Transcript Introduction to Biotechnology

BIOL 3340
Chapter 3
Chapter 3
Microbial Cell Structure
Types of Cells
Two major classes: eukaryotes & prokaryotes.
Differences: the materials making up the nucleus of
eukaryotic cells are separated from the rest of the cell
by the nuclear membrane, whereas in prokaryotic cells
these materials are not separated.
• All animals and plant cells are eukaryotic including
fungi. Bacteria, cyanobacteria and the mycoplasmas are
prokaryotic.
Size, Shape, and Arrangement of
Bacterial cells
Cocci (s., coccus) – spheres
 diplococci (s., diplococcus) – pairs
 streptococci – chains
 staphylococci – grape-like clusters
 tetrads – 4 cocci in a square
 sarcinae – cubic configuration of 8
cocci
……Size, Shape, and Arrangement
Bacilli (s., bacillus): – rods
 coccobacilli – very short rods
 vibrios – resemble rods, comma shaped
 spirilla (s., spirillum) – rigid helices
 spirochetes – flexible helices
 mycelium – network of long, multinucleate
filaments Check on line lab Manual for
Bacterial shapes)
……Size, Shape, and Arrangement
 Sizes:
 Typically
~ 0.1 - 20 m (with some exceptions)
 Typical
coccus: ~ 1 m (e.g. Staphylococcus)
 Typical
short rod: ~ 1 x 5 m (e.g. E. coli)
 Barely
within the best resolution of a
good compound light microscope
Bacterial Shapes
Cell Structure
of Procaryotes
Prokaryotic cells
The constituents of a typical bacterium are as follows:
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Bacterial Cell Wall and Capsule – bacteria are
surrounded by a cell wall, which not only contains
polysaccharide but also contains protein and lipid.
In some bacteria, the cell wall is surrounded by the
capsule.
The cell wall and capsule provide shape and form to the
bacterium and also acts as a physical barrier between
the bacterium and its environment.
Nucleoids – in bacteria the nuclear material is
concentrated in a region called the nucleoid within the
cytoplasm.
A typical Bacterial Cell
….Cell Structure
There is no membrane-bound nucleus in
prokaryotes.
 Instead the DNA is located within a specialized
region of the cytoplasm of the cell called the
nucleoid region.
 There is no nuclear membrane surrounding the
nucleoid.

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Bacterial flagella – many bacteria possess
one or more flagella for locomotion.
Gram-negative Cell Walls and Acid Fast
Fast cell wall in
Chapter 3
Procaryotic Cell Membranes
Cell Membranes:
 membranes are an absolute
requirement for all living organisms.
 plasma membrane encompasses the
cytoplasm
 some procaryotes also have internal
membrane systems
Functions of the Plasma Membrane
separation of cell from its environment
 selectively permeable barrier
 some molecules are allowed to pass into
or out of the cell
 transport systems aid in movement of
molecules
 detection of and response to chemicals in
surroundings with the aid of special
receptor molecules in the membrane

Fluid Mosaic Model of Membrane
Structure
…..Plasma membrane
…..Plasma membrane
…Phospholipid layer

polar ends
 interact
with water
 hydrophillic

nonpolar ends
 insoluble
in water
 hydrophobic
Membrane Proteins
Peripheral proteins:
 loosely
associated with the membrane and
easily removed
Integral proteins
 embedded
within the membrane and not
easily removed
Procaryotic Cytoplasm
Cytoplamic Matrix:
 Cytoplasm contains the nucleoid,
ribosomes and inclusion bodies
 lacks organelles bound by unit membranes
 composed largely of water
 is a major part of the protoplasm (the
plasma membrane and everything within)
..Cytoplasmic Matrix
 Viscous
aqueous suspension of proteins,
nucleic acid, dissolved organic
compounds, mineral salts
 Network
of protein fibers similar to the
eukaryotic cytoskeleton.
Cytoplasmic Inclusion Bodies:

granules of organic or inorganic
material that are stockpiled by the cell
for future use.
 some
are enclosed by a single-layered
membrane
….Cytoplasmic inclusions
Cytoplasmic inclusions:
 Glycogen
Granules
 Poly--hydroxybutyrate granules
 Lipid droplets
 Gas vacuoles
 Metachromatic granules
(Phosphate crystals or volutin granules)
 Sulfur Granules
Ribosomes
Ribosomes:
 complex structures consisting of protein
and RNA
 sites of protein synthesis
 smaller than eucaryotic ribosomes
ribosomes  70S
 eucaryotic ribosomes  80S
 procaryotic
The Nucleoid
Nucleoid:
 irregularly shaped region
 location of chromosome
 usually
 not
1/cell
membrane-bound
The Procaryotic Chromosome
The Chromosomes:
 usually a closed circular, double-stranded
DNA molecule
 looped and coiled extensively
Plasmids
Plasmids:
 usually small, closed circular DNA
molecules
 exist and replicate independently of
chromosome
 have relatively few genes present
Procaryotic Cell Walls
Prokaryotic Cell Wall:
 rigid structure that lies just outside the
plasma membrane (detail to continue)
Functions of Cell Wall
provides characteristic shape to cell
 protects the cell from osmotic lysis
 may also contribute to pathogenicity
 very few procaryotes lack cell walls

