Bacterial Cell Structure and Function

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Bacterial Cell Structure and Function

• Lecture

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• The Three Domains of Life
• Microbiological focus
• Archaea The Extremophiles
• Bacteria- Cyanobacteria and eubacteria
• Eukarya Protozoans, fungi, and worms

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Prokaryote and Eukaryote Cells
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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

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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

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Bacterial Shapes
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Bacillus- E. coli
Fluorescent stain
Freeze fracture
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Public enemy 1- Anthrax
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Streptococcus pyogenes- strep throat
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Staphylococcus
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Arrangement of bacteria

• Groups of two- diplo
• Chains- strepto
• Large groups- like grape clusters- staphylo
• Division on 3 planes- sarcinae- 8 cells
  arranged in a cube
• Division on two planes produces tetrads

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Cell Morphology
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Staphylococcus
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Diplococcus
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Streptobacilli
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Spirillum
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Spriochetes
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Cell Walls

• 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)

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Peptidoglycans - Cell Wall
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• Gram Positive Bacteria- Cell walls
• The cell wall is made of Teichoic acid-
  glycerol phosphatesribotol 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 Gram-negative
bacteria is a bilayer that forms the outermost
layer of the cell wall and is attached to the
peptidoglycan by lipoproteins molecules.
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Gram-negative cell wall
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• 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

Endotoxin
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.
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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

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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
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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.

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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

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Membrane structure
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Internal Structure
Ribosomes- consist of ribonucleic acid ( RNA) and
protein. They are abundant in the cytoplasm
as POLYRIBOSOMES
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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

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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

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The Nucleoid Region
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Mesosomes- Bacteria
Bacterial cells have large infoldings in their
membranes.
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Mesosomes

• Mesosomes provide the surface area for all of the
  chemical reactions in the cell
• respiration
• metabolic processes

Freeze fracture
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Inclusions

• Small bodies in the cytoplasm- some are called
  granules

Glycogen pyrrophosphate granules-
volutin Metachromatic granules Variable colors
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Endospores

• 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,dis
  infectants, and radiation

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Spore formation

• Spores form when nutrients are depleged form a
  culture
• Few spores are formed when nutrients are
  plentiful and environmental conditions are
  favorable.

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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
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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.

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They are indestructible

• 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

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Flagella

• Bacteria that are motile have appendages called
  flagella
• A bacteria can have one or many flagella
• monotrichous
• amphitrichous
• lophotrichous
• peritrichous

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What is this type of bacteria ?
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• The diameter of a prokaryotes flagellum is
  about one-tenth 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.

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Turns like a mixer
Flagellar motion
Flagella rotate like twirling L- shaped hooks
such as a dough hook on a kitchen rotor- or a
mixer
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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

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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

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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 clum-
  this is hemagglutination

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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

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Bacterial Slime Layer or Capsule