tumor that are dividing wrong
    6. Mutation of the genes that control the production of cell cycle regulating proteins is ultimately what causes cancer
    7. These mutations may come from poor genetics, the cell unable to fix its own DNA errors, UV radiation, Chemicals from the environment etc.
  1. How Gametes Form: Meiosis
    1. Making Haploid cells
    2. Importance of Crossing Over

Biology Main Page Chapter 6 main Chromosomes Mitosis Meiosis Vocabulary Notes Review