Download The Cell - University of South Carolina

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THE CELL
Robert W. Ogilvie, Ph.D.
Roger H. Sawyer, Ph.D.
Professor Emeritus
Professor , Biological Sciences
Medical University of South Carolina
Executive Associate Dean,
Visiting Professor
College of Arts & Sciences
University of South Carolina
University of South Carolina
This lecture will describe the generic cell, its organelles
and inclusions. It will explain how the more than 200
unique cell types in the body are derived from
embryological origins and how different cell populations
in the adult are maintained by mitosis and two means of
cellular death. This lecture is intended to review cell
structure and function for those who can recall courses in
high school and college that presented cell biology and to
serve as basic information for those who may have not
had such courses. Most all students who have reached
junior status in college have had some exposure to cell
structure and function.
Cell Structure, Function & Differentiation
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Relevant Resources

Textbook
 Cell
Biology Lecture PDF containing slides and
narrative text of this lecture

Laboratory Exercise
 WebMic
Program
 WebMic
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Study Guide
Unit 1: Study Guide Plan, WebMic Information & Tutorial
Learning Outcomes
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These are the resources that relate to the content of this
lecture. The lecture PDF downloadable from the
Blackboard Course Website contains all of the slides and
the narrative of this lecture. Continue to practice and
refine your interaction with WebMic and understanding
of the WebMic Study Guide Plan. There is no lab
exercise on cell structure.
These are the learning outcomes for this lecture. A quiz
is offered at the end of the lecture that will assist you in
assessing your understanding of the content of this
lecture.
After completing a study of this lecture, you should be able to:
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explain the difference between a prokaryotic and eukaryotic cell.
describe a generic cell, list organelles and inclusions , their
function and explain the difference between them.
explain the process of differentiation and how it plays a significant
role in the creation of more than 200 different types of cells in the
human body.
list 3 cell populations in the adult and give examples of each.
describe the cell cycle differentiating between the M phase and
the Interphase.
list the stages of mitosis.
distinguish between meiosis and mitosis.
define & differentiate between two mechanisms of cell death.
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Vocabulary
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The Cell
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Organelles
Inclusions
Mitochondria
Rough Endoplasmic Reticulum
Ribosomes
Smooth Endoplasmic Reticulum
Nucleus
Nucleolus
Golgi complex
Cell membrane
Centrioles
Euchromatin
Heterochromatin
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Prokaryotic Vs. Eukaryotic
Cells
Compartments of the Cell
Light & Electron
Microscopic Views of a cell
Cell Complexity
Cell Organelles and
Inclusions
Cell Factory Analogy
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Origin of Adult Cells
Examples of
Differentiated Cells
Cell Populations
Cell Cycle
Mitosis
Mitosis vs. Meiosis
Cell Death
Cell Homeostasis
The Cell: in levels of organization
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Cytoskeleton
Microfilaments
Intermediate filaments
microtubules
Cell Cycle
Mitosis
Meiosis
Necrosis
Apoptosis
Differentiation
Homeostasis
Static cell population
Stable cell population
Dynamic cell population
Lecture Topics
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This is the vocabulary of terms that you should be able to
define. Look for these terms as you view this lecture and
consult with the course glossary for the definitions.
Small molecules
Macromolecules and aggregates of molecules
Cells
Tissues
Organs
Organ Systems
Organism
Each of the topics listed on this slide is hyperlinked to the
first slide that begins that topic. You can jump to any
topic. When you reach the first slide for a certain topic,
you will find on that slide a button to click that will return
to slide. This should make it convenient during review.
To begin, let's see where the cell fits into the different
levels of organization of a biological organism. The cell
is defined as the smallest unit of a living organism
capable of independent existence. In this scheme of
organization from small molecules to the organism, the
cell is the basic living structure that is the ‘block’ or '
brick' with which the body is constructed. Cells and their
secretions constitute the material that is used to construct
tissues, organs and organ systems.
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The Cell
Prokaryotic vs. Eukaryotic Cells
Eukaryotic Cell
Prokaryotic Cell
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Without a nucleus
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 Bacteria
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With a nucleus
 Plant
nucleoid
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& Animal Cells
nucleus
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Cell Compartments
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Two Compartments: Cytoplasmic (c) and Nuclear (n)
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Cytoplasmic/nuclear (c/n) ratio
n
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epithelial cells
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n
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Cytoplasm and Nucleus (stain: hematoxylin & eosin)
Satellite cell nucleus
(heterochromatin)
