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Chapter 4
Functional Anatomy of
Prokaryotic and Eukaryotic Cells
Part 2
Structures Internal to the Cell Wall
(The Prokaryotic Cell)
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Plasma (Cell or Cytoplasmic) Membrane
Cytoplasm
Nuclear Area
Ribosomes
Inclusions
Endospores
Plasma Membrane
• A thin structure lying inside the cell wall
and enclosing the cytoplasm of the cell
• Consists primarily of phospholipids and
proteins (except Mycoplasma, contains
sterols)
Figure 4.14a
Plasma Membrane
Figure 4.14b
Plasma (Cytoplasmic) Membrane
• Phospholipid bilayer
– polar head composed of a phosphate group and
glycerol; hydrophilic (water-loving); on the
surfaces of the bilayer
– nonpolar tails composed of fatty acids;
hydrophobic (water-fearing); interior of the
bilayer
Plasma (Cytoplasmic) Membrane
• Peripheral proteins
– at the inner or outer surface of the membrane
– function:
• enzymes to catalyze chemical reaction
• a “scaffold” for support
• mediators of changes in membrane shape during
movement
Plasma (Cytoplasmic) Membrane
• Integral proteins (some are believed to span
across the entire phospholipid bilayer =
transmembrane proteins)
– some are channels that have a pore or a hole to
allow substances to enter and exit the cell
Fluid Mosaic Model
• The dynamic arrangement of phospholipids
and proteins comprising the plasma membrane
– phospholipids and proteins move quite freely
within the membrane surface
Figure 4.14b
Fluid Mosaic Model
• Membrane is as viscous as olive oil to allow
membrane proteins to move freely
• Proteins move to function without
destroying the structure of the membrane
• Phospholipids rotate and move laterally
Plasma Membrane
• Selective permeability (semipermeability)
allows passage of some molecules
– permeability depends on size, nature of
substances (easily dissolve in lipids), and
transporter molecule
• Enzymes to break down nutrients and
produce energy (ATP)
• Photosynthetic pigments (chromatophores or
thylakoids) found in infoldings (Fig. 4.15)
Plasma Membrane
• Mesosomes are artifacts, not true cell
structures
• Damage to the membrane by alcohols,
quaternary ammonium (disinfectants) and
polymyxin antibiotics causes leakage of
cell contents.
Movement of Material Across
Membranes
• Materials move across plasma membranes
by passive and active processes
– Passive process
substances move across the
membrane with the concentration gradient, or
difference; no expenditure of energy (ATP)
– active process substances move across the
membrane against the concentration gradient;
require expenditure of energy (ATP)
Movement Across Membranes
• Passive processes (simple diffusion,
facilitative diffusion, & Osmosis) stops
when the molecules or ions are evenly
distributed (equilibrium)
– Simple diffusion: Movement of a solute from
an area of high concentration to an area of
low concentration.
• used to transport small molecules (e.g. O & CO2)
Movement Across Membranes
– Facilitative diffusion: solute combines with a
transporter protein in the membrane
• the transporter undergoes a change in shape to
transport the substance
• Large molecules that cannot be transported into the
cells are degraded (broken down) by extracellular
enzymes produced by bacteria and released into the
surrounding medium
subunits move into the
cell with the help of transporters
Movement Across Membranes
Figure 4.17
Movement Across Membranes
– Osmosis: movement of water across a
selectively permeable membrane from an area
of high water concentration to an area of lower
water.
– Osmotic pressure: the pressure needed to stop
the movement of water across the membrane.
Figure 4.18a
Fig. 4.18a & b
Osmotic Solutions
• Bacterial cell may be subjected to any of
three kinds of osmotic solutions (isotonic,
hypotonic, & hypertonic)
Figure 4.18c-e
Movement Across Membranes
• Active processes (active transport & group
translocation) are used when a bacterial cell
is in an nutrient low environment to
accumulate the needed substances
– Active transport of substances requires a
transporter protein and ATP.
• move substance from outside to inside of a cell
although the concentration might be much higher
inside the cell
Movement Across Membranes
– Group translocation of substances requires a
transporter protein and PEP (phosphoenolpyruvic acid, high-energy phosphate
compounds).
