AP Biology-UNIT V: CELL REPRODUCTION Study Notes

➢ Cell division

•  Mechanism to replace dying cells
•  Small part of life cycle of a cell
•  Some types of cells are nondividing
  ■ Usually highly specialized cells derived from a less specialized type of cell
  ■ Made as needed, but cannot replicate themselves
  ■ Ex. red blood cells
•  Multicellular organisms depend on cell division for:
  ■ Development from a fertilized cell
  ■ Growth
  ■ Repair

➢ Binary Fission

•  Used by prokaryotes
• Chromosome replicates at origin of replication and the two daughter chromosomes actively move apart
•  Plasma membrane pinches inward, dividing cell into two Mitosis likely evolved from binary fission

■ Certain protists exhibit cell division that seem intermediate between binary fission and mitosis

A. Interphase

➢ Time span from one cell division to another

➢ Cell carries out regular activities

➢ All the proteins/enzymes the cell needs to grow are produced in interphase

➢ 3 Phases:$G_1$, S,$G_2$

•  $G_1$
  ■ Cell produces all enzymes required for replication
  ■ G=”Gap” or “growth”
•  S
  ■ Cell replicates genetic material
  ■ Every chromosome in nucleus is duplicated
  ● Sister chromatids created, held together by centromere
  ■ To be called a chromosome, they each need to have their own centromere; once chromatids separate, they will be “chromosomes”
  

■ To induce cell cycle progression, CDK binds to a regulatory cyclin. Once together, the complex is activate
                  ● Can affect many proteins in cell
                  ● Causes cell cycle to continue
                  ● To inhibit cell cycle progression, CDKs and cyclins are kept separate
                  ● Separated via dephosphorylation
■ MEtaphase Checkpoint
                ● Chromosome spindle attcachment
■ $G_1$ Checkpoint
                ● Check for:

•  Nutrients
•  Growth factors
• DNA damage
     ● Can put cell into $G_0$ is it doesn’t need to divide
  ■ $G_2$ checkpoint
     ● Check for:
•  Cell size
•  DNA replication
• Make sure cell division is happening properly in cells
•  Stops progression if cell is not ready to progress to next stage
•  In eukaryotes, checkpoint pathways mainly function ay phase boundaries
• When DNA damage is detected, cell will not progress until damage is fixed, or apoptosis is started
• Cancer can result from a mutation in a protein that normally controls progression, resulting in unregulated cell division
  ■ Oncogenes are genes that cause cancer
        ● Normally required for proper growth and regulation of he cell cycle
        ● Mutated versions can cause cancer
       ● proto-oncogene=normal, healthy oncogene

■ Tumor suppressor genes
              ● Produce proteins that prevent the conversion of normal cells into cancer cells
              ● Detect damage within cell and work with CDK/cyclin complexes to stop cell growth until damage can be repaired
              ● Can trigger apoptosis is damage is too severe to be repaired
■ In order for a cell to become a cancer cell. It must simultaneously override checkpoints, grow in an unregulated way, and avoid cell death

➢ Stop cell division

•  Density-dependent inhibition
•  Anchorage dependency