Nucleus
(euchromatin)
Cell
Limit
Nucleolus
cytoplasm
All cells have two main compartments: the cytoplasmic
compartment containing cytoplasm and the nuclear
compartment containing nucleoplasm. In normal cells there is
a constant ratio of nuclear volume to cytoplasmic volume. The
larger the volume of cytoplasm, the larger the volume of the
nucleus will be because the information contained within the
nucleus and nucleolus has to match the size and activity of the
cytoplasm. This normal ratio is upset in cancer cells because
cancer cells have a much higher volume of the nucleus to the
volume of cytoplasm………..in other words, the nucleus is
cancer cells abnormally large. The resulting shape difference
between the epithelial and nerve cells illustrated here is the
direct result of gene directed differentiation from stem cells.
This occurs first in the embryo and fetus and later in the adult,
resulting in specialized adult cells like these epithelial and nerve
cells as examples of the more than 200 unique cell types in the
human body.
nerve cells
Light Microscope View of a Cell
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Some cells have nuclei and others do not. All animal
cells have nuclei. The term karyose comes from a Greek
word meaning “kernal”. Pro means before or no kernal.
Eu means true or having a kernal. Biologists use karyo to
refer to the nucleus. A prokaryotic cell, example –a
bacterium, has no nucleus. It contains the DNA in a
circular organization with no end in a region called the
nucleoid that is only a region and not bounded or
confined by a membrane. Bacteria are so small that all
parts of the cell are close together and therefore, there is
no need for the organization as in eukaryotic cells.
Eukaryotic cells contain a nucleus enclosed by a
membrane. The nucleus sequesters the DNA in a
chamber for efficient exchange of genetic information
with the cytoplasmic structures. Eukaryotic DNA is
linear.
In this example of a nerve cell stained with hematoxylin
and eosin, you can see the extent to which you can
resolve cell components in the using a light microscope.
In this particular nerve cell, the nucleolus is large and the
DNA in the nucleus is fully extended in a form that is
called euchromatin. The combination of the extended
DNA and the large nucleolus is indicative of very active
protein synthesis with the DNA providing the gene code
information and the nucleolus providing the source of
ribosomal RNA. By contrast, look at the satellite cell
nucleus. The nucleolus is not visible and the DNA is
condensed in a form called heterochromatin. The
morphology of the nucleus where the DNA is condensed
is indicative of a cell that is not very active or not active
at all in protein synthesis. The cytoplasm of this nerve
cell has patches of blue distributed in a background of
pink. The blue staining indicates patches of ribosomes
containing RNA carrying a negative charge reacting with
the positive charged hematoxylin and the pink staining
indicates membrane carrying a positive charge reacting
with the negatively charged eosin. Observe also that the
The Cell
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Electron Microscope View of a Cell
Rough
Endoplasmic
Reticulum
(tiny dots are
ribosomes)
Cisterna of
endoplasmic
reticulum containing
newly synthesized
proteins showing as
flocculent material
Heterochromatin
of the
nucleus
Euchromatin of
the nucleus
Nucleolus
detail of the cell membrane cannot be
resolved……………only the cell limit. In the following
slides, the content of the nucleus, the cytoplasm and the
cell membrane will be presented. The purpose of
presenting more detail of cell structure that can only be
resolved with an electron microscope is to provide an
understanding of what is behind your observation of
different cell types in this course.
In this electron microscope view of a cell, one can see
cell components such as the rough endoplasmic
reticulum, the endoplasmic reticulum cisterna, the
nucleolus, a lysosome and the two expressions of DNA in
the nucleus –heterochromatin and euchromatin resolved
in greater detail than when using a light microscope.
When you encounter the many cell types as you learn
histology, keep in mind the structures in the cytoplasm
and nucleus that stain blue or pink with the hematoxylin
and eosin stain. In this way, you can appreciate whether
a cell is active and what components in the cytoplasm are
dominant. This is only an approximation but a helpful
one.
Lysosome
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Cell Complexity
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http://commons.wikimedia.org/wiki/File:Cell_structure_large.png
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This drawing from the commons wiki web site illustrates
the complexity of an eukaryotic cell. Just as the body is
divided into compartments by epithelial tissues and
basement membranes, the cell is also compartmentalized
by the cell membrane and intracellular membranes. The
next few slides will present the components /
compartments of the cell.
The Cell
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Cell Organelles and Inclusions
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Organelles –structures that serve to perform functions
that require energy
Membranous organelles are mitochondria, endoplasmic
reticulum, Golgi complex, lysosomes, cell membrane,
microbodies, multivesicular bodies, coated vesicles,
secretory granules and the nucleus.
 Non-membranous organelles are nucleolus, ribosomes,
microfilaments, microtubules, centrioles, cilia, flagella and
chromosomes
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Inclusions are chemically inert substances that appear
and disappear during cell activity
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Inclusions include glycogen, stored lipid, crystals,
