The document discusses why cells are small and how their size relates to surface area to volume ratio. As cells increase in size, their surface area does not increase as quickly as their volume, limiting nutrient exchange. The document then describes how light microscopes and electron microscopes are used to study cells given their small size. It provides an overview of the key organizational differences between prokaryotic and eukaryotic cells, including the presence of membrane-bound organelles in eukaryotes. Several organelles are then described in more detail, including their structure and function.

1. 1
•The answer is to be found in the surface area-to-
volume ratio (SA/V) of any object as
it increases in size.
•As a cell increases in volume, its surface area
increases also, but not to the same
extent.
•S.A. of a sphere = 4!r2
V of a sphere = 4/3!r3
•The surface area of a cell limits the exchange of
nutrients and waste products with its
environment.
•As the living cell grows larger, its rate of
production of wastes and need for
resources increase faster than its surface
area.
•Cells are small in volume and thus maintain a large surface area-to-volume ratio.
The cell theory:
1. All living things are made of cells
2. All cells come from previously existing cells
3. Cells are the basic units of structure and function in all
living things.
4. If you don't behave yourself and attend to your coursework, you will end up
in a cell.
All cells:
A. Use DNA as the hereditary material.
B. Make their own protein.
C.Provide their own energy.
D. Utilize enzymes to catalyze their reactions
Most cells:
1. Reproduce
2. Respond to the environment
Some cells:
(1) Move
Why Are Cells So Small?

2. 2
•In publicly funded schools, we use a compound light microscope!
•A cell’s anatomy is too small for a compound light microscope, so an electron
microscope is used to view organelle structure.
•An electron microscope can magnify images 100X more than a CLM.
•The two types of electron microscopes and their use are:
If Cells Are So Small, How Do We Study Them?
•Forest Hills Public Schools provides students
with a Swift Model M3200 microscope.
•These fine microscopes retail for $450.
•The objective lens magnifications are 4X,
10X,and 40X.
•The ocular lens has a constant magnification of
10X.
•Total magnifications, then, are 40X, 100X, and
400X.
•These microscopes have excellent resolution.
That is to say that they can distinguish
fine detail.
•These microscopes are also parfocal, meaning
that if you change from low power to
medium power, the image is still in view
(but might require fine focusing).
2 Types of Electron Microscopes
Transmission Electron Microscope (TEM)
(used to study thin sections of the interior
of cells)
Scanning Electron Microscope (SEM)
(used to study the surface of a specimen)

3. 3
Cytology – the study of cells.
•During cell fractionation, cells are broken apart so that their organelles can
be studied.
•Cells are fractionated with a centrifuge.
•A cell suspension is first centrifuged at low speed to
separate suspension into two layers:
•The supernatant consists of the smaller, lighter parts
and organelles.
•The pellet consists of the larger, heavier structures.
•The two are separated and each is centrifuged for
further separation.
•Found in the Domains Bacteria and
Archaea. Organisms in these domains are
called prokaryotes.
•These cells lack internal membranes that enclose
compartments. (ie. they lack membrane-
bound organelles.)
•All prokaryotic cells have a plasma membrane, a
nucleoid, and cytoplasm filled with ribosomes.
•Plasma membrane - encloses the cell, regulates
exchange traffic.
•Nucleoid - relatively clear area, contains a circular
loop of DNA.
•Cytoplasm - the rest of the material within the cell - consists of cytosol and
insoluble suspended particles (inclusion bodies).
•Ribosomes - assembled from r-RNA and proteins. Coordinate the synthesis of the cell's
proteins.
•All internal reactions in prokaryotes (and eukaryotes) are catalyzed by enzymes.
Cell Fractionation
Cells Show Two Organizational Patterns: Prokaryotic and Eukaryotic
Prokaryotic Cells

