PROKARYOTES ARCHAEA

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PROKARYOTESARCHAEA

• Cells that lack peptidoglycan, tend to live in
  harsh environments. Extremophiles
• Methanogens produce methane as a result of
  respiration
• Halophiles live in areas of extreme salinity
• Thermophiles live in extremely hot water
• Others can survive in extremes of pH

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Bacterial Cell Structure

• Structure
• Cell wall
• Cytoplasmic membrane
• Chromosome

• Relative functions
• Protect cells against osmotic shock (most
  important) and physical damage
• Regulation of substance transport into and out of
  cells.
• Contain genome.

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• Structure
• Plasmid
• Ribosome
• Flagella

• Relative functions
• Contain supplemental genetic information such as
  resistance to antibiotics, production of toxins
  and tolerance to toxic environment.
• Take part in protein synthesis.
• Movement of cells.

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• Structures
• Inclusion body
• Pili
• Endospore

• Relative functions
• Mineral storage of cells.
• Attachment to host, bacterial exchange of genetic
  material.
• Tough, heat resistance structure that help
  bacteria survive in adverse conditions.

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Cell WallThe cell wall of bacteria protects the
cell from osmostic shock and physical damage. In
addition, it also confers rigiditiy and shape of
bacterial cells.

• Gram Negative
• consist of a thin layer of peptidoglycan
  surrounded by an outer membrane composed of
  lipids, lipoproteins, and a large molecule known
  as lipopolysaccharide (LPS). LPS can play a
  protective role and can also act as an endotoxin,
  causing some of the symptoms characteristic of
  gram-negative bacterial infections there are no
  teichoic acids in gram-negative cell walls.
• Gram Positive
• consist of a thick layer of peptidoglycan and
  large amounts of teichoic acids

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Plasma Membrane

• Cytoplasmic membrane
• The cytoplasmic membrane encloses the cytoplasm.
  It regulates the specific transport of substance
  between the cell and the environment. The
  cytoplasmic membrane contains 2 main components
  lipid and protein.
• The lipid component of the bacterial cell is
  phospholipid bilayer.
• Thickness 6-8nm.
• Unit amphipathic phospholipid, consisting of 1
  phosphate group (hydrophilic ) and unbranched
  fatty acid chains (hydrophobic).
• Distribution of 2 portions hydrophilic heads are
  exposed to the external environment or the
  cytoplasm. The fatty acid chains point inward,
  facing each other due to hydrophobic effects
  (staying away from water).

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Plasma Membrane

• Membrane proteins are located in various
  positions within the membrane, through specific
  interactions with phospholipid molecules. These
  proteins consist of 3 main groups integral
  proteins, outer-surface proteins and
  inner-surface proteins. They play distinctive
  roles in cellular activities.
• Integral proteins firmly embedded in the
  membrane, transport substance across the
  cytoplasmic membrane in 3 main mechanisms known
  as uniport, symport and antiport.
• Outer-surface proteins usually in Gram-negative
  bacteria, interact with periplasmic proteins in
  the transport of large molecules into the cells.
• Inner-surface proteins cooperate with other
  proteins in enery yeilding reactions and also
  other important cellular functions.

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How Do Bacteria Store Genetic Information?

• Genetic information in bacteria is stored in the
  sequence of DNA in two forms, that is bacterial
  chromosome and plasmid.

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How Do Bacteria Attach To Surfaces?

• Glycocalyx
• Structure Polysaccharide layers can be thick
  and stable like capsule or loosely attached to
  cell wall like slime layer.
• Function  Assist cells in adhesion to solid
  surface, and also protect pathogenic bacteria
  from the attack of the host's immune system.

Encapsulated streptococci ?
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How Do Bacteria Attach To Surfaces?

• Pili
• Structure   Short, thin, straight, hairlike
  projections form surface of some bacteria.
  Composed of protein pilin, carbohydrate and
  phosphate. Pili are usually few.
• Function    Take part in adhesion of pathogen to
  specific host tissues. Sex pili are involved in
  genetic material exchange between mating
  bacterial cells.

