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Cell Biology
CELL STRUCTURE
Levels of Organization
The levels of life are organized hierarchically:
…from lowest to highest:

1. ATOMS
eg. carbon, oxygen atoms
2. MOLECULES
eg. glucose, proteins, neutral fats, cholesterol
3. ORGANELLES (structures that make up cells)
eg. nucleus, mitochondria, endoplasmic reticula
4. CELLS
eg. nerve cells, smooth muscle cells
5. TISSUES (comprised of similar cells)
eg. nerve tissue, muscle tissue, epithelial tissue, connective tissue
Nerve tissue – sense stimuli and transmit signals throughout animal.
Muscle tissue – movement, support; three types:
i. Skeletal (Striated) – voluntary bodily movements;
ii. Smooth (Visceral) – involuntary contractions (blood vessels, intestine, bladder, etc);
iii. Cardiac (Heart) – pumping of heart.
Epithelial tissue – Protects: covers outside of body, lines organs and cavities within body.
Connective tissue – binds and supports other three tissue types; six types:
i. Loose Connective tissue – most widespread; attaches epithelia to other tissues and
holds organs in place  strong and elastic in nature;
ii. Dense Connective tissue – tendons (muscle-to-bone) and ligaments (bone-to-bone);
iii. Bone – mineralized (Ca2+ & Mg2+) for support and protection;
iv. Cartilage – flexible support in certain areas (nose, ears, trachea, vertebrae);
v. Blood – ‘connects’ different parts of body by transporting materials;
vi. Fat (Adipose) tissue – pads and insulates body.
6. ORGANS (comprised of various tissue-types)
eg. heart, brain, liver.
7. ORGAN SYSTEMS (comprised of various organs)
eg. Nervous System, Digestive System
8. ORGANISM (comprised of organ systems)
eg. human beings, cats, wildebeest
9. POPULATIONS/COMMUNITIES
Definition: CELL – the structural and functional unit of life. It is the
smallest structure capable of performing all of the functions necessary
for life.
FUNCTIONS NECESSARY FOR LIFE:
1. Reproduce ON OWN! (excludes viruses which require cells to repr.)
2. Grow
3. Respire (Metabolize) – Cellular Respiration (mitochondria)
glucose (C6H12O6) + O2  CO2 + H2O + ATP energy
4. Contain genetic material (RNA and DNA)
5. Respond to stimuli
Molecules Making Up Cells
1.
2.
3.
4.
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Carbohydrates (energy, identification)
Proteins (energy, digestion, structure, hormones etc)
Lipids (incl. fats, steroids) – (energy, insulation,
hormones, cushioning)
Nucleic Acids (RNA/DNA) – (blueprint for
proteins)
All of these molecules are made up of atoms
(elements); the main elements comprising living
organisms are: C, H, N, O.
Organic = C and H.
Classifying Cells
CELLS
PROKARYOTIC
-- smaller, less organized
-- lack a true nucleus
-- lack membrane-bound
organelles
-- bacteria
-- single circular chromosome
EUKARYOTIC
-- have a true nucleus
with a cell membrane
-- possess membranebound organelles
-- 10X size of prok.
cells
-- focus of Biology 12
Eukaryotic Cells
Plant Cells
“Eu” = True
“karyon” =
nucleus
Animal Cells
-- p. 51 Figure 3.3
-- p. 50 Figure 3.2
-- possess a cell wall
-- main focus of Biology 12
-- have chloroplasts
-- lacking the three structures
-- large, contractile vacuole mentioned to the left
Examples of Plant/Animal Cells
The three differences…
Cell Structures/Organelles
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All cells have a CELL MEMBRANE that acts as
a “gatekeeper,” allowing only certain molecules
into/out of the cell.
The cell membrane (mb) is therefore described
as being SELECTIVELY PERMEABLE.
The cell mb separates the cytoplasm (the inner
contents of the cell) from the extracellular
fluid (ECF).
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
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The cell mb also compartmentalizes the cell into
various organelles which are highly specialized
structures with specific functions.
