Functional Anatomy of
Prokaryotic and Eukaryotic Cells
Comparing Of Prokaryotic And Eukaryotic Cells: An Overview
1. Prokaryotic cells are similar in their chemical
composition and chemical reactions.
2. Prokaryotic cells lack membrane-enclosed organelles (including
a nucleus.)
3. Peptidoglycan is found in prokaryotic cell walls but
not in eukaryotic cell walls.
4. Eukaryotic cells have a membrane-bound nucleus and
other organelles.
The Prokaryotic Cell
1. Bacteria are unicellular and most of them multiply by
binary fission.
2. Bacterial species are differentiated by morphology,
chemical composition, nutritional requirements, biochemical activities, and
source of energy.
1. Most Bacteria Are 0.2 μm In Diameter And 2-8 μm
In Length.
2. The 3 Basic Bacterial Shapes Are Coccus (Spherical),
Bacillus (Rod-Shaped), And Spiral (Twisted).
3. Pleomorphic Bacteria Can Assume Several Shapes.
Structures External To The Cell Wall
Glycocalyx
1. The glycocalyx (capsule, slime layer, or extra
cellular polysaccharide) is a gelatinous polysaccharide and/or polypeptide
covering.
2. Capsules may protect pathogens from phagocytosis.
3. Capsules enable adherence to surfaces, prevent
desiccation, and may provide nutrients.
Flagella
1. Flagella are relatively long filamentous appendages
consisting of a filament, hook, and basal body.
2. Prokaryotic flagella rotate to push the cell.
3. Motile bacteria exhibit taxis; positive taxis is
movement toward an attractant, and negative taxis is movement away from a
repellent.
4. Flagellar (H) protein functions as an antigen.
Axial Filaments
1. Spiral cells that move by means of an axial filament
(endoflagellum) are called spirochetes.
2. Axial filaments are similar to flagella, except that
they wrap around the cell.
Fimbriae And Pili
1. Fimbriae and pili are short, thin appendages.
2. Fimbriae help cells adhere to surfaces.
3. Pili join cells for the transfer of DNA from one cell
to another.
The Cell Wall
Composition And
Characteristics
1. The cell wall surrounds the plasma membrane and
protects the cell from changes in water pressure.
2. The bacterial cell wall consists of peptidoglycan, a
polymer consisting of NAG and NAM and short chains of amino acids.
3. Penicillin interferes with peptidoglycan synthesis.
4. Gram-positive cell walls consist of many layers of
peptidoglycan and also contain teichoic acids.
5. Gram-negative bacteria have a
lipopolysaccharide-lipoprotein-phospholipid outer membrane surrounding a thin
peptidoglycan layer.
6. The outer membrane protects the cell from
phagocytosis and from penicillin, lysozyme, and other chemicals.
7. Porins are proteins that permit small molecules to
pass through the outer membrane; specific channel proteins allow other
molecules to move through the outer membrane.
8. The lipopolysaccharide component of the outer
membrane consists of sugars (O polysaccharides) that functions as antigens and
lipid A, which is an endotoxin.
Cell Walls And The Gram
Stain Mechanism
1. The crystal violet-iodine complex combines with
peptidoglycan.
2. The decolorizer removes the lipid outer membrane of
gram-negative bacteria and washes out the crystal violet.
Atypical Cell Walls
1. Mycoplasma is a bacterial genus that naturally lacks
cell walls.
2. Archaea have pseudomurein; they lack peptidoglycan.
Damage To The Cell Wall
1. In the presence of lysozyme, gram-positive cell walls
are destroyed, and the remaining cellular contents are referred to as a
protoplast.
2. Proteus
and some other genera can lose their cell walls spontaneously or in response to
penicillin and swell into L forms (Lister Institute). L forms can live and divide and/or return to the normal walled
state.
3. In the presence of lysozyme, gram-negative cell walls
are not completely destroyed, and the remaining cellular contents are referred
to as spheroplast.
4. Protoplasts and spheroplast are subject to osmotic
lysis.
5. Antibiotics such as penicillin interfere with cell
wall synthesis.
Structures Internal To
The Cell Wall
The Plasma (Cytoplasmic)
Membrane
1. The plasma membrane encloses the cytoplasm and is a
phospholipid bilayer with peripheral and integral proteins (the fluid mosaic
model).
2. The plasma membrane is selectively permeable.
3. Plasma membranes carry enzymes for metabolic
reactions, such as nutrient breakdown, energy production, and photosynthesis.
4. Mesosomes, irregular infoldings of the plasma
membrane, are artifacts, not true cell structures.
5. Plasma membranes can be destroyed by alcohols and
polymyxins.
1. Movement across the membrane may be by passive
processes, in which materials move from areas of higher to lower concentration,
and no energy is expended by the cell.
2. In simple diffusion, molecules and ions move until
equilibrium is reached.
