BISC 101 Lecture 2: Cells

Lecture 2: Cells

-          All living organisms are comprised of cells

-          Single-celled organisms, e.g. amoeba, bacteria

-          Multi-celled organisms, e.g. humans

-          Cells arise from pre-existing cells

Humans: ~ 2 x 10¹⁴ cells / body ; 200 trillion cells

Characteristics:

1.      Structure

2.      Function

3.      Reproduce (division)

4.      Cell cycle

Cell Division:

a.       Cell reproduction to produce new cells

b.      Repair tissue damage

c.       For growth and development

-          The outcome of cell division is to produce genetically identical daughter cells

-          The nuclei have to divide and then the cells divide

-          Mitosis ensures the above

-          Single-celled orgamisms:

o   Bacteria divide by binary fission

-          Multi-cellular organisms:

o   More complex cell cycle

§  G₁ = cell growth phase (first gap phase)

§  S = synthesis of DNA (duplicate the DNA)

§  G₂ = ready for cell division (second gap phase)

§  G₁ + S + G₂ = Interphase

Mitosis (Mitotic Phase [M]):

1.      Prophase:
- Chromosomes appear with sister chromatids
- Mitotic spindle forms (microtubules)

2.      Prometaphase:
- Nuclear envelop breaks down
- Microtubules organize at poles (end)

3.      Metaphase:
- Chromosomes migrate to center of cell, align themselves by centromere
- Spindle tubule is formed

4.      Anaphase:
- Chromatids separate and migrate to poles

5.      Telophase:
- Separate nuclei form, cell undergoes division
Cytokinesis:
- Division of cytoplasm

Two genetically identical daughter cells form.

Regulation of cell cycle:

-          Most cells in the body are in the G₀ phase (non-dividing)

-          Timing of cell division must be controlled

-          Signals are released to induce cell division

Not all cells divide:

-          Skins cells divide frequently

-          Liver cells divide infrequently

-          Nerve cells do not divide

Stem cell research:

-          Early stage cells that can differentiate different tissues (lung, brain, liver, nerve)

-          Derived from embryos, placenta, fetus, or adults

Chemical signals and the cell cycle:

-          Regulate cell cycle

-          Respond to signals (internal, external)

-          G₁ “check-point” = most important check-point

Protein kinases:

-          For cell cycle control

-          Kinases must be activated by cyclin (cyclin-dependent kinases [cdk])

-          Cyclin levels fluctuates in cell

The first cdk discovered was MPF: Mitosis Promoting Factor

-          Forms a kinase-cyclin complex

To be concluded in Lecture 3.