Organelles are to the cell as organs are to our
body.
The cell mb is a very fluid, flowing structure but
it does work to maintain the cell’s shape (with
help from the cytoskeleton).
Structure of the Cell Membrane


The cell mb is made up
of a phospholipid
bilayer along with
embedded proteins.
Carbohydrates can be
found associated with
the cell mb as well, either
attached to the proteins
or to the phospholipids
themselves.
Cholesterol!
A closer look at the phospholipid
molecules…

Organelles – small, membrane-bound structures
found within the cytoplasm of the cell.
Eukaryotic Cell Organelles
A recurring theme in Biology 12 is the relationship between
structure and function, both at the cellular and organ system
levels.
CELL SIZE
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For an organism to grow, its cells must divide.
Metabolic requirements impose upper limits on the size that is
manageable for a single cell.
As a cell (among other things) grows, its volume and its
surface area increase, but they do so at different rates.
Volume is a cubic function (V(sphere) = 4/3πr3), whereas
surface area is a quadratic function (SA(sphere) = 4πr2).
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therefore, as a cell grows, its surface area-tovolume ratio (SA:V) decreases.
- It is the surface area that governs a cell’s ability to import/export
materials (‘good things and bad things’)…AND…it is the volume that
imposes the demands upon the cell’s surface area…thus, if the demands
are increasing faster than the import/export abilities, the cell may
eventually reach a point where it cannot sustain living; it will either
have to divide or die.
furthermore, a cell’s nucleus has a limit as to what
size of a volume that it can service.
- Once a cell divides, its SA:V increases to a level that
is conducive to ‘healthy living’.
Organelles, which are structures within the cell that are
compartmentalized by membranes similar in
structure to the cell membrane, are able to sustain
many different local environments that facilitate
specific metabolic functions that might be
incompatible with each other in an ‘open’
(prokaryotic-like) cytoplasm.
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AND NOW…THE ORGANELLES THEMSELVES!!!
NUCLEUS (fig. 3.2 p.50; 3.4 p.52)
STRUCTURE
FUNCTION
Surrounded by the nuclear envelope
(bilayered membrane), which serves to separate
the nucleus from the cytoplasm while also
serving as a “gatekeeper”.
Main General Function: serves as the “control
centre” of the cell.
The nuclear envelope possesses nuclear pores
that help to determine which substances
enter/exit the nucleus (generally by size).
Directs Protein Synthesis (DNA does this,
serving as a “blueprint” for the production of
proteins in the cytoplasm).
DNA is found here – mostly as a thread-like
material called chromatin.
In fact, within the nucleus, DNA is converted
to mRNA during the process called
transcription.
During cell division (mitosis/meiosis),
chromatin condenses into thick, cylindrical
structures called chromosomes, with help
from rod-like proteins called histones.
The proteins that are eventually produced (in
the cytoplasm) determine the structure and
function of the cell.
NUCLEOLUS (fig. 3.2 p.50; 3.4 p.52)
STRUCTURE
FUNCTION
Located within the nucleus and possesses its
own bi-layered membrane.
The rRNA that is produced serves as a
structural element of ribosomes (another
organelle found in the cytoplasm).
Has its own DNA in the form of chromatin;
this DNA produces rRNA (ribosomal RNA).
Ribosomes are comprised of rRNA and
specific proteins, both of which are produced
in the nucleolus.
Also made up of structural proteins.
RIBOSOMES (fig. 3.2 p.50; 3.5 p.53)
STRUCTURE
FUNCTION
Consist of two subunits, each made up of
rRNA and nucleolar proteins.
Serve as the site for protein synthesis by
acting as an anchor for mRNA during a
process called translation.
These two subunits are not assembled until
they enter the cytoplasm (so that they are small
enough to exit through the pores).
Ribosomes attached to the ER produce
proteins that are to be exported from the cell.
Ribosomes either attach to the endoplasmic
reticulum (ER) or ‘survive’ on their own
within the cytoplasm.
