Chapter 3
Cells
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
Introduction:
A. Human body consists of 75 trillion cells that vary
in shape & size yet have much in common
B. Differences in cell shape make different
functions possible
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A
Composite Cell:
A. includes many different cell structures
B. main parts: nucleus, cytoplasm, cell
membrane
C. specialized organelles perform specific
functions for the cell
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D. Cell Membrane
1. regulates movement of substances in & out
of the cell, participates in signal transduction,
helps cells adhere to other cells
2. General Characteristics
a. extremely thin & selectively permeable
b. complex surface w/ adaptations to
increase surface area
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3. Cell Membrane Structure:
a. phospholipid bilayer, fatty acids tails
turned inwards
b. lipid soluble molecules can pass through
c. embedded cholesterol molecules add
strength & make the membrane less
permeable to water-soluble substances
d.many types of proteins are found in the
cell membrane, including transmembrane &
peripheral membrane proteins
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e. Membrane proteins perform a variety of
functions & vary in shape
i. receptors on the cell surface
ii. aid the passage across membrane
iii. carbohydrates attached for cell ID
iv. cellular adhesion molecules
help determine cell interactions
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E. Cytoplasm:
1. clear liquid = cytosol, a supportive
cytoskeleton, networks of membranes &
organelles
a. Endoplasmic reticulum (ER)- made up of
membranes, flattened sacs, & vesicles.
Provides a tubular transport system inside
the cell
i. Rough = has ribosomes, functions
in protein synthesis & transport
ii. Smooth = no ribosomes functions
in lipid transport
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b. Ribosomes - found w/ RER or scattered
throughout the cytoplasm, composed of protein
& RNA, provide structural support for the RNA
molecules that come together in protein synthesis
c. Golgi apparatus - composed of flattened sacs;
refines, packages, modifies, & delivers proteins
i. Vesicles formed on ER travel to the Golgi
which modifies their contents chemically
ii. Vesicles then move to cell membrane &
secrete its contents to the outside
iii. Vesicles form a “delivery service”,
carrying materials throughout the cell
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d. Mitochondria - powerhouses of the cell,
contain enzymes needed for aerobic
respiration
i. make ATP
ii. more active cells have more
mitochondria
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e. Lysosomes - "garbage disposals" of the cell;
contain digestive enzymes to break up old cell
components & bacteria.
f. Peroxisomes contain enzymes that function
in the synthesis of bile acids, breakdown of
lipids, degradation of rare biochemicals, and
detoxification of alcohol.
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g. Microfilaments & microtubules are thin,
threadlike structures that serve as the
cytoskeleton of the cell
i. Microfilaments: made of actin
ii. Mictotubules: made of the globular
protein tubulin
h. Centrosome - made up of two hollow
centrioles; function in the separation of
chromosomes during cell division
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i. Cilia & flagella - motile extensions from
the cell; shorter cilia are abundant on the
free surfaces of certain epithelial cells
(ex:respiratory linings) cause movement
of substances across the surface of the
cell and a lengthy flagellum can be found
on sperm cells
j. Vesicles form part of the cell membrane
or the Golgi/ER and store materials
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F. Cell Nucleus:
1. bounded by a double-layered nuclear
membrane w/ relatively large nuclear pores
that allow the passage of certain substances
a. Nucleolus: inside the nucleus,
composed of RNA & protein; site
of ribosome production, doesn’t
have a membrane
b. Chromatin consists of loosely
coiled fibers of protein & DNA
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 Movements Through Cell Membranes
A. Passive: no energy
1. diffusion
2. facilitated diffusion
3. osmosis
4. filtration
B. Active: cellular energy (ATP)
1. active transport
2. endocytosis
3. exocytosis
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C. Passive Mechanisms
1. Diffusion
a. caused by the random motion
of molecules along the concentration
gradient, from greater to lesser
concentration until equilibrium is
reached
b. enables O2 & CO2 exchange btwn
air & blood in the lungs, & btwn blood
& tissue cells
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2. Facilitated Diffusion
a. membrane proteins function as
carriers to move molecules (glucose)
across the cell membrane
b. the # of carrier molecules in the cell
membrane limits the rate of this
process
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3. Osmosis
a. diffusion of water from greater water
concentration (less osmotic pressure) to lower water
concentration (greater osmotic pressure)
b. Osmotic pressure is the ability of osmosis to lift
a volume of water
c. Compared to bodily fluids, a solution with
i. the same osmotic pressure is isotonic
ii. higher osmotic pressure is hypertonic
iii. lower osmotic pressure is hypotonic
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4. Filtration
a. Because of hydrostatic pressure,
molecules can be forced through membranes
by the process of filtration.
ex. Blood pressure in the kidneys
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D. Active Mechanisms
1. Active Transport
a. Uses ATP to move molecules from low
to high concentration through transport
proteins in cell membranes
b. Up to 40% of a cell's energy may be
used to fuel this process to get needed
materials or eliminate wastes
c. Actively transported substances include:
sugars, amino acids, Na+, K+, Ca+2, H+,
& nutrient molecules in the intestines
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2. Endocytosis & Exocytosis
a. Endocytosis - molecules too large to be
transported by other means are engulfed by an
invagination of the cell membrane & carried into
the cell surrounded by a vesicle
b. Exocytosis is the reverse of endocytosis
c. 2 forms of endocytosis
i. Pinocytosis - cells engulf liquids
ii. Phagocytosis - cells engulf large
particles (WBC eat bacteria)
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The Cell Cycle
A. series of changes a cell undergoes from the
time it is formed until it reproduces
B. interphase, mitosis, cytokinesis, and
differentiation
C. Highly regulated, most cells do not divide
continually. Cells have a maximum number
of times they can divide because of built-in
“clocks” (telomeres) on the tips of
chromosomes
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Animations
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Cell Cycle
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http://www.cellsalive.com/cell_cycle.htm
E. Mitosis/Meiosis
1. Meiosis, four cells, gametes (sperm/ova)
are produced, each of which contains half
of the parent cell’s genetic information
2. Mitosis is a carefully orchestrated
division of the nucleus of the cell that
results in 2 daughter cells receiving an
exact copy of the mother cell's genetic
material
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D. Interphase
1. a period of great metabolic activity in
which the cell grows & synthesizes new
molecules and organelles
2. S phase: the DNA is replicated in
preparation for cell division
3. G1 & G2 phases: of interphase, the cell
grows & other structures are duplicated
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3. Mitosis is described as a series of 4
stages, but the process is continuous
4. Prophase: DNA condenses into
chromosomes, centrioles migrate to the
poles, microtubules of the cytoskeleton
reorganize into spindle fibers, & the
nuclear envelope disappears
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5. Metaphase: spindle fibers attach to
centromeres on the chromosomes &
chromosomes align midway btwn
centrioles
6. Anaphase: spindle fibers contract &
pull sister chromatids apart
7. Telophase: chromosomes have
completed their migrations making 2
identical groups, nuclear envelopes
reappear, chromosomes begin to unwind
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F. Cytoplasmic Division
1. Cytokinesis begins during anaphase of
mitosis & continues as a contractile ring
pinches the two new cells apart
2. The two daughter cells may have
varying amounts of cytoplasm & organelles,
but they share identical genetic info.
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G. Cell Differentiation
1. Process by which cells develop into
different types of cells with specialized
functions.
2. reflects genetic control of the nucleus as
certain genes are turned on while
others are turned off
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H. Cell Death
1. Apoptosis is a form of cell death that is
a normal part of development
Cancer – uncontrolled cell division
Metastasis – cancer spreads
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