4. 4
•Many (but not all) prokaryotes
have a cell wall located
outside the plasma
membrane. In some
bacteria, an outer membrane
encloses the cell wall.
Outside this membrane may
be a layer of slime composed
mostly of polysaccharide. It
is simply called the capsule.
•The capsule aids in protection
(from viruses called
bacteriophages and white
blood cells), retards drying,
entraps cells for bacteria to
attack, or sticks them to
their food source.
•Some prokaryotes carry on photosynthesis. In these bacteria, the plasma
membrane folds into the cytoplasm to form an internal membrane system
that contains bacterial chlorophyll and other compounds needed for
photosynthesis.
•Other groups of prokaryotes possess membranous structures called
mesosomes (also infoldings of the plasma membrane) that may function in
cell division or in energy-releasing reactions.
•Some prokaryotes swim by using flagella.
•Structures called pili (s. pilus) project from the surface of some groups of
bacteria – adherence during mating (conjugation), help adhere to animal
cells. (See the electron micrograph above)
•Bacteria utilize binary fission for reproduction.
Flagella
Pili

5. 5
Eukaryotic Cells
•These are the cells of the Domain Eukarya -Animals, Plants, Fungi, and Protists.
•Cells are larger (typically 10X) and more structurally complex than prokaryotes.
•Eukaryotes have in internal cytoskeleton to maintain shape and aid in movement.
•Eukaryotes possess membrane-bound organelles. (Compartmentalization)
•The membranes of all organelles have a similar structure, the phospholipid bilayer.
•The number of internal membranes in a eukaryotic cell is stunning and remarkable.
What do they all do?
What is their structure?
How do they regulate materials movement?
Why can't FHC A.P. Biology students get a date?
•Membranes are very useful in forming compartments whose internal contents are
dissimilar to the cytoplasm.
•Membranes are also very helpful in regulating the flow of molecular traffic.
•Much more about membranes in the next chapter!
The Nucleus
•Cells store information in the sequence of bases (A,T,C, and G) in DNA.
•Most of the DNA in eukaryotes resides in the nucleus.
•The nucleus is nearly always the largest subcellular structure.
•A nucleus is surrounded by two membranes, the nuclear envelope.
•This membrane is stable during all parts of the cell cycle except mitosis.
•During mitosis it fragments into vesicles, then re-forms.
•The nucleus is permeated by pores. RNA and water-soluble molecules pass
through these pores.
•DNA combines with proteins to form a fibrous complex called chromatin (long,
thin, entangled threads that cannot be clearly seen by our microscopes.)
•Surrounding the chromatin are water and dissolved substances composing the
nucleoplasm.

6. 6
.
Nuclear lamina - a
meshwork of proteins
just inside the nuclear
envelope that help
maintain the shape of
the nucleus
•Some nuclear envelope pores are
continuous with the E.R.
•When the nucleus is ready to divide
(mitosis), the chromatin replicates
and then condenses and coils
tightly to form easily visible
structures called
chromosomes. Each chromosome
contains 2 chromatids, both
containing a single long molecule
of DNA.
Nucleoli
•Dense, roughly spherical bodies located
in the nucleus.
•Contain 10-20% of a cell's RNA.
•Ribosomal subunits are assembled in the
nucleolus from r-RNA and protein.
•Ribosome assembly is completed in the
cytoplasm
•Nucleoli disappear during mitosis.
•Appear and disappear as RNA
concentrations change.
•There may be more (or less) than 1
nucleolus per cell.