“Free” ribosomes produce maintenance
proteins that remain inside the cell.
Ribosomes that ‘survive’ on their own
Polysomes tend to produce maintenance
sometimes group together to form polysomes. proteins more rapidly.
VACUOLES (fig. 3.2 p.50)
STRUCTURE
FUNCTION
Membranous sacs (much larger in plant cells) Storage areas for water, sugars, salts, and
other nutrients.
VESICLES (fig. 3.2 p.50; 3.5 p.53; 3.6 p.54)
STRUCTURE
Smaller membranous sacs
FUNCTION
Serve as transporters of materials either for
export from the cell or for use in other parts of
the cell.
ROUGH ENDOPLASMIC RETICULUM (ROUGH
ER) (fig. 3.2 p.50; 3.5 p.53)
STRUCTURE
FUNCTION
Membranous system of tubular canals
(picture hollowed out linguine noodles) that
branches throughout the cytoplasm.
Site for Protein Synthesis – ribosomes act as
anchors for mRNA, which codes for the
construction of proteins.
For the most part, it is continuous with the
nuclear envelope at its beginning, and the
Smooth ER at its end.
Constructed proteins then enter the lumen
(interior, hollowed-out gap) of the Rough ER
and are modified as they pass through towards
the lumen of the Smooth ER.
Has ribosomes attached to it, making it appear Once through the Smooth ER, the proteins are
‘rough’ in texture.
placed inside a transition (transfer) vesicle,
which carries the protein to the Golgi for
further processing.
Very closely associated with, but not generally
touching, the Golgi Body (Apparatus).
Thus, the Rough ER (and Smooth ER, for that
matter) serves as a transporter, of sorts, as
well.
SMOOTH ER (fig. 3.2 p.50; 3.5 p.53)
STRUCTURE
FUNCTION
More of a tubular type structure than the
ribbon-like Rough ER (picture hollowed out
spaghetti noodles).
Modifies then packages proteins created in the
Rough ER into transition vesicles bound for
the Golgi.
Possesses the same membrane as the Rough
ER, except that there are no ribosomes
attached.
Lipid synthesis (including steroids, fats, and
phospholipids) – eg. Steroid hormones such as
testosterone, estrogen, and aldosterone are
produced in the Smooth ER. Thus, high
Smooth ER numbers in testes, ovaries, and
adrenal glands respectively.
Continuous with Rough ER, or, in some
cases, with the nuclear membrane.
Carbohydrate synthesis and metabolism –
primarily in the liver cells (converting glycogen
to glucose).
In the liver, Smooth ER is involved in the
detoxification of drugs, including alcohol.
Special vacuoles called peroxisomes are often
attached to the Smooth ER, and they possess
enzymes capable of detoxifying drugs.
GOLGI BODY (fig. 3.2 p.50; 3.6 p.54)
STRUCTURE
FUNCTION
Composed of a stack of 4-8 saccules
(flattened sacs).
Packaging, storing, and distributing of
materials produced in the ER.
One side of the stack is called the cis-face
(inner face)…it is directed toward the ER and
receives transition vesicles.
Modifications occur here as well (this occurs
as the proteins move from saccule to saccule).
The outer face (trans-face) is directed toward
the cell membrane and has secretory vesicles
or transition vesicles bud off of it.
Final products are packaged into secretory
vesicles that move to the cell membrane for
export, or into transition vesicles for
maintenance materials.
LYSOSOMES (fig. 3.2 p.50; 3.6 p.54)
STRUCTURE
FUNCTION
Large vesicles formed by the Golgi that contain
hydrolytic enzymes capable of digesting
(breaking down) materials into smaller, more
usable bits.
Intracellular Digestion of Macromolecules such
as proteins, carbohydrates, fats, and nucleic
acids. The products of digestion may be sent
to a mitochondrion for energy production, or
may be stored in a vacuole.
Can fuse with vesicles containing materials that
need to be digested.
Cell Protection – lysosomes can kill some
pathogens (viruses/bacteria).
