Download Introduction to Microbiology

Bacterial Cell Structure
and Function
Lecture
The Three Domains of Life
Microbiological focus
• Archaea – The Extremophiles
• Bacteria- Cyanobacteria and eubacteria
• Eukarya – Protozoans, fungi, and worms
Prokaryote and Eukaryote Cells
The Structure of the Prokaryote Cell
• Small size ( 0.5 to 2um)
• Large surface area to volume ratio
• A variety of shapes
• Outer cell wall- very thick made of specialized
molecules
• Cell membranes may have a different constituency
of molecules from eukaryote cells
• Ribosomes smaller
• No organelles, no nuclear membrane
•1 ds circular loop of DNA
Shapes of the Bacteria
• Bacillus
• Coccus
• Vibrio
• Spirillum
• Spirochete
• Pleiomorphism- Some bacterial shapes vary
within a culture. This can occur when the
nutrients are used and wastes have built up
Bacterial Shapes
Bacillus- E. coli
Fluorescent stain
Freeze fracture
Public enemy # 1- Anthrax
Streptococcus pyogenes- strep
throat
Staphylococcus
Arrangement of bacteria
• Groups of two- diplo
• Chains- strepto
• Large groups- like grape clustersstaphylo
• Division on 3 planes- sarcinae- 8
cells arranged in a cube
• Division on two planes produces
tetrads
Cell Morphology
Staphylococcus
Diplococcus
Streptobacilli
Spirillum
Spriochetes
• Peptidoglycan
•the single most important molecule
in the cell walls of bacteria
•One immense- covalently linked
molecule
• The molecule forms a chain- the
constituents are sugar-amino
molecules( glucosamines)
Peptidoglycans - Cell Wall
Gram Positive Bacteria- Cell walls
• The cell wall is made of Teichoic acidglycerol+ phosphates+ribotol which an alcohol
sugar. These polymers extend beyond the cell
even beyond the capsule
Gram Negative Bacteria- Cell Walls
The outer membrane found primarily in Gramnegative bacteria is a bilayer that forms the
outermost layer of the cell wall and is
attached to the peptidoglycan by lipoproteins
molecules.
The Cell Membrane
•LPS- this is actually a part of the outer
cell membrane and can b be used to help
to identiry Gram- bacteria. It is also
important to the cell wall and is usually
not released until a bacterium is dead.
It consists of polysaccharides and lipid
A
The toxins gram negative bacteria release are from this
portion of the cell membrane. Gram negative bacteria
release endotoxin and the result is fever, the dilation of
blood vessels, so the blood pressure drops and causes other
related effects.
Gram-Positive Bacteria
•The cell wall has a thick layer of
peptidoglycan 20 to 80um thick
• 60-90% of the cell wall is peptidoglycan
•Except for the strptococci most gram
positive bacterial cell walls contain very
little protein
Gram-negative Bacteria
•The wall of a Gram-negative bacterium
is thinner but more complex than a
Gram-positive bacterium
Only10 to 20 % of the cell wall is
peptidoglycan- the remainder consists
of various polysaccharides, protein,
lipids.
The cell wall contains an outer
membrane- the LPS
The Periplasmic Space
•The periplasmic space is between the
outer surface of the cell wallo and
the cell membrane
•Enzymes and toxins remain in the
periplasmic space in sufficient
concentrations to help destroy
substances that might harm the
bacterium.
The Cell Membrane
•The cell membrane consists of molecules called
phospholipids.
•Phospholipids have two long tails consisting of
hydrocarbon chains ( HYDROPHOBIC)
• Phospholipids have a phosphate head
(HYDROPHILIC)
•The membrane is formed by a double layer of
these molecules
• The membrane also contains PROTEINS
Internal Structure
Ribosomes- consist of ribonucleic
acid ( RNA) and protein. They are
abundant in the cytoplasm as
POLYRIBOSOMES
Nucleoid Region- Central
•The nucleoid region contains 1 ds ciruclar
loop of DNA.
• The DNA may be attached to the cell
membrane as well at some point
•There may be RNA associated with the
DNA
Chromatophores- photosynthetic bacteria
+
Molecules of life
•Chromatophores are derived from the cell
membrane. They contain pigments used to
capture light energy for the synthesis of
sugars. Nitrifying bacteria also may have
these internal membranes.
•They contain the enzymes necessary for
the energy transformation process of
photosynthesis
The Nucleoid Region
Mesosomes- Bacteria
Bacterial cells have large
infoldings in their membranes.
Mesosomes
Mesosomes provide the surface
area for all of the chemical
reactions in the cell
• respiration
• metabolic processes
Freeze fracture
Inclusions
•Small bodies in the cytoplasm- some are
called granules
Glycogen
pyrrophosphate granules- volutin
Metachromatic granules
Variable colors
• Vegetative cells of bacteria like Bacillus or Clostrium
produce resting stages
•These spores are designed for survival and not
reproduction.
• These are formed within cells
•They are resistant to heat,
drying,acids,bases,disinfectants, and radiation
Spore formation
•Spores form when nutrients are depleged
form a culture
• Few spores are formed when nutrients
are plentiful and environmental conditions
are favorable.
Spore Structure
• An endospore consists of a core,
surrounded by a cortex, a spore coat
and in some species a thin layer called
the exosporium
spore
How do spores survive ?
• They contain dipicolinic acid and a large
number of calium ions.
• These materials contribute to heat
resistance
• The lose water content enables them to
survive.
• Endospores have survived over
10,000 years
• Special methods may be used to skill
them during sterilization
• When conditions are favorable they
can still germinate
Flagella
• Bacteria that are motile have
appendages called flagella
• A bacteria can have one or many
flagella
•monotrichous
•amphitrichous
•lophotrichous
•peritrichous
What is this type of bacteria ?
• The diameter of a prokaryote’s flagellum is about onetenth of that of a eukaryote
•It is made of flagellin
•The basal region has a hook like structure and a complex
basal body
• The basal body consists of a central rod or shaft
surrounded by a set of rings
• Gram negative bacteria have a pair of rings embedded
in the cell membrane and another pair of rings associated
with the peptidoglycan and lipopolysaccharide layer of the
cell wall. Gram positive have one ring.
Turns like a mixer
Flagellar motion
Flagella rotate like twirling Lshaped hooks such as a dough
hook on a kitchen rotor- or a
mixer
Twiddling ? HHMM!
When flagella bundle together they
rotate counterclockwise and the
bacteria run
•
• When the flgella rotate clockwise the
flagellar bundle comes apart and the
bacteria twiddle- tumble randomly
Chemotaxis
• Sometimes bacteria move toward or away from
substances in their environment. This is called
chemotaxis
• Concentrations of most molecules in the
environment form a gradient.
• When a bacteria is running a long an increasing
gradient if reduces the frequency of its twiddles
PILI
Attachment pili-
•These are structures on the surface of the
bacteria that aid the bacterium in atttching to
surfaces
• These acid the bacterium by allowing colonization
of the mucus membranes of organisms.
• Some bacteria adhere to red blood cells by
attachment pil and cause red blood cells to clumthis is hemagglutination
SEX PILI- Conjugation
• Conjugation pili or sex pili are found only in
certain groups of bacteria.
•This structure exists exclusively for the
transfer of DNA between bacteria
•The DNA passes between bacteria tend to
develop antibiotic resistance
Bacterial Slime Layer or Capsule