7. 7
Ribosomes
•Ribosomes are synthesized in the nucleolus.
•Proteins are made upon the ribosomes after the ribosomes have migrated from
the nucleus to the cytoplasm.
•Ribosomes are found in 3 sites in eukaryotic cells:
1. bound to the outer surface of the Rough E.R.
2. unbound in the cytoplasm
3. within the mitochondria and chloroplasts (these ribosomes are different
in structure!)
•Ribosomes are also found in prokaryotic cells (because they are NOT membrane-
bound)
•Ribosomes in both prokaryotes and eukaryotes consist of a pair of subunits:
•Blue = large subunit Yellow = small subunit in the diagram below
•Chemically, ribosomes consist of ribosomal RNA and protein.
•The function of the ribosome is to temporarily bind two other types of RNA (t-RNA
and m-RNA) during translation (the construction of protein.)
Large
Subunit
Small
Subunit
Ribosomes are the sites where the cell assembles proteins
according to genetic instructions. A bacterial cell may
have a few thousand ribosomes, although a human cell
has a few million. Cells that have high rates of protein
synthesis have a particularly great number of ribosomes.
Cells active in protein synthesis also have prominent
nucleoli, which make the ribosomes.
Ribosomes function in two cytoplasmic areas. Free
ribosomes are spread throughout the cytosol, while
bound ribosomes are attached to the outside of a
membranous network, endoplasmic reticulum. Most of
the proteins that are made by free ribosomes will function
inside the cytosol. The proteins produced by bound
ribosomes usually exported from the cell.
Each ribosome is built from two subunits, each having its
own mix of ribosomal RNA and proteins. Ribosomes are
built with RNA from the nucleolus and are made in the
nucleolus itself. These subunits join together to form a
functional ribosome only when they attach to a
messenger RNA molecule. The ribosomes present in
eukaryotic cells are slightly larger than those found in
prokaryotic cells.
Ribosomes function in protein synthesis. As they move
along messenger RNA, amino acids are joined in an order
originally dictated by DNA. Several ribosomes can be
moving along the same messenger RNA at once and the
entire complex is called a polysome.

8. 8
Energy-Processing (ATP-Generating) Organelles
Mitochondria
•Function - convert the potential chemical energy of fuel molecules into a form that
cells can use, namely ATP (or adenosine triphosphate).
•This process is termed cellular respiration.
•Small - about the size of bacteria.
•Consist of two membranes, an outer and an inner membrane. Both are
phospholipid bilayers.
•The outer membrane is merely protective.
•The inner membrane has many irregular folds, called cristae.
•It is within the cristae that ATP is generated. The cristae house the protein
molecules (cytochromes) that participate in chemiosmosis.
•Inside the cristae is a region called the mitochondrial matrix. Here we find
enzymes, ribosomes, and a circular loop of DNA.
•Mitochondria bear a striking resemblance to bacteria. Remember this.
•Cells that require the most energy have the most mitochondria.
Chloroplasts
•Site of photosynthesis, contains the green protein pigment chlorophyll.
•Like the mitochondrion, the chloroplast possesses 2 membranes.
•There is more variety in the arrangement of these membranes than there is in
mitochondria.

9. 9
•Within the inner membrane is a third membrane, the thylakoid, which is arranged
as interconnected foldings AND stacks.
•The structures that resemble stacks of coins are called grana.
•The fluid surrounding the thylakoid is called stroma.
•The chloroplast stroma contains ribosomes and DNA.
•ATP generation occurs in chloroplasts via chemiosmosis. This ATP is then used
(along with NADPH) to drive the light independent reactions of
photosynthesis (the Calvin cycle).
Other Plastids
•Contain carotenoid pigments. Red, orange, or yellow.
•Give color to petals and fruits to aid in pollination and
seed dispersal.
•No one, however, knows why carrots are orange.
Chromoplasts

10. 10
•Leucoplasts are storage sites in plant
cells for starch and fats.
•It is interesting to note that:
•All plastid types are related to
one another.
•All plastid types develop from
small protoplastids.
•Leucoplasts are sometimes called
amyloplasts.
Both Chloroplasts and Mitochondria are capable of self-replication. They are both the
size of whole prokaryotes. They both contain DNA and have ribosomes that are
similar to prokaryotic ribosomes.
Leucoplasts
Dr. Lynn Margulis, a Distinguished Professor of
Biology at The University of Massachusetts at
Amherst and a member of the National Academy
of Sciences, played a crucial role in introducing
the radical theory that eukaryotic cells (cells with
nuclei: protists, fungi, plants and animals)
evolved through a symbiotic relationship between
different kinds of prokaryotic cells (cells without
nuclei: bacteria and cyanobacteria). This
"Endosymbiosis Theory" is has become widely
accepted by biologists. Another widely accepted
theory, the "infolding theory," suggests that the
complex internal endomembrane system of
eukaryotic cells--such as the nuclear envelope,
endoplasmic reticulum, and Golgi body, evolved
as infoldings of the cell membrane that allowed
for the separate packaging of cellular processes.
Endosymbiosis
I have
Lynn's
autograph.