Cell Walls of Bacteria
Gram Staining developed by Gram in 1888:
 bacteria are divided into two major groups
based on the response to gram-stain
procedure
 gram-positive
bacteria stain purple
 gram-negative bacteria stain pink

staining reaction due to cell wall structure
Gram Positive and Gram negative
Gram-Positive Cell Walls
Gram positive bacteria composed primarily
of peptidoglycan
 Peptidoglycan are polymers which
contains N-acetylglucosamine and Nacetylmuramic acid and several different
amino acids
• Walls contain teichoic acid ( polymers of
glycerol or ribitol joined by phosphate groups)

..Gram-Positive Cell Walls
The periplasmic space lies between
plasma membrane and cell wall and is
smaller than that of gram-negative
bacteria
 periplasm has relatively few proteins
 enzymes secreted by gram-positive
bacteria are called exoenzymes

Gram-Negative Cell Walls
consist of a thin layer of peptidoglycan
surrounded by an outer membrane
 outer membrane composed of lipids,
lipoproteins, and lipopolysaccharide (LPS)
 no teichoic acids

…..Gram Negative
more complex than gram-positive walls
 periplasmic space differs from that in
gram-positive cells

 may
constitute 20-40% of cell volume
 many enzymes present in periplasm
Gram Positive and Negative cell
Wall
Assignments
Features of a prokaryotic cell
 List the differences between a gram
positive and gram negative cell wall.

Variations on Cell Wall Architecture
Acid-fast Cell Walls:
 Many
genera in the “High GC gram-positive”
bacterial group contain mycolic acids,
embedded in the peptidoglycan .
 Mycolic acids are a class of waxy, extremely
hydrophobic lipids.
 Certain genera contain very large amounts of
this lipid, and are difficult to gram stain.
 These genera may be identified by the “acidfast” staining technique.
 Includes Mycobacterium and Nocardia.
..Variations on Cell Wall
Architecture
Mycoplasmas:
 Bacteria
that are naturally have no cell walls
 Includes Mycoplasma and Ureaplasma
Archaea :
 Have
archaea cell walls with no
peptidoglycan
 Many have cell walls containing
pseudomurein, a polysaccharide similar to
peptidoglycan but containing Nacetylglucosamine and Nacetyltalosaminuronic acid .
Capsules, Slime Layers, and
S-Layers
Layers of material lying outside the cell wall
 capsules
 usually
composed of polysaccharides
 well organized and not easily removed from cell
 slime
layers
 similar
to capsules except diffuse, unorganized and
easily removed.
 a capsule or slime layer composed of
polysaccharides can also be referred to as a
glycocalyx
Glycocalyx
S-layers:
S-layers:
 regularly
structured layers of protein or
glycoprotein.
 in bacteria the S-layer is external to the cell
wall.
 Regular “floor tile” pattern.
 Function not clear -- Stability?
Functions of Capsules, Slime
Layers, and S-layers
protection from host defenses (e.g.,
phagocytosis)
 protection from harsh environmental
conditions (e.g., desiccation) , chemicals
or osmotic stress
 attachment to surfaces
 facilitate motility
 nutrient Storage

Pili and Fimbriae
Fimbriae (s., fimbria)
 short,
thin, hairlike, proteinaceous
appendages up to 1,000/cell
 mediate attachment to surfaces
sex pili (s., pilus):
 similar
to fimbriae except longer, thicker, and
less numerous (1-10/cell)
 required for mating
Fimbriae
…Fimbriae
Function s:
 Mobility
 Almost
all motile bacteria are motile by means
of flagella
 Motile vs. non motile bacteria.
 Different species have different flagella
arrangements
Structure:

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Filament composed of the protein flagellin
Hook & Rotor Assembly & Permits rotational "spinning"
movement
…Fimbriae
Chemotaxis
movement towards a chemical attractant
or away from a chemical repellent
 concentrations of chemical attractants and
chemical repellents detected by
chemoreceptors on surfaces of cells

Bacterial Endospores
Bacterial Spores
 are formed by some bacteria as dormant
structures.
 resistant to numerous environmental conditions
e.g heat, radiation,chemicals, nutrient depletion,
desiccation, and waste buildup .
 Bacterial spores are NOT a reproductive
structure, like plant or fungal spores.
 Produced by very few genera of bacteria
 Major examples Bacillus & Clostridium
…endospores
Sporogenesis
Sporogenesis
Sporogenesis:
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Also called endospore formation or sporulation
normally commences when growth ceases
because of lack of nutrients
A copy of the bacterial chromosome is
surrounded by a thick, durable spore coat .
When the vegetative cell dies and ruptures, the
free spore is released.
When spore encounters favorable growth
conditions, spore coat ruptures and a new
vegetative cell is formed.
..Sporogenesis
Complex multistage process
Spore Germination
Bibliography
http://en.wikipedia.org/wiki/Scientific_metho
d
 https://files.kennesaw.edu/faculty/jhendrix/bi
o3340/home.html
 Lecture PowerPoints Prescott’s Principles of
Microbiology-Mc Graw Hill Co.

http://www.bio.mtu.edu/campbell/prokaryo.htm
http://molecularbiology.suite101.com/article.cfm/cell_structure
 http://water.me.vccs.edu/courses/ENV108/lesso
n5_2.htm
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