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
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