pigments, keratin
Plasma Membrane
Membranous Organelle
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These molecules projecting from the
Plasma membrane surrounds the
cell membrane form the cell coat
cytoplasm controlling traffic into
and out of the cell
Carbohydrates Glycolipids Glycoproteins
Consists of a lipid bi-layer
interspersed with cholesterol
molecules and with proteins that
float in this layer
Proteins serve as
lipid
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Pumps
Channels
Receptor proteins
Linker proteins
Enzymes
Structural proteins
bilayer
The cell coat (glycocalyx) serves
to give identity to the cell as cells
interact in the immune reaction,
receptors for hormones and
influence cell to cell associations
cholesterol
molecule
microfilaments of the cytoskeleton
cytoplasm
Organelles are structures in the cell that perform
functions that require energy and are contrasted with
inclusions that are inert substances that appear and
disappear during cell activity. There are two classes of
organelles depending on whether or not they are bound
by a membrane; membranous or non-membranous
organelles. Membranous organelles include
mitochondria, endoplasmic reticulum, the Golgi complex,
lysosomes, the cell membrane, microbodies,
multivesicular bodies, coated vesicles, secretory granules
and the nucleus. Non-membranous organelles include the
nucleolus, ribosomes, microfilaments, microtubules,
centrioles, cilia, flagella and chromosomes. Inclusions
include pigments and other substances such as glycogen,
lipid that are stored and not a part of a cell structure,
crystals such as cholesterol crystals and keratin, the
protein that fills the dead cells in the superficial layers of
cells in the skin. The following slides will present
organelles in more detail.
The plasma membrane and other membranes within the
cell are of paramount importance in maintaining
compartments and regulating ions and water levels. The
membranes are semipermeable and composed of two
lipid layers (lipid bilayer) with proteins that are fixed or
float in that lipid bilayer. Cholesterol molecules inserted
into the lipid bilayer provide an element of stiffness to the
plasma membrane. The proteins integral within the
membrane act as pumps, channels, receptors, linkers,
enzymes and provide structure. The proteins provide a
link to the extracellular environment. The plasma
membrane is intimately connected with the interior of the
cell via linker molecules and the microfilaments of the
cytoplasm. Molecules projecting from the cell are
carbohydrates, glycolipids (complexes of carbohydrates
and lipids) and glycoproteins (complexes of
carbohydrates and proteins). This forms the cell coat that
gives unique identity to each cell, provides receptors for
hormones and influences association between cells.
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Nucleus
membranous organelle
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The Cell
Contains DNA
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Usually in the form of euchromatin and/or heterochromatin
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Contains genetic information
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Composed of DNA
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Thicken to form chromosomes for cellular division
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Set number per species (23 pairs for humans)
Nuclear membrane
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Surrounds nucleus
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Composed of two layers
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Numerous openings (pores) for nuclear-cytoplasmic traffic
The nucleus is the main repository of DNA. The DNA
takes several forms. If it is uncoiled, it is euchromatin, if
coiled it is heterochromatin, and if fully condensed, it is
in the form of chromosomes. The nuclear membrane is
porous to provide for interchange of information between
the nucleoplasm and the cytoplasm. The nucleolus is
located within the nucleoplasm and is not bounded by
any membrane. It contains RNA that contributes
particles called ribosomes that function in protein
synthesis in the cytoplasm.
Nucleolus
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Spherical shape
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Visible when cell is not dividing
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Contains RNA for protein manufacture
The rough endoplasmic reticulum (rER) is a membrane
shaped into tubules that form a network that
communicates with the nuclear membrane and the plasma
membrane. It is involved in synthesis and transport of
protein molecules. A reticular membrane without
ribosomes attached is called the Smooth Endoplasmic
Reticulum (sER). The next slide explains and illustrated
sER.
Rough Endoplasmic Reticulum
membranous organelle
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Network of tubes or flattened
sacs fused to the nuclear
membrane
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Goes through cytoplasm and is
continuous with the cell
membrane
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Stores, separates and serves as
cell’s transport system
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Rough type: ribosomes
embedded in the reticulum
membrane and functions to
synthesize proteins
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Smooth type: lacks ribosomes
and functions in steriod
synthesis and glycogen
metabolism
see next slide
Smooth Endoplasmic Reticulum
membranous organelle
 Contains
no ribosomes
metabolism
 Sequesters calcium in
muscle cells
 Detoxification
function in liver cells
 Glycogen metabolism
M
 Lipid
sER
M
M
M
M
L
M = mitochondria, L = Lipid, sER = smooth endoplasmic reticulum
M
Smooth endoplasmic reticulum (sER) is a network of
