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

 

 

 

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 (sex cell division)

 

 

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 (duplicated) 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 (p. 59):    a process by which the chromatids fail to properly separate during meiosis

 

 

 

 

 

 

 

 

 

 

 

 

 

Which statement is TRUE about meiosis?

 

a. it is a type of cell division whereby somatic cells are formed

 

b.the daughter cells each contain 23 pairs of chromosomes

 

c. the daughter cells are genetically different from the parent cell

 

d.the daughter cells are diploid

 

e. crossing over occurs during the 2nd meiotic prophase

 

 

 

 

 

 

 

Back to the A215 home page