Beth
Cytology
The study of the structure and function of cells.
Structures
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Cell Membrane
Cytosol
Cytoskeleton
Microvilli
Cilia
Centrioles
Ribosomes
Mitochondria
Nucleus
Nucleolus
Rough Endoplasmic Reticulum
Smooth Endoplasmic Reticulum
Golgi Apparatus
Lysosomes
Peroxisomes
Nuclear Pores
Functions
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Isolation and protection
Distributes materials by diffusion
Internal Support
Absorption of extracellular material
Movement of materials over surfaces
Movement of chromosomes during cell division
Protein Synthesis
Produce 95% of the ATP required by the cell
Control of metabolism
Site of RNA synthesis
Secretory protein synthesis
Lipid and carbohydrate synthesis
Storage, alteration, and packaging of secretory products and
lysosomes
Intracellular removal of damaged organelles or pathogens
Neutralization of toxic compounds
Allow the movement of ions and small molecules
Cell Theory
1. Cells are the building blocks of all plants and
animals.
2. Cells are produced by the division of preexisting
cells.
3. Cells are the smallest units that perform all vital
physiological functions.
4. Each cell maintains homeostasis at the cellular
level.
5. Homeostasis at the tissue, organ, system, and
individual levels reflects the combined and
coordinated actions of many cells.
Two most common methods used to
study cell and tissue structure:
• Light Electron Microscopy
• Scanning Electron Microscopy
Light Microscopy
Can magnify cellular structures about
1,000 times and show details as fine as
0.25 µm (micrometer or micron). With
a light microscope one can identify cell
types and see large intracellular
structures.
Electron Microscopy

Transmission Electron Microscopy
Electrons pass through
an ultrathin section to
strike a photographic
plate. Transmission
Electron Microscopy
shows the fine structure
of cell membranes and
intracellular structures.

Scanning Electron Microscopy
Electrons bouncing off
exposed surfaces create a
scanning electron
micrograph. Although
Scanning Electron
Microscopy provides less
magnification, it provides a
three-dimensional
perspective on cell structure.
The Study of Cell Structure
THE CELL
Cell Membrane
Cytoplasm
Cytosol
Organelles
NonMembranous
Organelles
Membranous
Organelles
Non-membranous
Organelles
• Cytoskeleton
• Microvilli
• Centrioles
• Cilia
• Flagella
• Ribosomes
Membranous
Organelles
• Mitochondria
• Nucleus
• Endoplasmic
Reticulum
• Golgi Apparatus
• Lysosomes
• Peroxisomes

The net movement of material from an area
where its concentration is relatively high to an
area where its concentration is relatively low.

The difference between the high and low
concentrations represents a concentration
gradient and diffusion takes place until that
gradient has been eliminated.
Diffusion
Important factors that influence
Diffusion rates:
 Distance- The greater
the distance, the longer
the time required.
 Size of Gradient- The
larger the concentration
gradient, the faster
diffusion proceeds.
 Molecular Size- Ions and
small organic molecules
such as glucose diffuse
faster than large
proteins.
 Temperature- The higher
the temperature, the
faster the diffusion rate.
Diffusion (continued)
 Three major factors determine whether or not a
substance can diffuse across a cell membrane.
 These major factors are lipid solubility, channel size,
and electrical interactions.
Osmosis
 The movement of water across
a semipermeable membrane
toward a solution containing a
relatively high solute
Three characteristics of osmosis should
concentration.
be remembered:
1.
2.
3.
Osmosis is the diffusion of water
molecules across a membrane.
Osmosis occurs across a selectively
permeable membrane that is freely
permeable to water but not freely
permeable to solutes.
In osmosis water will flow across a
membrane toward the solution that
has the highest concentration of
solutes, because that is where the
concentration of water is lowest.
Osmosis (continued)
 Isotonic is one that has the same solute concentration
as does the cytoplasm.
 Hypotonic solution has a solute concentration lower
than that of the cytoplasm.
 Hypertonic solution has a solute concentration higher
than that of the cytoplasm.
Facilitated Diffusion
Receptor-Mediated
Endocytosis
• Produces vesicles that
contain a specific
target molecule in high
concentrations.
• Begins when materials
in the extracellular fluid
bind to receptors on
the membrane surface.
• Resembles pinocytosis,
but is far more
selective.
Filtration
Phagocytosis
• Produces vesicles containing solid objects that may
be as large as the cell itself.
Active
Active Transport
Endocytosis
• Carrier molecules work
regardless of any
concentration
gradients.
• Creation of vesicles
containing fluid or solid
material.
• Gap Junctions- Two cells are
held together by an
interlocking of membrane
proteins.
• Tight Junctions- Partial fusion
of the lipid portions of the two
cell membranes.
Cell Attachments

Intermediate Junctions- The opposing cell membranes, while
remaining distinct, are held together by a thick layer of
proteoglycans.

Desmosomes- There is a very thin proteoglycan layer
between the opposing cell membranes.
CELL
ATTACHMENTS
(CONTINUED)
Junctional Complexes

Hold together the cells lining
passageways such as the
digestive tract and respiratory
tract.
Interphase

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G0 Phase- the cell is not
preparing for mitosis.
G1 Phase- the cell
manufactures enough
mitochondria, centrioles,
cytoskeleton elements,
endoplasmic reticulum,
ribosomes, Golgi bodies,
and cytosol to make 2
functional cells.
• S Phase- over the next 6-8
hours the cell duplicates
itself.
Interphase
(continued)


Gm Phase- begins
mitosis.
G2 Phase- the cell does
last minute protein
synthesis.
4 stages
MITOSIS

Begins when the
chromosomes coil so
tightly that they
become visible as
individual structures.
As a result of DNA
replication during the S
phase, there are 2
copies of each
chromosome, called
chromatids, connected
at a single point, the
centromere.

As the chromosomes
appear, the 2 pairs of
centrioles move apart.
Spindle fibers extend
between the centriole
pairs; smaller
microtubules radiate
into the disappearance
of the nuclear
envelope.
Stage 2:
Metaphase
The chromatids now move to a narrow central zone called the metaphase plate.
A microtubule of the spindle apparatus attaches to each centromere.

This stage is in many ways the reverse of
prophase, the nuclear membranes form, the
nuclei enlarge, and the chromosomes
gradually uncoil. Once the chromosomes
disappear, nucleoli reappear and the nuclei
resemble those of interphase cells.
Cytokinesis
Is the separation of the two daughter cells. It usually begins in late Anaphase
and continues through Telophase. The completion of cytokinesis marks the end
of cell division.