Autodigestion – recycling of older cell parts.
Cell Death
PEROXISOMES (fig. 3.2 p.50; 3.7 p.55)
STRUCTURE
FUNCTION
Similar in structure to lysosomes.
Digest only certain organic materials where the
product is hydrogen peroxide (H2O2) – some
lipids and alcohol are examples.
Exist primarily in liver and kidney cells and in
cells that metabolize lipids (skeletal muscles).
Toxic hydrogen peroxide is then broken down
by the peroxisome-specific enzyme catalase.
MITOCHONDRIA (fig. 3.2 p.50; 3.8 p.56)
STRUCTURE
FUNCTION
Bound with a bi-layered membrane.
Powerhouses of the cell – carry out metabolic
activity by performing Aerobic Cellular
Respiration –>
Glucose + O2  CO2 + H2O + ATP energy
The inner membrane is folded into ‘shelves’
called christae.
Christae are directly involved in ATP energy
production.
Inner fluid is called the matrix.
The matrix contains enzymes capable of breaking
down glucose to smaller pieces to improve the
efficiency of the above rxn.
CHLOROPLASTS (fig. 3.3 p.51; 3.8 p.56)
STRUCTURE
FUNCTION
Found only in plant cells and plant-like protist
cells.
Photosynthesis – the opposite of cellular
respiration, except that the energy required is in
the form of sunlight, which is fixed by the
pigment chlorophyll found in the grana.
Bounded by a bi-layered membrane.
Plants are autotrophs – they can produce their
own glucose, then metabolize it for energy!
Coin-like thylakoids are stacked into grana
and connected by lamellae tubes. The fluid in
between these structures is known as stroma.
CELL WALL (fig. 3.3 p.51)
STRUCTURE
Consists of the carbohydrate cellulose, a
special carb with a very rigid structure.
FUNCTION
Provides structural strength to allow plants to
grow upwards against gravity. Allows most
molecules to pass through it.
CYTOSKELETON (fig. 3.2 p.50; 3.10 p.59)
STRUCTURE
FUNCTION
Microtubules – cylindrical tubules comprised
of the protein tubulin.
Constructed by the M.T.O.C. (Microtubule
Organizing Centre), which contains the
centriole.
Anchor organelles and helps them move
through the cytoplasm by acting as tracts.
Maintains cell shape.
Promotes chromosomal movement.
Helps entire cell move (flagella, cilia).
Microfilaments (aka Actin Filaments) – made
of the protein actin.
Muscle contractions.
Cytoplasmic Streaming.
Maintenance/Changes to cell shape.
Intermediate Filaments – hollow tubes of
intermediate size.
Tension-bearing elements utilized to maintain
cell shape.
Relationship Between Organelles with
respect to Importing/Exporting
Importing:
- Cell membrane indents to form a vesicle that is
sent to the target if it is a hormone, enzyme, or
neurotransmitter.
- If the vesicle holds a macromolecule that is to be
digested, the vesicle travels to a lysosome.
- If the vesicle holds a macromolecule that is to be
stored, the vesicle travels to a vacuole.
Exporting:
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Proteins created at ribosomes on the Rough ER are funneled into
the ER’s lumen where they are modified/packaged into a transition
vesicle and sent to the cis-face of the Golgi Body.
Further processing/modifying occurs in the Golgi before the
proteins are packaged into another vesicle (secretory vesicle) at the
trans-face.
Secretory vesicle travels to the cell membrane and releases contents
into the extracellular fluid (ECF)
Proteins created at ‘free’ ribosomes travel through the Golgi similar
to Rough-ER-produced proteins, except that instead of being placed
into a secretory vesicle, they are placed into a second transition
vesicle bound for a lysosome (for digestion), a vacuole (for storage),
or anywhere else in the cell where it is in demand.
See handout and fig. 3.6 p.54
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Studying the Concepts Questions #1-9 p.65
Testing Yourself Questions #1-7, 10, 11.
Thinking Scientifically Question #2 p.66
Understanding the Terms Questions a-e.