membranes that lacks any association with ribosomes. It
has a large presence in cells that are involved in lipid
metabolism. It sequesters calcium in muscle cells to relax
muscle. It proliferates in liver cells when excess lipid is
in the diet. It contains a variety of detoxifying enzymes
that modify and detoxify hydrophobic compounds such
as pesticides and carcinogens by converting them into
water-soluble products that can be eliminated from the
body; sER also contains glycogen metabolizing enzymes.
Note in the electron micrograph the network of smooth
endoplasmic reticulum (sER) with several mitochondria
in intimate association. Note the large lipid droplet (L)
around which is a mitochondrion. Mitochondria (M) are
involved in lipid metabolism.
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The Cell
Golgi Apparatus & Lysosomes
Membranous Organelles
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Golgi Apparatus-membranous organelle
Protein ‘packaging plant’
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A membrane structure found near nucleus
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Composed of numerous layers forming a sac
Lysosome-membranous organelle
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Digestive ‘plant’ containing enzymes for
degrading proteins, lipids, and carbohydrates
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Transports undigested material to cell
membrane for removal
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Vary in shape depending on process being
carried out
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Cell breaks down if lysosome explodes
Mitochondrium
Membranous Organelle
Mitochondriamembranous organelle
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Second largest organelle
with unique genetic
structure
Double-layered outer
membrane with inner folds
called cristae
Energy – producing
chemical reactions take
place on cristae
Controls level of water and
other materials in cell
Recycles and decomposes
proteins, fats and
carbohydrates and forms
urea
Ribosome
Non-membranous Organelle
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Ribosomes*
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The Golgi apparatus is a membranous organelle that
serves to add to or modify and package products
synthesized on the rough endoplasmic reticulum. It also
forms lysosomes. The lysosome is a membranous bag
which contains hydrolytic enzymes that are used to digest
macromolecules. The lysosome contains over 40
enzymes, some of which are the proteases, nucleases, and
phopholipases.
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Each cell contains thousands
Miniature ‘protein factories’
Composes 25% or more of cells’
mass if cell is mainly synthesizing
protein
Stationary type: embedded in rough
endoplasmic reticulum
Mobile type, unattached to
membrane: injects proteins directly
into cytoplasm
*When ribosomes are not attached to the endoplasmic reticulum they are
considered non-membranous organelles, but when attached they are part
of a membranous organelle – the rough endoplasmic reticulum.
A mitochondrion (plural mitochondria) is a membraneenclosed organelle found in most eukaryotic cells. These
organelles range from 0.5 to 10 micrometers (µm) in
diameter. Mitochondria are sometimes described as
"cellular power plants" because they generate most of the
cell's supply of adenosine triphosphate (ATP), used as a
source of chemical energy. In addition to supplying
cellular energy, mitochondria are involved in a range of
other processes, such as signaling, cellular differentiation,
cell death, as well as the control of the cell cycle and cell
growth. Mitochondria have been implicated in several
human diseases, including mitochondrial disorders and
cardiac dysfunction, and may play a role in the aging
process. The word mitochondrion comes from the Greek:
mitos, meaning thread and chondrion, meaning granule.
Eukaryotic ribosomes are between 25 and 30 nm (250300 ångströms) in diameter and the ratio of rRNA to
protein is close to 1. Ribosomes translate messenger
RNA (mRNA) and build polypeptide chains (e.g.,
proteins) using amino acids delivered by transfer RNA
(tRNA). Their active sites are made of RNA, so
ribosomes are now classified as "ribozymes". Ribosomes
build proteins from the genetic instructions held within
messenger RNA. Free ribosomes are suspended in the
cytosol (the semi-fluid portion of the cytoplasm); others
are bound to the rough endoplasmic reticulum, giving it
the appearance of roughness and thus its name.
Ribosomes are also bound to the nuclear envelope.
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Vaculoles
Membranous Organelles
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The Cell
Vacuoles
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Membrane-bound sacs for
storage, digestion and
waste removal
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Contains water solution
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Contractile vacuoles for
water removal (in
unicellular organisms such
as an amoeba)
Centrioles
Non-membranous Organelles
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Centrioles-non membranous
organelle
Paired cylindrical organelles near
nucleus arranged at right angles to
each other
 Composed of nine tubes, each with
three tubes
 Involved in cellular division & the
formation of cilia
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Cytoskeleton
Non-membranous Organelle
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The cytoskeleton is a system of
microfilaments, microtubules,
intermediate filaments
 The cytoskeleton organizes the
cytoplasm by:
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creating a dynamic organization of
cytoplasmic structures
providing the means of transport of
