Lecture 3 - Prokaryotes-7

Prokaryotes: Bacteria & Archaea
Lecture 3 Introduction
• 3 Major Bacterial Shapes
– Cocci, Bacilli, Spiral-shaped
• Prokaryotic Structures
– Flagella and Motility
– Fimbriae and Pili
– Cell Envelope
• Glycocalyx
• Cell Wall
• Cell Membrane
Gram Positive vs Gram Negative Cells
Cytoplasm and Bacterial Genome
Ribosomes, Inclusions, Granules
Bacterial Endospores
Three Major Bacterial Shapes
• Cocci – round, spherical
• Bacilli – rod
• Spiral – helical, comma, twisted rod,
Coccus – single spherical bacteria
• Bacteria can also be categorized
according to arrangement, or
style of grouping.
• The greatest variety of
arrangement occurs in cocci.
• Factors determining arrangement
include pattern of division and
how the cells remain attached
Diplococci – pair
Streptococci – long chain
Tetrad – group of four
Sarcinae – cubical packet
Staphylococci – irregular cluster
• Divide only in one plane
• Have varied forms depending
on species: blocky, spindles,
clubbed, drumstick, threadlike
Diplobacilli – pair
Streptobacilli – long chain
Coccobacillus – short and
plump rod
Palisades – cells of a chain
remaining partially attached
by a small hinge region at the
Vibrio – curved Rod, comma
Spirillum – 2 or more turns with
a rigid helix; external flagella
Spirochete – 3 or more turns
with a flexible helix; internal
• Spirilla are occasionally
found in short chains
• Spirochetes rarely remain
attached after division
Pleomorphism: Cells of a single species varying in shapes and sizes
Structure of a Typical Bacterial Cell
Prokaryotic Flagella
• 3 parts
- filament
- hook
- basal body
• Made of flagellin
• Rotates 360º
• Used for motility
• Outside of cell wall
Flagellar Arrangement
Flagellar Motility
• When flagella rotate counterclockwise, the cell swims forward in runs.
• When flagella reverses direction and rotate clockwise, the cell stops and
Bacterial Chemotaxis
Chemotaxis: movement in response to a chemical gradient
(toward an attractant or to avoid a repellant)
Axial Filament
• Periplasmic Flagella: internal flagella enclosed in the space between the outer
sheath and the cell wall
• Found only in Spirochetes
• Made of Flagellin protein
• Short,
fine and numerous fibers
• Promote virulence by being
involved in Adhesion & Attachment
Neisseria gonorrhoeae
Escherichia coli
• Also called a Sex Pilus
• A rigid, tubular structure
made from Pilin protein
• Found only in Gram (-)
• Involved in Conjugation:
bacterial “mating” process
Cell Envelope
• Coating layer outside of the
cell wall
• Made of proteins & many
carbohydrates (very sticky)
• 2 types of Glycocalyx
- Slime layer (loose)
- Capsule (structured)
• Involved in Attachment,
Resisting Osmolarity changes,
Phagocyte avoidance
What a difference a Glycocalyx makes!
Streptococcus pneumoniae
Klebsiella pneumonia
A complex association that arises from
microorganisms growing together and
interacting on the surface of a habitat
Occur naturally in the environment but
in humans can pose a threat when
accumulate on catheters, heart valves,
hip joints, and teeth.
Cell Wall
• Determines shape of bacteria
• Prevents osmotic lysis
• Generally composed of
Peptidoglycan (in bacteria)
A network of polysaccharide chains
cross-linked by short peptides that
forms the rigid part of bacterial cell
• Polymer of 2 glycans
- N-acetylglucosamine (NAG)
- N-acetylmuramic acid (NAM)
• Linked by polypeptides
Gram Positive Cell Wall
Consists of:
• Thick peptidoglycan
layer (20-80 nm)
• Teichoic and
lipoteichoic acids
• Narrow Periplasmic
• Cell membrane
Gram Negative Cell Wall
Consists of:
• An outer membrane
that contains
• Thin peptidoglycan
layer (8-11 nm)
• Extensive Periplasmic
• Inner cell membrane
Gram (+) vs. Gram (-)
The Gram Stain
Plasma Membrane
• Phospholipid bilayer with proteins and carbohydrates
• Selectively permeable
• No sterols in Prokaryotes (except Mycoplasma)
• Involved in Transport of molecules
• Involved in Metabolic Activity
Atypical Cell Walls and/or Membranes
• Bacteria without cell walls - Mycoplasma
– Have only a cell membrane containing sterols for
• Bacteria with some peptidoglycan and a lot of
mycolic acid - Mycobacterium
• Archaea have protein cell walls, polysaccharide
cell walls or no cell wall at all.
– No Peptidoglycan
• Dense gelatinous
solution of sugars,
amino acids, & salts
(70-80% water)
• Nucleoid: a central area in
the cell where the bacterial
chromosome aggregates
• Ribosomes
• Inclusions & Granules
Bacterial Genome
1. Bacterial Chromosome
2. Plasmids
Single (One Copy)
Circular DNA
Circular DNA
Double Helix
Codes for all essential
Genes not essential
for cell growth but
can code for genes
for adaptive traits
• Can be transmissible
to other bacteria
• Can contain genes
that provide antibiotic
• Made of ribosomal
RNA & protein
• Prokaryotic differ
from eukaryotic
ribosomes in size
• Site of protein
• All cells have
Inclusions & Granules
• Inclusions: intracellular storage of
metabolic products
• Vary in size, number & content
• Granules: contain crystals or
inorganic compounds
Magnetotactic Bacteria
Purple Sulfur Bacteria
Bacterial Endospores
• Resting, dormant cells
• Only produced by three G+ genera: Clostridium, Bacillus &
• Have a 2-phase life cycle – vegetative cell & an endospore
- sporulation
- germination
• Dehydrated,
metabolically inactive
• Spore coat
• Extraordinarily resistant
and long lasting