Prokaryotic and Eukaryotic Cells

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Prokaryotic and Eukaryotic Cells

• Chapter 4

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Structure Function

• Linkage of Structure function operates at all
  levels
• NS acts by changing structures to improve
  function
• Useful ones persist, less useful improve
• Useless ones are eventually lost

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Living Organisms

• All organisms except Viruses are cellular
• There is and enormous diversity
• Only Two fundamental types

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Fundamental Cell Types

• Prokaryotic Domains Bacteria Archaea
• Eukaryotic Animals, plants, protozoa, fungi
  algae
• Differences important from the scientific human
  health standpoint

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Prokaryotes vs. Eukaryotes

• Structural Difference
• Chemical Difference
• Size Difference

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Structural Difference

• Prokaryotes
• Have organelles but are not membrane bound
• Have irregular area containing DNA
• Eukaryotes
• Membrane bound organelles
• Defined nucleus

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Chemical Difference

• Prokaryotes
• Cell Wall composed of peptidoglycan
• Eukaryotes
• Do not contain peptidoglycan in their cell walls

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Size Difference

• Prokaryotes
• High surface area relative to volume- easier to
  take in nutrients and excrete wastes
• multiply rapidly
• Eukaryotes
• About 10x larger than prokaryotes

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• As a cell increases in size its volume increases
  faster than its surface area.
• Smaller objects have a greater ratio of surface
  area to volume.

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Prokaryote Cell Structure
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The Bacterial Cell Structure

• The Envelope Capsule
• Pili Flagella
• Cytoplasm Inclusions

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The Envelope Capsule

• The bacterial envelope can be a three layered
  structure
• Outer Membrane
• Cell Wall
• Cytoplasmic Membrane
• A capsule may or may not surround the envelope

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The Envelope

• Gram negative bacteria contain all 3 layers
• Have an extra compartment between the OM the CM
  ? periplasm
• Gram positive bacteria lack the OM
• Mycoplasma lack OM CW

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Bacterial Envelopes
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Outer Membrane

• Only Gram negatives have an OM
• Composed of a lipid bilayer
• Inner layer ? phospholipids
• Outer layer ? lipopolysacchride (LPS)
• Lipid A
• O-specific side chain
• Core polysaccharide
• LPS also known as endotoxin

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Lipopolysaccharide

• Lipid A ? hydrophobic
• Polysaccharide ? hydrophilic
• Act as barriers to both polar nonpolar
  substances
• Only water and a few gases can cross the lipid
  part of the OM
• Other molecules pass through pores in the OM
• Pores formed by proteins ? Porin

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Lipopolysaccharide

• Held to the envelope by lipoprotein
• Bonded to the cell wall on one end, other end
  carries lipid that is inserted into the inner
  surface
• Most important function is protection
• Makes Gm (-) bacteria more resistant to
  antibiotics
• Ex rifampin equally inhibits RNA pol. But in Gm
  (-) cant reach target

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Periplasmic Space

• In gram (-) lies between the OM and the
  cytoplasmic membrane
• In gram() lies between the CW and the
  cytoplasmic membrane
• Contains water, nutrients and substances secreted
  by the cell, such as enzymes and proteins ?
  transport

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Cell Wall

• Prokaryotic Cell Walls
• Provides structure and shape
• Protects cell from osmotic forces
• Assists cells in attaching to other cells or
  eluding anti-microbial drugs
• Animal Cells ? Do not have cell walls
• Bacterial Cells ? Can target cell wall with
  antibiotics

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Bacterial Cell Walls

• Most have cell walls composed of peptidoglycan.
  Few lack a cell wall.
• Peptidoglycan ? protein polysaccharide, also
  called Murein
• Peptidoglycan ? form long chains of alternating
  sugars, NAG and NAM
• NAG and NAM ? held together by protein chains

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Bacterial Cell Walls

• Chains of NAG and NAM are attached to other
  chains by tetrapeptide cross bridges
• Tetrapeptide cross bridges ? two amino acids are
  L-isomers and two are D-isomers
• Glycan and peptide linked form a mesh-like
  structure

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Bacterial Cell Walls

• Two basic types
• Gram Positive
• Gram Negative

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Gram Positive Cell Walls

• Relatively thick layer of peptidoglycan
• Contains unique polysaccharides called techoic
  acid
• Techoic Acid ? Glycerol or Ribitol linked to a
  phosphate group
• Techoic Acid ? penetrates the multi-layer cell
  wall, making it stronger

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Gram Negative Cell Walls

• Have a only a thin layer of peptidoglycan
• Peptidoglycan mesh is only one layer thick

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Cell Shape

• Peptidoglycan confers shape
• Bacteria come in many sizes , shapes
  arrangements