information and structures through
the cytoplasm
creating and maintaining the different
morphological design and shape that
is unique to each the more than 200
different cell types in the body
A vacuole is a membrane-bound organelle which is
present in all plant and fungal cells and some protist,
animal and bacterial cells. Vacuoles are essentially
enclosed compartments which are filled with water
containing inorganic and organic molecules including
enzymes in solution, though in certain cases they may
contain solids which have been engulfed. Vacuoles are
formed by the fusion of multiple membrane vesicles and
are effectively just larger forms of these. The organelle
has no basic shape or size, its structure varies according
to the needs of the cell.
A centriole is a barrel-shaped cell structure found in most
animal eukaryotic cells, though absent in higher plants
and most fungi. The walls of each centriole are usually
composed of nine triplets of microtubules (protein of the
cytoskeleton). An associated pair of centrioles, arranged
perpendicularly and surrounded by an amorphous mass of
dense material (the pericentriolar material) constitute the
compound structure known as the centrosome (the center
of the cell). Centrioles are involved in the organization of
the mitotic spindle in mitosis and in the completion of
cytokinesis in cell division. Centrioles are a very
important part of centrosomes, which are involved in
organizing microtubules in the cytoplasm. The position
of the centriole determines the position of the nucleus and
plays a crucial role in the spatial arrangement of the cell.
Centrioles are the source of basal bodies that lie just
within the peripheral aspect of some epithelial cells.
Basal bodies form cilia.
As the human body has shape and form due to the bones
that comprise the skeleton, each cell of the body has its
own skeleton resulting in unique shape and form. The
cytoskeleton of each cell consisting of microfilaments,
microtubules and intermediate filaments is responsible
for this. In addition, the cytoskeleton provides the solid
state structures upon which some organelles, such as
secretory granules and coated vesicles, are transported
within the cytoplasm of the cell. Without the
cytoskeleton, the cytoplasm would be like a soup with its
components suspended, but, no chance for organized
movement of its components. The next slide illustrates
two cytoskeletal components, microfilaments and
microtubules.
The Cell
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Cytoskeletal Components
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Microfilaments
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Microtubules
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Actin protein
Diameter, 6-8 nm
Core of microvilli, beneath
plasma membrane, contractile
element in muscle
Tubulin
Diameter, 20-25 nm
Form the core of cilia, present
in all cells – especially
numerous in neurons where
neuronal transport with the
nerve cell processes is made
possible by microtubules
Cell – Factory Analogy
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The nucleus (1) is the managing
director of the factory consulting the
blueprint (the chromosomes) (2);
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The mitochondria (3) supply the power
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The ribosomes (4) make the products;
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The chloroplasts of plant cells (5)
supply the fuel (food)
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The Golgi apparatus (6) packages the
products ready for dispatch;
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The ER (7) modifies, stores and
transports the products around the
factory;
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The plasma membrane is the factory
wall and the gates (8);
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The lysosomes dispose of the waste
and worn-out machinery.
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Microfilaments (mf) and microtubules (mt) are
illustrated. Microfilaments are composed of actin, have
diameter of 6-8 nm and form the core of microvilli. They
also form a network at the peripheral aspect of the
cytoplasm of most cells. Microfilaments made of actin
are also one of the contractile elements in a muscle cell.
Microtubules are composed of subunits of the protein
tubulin, have a diameter of 20-25 nm and form the core
of cilia. They play a very important role in the transport
of molecules throughout the extensive processes of nerve
cells.
This illustration and analogy comparing a cell to a factory
may be helpful in understanding cell structure and
function. The nucleus is like the manager of a factory
giving out instructions for all cell activity. The
mitochondria supply the electricity. The ribosomes are
like the employees of a factory making the products. The
Golgi apparatus is like the wrapping and packaging
department where the products are prepared for shipping.
The ER (endoplasmic reticulum) is like a system of
transport devices or vehicles in a factory that carry out
transportation of components used to make the products.
The plasma membrane is like the external walls, doors,
gates of a factory that control what comes in and what
leaves the factory. The lysosomes are like recycling
processes in a factory where some materials are recycled
and others are disposed of in dumpsters.
So, where do specialized adult cells come from? Of course, the most
early origin is the fusion of the sperm and egg to form a zygote. The
earliest form where cells can be traced back to in the embryo is the
blastocyst containing the inner cell mass where experimenters obtain
stem cells for experimentation. In this scheme that displays the
pathways of differentiation of cells from the three germ layers, you can
