BISC 130 - Chapter 10: Cell Reproduction

Prokaryotic Genome - Haploid

• Genome - The total genetic information of a cell or organism

• A single DNA macromolecule

• A closed circle

• Eukaryotic Genome

  • Several DNA macromolecules

• Humans have 23 different chromosomes

  • Most of our cells are diploid - a cell, nucleus, or organism containing 2 sets of chromosomes

  • Some cells/organisms are haploid -  a cell, nucleus, or organism containing 1 set of chromosome.

    • Ex: Protists, Mosses

• The DNA double helix is wound around histone proteins to form many nucleosomes, which are collectively called chromatin.

• Chromosomes are linear in Eukaryotic genome.

• Prokaryotic cell division is Binary Fission.

  1. DNA Replication -  The circular chromosome gets replicated so that each of the resulting products have one chromosome each

1. Cell Elongation

   1. FtsZ Protein moves to the center of the cell. (Not the only type of protein)

1. Chromosomes moved to opposite sides of the cell.

   1. FtsZ forms a ring

1. FtsZ directs the formation of septum (a dividing cell wall) in the cell's center.

1. Cell pinches in two, forming two identical daughter cells.

• In Eukaryotes, cell growth and division are a part of a complex cell cycle.

Eukaryotic Cell Cycle

• G1 (Gap Phase 1):

  • Growth, accumulation of resources

  • Longest stage

• S (Synthesis):

  • DNA replication - 96 total chromosomes in the cell after S Phase.

  • In Animals: Replication of centrosome (contains centrioles, which contain contain microtubules).

• G2 (Gap Phase 2)

  • Replication of some organelles

  • Further growth

  • Interphase = G1 + S + G2 (All refer to interphase)

    • Interphase - the getting ready phase of the Eukaryotic cell cycle.

• Mitosis**

  • Several steps

  • Prophase, Prometaphase, Metaphase, Anaphase, Telophase (PPMAT)

    • Prophase:

      • Nucleus, golgi, ER break down.

      • Chromosomes condense - become visibly distinct

      • Spindle Apparatus forms

LECTURE STOPPED - 19:30

• Prometaphase:

  • The microtubules (part of the spindle apparatus) attach to sister chromatids at points called kinetochores

• Metaphase:

  • Sister chromatids align at the center of the cell.

    • Positioned to move to the opposite sides of the cell

• Anaphase:

  • Sister chromatids split

    • Spindle apparatus pulls them to opposite sides of the cell.

• Telophase:

  • Chromosomes de-condense

  • Nucleus, golgi, ER re-form x2.

• Cytokinesis

  • Cleavage furrow (in animals) or cell plate (in plants) separates the cell into 2 identical daughter cells.

• M Phase  = Mitosis + Cytokinesis

• G0 (resting phase)

  • Not part of the cell cycle

    • Offshoot- after cytokinesis, before G1.

• Cells in G0 are not actively dividing.

  • Are fulfilling their normal functions

• Most of our cells are in G0.

• Cell Cycle is regulated by internal factors

  • There are 3 main cell cycle checkpoints

    1. G1 Checkpoint

       1. Checks for:

          1. Energy and resources for DNA replication

          2. Damage to DNA

1. G2 checkpoint

   1. Damage to DNA

1. M Checkpoint

   1. The 'M' stands for metaphase

      1. Cell checks that all sister chromatids are connected to a spindle apparatus

• Cell cycle is regulated by external factors

  1. Cells need permission from surrounding cells to divide

     1. This maintains normal cell number and density

• Many proteins involved in regulating cell cycle.

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Attendance quiz code: 92045

4/11/25 NOTES:

• Cancer: Uncontrolled cell growth, which causes harm

  • Caused by faulty cell cycle control proteins

    • Caused by mutations in their DNA sequence

      • These mutations are caused by unrepaired DNA damage

• Proto-oncogenes ---> Oncogenes (Onco- refers to cancer)

  • Mutations are causing Proto-oncogenes to become Oncogenes

• Mutations are prevented by "tumor-suppressor genes/proteins".

  • Ex: p53

    • p53 locates damaged DNA and brings in DNA repair proteins

      • If repair is successful, cell cycle proceeds

• If damage is too severe, it causes apoptosis.

• If p53 gene is mutated, it no longer encodes a functional protein.

  • Allows cells with damaged DNA to divide

    • Leads to more mutations

      • Leads to more oncongenes

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