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Cocci
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Rods
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Comma Spirals
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Other Shapes
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Turgor Pressure

• Osmotic pressure within the cell
• Approx. 350 lbs/sq in
• Cell must be protected
• Cell ? inside highly conc.? unprotected? water
  enters? cell bursts

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Autolysins Transpeptidases

• Bacterial cells to increase in size, the
  peptidoglycan has to increase
• Autolysin breaks the cross bridges
• Transpetidases reseals by adding new monomers
• Peptidoglycan increases in size
• Highly regulated precise process
• Penicillin/antibiotics inactivate peptidase

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Mycoplasma, L-Forms and Spheroplasts

• Mycoplasma ? no cell walls, CM is strengthened by
  sterols
• L-Forms ? wall-less strains of certain bacteria,
  can return to original form
• Spheroplasts ? bacteria that have lost cell wall

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Cytoplasmic Membrane

• Membrane that encloses cytoplasm
• Also called a plasma membrane
• In prokaryotes eukaryotes, the membranes are
  quite similar
• Called a unit membrane

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Unit Membrane

• Phospholipid bilayer
• Hydrophilic head ? sticks out on both sides
• Hydrophobic tail ? 2 Fatty Acids, facing each
  other
• Bilayer studded with proteins ? Carrier or
  transporter proteins ½ the dry weight of the CM
• Proteins can move with in the membrane ? Fluid
  Mosiac model
• Bacteria have energy-generating proteins

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Fluid Mosiac Model
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Movement Across Membranes

• Osmosis
• Facilitated diffusion
• Active transport
• Group translocation
• Engulfment

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Movement Across Membranes
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Exocytosis Endocytosis
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Capsule

• A gelatinous covering made of organic chemicals
• Firmly attaches to the cell surface
• Capsule help anchor S.mutans to anchor to
  surface of tooth

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Capsule

• Protects the cell from drying out
• Prevents the bacteria from being recognized by
  the host
• S. pneumoniae ? strain that lack capsule do not
  cause pneumonia

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Pili Flagella

• Presence or absence depends on species and
  conditions under which organism is grown
• Spirochetes have a modified flagella?
  endoflagellum from the periplasmic space.

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Pili

• Straight hair like projections made of protein
  pilins
• May be short or several cell lengths long

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Pili

• Main function is attachment? each type of
  bacteria attach to sp. surfaces
• Present in virtually all Gm(-), absent in many
  Gm()

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Sex Pili

• Attaches one bacterial cell to another during
  mating

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Flagella

• Whip like structures that extend from the surface
  of the envelope
• Function? Locomotion, allow bacteria to seek
  favorable conditions

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Flagella Structure

• Three distinct parts
• Filament? flagellin protien arranged in chains
  forms a helix around a hollow core
• Hook? short thickened bent region, act as a joint
• Basal body? anchors filament hook to cell wall

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Flagella Arrangement

• Monotrichous? single flagellum at one pole
• Amphitrichous? single flagellum at each pole
• Lopotrichous? two or more at one or both poles
• Peritrichous? flagella all over the surface

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Taxis

• Chemotaxis ? bacteria sense certain chemicals and
  move toward nutrients or away from toxins
• Phototaxis ? swim to optimum light
• Magnetotaxis ?movement magnetic lines of force

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Chemotaxis
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Cytoplasm Inclusions

• Cytoplasm ? grainy material that lies inside the
  CM
• 90 water
• Metabolism takes place here
• Nucleoid? irregular mass of DNA in the cytoplasm,
  single circular molecule, carries genetic info.
• Ribosomes ? protein making unit, 20,000/cell,
  smaller than eukaryotic ribosomes, 70S

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Endospores

• Resting structures
• Most resistant biological structure known
• Can withstand harsh environments
• Can survive for 100s of years
• Forms under unfavorable conditions, if conditions
  become favorable? germinate

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Archeon

• Do not have peptidoglycan
• Cell Walls contain pseudomurein
• Cytoplasmic membrane is also different

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The Eukaryotic Animal Cell
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The Eukaryotic Plant Cell
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Eukarytotic Structures

• External structures? cilia, flagella
• Cell walls, Cell membranes
• Cytoplasmic inclusions
• Ribosomes
• Cytoskeleton
• Centrioles Centrosomes

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Eukarytotic Structures

• Nucleus contents
• Endoplasmic Reticulum (rough smooth)
• Golgi Body
• Lysosomes
• Mitochondria Chloroplasts

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Nucleus contents
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Endoplasmic Reticulum (rough smooth)
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Ribosome
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Protein Synthesis
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Golgi Body
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Lysosomes
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Mitochondria
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Chloroplasts