see where the Trilaminar Disc of Early Embryological Development fits
into the context of the overall process of development. It is the next
stage in development after the blastocyst stage where the inner cell mass
contains the totipotential cells that give rise to all of the cells of the
human body. Following the color scheme, we can see the components
of the body that are derived from the three germ layers. Cellular
differentiation is the process where Gene expression results in uniquely
different cell types. Genes determine the final differentiation of each of
the more than 200 cell types in the human body resulting 1) the final
shape and size of the cell, 2) the shape of the nucleus, and 3) the unique
presence and proportion of the cytoplasmic components – for example,
the quantity and proportion of smooth and rough endoplasmic
reticulum, the number of lysosomes and intracellular vacuoles, the
quantity and organization of intracytoplasmic microtubules and
microfilaments. The next slide will illustrate and explain specifically
what happens in the trilaminar disc stage.
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The Cell
The Trilaminar Disc of the Embyro
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The more than 200 cell types of the human body begin to
take on their unique shape and composition just after the
blastocyst stage of human embryological development
when a trilaminar disc shaped structure forms as the
result of migration of embryonic cells. The cells in the
three layers are pluripotential, meaning that they can each
differentiate into multiple cells types. The top layer
(blue) consists of neuroectodermal cells that give rise to
nerve and epithelial tissue cells. The middle layer (red)
consists of mesodermal (mesenchymal) cells that will
form muscle and connective tissue. The lower layer
(yellow) consists of cells that will form the epithelium
that lines the gastrointestinal tract and the glands
associated with the intestinal tract.
Process of differentiation produces >200 Cell Types & their products
that make up body structures & organs
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Examples of Differentiated Cells
erythrocyte
neuron
monocyte
fibroblast
goblet cell
eosinophil
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plasma cell
Skeletal muscle cell
thyroid cell
mast cell
Here are some examples to illustrate the variety of cells that are derived
from the cells of the trilaminar disc by the process of differentiation
creating cells that have unique architectures and perform unique
functions. From left to right and top to bottom:
•
erythrocyte (from mesoderm) that is a cell that loses its
nucleus and assumes a biconcave disc shape to maximize the
surface area for carrying oxygen.
•
The neuron (from neuro ectoderm) with its large nucleus
mostly of euchromatin and a prominent nucleolus is
constantly synthesizing protein (e.g. acetylcholine esterase)
and transporting it down the long axons via a microtubule
associated transport system.
•
The monocyte (from mesdoderm) with its large nucleus to
support the formation of many lysosomes for phagocytosis.
•
The fibroblast (from mesoderm) with its elongated shape
lies along collagen fibers and synthesizes collagen protein
(thus the blue staining rough endoplasmic reticulum).
•
•
parietal cell
•
•
•
•
•
•
•
•
•
duct cell
Intestinal cell
taste bud cell
Fat cell
The goblet cell (from endoderm) becomes engorged
with mucus and then spits it out in cycles.
The eosinophil (from mesoderm) loaded with
granules interacts and neutralize parasites.
The plasma cell (from mesoderm) with lots of rough endoplasmic reticulum for manufacturing antibodies (protein).
The skeletal muscle cell (from mesoderm) composed mostly of actin (thin) and myosin (thick) filaments for
contraction for movement.
The thyroid follicular cell (from endoderm) that synthesizes thyroglobulin and thyroid hormone.
The mast cell (from mesoderm), full of eosinophilic granules that store and release histamine and a variety of other
substances.
The parietal cell (from endoderm), the hydrochloric acid producing cell of the stomach that has a very red
acidophilic cytoplasm because of the large amount of mitochondria it contains to provide the energy for the
membrane pumps that create the hydrochloric acid.
A duct cell (from oral ectoderm) that lines, for example, the ducts of salivary glands………….the cell acts to add and
remove substances from the secretion of the gland….its acidophilic cytoplasm reflects basal infoldings of the plasma
membrane with lots of mitochondria.
The intestinal cell (from endoderm) responsible for absorption of molecules from the intestinal lumen has a border
rich in tiny projections called microvilli that increase the surface area for absorption.
The taste bud cell (from ectoderm) with it projections into the pore in the oral cavity for picking up ions and
transducing them into taste.
And finally, the fat cell (from mesoderm) that stores fat. It looks empty because the lipid that it contained in its huge
vacuole was dissolved by the chemicals use to process the tissue for microscopy. Note the single flattened nucleus to
one side within a very thin rim of cytoplasm…………..the majority of the cell is the lipid in a large vacuole.
Hopefully this tour 15 of the more than 200 cell types in the human body has helped in your appreciation of the
process of differentiation and the importance of unique architecture designed for function. As you proceed through the
course consider listing each cell type you learn logging in a brief description and its function. This will not only help you realize
how many cell types you learn, but will also serve to put the structure and function of organs into context because cells are the key
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Cell Populations

