Cell Processes

1. Cellular Transport
   
   1. Osmosis is the diffusion of water across a selectively permeable membrane
      This maintains homeostasis in the cell
   2. Isotonic solution - the concentration of dissolved substances in the solution is the same as the concentration of dissolved substances inside the cell
      
      1. Water does go in and out of the cell, but there is no net change in concentration
         
   3. Hypotonic solution - the concentration of dissolved substances is lower in the solution outside the cell than the concentration inside the cell
      
      1. Therefore, water moves through the plasma membrane into the cell
         o Pressure increases inside against the cell membrane and
   4. Cells in a Hypertonic Solution
      
      1. Hypertonic solution - the concentration of dissolved substances outside the cell is higher than the concentration inside the cell
         o Water moves out of the cell
   5. Passive Transport- The movement of molecules across a membrane by diffusion (no energy required)
      
      1. Facilitated Diffusion is passive transport across the cell membrane using proteins
         - Transport proteins form a channel to alloow specific molecules to flow across
         - Carrier proteins change shape to allow a substance to pass through the plasma membrane
      2. Active Transport- The movement of materials through a membrane against a concentration gradient
         
         1. Requires energy
            Carrier proteins have a specific shape to allow them to bind with specific molecules
            Then then change shape (with energy) so molecule can be transported across
            Carrier protein resumes original shape
   6. Transport of Large Molecules
      
      1. Endocytosis - process by which a cell surrounds and takes in material from its environment
         - Membrane forms around material and engulffs it
      2. Exocytosis - the expulsion of materials from a cell (wastes, hormones)
         - Membrane surrounds material and takes it to membrane, opens up.
2. Cell Size Limitations
   
   1. Diffusion works slowly over large distances
      
   2. DNA can only work so fast
      
   3. Surface to volume ratio - As size increases, the volume increases faster than the surface area
      - Cell membrane would back up with all the nutrients coming into and out of a large cell
3. Cell Division is the process by which new cells are produced from one cell
   
   1. Chromosomes
      
      1. When not dividing, chromosomes exist as chromatin - long strands of DNA wrapped around proteins called histones (groups of histones are called nucleosomes)
         - Upon division, they condense and organizee into chromosomes
4. The Cell Cycle is the sequence of growth and division of a cell
   
   1. The majority of a cell's life is spent in a period of growth and normal function called interphase
      
   2. Following interphase, a cell enters its period of division, called mitosis
      
   3. Mitosis is the process by which two daughter cells are formed, each containing a complete set of chromosomes
      
   4. Following mitosis, is cytokinesis, where the cytoplasm divides, separating the two daughter cells
      
5. MItosis
   
   1. Prophase - 1st and longest phase
      
      1. Chromatin condenses into chromosomes
         Each duplicated chromosome has two halves, called sister chromatids
         The nucleus begins to disappear
         The nucleolus and nuclear envelope disintegrate
         Centrioles migrate to opposite corners
         Centrioles are small, dark, cylindrical structures made of microtubules that play a role in chromatid separation
         We're still on Prophase
         The spindle starts to form between the centrioles
   2. - Metaphase - Shortest phase
      
      1. The doubled chromosomes (sister chromatids) become attached to the spindle fibers by their centromeres
         
   3. Anaphase -
      
      1. The spindles pull the sister chromatids apart
         
   4. Telophse
      
      1. Begins as the chromatids reach the opposite poles of cell
         
6. Cytokinesis
   
   1. In plants, a cell plate is laid down across the cell equator
      
7. Levels of Organization
   
   1. Cell
      
   2. Tissue
      
   3. Organ
      
   4. Organ System
      
   5. Organism
      
8. Control of the Cell Cycle
   
   1. Normal Control of the Cell Cycle
      
      1. Proteins called cyclins and a set of enzymes that attach to the cyclin control the cell cycle. Research points to the portion of interphase just before DNA replication as a key "control period" in the cell cycle
         
   2. Cancer is a malignant growth resulting from uncontrolled cell division
      
      1. Or a failure during programmed cell death
         
      2. This failure to control cell growth may result from not producing enzymes, overproducing enzymes, or producing the wrong enzymes at the wrong times.
         
      3. Currently, scientists think cancer starts because of changes in one or more of the genes that produce substances to control the cell cycle
         
   3. Cancer Prevention
      
      1. Diets low in fat and high in fiber can reduce the risk of cancer
         
      2. Vitamins and minerals may also help prevent cancer
         
      3. Exercise, not smoking and other healthy habits are known to reduce the risk also
         
9. Haploid and Diploid Cells
   
   1. Haploid Cells
      
      1. Organisms produce gametes that contain one of each kind of chromosome
         
         1. Called haploid, and has a haploid, or n, number of chromosomes
            
   2. Diploid Cells
      
      1. In animals and most plants, chromosomes occur in pairs - one from each parent
         
      2. A cell with two of each kind of chromosome is called a diploid cell and contains a diploid, or 2n, number of chromosomes
         
   3. Homologous Chromosomes
      
      1. The two chromosomes of each pair in a diploid cell are called homologous chromosomes
         
      2. The chromosomes contain the same genes in the same order, but might not be identical (unless parents genotypes are identical
         
10. Meiosis
    
    1. Meiosis consists of two seperate divisions - Meiosis I and Meiosis II
       
       1. By the end of meiosis II, there are four haploid cells called sex cells or gametes
          
       2. Fertilization is when sperm and egg unite - produces a zygote (fertilized cell)
          
          1. Fusion of haploid sex cells is called sexual reproduction
             
    2. Phases of Meiosis
       
       1. Other than what happens to the chromosomes, everything else in meiosis is essentially the same as in mitosis
          
       2. Prophase I - Chromosomes coil, spindle forms, etc.
          
          1. Homologous chromosomes line up with other to form a four-part structure called a tetrad
             
             1. A tetrad is two homologous chromosomes (one from mom, one from dad), each made of two sister chromatids
                
             2. The chromatids are paired so tightly that chromosomes can actually break and exchange genetic material. Process called crossing over
                
             3. Crossing over results in the new combinations of alleles resulting in different people
                
       3. Metaphase I
          
          1. Centromeres become attached to spindle fiber
             
          2. Tetrads pulled to equator of cell
             
       4. Anaphase I
          
          1. Homologous chromosomes, each with its two chromatids, separate and move to opposite ends of the cell
             
          2. Errors happen here often
             
       5. Telophase
          
          1. Splndle broken down, chromosomes uncoil, cytoplasm divides
             
             1. Each cell is not haploid (but duplicated)
                
       6. Meiosis II
          
          1. Some rest between stages
             
          2. Others go from Anaphase I straight to metaphase of meiosis II
             
          3. PMAT proceeds much like mitosis
             
          4. End up with one copy of each chromosome