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The Cell
Has Similar and Specialized Functions
Cell or Plasma Membrane
Structure - fluid mosaic hypothesis

Phospholipid bilayer

Cholesterol - stabilizes membrane

Integral proteins - may be internal to
the bilayer, extend through it, or extend
beyond only one side

Peripheral proteins - seem bound to
integral proteins

Cell Membrane Functions
Enclose cell components
 Integral proteins form channels
 Integral proteins may act as carriers
 Integral proteins may act as receptors
 Peripheral proteins may act as enzymes
and are involved in cell shape changes
 Both types of protein may attach to
sugars for cell recognition; a glycocalyx

Factors Affecting Permeability
 Size
of molecules - small ones can
fit thru channels
 Solubility in lipids increases
permeability - steroids, alcohol
 Charges - proteins in membranes
have charges; opposites attract
 Presence of protein carriers
 How
Things Enter and Leave
the Cell
 Passive
processes - require no
energy expenditure by the cell to
move things
 Active processes - require the cell
to expend some of its energy to get
things into and out of the cell

Due to Brownian motion – the
random movement of all
substances due to their charges
Diffusion - movement of substance
from where there is more of it to
where there is less of it
Osmosis - diffusion of water thru a
semipermeable membrane

Solvent – the substance present in
greatest quantity

Solute – the substance present in
smallest quantity

Hypotonic solution - contains fewer
non-penetrating molecules than the cell

Hypertonic solution - contains more
non-penetrating molecules than the cell

Isotonic solution - contains the same
number of non-penetrating molecules
as the cell
 Filtration - movement of solvent and
solute thru a membrane via mechanical
(hydrostatic) pressure; occurs at the
capillary and in the kidney
 Dialysis - separates small from large
molecules by diffusion and osmosis thru
a semipermeable membrane

 Facilitated
diffusion - diffusion of
a substance via a carrier
Active transport - movement of a
substance from a lower concentration to
a higher concentration using a carrier
and energy
 Endocytosis - brings substances into
the cells

Phagocytosis - cell eating;
important defense mechanism
Pinocytosis - cell drinking;
occurs in the kidney, bladder
and intestine
Receptor-Mediated Endocytosis large particle binds to a receptor, the
membrane invaginates and forms a
vesicle (coated pit).
Exocytosis - vesicle fuses with the
plasma membrane and then
ruptures; used in hormone and
neurotransmitter release
Cell-to-Cell Communication
 Cells
far apart - chemical acts
on receptors
 Cells close together - gap
junctions allow small molecules
and ions to move between them
 Cytosol
 Organelles
 Inclusions
 Outside
nucleus and inside cell
membrane
 75-90% water
 Sol-Gel
 Function - chemical reactions occur
here
I. Nucleus



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A. Structure
1. Nuclear
membrane (envelope)
2. Karyolymph a gel
3. Nucleoli produce ribosomes
4. Chromatin chromosomes, genes
B. Functions

1. Cell reproduction

2. Cell differentiation - also
involves the environment

3. Directs cell metabolism

II. Endoplasmic reticulum
(ER)


A. Smooth ER synthesizes lipids,
stores Ca in muscle
cells, breaks drugs
down in the liver
B. Rough ER makes new plasma
membrane; contains
ribosomes
III. Ribosomes

A. Free - make protein for the cell

B. Attached - make protein for
secretion from the cell

IV. Golgi Complex (Apparatus)


A. Receives protein
from ER and
remakes them into
enzymes in
lysosomes
B. Synthesizes
polysaccharides,
glycolipids,
glycoproteins,
lipoproteins, mucous
and secretes many
of them from the cell

V. Mitochondria
- contain
oxidative
enzymes involved
in cellular
respiration to
make ATP

VI. Lysosomes - contain digestive
enzymes, many are in osteoclasts,
important in phagocytosis (Tay-Sachs
disease is due to a lysosomal problem)

VII.
Centrosomes - 2
centrioles
involved in cell
division
 VIII.
Flagellum
- sperm
movement
 IX. Cilia - oarlike motion
moves
substances
across the cell
surface

X. Peroxisomes - contain enzymes to
break down toxins; prevent harmful
oxidation reactions from forming free
radicals which are disruptive
compounds
XI. Cytoskeleton

A. Microfilaments - solid; actin,
myosin involved in muscle contraction,
assist in cell movement

B. Microtubules - hollow; in cilia and
flagella, centrioles and mitotic spindles

C. Intermediate filaments - act as
guy wires

 Pigments
- hemoglobin, melanin
 Fat
 Mucous
 Glycogen
- in liver and muscle
 Mitosis
- nuclear division
 Cytokinesis - division of the
cytoplasm
Why Do Cells
Divide?
 To
keep the surface area
proportional to the volume of
the cell
 Some cells divide continually RBC, skin cells
 Some lose the ability - CNS
 Nucleotides
- P-S-NB; adenine,
thymine, guanine, cytosine are
the nitrogenous bases thus
there are 4 types of nucleotides
 Double helix
Protein Synthesis
Transcription - m-RNA is made from
one strand of unzipped DNA
 m-RNA moves out of the nucleus and
attaches to the ribosomes
 Translation - t-RNA attaches to specific
amino acids and aligns with m-RNA at
the ribosomes


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At one end of t-RNA is a sequence of 3 bases
(triplet) that code for a specific amino acid.
This allows for 64 combinations (4 bases
cubed) that may code for 20 amino acids the genetic code
These 3 bases attach to the m-RNA in a
complementary fashion, A-U, C-G, bringing
the amino acids close together and allowing
them to bond in a sequence determined by
the DNA in the nucleus
Interphase

G1 - gap between cell divisions;
mature cells stay in this stage

S - DNA is synthesized (replicated)
here prior to division

G2 - cell prepares for division;
enzymes needed for division are made

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Prophase
Chromatin shortens into a chromosome
and becomes visible
Nucleoli become less distinctive
Nuclear membrane disappears
Centrioles move to the opposite poles and
seem to form the mitotic spindle, some of
which attaches to the centromeres of the
chromosomes
Chromosomes begin to move toward the
equator
 Metaphase
- chromosomes line up
randomly on the equatorial plate
 Anaphase - centromeres divide
and the replicated parts of each
chromosome move to opposite
poles
 Telophase - the reverse of
prophase occurs
Cytokinesis
 Division
of the cytosol; occurs
in late anaphase or early
telophase via a cleavage furrow
that pinches in

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Diploid -> haploid; 2N -> N (N = sets of
chromosomes); each set has 23
chromosomes
Meiosis I - reduction division
Prophase I
Synapsis - the lining up of homologous
chromosome pairs in prophase I; the
crossing over and exchange of chromosome
parts allows for variation in the offspring
Metaphase I

Independent Assortment - one
chromosome of a homologous pair
assorts independently with another
chromosome of a different homologous
pair in metaphase I providing for more
variation in the offspring. (Maternal #1
can assort with either maternal or
paternal #2)

Anaphase I - one chromosome of each
homologous pair of chromosomes
moves to the opposite pole
 Result - 2 haploid cells each containing
23 replicated chromosomes
 There is no interphase II as the
chromosomes are already replicated

Meiosis II - equatorial division, the
same as mitosis;

Results in 4 haploid cells each with
23 unreplicated chromosomes

Turner’s Syndrome - XO
22 year old
woman
 Webbed neck
 Widely spaced
nipples
 Lack of sexual
development