Three cell populations
 Static:
no longer divide (post mitotic)
 Neurons,
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The Cell
 Stable:
cardiac or skeletal muscle cells
divide episodically and slowly
 Smooth
muscle and lining cells of blood vessels
 Dynamic
and Renewing: regular reoccurring mitosis
 Blood
cells in the bone marrow
 Epithelial cells

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Skin is example of slow, every 2 two weeks cells are renewed
Oral cavity lining is example of fast, every three days epithelial
lining is renewed
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Cell Cycle
State
Phase
Abbreviation
quiescent /
senescent
Gap 0
G0
A resting phase where the cell has left the cycle and
has stopped dividing
Interphase
Gap 1
G1
Cells increase in size in Gap 1. The G1 checkpoint
control mechanism makes certain that everything is
ready for DNA synthesis.
Synthesis
S
DNA replication occurs during this phase
Gap 2
G2
During the gap between DNA synthesis and mitosis,
the cell will continue to grow. The G2 checkpoint
control mechanism makes certain that the cell is
ready to enter the M (mitosis phase and divide.
Mitosis
M
Cell growth stops at this stage and cellular energy is
focused on the orderly division into two daughter
cells. A checkpoint in the middle of mitosis
(metaphase) makes certain the cell is ready to
complete cell division.
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Cell
division
Description
The cells of the body fall into three different populations:
1) Static, 2) Stable and 3) Dynamic. The static
population consists of cells that are post-mitotic in the
adult human meaning that these cells cannot divide at all
and if lost, then the organ is less those cells. In the brain,
a stroke usually results in the death of a variable number
of neurons that are not replaced. In the heart after a heart
attack, a variable number of cardiac myocytes die
depending on the severity of the infarct. These cells are
replaced by scar tissue, not cardiac myocytes, so the
function of the heart may be weakened. Another
population category is call Stable and these cells divide,
but only episodically and slowly. Cells, like smooth
muscle cells that make up part of the structure of the
walls of blood vessels and the gastrointestinal tract, may
divide, but very slowly and intermittently. A third
population category is called Dynamic or Renewing.
Cells in this population undergo regular recurring mitosis.
In the bone marrow, as one example, a huge number of
cells are constantly dividing to provide replacements for
the equally huge number of blood cells that are destroyed
in the normal function of the body. Epithelial tissue cells
divide often, very often in the GI tract and slower in the
skin. Every two weeks the surface layer of your skin is
renewed by cell division producing replacements for the
epidermal cells that fall off of the body constantly.
Now, let's consider the cell cycle, a dynamic process in
which cells are either resting, preparing for mitosis or
undergoing mitosis. There are two phases of the cell
cycle – the Interphase and Mitosis. Cells in interphase
are preparing to divide and in the mitosis phase, they are
dividing. Preparing for cell division in interphase, a cell
first increases in size while checking that all is ready for
DNA synthesis and this is termed the Gap 1 phase. Next,
DNA is replicated and this is the synthesis phase of
interphase. Next, the cell enters a gap between synthesis
and mitosis when the cell increases further in size and
continues checking for readiness of cell division and this
is the Gap 2 phase. Finally, when ready, the cell enters
the mitosis phase known as the M phase. Cells that have
left the cycle and stopped dividing are referred to as
quiescent / senescent and are designated to be in the Gap
0 phase. Mitosis is the process of chromosome
segregation and nuclear division followed by cell division
that produces two daughter cells with the same
chromosome number and DNA content as the parent cell.
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The Cell
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Mitosis
prophase
> metaphase
> anaphase
> telophase
3
0
Drawing copied from http://en.wikipedia.org/wiki/Mitosis
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Mitosis and Meiosis Compared
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prophase > metaphase > anaphase > telophase
Drawing copied from http://en.wikipedia.org/wiki/Mitosis
Four
haploid
cells
Drawing copied from http://en.wikipedia.org/wiki/Meiosis
Mitosis is the process by which a eukaryotic cell
separates the chromosomes in its cell nucleus into two
identical sets and sequesters the chromosomes in two
nuclei. This process undergoes 4 main phases: 1)
prophase, when the chromatin in the nucleus condenses
and forms chromosomes followed shortly by the
disappearance of the nuclear membrane, 2) metaphase,
when the chromosomes align along a plate region in the
center of the cell, 3) anaphase, when, by shortening of the
microtubules, the duplicate chromosomes are separated
moving to the two poles of the cell, and finally, 4)
telophase, when the two groups of chromosomes are
surrounded by nuclear membranes that is immediately
followed by an uncoiling of the DNA with
simultaneously disappearance of the chromosomes and
the beginning of cytokinesis as evidence by the presence
of a cleavage furrow. Mitosis is generally followed
immediately by cytokinesis, which divides the nuclei,
cytoplasm, organelles and cell membrane into two cells
containing roughly equal shares of these cellular
components. Mitosis and cytokinesis together define the
mitotic (M) phase of the cell cycle—the division of the
mother cell into two daughter cells, genetically identical
to each other and to their parent cell. This accounts for
approximately 10% of the cell cycle.
So now, let's compare mitosis with meiosis, the process
that produces a sperm and egg. Mitosis is the process by
which a eukaryotic cell separates the chromosomes in its
cell nucleus into two identical sets in two nuclei. It is
generally followed immediately by cytokinesis, which
divides the nuclei, cytoplasm, organelles and cell
membrane into two cells containing roughly equal shares
of these cellular components.
Meiosis involves two sequential nuclear divisions
followed by cell divisions that produce gametes
containing half the number of chromosomes and half the
DNA found in somatic cells. Anaphase I and telophase I
are similar to the same phases in mitosis except the
centromeres do not split. The sister chromatids remain
together. At the completion of meiosis I the cytoplasm
divides. Each daughter cell is haploid in chromosome
number (1n) but the cell is still diploid in DNA content
(2d). After meiosis I the cells enter meisois II without
passing through the S phase. Sister chromatids are now
separated and after passing through prophase II,
metaphase II, anaphase II, and telophase II, the
chromosome number is haploid (23 chromosomes N) and
the DNA content is haploid (1d).
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Cell Death: Two Mechanisms

