Morphology of Prokaryotic Cells: Cell Shapes

Morphology of Prokaryotic Cells: terminology in practice

• Curved rods:– Campylobacter species– Vibrio species

• Spiral rods:– Helicobacter species– Spirillum species– Spirochetes:

• Leptospirosa species

Morphology of Prokaryotic Cells: Cell Groupings

**Bacterial Structures**

You should know what all of the structures on this diagram are - what their basic composition is and what their function is

The Glycocalyx: Capsules and Slime Layers

• Outermost layer • Polysaccharide or

polypeptide• May allow cells to adhere

to a surface• Contributes to bacterial

virulence by preventing phagocytosis

• An important virulence factor

Filamentous Protein Appendages

Escherichia coli

Enterococcus faecium

Rotate like a propellerProton motive force used for energy

Presence/arrangement can be used as an identifying marker

Flagella - motilityE. coli O157:H7

Flagella - motility

Presence/arrangement can be used as an identifying marker

PeritrichousPolarOther (ex. tuft on both ends)

Rotate like a propeller

Proton motive force used for energy

Chemotaxis - Directed movement towards/away from a chemical

Pili - attachmentCommon pili (fimbriae); singular = pilus

Function in adhesion = virulence factorHelical arrangement of protein subunits

Sex pili - ConjugationSharing of mobilegenetic information – plasmids

Cell Wall

Provides rigidity to the cell (prevents it from bursting)

Cell Wall

Provides rigidity to the cell (prevents it from bursting)

**Cell Wall**

• Peptidoglycan - rigid molecule; unique to bacteria

• Glycan chains are connected to each other via peptide chains on NAM molecules

• Alternating subunits of NAG and NAM form glycan chains

Know the basic structure/composition of the bacterial cell wall; know the structureal and chemical differences between the cell walls of Gram-negative and Gram-positive bacteria and how these differences relate to how they appear in a Gram stained slide

Cell Wall

Cell WallMedical 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 peptidoglycanTeichoic acids

Cell WallGram-negative

Thin layer of peptidoglycanOuter membrane - additional membrane barrier

Lipopolysaccharide (LPS)

O antigen

Core polysaccharide

Lipid A

Cell WallGram-negative

Thin layer of peptidoglycanOuter membrane - additional membrane barrier; porins permit passage

lipopolysaccharide (LPS) endotoxin

- recognized by innate immune system

- ex. E. coli O157:H7

Cell WallGram-negative

Thin layer of peptidoglycanOuter membrane - additional membrane barrier; porins permit passage

lipopolysaccharide (LPS)periplasm

Cytoplasmic membrane

• Defines the boundary of the cell

• Transport proteins function as selective gates (selectively permeable)• Control entrance/expulsion of

antimicrobial drugs• Receptors provide a sensor system

• Semi-permeable; excludes all but water, gases, and some small hydrophobic molecules

• Phospholipid bilayer, embedded with proteins

The Gram stain

Acid fast stains:Fite’s, modified Fite’s, Kinyoun

Primary stain: carbolfuchsinDecolorizing agent: acid alcoholSecondary stain: methylene blue

• Defines the boundary of the cell

• Transport proteins function as selective gates (selectively permeable)• Control entrance/expulsion of

antimicrobial drugs• Receptors provide a sensor system

• Semi-permeable; excludes all but water, gases, and some small hydrophobic molecules

• Phospholipid bilayer, embedded with proteins

Cytoplasmic membrane

Cytoplasmic membrane

• Defines the boundary of the cell

• Transport proteins function as selective gates (selectively permeable)• Control entrance/expulsion of

antimicrobial drugs• Receptors provide a sensor system

• Semi-permeable; excludes all but water, gases, and some small hydrophobic molecules

• Phospholipid bilayer, embedded with proteins

Cytoplasmic membrane

• Defines the boundary of the cell

• Transport proteins function as selective gates (selectively permeable)• Control entrance/expulsion of

antimicrobial drugs• Receptors provide a sensor system

• Semi-permeable; excludes all but water, gases, and some small hydrophobic molecules

• Phospholipid bilayer, embedded with proteins• Fluid mosaic model

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

Cytoplasmic membrane

Electron transport chain

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

Facilitated Diffusion

Diffusion of water is Osmosis

Active transport: Proton Motive Force

Active transport: Use ATP

Active transport: Group translocation

Internal structures: Chromosome

Internal structures: Ribosomes

Internal structures:Storage Granules

Internal structures: Cytoskeleton

Internal structures: Endospores