Bacterial and Cellular Structures
Chapter 3
Objectives for today
• Understand the function of a variety cellular
structures
• The uses of the cell membrane
• Overview of some differences between
prokaryotes and eukaryotes
– Important for medical targets!
Definitions
Poly = Many, Mono = 1, Di = 2, Tri = 3
• Polysaccharide
Sugar
• Lipid/phospholipid
– Non-polar, hydrophobic molecule comprising the cell
membrane
• ATP (Adenosine Triphosphate)
– The energy containing molecule
Bacterial Structures
Capsule or Glycocalyx
• Outermost layer
• Polysaccharide or
polypeptide
• Allows cells to adhere to a
surface
• Contributes to bacterial
virulence-avoid
phagocytosis
Filamentous Protein Appendages
Flagella - motility
Rotate like a propeller
Proton motive force used for energy
Presence/arrangement can be
used as an identifying marker
Flagella - motility
Rotate like a propeller
Proton motive force used for energy
Presence/arrangement can be
used as an identifying marker
Peritrichous
Polar
Other (ex. tuft on both ends)
Flagella - motility
Chemotaxis - Directed movement towards/away from a chemical
•Cell movement is due to a series of “runs” and “tumbles”
•“Runs” are longer when cell
is going in the right direction
https://www.youtube.com/watch?v=EpC6G_DGqkI
Different types of pili
Common pili (fimbriae)
Sex pili - Conjugation
Cell Wall
Provides rigidity to the cell
•Protection against osmotic
forces
• Bursting from massive
influx of water
Cell Wall
Provides rigidity to the cell
(prevents it from bursting)
Cell Wall
•Peptidoglycan - rigid molecule; unique to
bacteria
•Alternating subunits of NAG and NAM
form glycan chains
•Glycan chains are connected to each other
via peptide chains on NAM molecules
Cell Wall
Cell Wall
•Peptidoglycan - rigid molecule; unique to
bacteria
•Alternating subunits of NAG and NAM
form glycan chains
•Glycan chains are connected to each other
via peptide chains on NAM molecules
Medical significance of peptidoglycan
•Target for selective toxicity; synthesis is
targeted by certain antimicrobial
medications (penicillins, cephalosporins)
•Recognized by innate immune system
•Target of lysozyme (in egg whites, tears)
Cell Wall
Gram-positive
Thick layer of peptidoglycan
Teichoic acids
Cell Wall
Gram-negative
Thin layer of peptidoglycan
Outer membrane - additional membrane
barrier; porins permit passage
lipopolysaccharide (LPS)
Cell Wall
Gram-negative
Thin layer of peptidoglycan
Outer membrane - additional
membrane barrier; porins permit passage
lipopolysaccharide (LPS)
- ex. E. coli O157:H7
endotoxin
- recognized by innate immune system
Cell Wall
Gram-negative
Thin layer of peptidoglycan
Outer membrane - additional
membrane barrier; porins permit passage
lipopolysaccharide (LPS)
periplasm
Cytoplasmic membrane
•Defines the boundary of the cell
•Semi-permeable; excludes all
but water, gases, and some
small hydrophobic molecules
•Transport proteins function as
selective gates (selectively permeable)
•Control entrance/expulsion of
antimicrobial drugs
•Receptors provide a sensor system
•Phospholipid bilayer, embedded with proteins
Cytoplasmic membrane
•Defines the boundary of the cell
•Semi-permeable; excludes all
but water, gases, and some
small hydrophobic molecules
•Transport proteins function as
selective gates (selectively permeable)
•Control entrance/expulsion of
antimicrobial drugs
•Receptors provide a sensor system
•Phospholipid bilayer, embedded with proteins
Cytoplasmic membrane
•Defines the boundary of the cell
•Semi-permeable; excludes all
but water, gases, and some
small hydrophobic molecules
•Transport proteins function as
selective gates (selectively permeable)
•Control entrance/expulsion of
antimicrobial drugs
•Receptors provide a sensor system
•Phospholipid bilayer, embedded with proteins
•Fluid mosaic model
Cytoplasmic membrane
Electron transport chain - Series of proteins that eject protons from the cell,
creating an electrochemical gradient
Proton motive force is used to fuel:
•Synthesis of ATP (the cell’s energy currency)
•Rotation of flagella (motility)
•One form of transport
If a function of the cell
membrane is transport…..
• How is material transported in/out of the
cell?
– Passive transport
• No ATP
• Along concentration gradient
– Active transport
• Requires ATP
• Against concentration gradient
Types of transport
• Passive transport
• Simple diffusion
• Facilitated diffusion
• Osmosis
• Active transport
• System that uses proton motive force
• System that uses ATP
• Group translocation
Permeability of the membrane
Osmosis
http://www.dnatube.com/video/2775/Onion-Cells-Plasmolysis
Facilitated Diffusion
https://www.youtube.com/watch?v=I4123hUU8xo
Active Transport
Internal structures: Chromosome
Internal structures: Ribosomes
https://www.youtube.com/watch?v=hEtONGf4Z0A
Internal structures:Storage
Granules
Internal
Structures:
Endospores
Eukaryotes
• Larger than prokaryotes
– 600uM vs 10uM
• Nucleated
• Many organelles not found in prokaryotes
– ER, golgi, mitochondria, etc
Encyclopedia of worlds, David Darling
Plant Cells
• Eukaryote
• Photosynthesis in chloroplasts
• Cellulose cell walls
Mitochondria (all eukaryotic cells)
Chloroplasts (plant cells only)