The Cell
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Necrosis
 Accidental
cell death due
to injury
 Rapid cell swelling and
lysis
 Inflammatory response
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
Apoptosis
 Programmed
 External
cell death
and internal
signals
Fig. 3.18, p. 89, Ross & Pawlina, 5th edition
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Cellular Homeostasis

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When the rate of cell division and cell death are
similar a condition known as homeostasis exists.
The following illustration demonstrates this.
The body maintains cell populations by mitosis and
death. We now have an understanding of mitosis and
cell proliferation. Cell death is an important component
of maintaining normal population levels of cells. Cells
die by two mechanisms – Necrosis and Apoptosis.
Necrosis is cell death as a result of injury. In necrosis,
injury can be due to hypoxia (low oxygen) or anoxia (no
oxygen) due to inadequate blood flow or complete
stoppage of blood flow due to clotting and thrombosis.
The mitochondria of the cell stop producing energy that,
in turn, upsets the integrity of the membranes. The
plasma membrane then leaks and calcium (which is much
higher in concentration outside of the cell) rushes in and
completely overwhelms the mitochondria that normally
can handle a slight increase in calcium. Immediately,
water is taken into the cell and it swells…..then
ultimately, the cell breaks apart and its components
attract inflammatory cells and macrophages that
eventually resorb the cell fragments. Apoptosis occurs
differently and is the mode of cell death that occurs under
normal physiologic conditions. The cell is an active
participant in its own demise (cellular suicide). One
external mechanism of apoptosis involves cytotoxic T
lymphocytes in which pores are induced in the cell and
endonucleases are activated resulting in DNA
fragmentation.
So, by means of regulated cell proliferation and cell
death, a balance or homeostasis is achieved. The top
drawing illustrating a balanced teeter totter illustrates two
new cells being formed while two cells are dying. This
is homeostasis of body cell population that occurs in the
normal condition. Pathological conditions may tip the
balance one way or another. When cell deaths exceed
cell division, pathological conditions characterized by
loss of cells occurs such as in AIDS, Alzheimer’s,
Parkinsons, Aplastic Anemia and Myocardial Infarction.
When cell division exceeds cell death, abnormal cell
numbers accumulate creating pathological disorders such
as benign and malignant cancer, lupus,
glomerulonephritis and viral infections.
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Summary
The Cell

Prokaryotic and eukaryotic cell prototypes were illustrated and explained.

Cellular Compartments: Plasma Membrane, Cytoplasm and Nucleus were
presented.

Light microscope and Electron Microscope views of a cell were compared

Cell complexity was emphasized

Cell organelles and inclusions were defined, listed and their structure and function
was presented.

The embyrological origin of cells was presented and examples of differentiated
cells were illustrated.

Three populations of cells –static, stable and dynamic, were defined and examples
given.

Two mechanisms of cell death, necrosis and apoptosis, were defined and illustrated.

Finally, cellular homeostasis was defined and two examples given where
homeostasis was interfered with by either excessive cell proliferation or death.
.