• occurs only in prokaryotes
• substance is chemically altered during transport
across the membrane (membrane is impermeable to
the altered substance)
• allows a cell to accumulate various substances
although they may be in low concentrations outside
the cell
Cytoplasm
• Cytoplasm is the substance inside the plasma
membrane
– thick, aqueous, semitransparent, and elastic
Cytoplasm
Figure 4.6a, b
Cytoplasm
– about 80% water and contains primarily
proteins (enzymes), carbohydrates, lipids,
inorganic ions, and many low-molecular-weight
compounds
• Major structure are a nuclear area
(containing DNA), ribosomes, and
inclusions (reserve deposits)
Nuclear Area
• Nuclear area (nucleoid) contains a single long,
continuous, circularly arranged thread of doublestranded DNA (bacterial chromosome)
Nuclear area
(nucleoid)
containing DNA
Plasmid
Figure 4.6a, b
Nuclear Area
– No nuclear envelope and do not include histones
– can be spherical , elongated, or dumbbell-shaped
– chromosomes attached to the plasma membrane
• Plasmids: small circular, doublestranded DNA
– extrachromosomal genetic elements, replicate
independently of chromosomal DNA
– can be transferred from one bacterium to another
– used for gene manipulation in biotechnology
Nuclear Area
– associated with plasma membrane proteins
– usually contain from 5 - 100 genes that are
generally not crucial for the survival of the
bacterium; maybe gained or lost without
harming the cell
– Under certain condition, provide advantage to
cells
• carry genes for antibiotic resistance, tolerance to
toxic metals, production of toxins and synthesis of
enzymes
Ribosomes
• Sites of protein synthesis
– If actively growing, have high number
Ribosomes
Figure 4.6a
Ribosomes
• Composed of two subunits (each consists of
protein and ribosomal RNA (rRNA)
– 70S ribosomes (S = Svedberg units) has
subunits of a small 30S (one molecule of rRNA)
and a larger 50S (two molecule of rRNA)
Streptomycin
and
Gentamicin
Erythromycin and
Chloramphenicol
Figure 4.19
Inclusions
• Reserve deposits
– may accumulate certain nutrients when they are
plentiful and use them when it is low or
deficient in the environment
– macromolecules concentrated in inclusions
does not cause the increase in osmotic pressure
– may serve as a basis for identification (some are
limited to a small number of species)
Inclusions
• Matachromatic granules (volutin)
– large inclusions; sometimes stain red with
certain blue dyes (methylene blue)
– inorganic phosphate (polyphostate) reserve that
can be used to synthesize ATP
– generally formed in cells grown in phosphaterich environments
– characteristic of Corynebacterium diphtheriae
(cause diphtheria)
– also found in algae, fungi and protozoa
Inclusions
• Polysaccharide granules
– consist of glycogen and starch; glycogen appear
reddish brown and starch appear blue when
stained with iodine
– energy reserve
• Lipid inclusions
– stained by fat-soluble dyes (e.g. Sudan dyes)
– energy reserve
Inclusions
– Poly-b-hydroxybutyric acid (polymer, common
lipid-storage material unique to bacteria)
– Appear in various species of Mycobacterium
Bacillus, Azotobacter, Spirillum, and other
genera
• Sulfur granules
– energy reserve deposited by certain bacteria
(e.g. sulfur bacteria, Thiobacillus)
Inclusions
• Carboxysomes
– contain enzyme ribulose 1,5-diphosphate
carboxylase for CO2 fixation during
photosynthesis (CO2 is used as the sole carbon
source)
– found in nitrifying bacteria, cyanobacteria, and
thiobacilli
Inclusions
• Gas vacuoles
– hollow cavities found in many aquatic
prokaryotes (cyanobacteria, anoxygenic
photosynthetic bacteria, and halobacteria)
– consists of rows of several individual gas
vesicles
– maintain buoyancy
Inclusions
• Magnetosomes (Fig. 4.20)
– inclusions of iron oxide formed by several
gram-negative bacteria (Aquaspirillum
magnetotacticum)
– act like magnets; allow bacteria to move
downward until they reach a suitable
attachment site
– In vitro, can decompose hydrogen peroxide
(toxic by-product of respiration); protect cell
against accumulation of hydrogen peroxide
Endospores
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Specialized resting cells; unique to bacteria
Can remain dormant for thousands of years
Bacillus & Clostridium (both are gram-positive)
Dehydrated cells with thick walls and
additional layer
– contains only DNA, small amounts of RNA,
ribosomes, enzymes, and a few important small
molecules (e.g dipicolinic acid and calcium ions)
Endospores
• Resistant to desiccation, heat, freezing,
(toxic) chemicals, and radiation due to a
thick spore coat
– true endospores found in gram-positive bacteria
– Coxiella burnetti (gram-negative, cause Q
fever) form endospore like structures
• Sporulation (sporogenesis): process of
endospore formation
– takes several hours within a vegetative (parent)
cell
Endospores
– triggered by adverse environmental condition
(e.g. nutrient depletion)
– Endospore can be located terminally,
subterminally, or centrally
• Germination: process of returning to
vegetative state
– Triggered by physical or chemical damage to
the spore coat
The Eukaryotic Cell
• Include algae, protozoa, fungi, higher
plants, and animals
• Larger and structurally more complex
• Contains membrane-enclosed organelles
Flagella and Cilia
• Projections used for Cellular locomotion or
for moving substances along the cell surface
• Both flagella and cilia are anchored to the
plasma membrane by a basal body
• Flagellum moves in a wavelike manner
Flagella and Cilia
– projections are few and are long = flagella
– Projections are numerous and short, resembles
hairs = cilia
Figure 4.23a, b
• Microtubules
– Long, hollow tubes made up of a protein (tubulin)
• 9 pairs + 2 arrangements of a flagellum or
cilium
Figure 4.23c
Cell Wall and Glycocalyx
• Cell wall (simpler than prokaryotic cell wall)
– Plants, algae, fungi
– Carbohydrates
• Cellulose, chitin, glucan, mannan
• Glycocalyx
– Carbohydrates extending from animal plasma
membrane
– Bonded to proteins and lipids in membrane
Plasma Membrane
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Phospholipid bilayer
Peripheral proteins
Integral proteins
Transmembrane proteins
Sterols (e.g. cholesterol)
Glycocalyx carbohydrates
Plasma Membrane
• Selective permeability allows passage of some
molecules
• Simple diffusion
• Facilitative diffusion
• Osmosis
• Active transport
Plasma Membrane
• Endocytosis
– Phagocytosis: Pseudopods extend and engulf
particles
– Pinocytosis: Membrane folds inward bringing
in fluid and dissolved substances