3. In facilitated diffusion, substances are transported
by transporter proteins across membranes from areas of high to low
concentration.
4. Osmosis is the movement of water from areas of high
to low concentration across a selectively semi permeable membrane until
equilibrium is reached.
5. In active transport, materials move from areas of low
to high concentration by transporter proteins, and the cell must expend energy.
6. In group translocation, energy is expended to modify
chemicals and transport them across the membrane.
Cytoplasm
1. Cytoplasm is the fluid component inside the plasma
membrane.
2. The cytoplasm is mostly water, which inorganic and
organic molecules, DNA, ribosomes, and inclusions.
The Nuclear Area
1. The nuclear area contains the DNA of the bacterial
chromosome.
2. Bacteria can also contain plasmids, which are
circular, extra-chromosomal DNA molecules.
Ribosomes
1. The cytoplasm of a prokaryote contains numerous 70S
ribosomes; ribosomes consist of rRNA and protein.
2. Protein synthesis occurs at ribosomes; it can be
inhibited by certain antibiotics.
Inclusions
1. Inclusions are reserve deposits found in prokaryotic
and eukaryotic cells.
2. Among the inclusions found in bacteria are
metachromatic granules (inorganic phosphate), polysaccharide granules (usually glycogen
or starch), lipid inclusions, sulfur granules, carboxysomes (ribulose
1,5-diphosphate carboxylase), magnetosomes (Fe3O4), and
gas vacuoles.
Endospores
1. Endospores are resting structures formed by some
bacteria for survival during adverse environmental conditions.
2. The process of endospore formation is called
sporulation; the return of an endospore to its vegetative state is called
germination.
The Eukaryotic Cell
Flagella And Cilia
1. Flagella are few and long in relation to cell size;
cilia are numerous and short.
2. Flagella and cilia are used for motility, and cilia
also move substances along the surface of the cells.
3. Both flagella and cilia consist of an arrangement of
nine pairs and two single microtubules.
The Cell Wall And
Glycocalyx
1. The cell walls of many algae and some fungi contain
cellulose.
2. The main material of fungal cell walls is chitin.
3. Yeast cell walls consist of glucan and mannan.
4. Animal cells are surrounded by a glycocalyx, which
strengthens the cell and provides a means of attachment to other cells.
1. Like the prokaryotic plasma membrane, the eukaryotic
plasma membrane is a phospholipid bilayer containing proteins.
2. Eukaryotic plasma membranes contain carbohydrates
attached to the proteins and sterols not found in prokaryotic cells (except Mycoplasma bacteria).
3. Eukaryotic cells can move materials across the plasma
membrane by the passive processes used by prokaryotes, in addition to active
transport and endocytosis (phagocytosis and pinocytosis).
Cytoplasm
1. The cytoplasm of eukaryotic cells includes everything
inside the plasma membrane and external to the nucleus.
2. The chemical characteristics of the cytoplasm of
eukaryotic cells resemble those of the cytoplasm of prokaryotic cells.
3. Eukaryotic cytoplasm has a cytoskeleton and exhibits
cytoplasmic streaming.
Organelles
1. Organelles are specialized membrane-enclosed
structures in the cytoplasm of eukaryotic cells.
2. The nucleus, which contains DNA in the form of
chromosomes, is the most characteristic eukaryotic organelle.
3. The nuclear envelope is connected to a system of
membranes in the; cytoplasm called the endoplasmic reticulum (ER).
4. The ER provides a surface for chemical reactions,
serves as a transporting network, and stores synthesized molecules. Protein
synthesis and transport occur on rough ER; lipid synthesis occurs on smooth ER.
5. 80S ribosomes are found in the cytoplasm or attached
to the rough ER.
6. The Golgi complex consists of flattened sacs called
cisterns. It functions in membrane formation and protein secretion.
7. Lysosomes are formed from Golgi complexes. They store
powerful digestive enzymes.
8. Vacuoles are membrane-enclosed cavities derived from
the Golgi complex or endocytosis. They are usually found in plant cells that
store various substances, help bring food into the cell, increase cell size,
and provide the rigidity to leaves and stems.
9. Mitochondria are the primary sites of ATP production.
They contain 70S ribosomes and DNA, and they multiply by binary fission.
10. Chloroplasts contain chlorophyll and enzymes for
photosynthesis. Like mitochondria, they contain 70S ribosomes and DNA and
multiply by binary fission.
11. A variety of organic compounds are oxidized in
peroxisomes. Catalase in peroxisomes destroys H2O2.
12. The centrosome consists of the pericentriolar area
and centrioles. Centrioles are 9 triplet microtubules involved in formation of
mitotic and flagellar microtubules.
The Evolution Of Eukaryotes
1. According to the endosymbiotic theory, eukaryotic
cells evolved from symbiotic prokaryotes living inside other prokaryotic cells.