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How Do Bacteria Attach To Surfaces?

• Fimbriae
• Structure   Similar to pili, but shorter and
  more abundant on the cell surface.
• Function    Adhesion of cells to surface and
  formation of pellicles (biofilms) containing thin
  sheets of cells on a liquid surface.

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Movement of Bacteria

• Motility of most bacteria is away from or toward
  a stimulus.
• Chemotaxis chemical stimuli
• Phototaxis light stimuli
• Magnetotaxis movement along the Earths
  magnetic field. Occurs in bacteria that contain
  magnetosomes including iron.

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• Structure of flagella
• Long filamentous appendages containing a
  filament, hook and basal body.
• Filament consists of protein flagellin.
• Hook single type of protein, connects filament
  to the basal body.
• Basal body contains a rod and several rings in
  gram-negative bacteria. ( Gram-positive bacteria
  only have the inner pair of rings). This
  contributes to rotation of flagella, using energy
  from the activity of proton pumps.

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• Most bacteria can locomote to different parts of
  their environment, which helps them to find new
  resources to survive. This process is due to
  flagellum (plural, flagella) pushing or pulling
  the cell through a liquid medium.
• Types of Flagella distribution
• Monotrichous flagella one flagellum, if it
  originates from one end of the cell, it is called
  polar flagellum. Rapid swimming caused by the
  rotation of flagella.
• Peritrichous flagella flagella surround the
  cell. Bundled peritrichous flagella give rise to
  slower forward motion than polar flagella.
• Amphitrichous flagella groups of flagellum at
  each end of the cell.
• Lophotrichous flagella two or more at one end.

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The SLEEPING Bacteria

• An endospore, a heat-resistant and non-growing
  structure, can retain its viability over long
  periods of time under adverse environmental
  conditions. When the environment becomes more
  favourable, the endospore then germinates to a
  vegetative cell.

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The SLEEPING Bacteria

• Endospore structure
• Exosporium  Outer-most layer consisting of
  protein.
• Spore coat     Several layers of spore-specific
  proteins.
• Cortex          Loosely cross-linked
  peptidoglycan.
• Core             Core wall, cytoplasmic
  membrane, cytoplasm, nucleoid, ribosomes and
  other cellular compartments. Additionally.
  dipicolinic acid-calcium complex maintains
  dehydrated conditions inside the spore and helps
  to stablise DNA against heat denaturation.

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Genetic Material
Anatomy of a Cell
The differences and similarities of prokaryotic
and eukaryotic cells.

• Prokaryotic
• Genetic material not enclosed within a membrane,
  generally a singular circular chromosome

• Eukaryotic
• Genetic material (DNA) found in the nucleus as
  multiple chromosomes

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DNA

• Prokaryotic
• DNA is not associated with histones

• Eukaryotic
• DNA is associated with chromosomal proteins
  called histones and non-histones. Histones help
  coil and shorten chromosomes

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Organelles

• Prokaryotic
• Lack membrane enclosed organelles

• Eukaryotic
• Most organelles are membrane enclosed

Cell Walls
Prokaryotic Contain complex polysaccharide
peptidoglycan
Eukaryotic Chemically simple (if present)
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Cell Division

• Prokaryotic
• Generally divide by binary fission

• Eukaryotic
• Generally divide by mitosis
• (Sexual reproduction involves meiosis)

Cell Size
Prokaryotic 0.2 to 2.0 µm diameter
Eukaryotic 10 to 100 µm diameter
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Flagellum

• Prokaryotic
• Consist of two protein building blocks

• Eukaryotic
• Are complex consisting of multiple microtubiles

Plasma Membrane
Prokaryotic No carbohydrates, few sterols
Eukaryotic Includes carbohydrates and sterols
as receptors