CELLS AND CELL DIVISION

I. BASIC CELL COMPOSITION (fig. 2.1)

    A. Plasma Membrane (Cell Membrane) - surrounds cell and gives it form

    B. Cytoplasm - consists of:
        1) cytosol:

        2) organelles:

    C. Nucleus - contains DNA (deoxyribonucleic acid)

II. PLASMA MEMBRANE  (fig. 2.4)
-- Structure: double layer of phospolipids
        * proteins

* glycoproteins

* glycolipids
 

    -- selectively permeable

 

What do you think? what are some benefits and some disadvantages of having a selectively permeable membrane?

 

 

    -- Some plasma membranes have:
        1) microvilli (fig 2.3):
            *

        2) cilia (figs 2.3, 2.16):
            *
 

   

III. CYTOPLASMIC ORGANELLES (fig. 2.3 and others)  

    A. Mitochondria
        * make ATP (adenosine triphosphate)
        * contains its own DNA
 

    B. Ribosomes - involved in protein synthesis (synthesis = production)
        * two kinds: Free ribosomes or ribosomes attached to Rough ER
 

    C. Endoplasmic Reticulum (ER) - a network of tubules used to transport & synthesize
        (produce) materials

        1) Rough ER - has ribosomes on walls
            * synthesizes & distributes proteins
 

        2) Smooth ER - has no ribosomes
            * synthesizes lipids, mainly steroids
            * detoxify drugs and alcohol
 

    D. Lysosomes - contain digestive enzymes
 

    E. Centrioles (fig 2.15) - involved in cell division
 
 

IV. NUCLEUS (fig 2.3, 2.17)
    --  contains DNA (deoxyribonucleic acid)

    --  when cell is NOT dividing, DNA in the form of chromatin
 

    --  some nuclei have a nucleolus
        * makes the "parts" that form ribosomes
 

REVIEW AND LEARN THE FUNCTIONS OF THE CELLULAR
STRUCTURES WITH A STUDY PARTNER.  WORK TOGETHER
ON THE Cellular structures memory matrix
 

V. CELL CYCLE (fig. 2.19)

    -- cells divided into:
        1) Sex cells (sperm and oocytes)
        2) Somatic cells (all other cells)

    -- cell cycle subdivided into 2 phases:

        1) Interphase - cell not dividing
            * DNA is duplicated during this time

        2) Mitosis (cell division for somatic cells)
            or Meiosis (cell division for sex cells)

VI. MITOSIS (fig. 2.20)

    1) Prophase ("Puffy")
        * DNA in form of double-stranded chromosomes

        * double-stranded (duplicated) chromosomes consist of 2 chromatids
            joined at a centromere
            ** (chromatid = each half of the duplicated chromosome)
 

        * spindle fibers go from centrioles to chromatids
 

        * breakdown of nuclear membrane
 
 

    2) Metaphase ("Middle")
        * chromosomes along center of cell
 

    3) Anaphase ( "Apart")
        * chromatids split apart at centromere

        * each set of chromatids (now called single-stranded chromosomes) pulled to
        opposite ends of cell
 
 

    4) Telophase ("Two")
        * nuclear envelope reforms
        * nucleolus reappears

        * cleavage furrow develops
        * cytokinesis occurs
 

    -- Cell now re-enters interphase
 

VII. MEIOSIS (figs. 3.1, 3.2)
    Def: cell division where gametes (sperm cells or oocytes) are formed

    -- Differences between mitosis and meiosis:
        1) Mitosis produces 2 cells containing 46 chromosomes (23 pairs)
            * daughter cells identical to original (parent) cell

            * cells are diploid: they have 2 of each chromosome
 

        2) Meiosis produces 4 cells containing only 23 chromosomes
            * daughter cells genetically different from parent cell

            * these cells have a haploid number of chromosomes (only 1 of each
                chromosome)

    -- Start off with one cell that has 23 pairs of chromosomes
        * one set of chromosomes came from MOTHER, the other from FATHER
 

    -- Interphase: DNA is duplicated
        * DNA will form double-stranded chromosomes

        * cell now contains 23 pairs of double-stranded (duplicate) chromosomes
 

    -- 1st meiotic prophase, homologous chromosomes pair up
 
 

    --Crossing Over: process by which genetic material is exchanged between
        homologous chromosomes
            * occurs during 1st prophase
 

What do you think? How does crossing over relate to genetic diversity among individual sex cells?

 

    -- cell finishes 1st meiotic division, producing 2 daughter cells

        * daughter cells each have 23 double-stranded chromosomes (each chromosome
            consists of 2 chromatids)

        * parent cell had 23 PAIRS of chromosomes, but daughter cells have
            only 23 chromosomes!
 
 
 

    -- cells go through 2nd meiotic division:
        * 4 cells produced, each with 23 single-stranded chromosomes (each chromosome
            has only 1 chromatid now)

        * these 4 cells are gametes
 

-- Nondisjunction (page 59): a process by which the chromatids fail to properly separate during meiosis

 

 

COMPARE AND CONTRAST MITOSIS VERSUS MEIOSIS.  WORK WITH
A STUDY PARTNER ON THE  mitosis/meiosis learning exercise .
 

Which statement is TRUE about the plasma membrane?

a.  it is composed of a triple layer of carbohydrates

b.  all materials may easily pass through (diffuse through) the cell membrane

c.  all plasma membranes contain microvilli

d.  proteins are scattered within and "float" within the membrane

e.  none of the above are true
 

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