Prokaryotic Cell Shapes, Arrangements, and Flagella

• Prokaryotic cells lack a nucleus
• Bacteria and Archaea are examples, both are single-celled organisms that often work in groups

Basic Shapes of Prokaryotic Cells

• Bacillus: rod shaped
• Coccus: spherical
• Spiral: includes Spirillum (Lyme disease), Vibrio (diarrheal diseases), and Spirochete (syphilis/Lyme disease)
• 80% of bacteria have one of these basic shapes

Arrangements of Prokaryotic Cells

• Pairs: Diplococci
• Clusters: Staphylococci
• Chains: Streptococci, Streptobacilli
• Staph is skin bacteria and is clusters of bacteria
• Strep looks like chain of bacteria

Outside Structures: Flagella

• Flagella is a protein structure outside the cell wall used for bacterial movement, made of chains of flagellin, and uses rotation
• Chemotaxis involves movement toward nutrition or away from toxins
• Phototaxis involves movement toward or away from light

Arrangements of Bacterial Flagella

• Peritrichous: flagella/cilia spread evenly over the organism's surface
• Monotrichous and polar: a single flagellum located at one end ("polar") of the organism, allowing movement in one direction
• Lophotrichous and polar: multiple flagella located at the same spot on the bacterial surface, moving in one direction
• Amphitrichous and polar: flagella going through bacteria from outside to inside
• Axial Filaments (Endoflagella): found inside bacterial cells

Axial Filaments (Endoflagella)

• Spirochetes: looks twisted
• Rotation drives cell movement, anchored at one end

Fimbriae

• Fimbriae: specifically bind to receptors on host cells, potentially causing disease by aiding bacterial attachment
• Composition: made of the protein "pilin," with a few to hundreds per cell, resembling hair-like structures
• Conjugation: involves one or two sex pili that facilitate DNA transfer between cells

Pili

• Pili is structurally similar to fimbriae but longer, with only 1-2 per cell
• They facilitate DNA transfer and maintain gut health

Glycocalyx

• Glycocalyx role is to help escape phagocytosis
• Glycocalyx is located outside the cell wall and is sticky
• Capsule: neatly organized, prevent phagocytosis
• Slime layer & biofilm: unorganized and loose
• Extracellular polysaccharide allows cell to attach

Cell Walls and Membranes

• Cell Wall: prevents osmotic lysis
• Peptidoglycan: linked by polypeptides
• Polymer of disaccharide:
  • N-acetylglucosamine (NAG)
  • N-acetylmuramic acid (NAM)
• Retain shape

Gram-Positive

• Gram (+) has a thick wall (purple)
• 90% peptidoglycan
• Up to 40 layers thick in some bacteria of peptidoglycan
• NAG-NAM chains (sugar chains) joined by peptide cross bridges (covalent bonds)
• Teichoic acids:
  • Lipoteichoic acids: extend from the cell membrane through the cell wall
  • Wall teichoic acids: link to the peptidoglycan layers only

Gram-Negative

• Gram (-) has a thin cell wall (Pink)
• Up to 20% of wall is peptidoglycan
• NAG / NAM chains joined by peptide bonds directly between the tetrapeptide side chains
• Surrounded by outer membrane
  • Has LPS
  • Between cell wall and plasma membrane
  • (lipid polysaccharide “LPS”) = lipid a + polysaccharide
• Difficult to treat

Lipids

• Lipid a is an endotoxin that confuses immune system
• PS provides antigenic

Gram Negative Outer Membrane

• Strong negative charge helps evade phagocytosis
• Provides barrier hydrophobic molecules and those above ~1000 MW (including antibiotics and detergents)
• Helps stabilize the inner cell membrane to withstand osmotic stress

Atypical Cell Walls

• Acid-fast cell walls, like gram +, contain a waxy lipid (mycolic acid) bound to peptidoglycan
• Bacteria in the Mycobacterium genus cause tuberculosis and are an exception to gram + and -
• Mycoplasmas lack cell walls and are also an exception to gram + and -
• Archaea: cell walls without peptidoglycans. Made of pseudomurein

The Plasma Membrane

• Phospholipid bilayer
• Peripheral proteins
• Integral proteins
• Transmembrane
• Proteins
• Function: selective permeability
• Passive process: simple: high concentration to low concentration
• Facilitated diffusion: solute combines w/ transport protein in membrane
• Osmosis
• Active processes: use ATP (ex: Na+ and K+ pump)

Osmosis

• Isotonic solution: no net movement of h20
• Hypotonic solution: h20 moves into cell (burst)
• Hypertonic solution: h20 moves outside cell (plasmolysis)

Inside Membrane

• Cytoplasm
• Nucleoid (bacterial chromosome)
  • Usually single chromosome
  • What shape?
  • Chromosome attached to cell membrane
  • Occupy 20% of cell volume
• Ribosome (protein factory)
  • Actively growing = a lot of ribosomes
  • Thousands per cell giving cytoplasm granular appearance
  • Humans don't have same size ribosome
  • Subunits made up of rRNA
    • Small subunit = 30s
    • Large subunit = 50s
    • Complete ribosome = 70s (50 on top of 30)

Plasmid DNA

• Antibiotic resistant / survive in high temperature
• Specialized form of genetic material in bacteria away from chromosomes (not connected to main chromosomes)
• Replicate independently
• Can be antibiotic resistant gene

Spores

• Formed by Gram (+) bacteria in response to environmental stress
• Endospores:
  • Resting cells
  • Resistant to desiccation, heat, chemicals
  • Bacillus, Clostridium
  • Sporulation: endospore formation
  • Germination: return to vegetative state

Explore prokaryotic cell shapes like bacillus, coccus, and spiral. Understand arrangements such as diplococci, staphylococci, and streptococci. Learn about flagella structure, function in bacterial movement, chemotaxis, phototaxis, and different flagella arrangements.