Microbio Chapter 4

Cell Structures of Prokaryotes vs Eukaryotes (Learning Objective 1)

Prokaryotes

  • Contains one circular chromosome, not in a membrane.

  • Lacks histones.

  • No membrane-enclosed organelles.

  • Bacteria have peptidoglycan cell walls.

  • Archaea have pseudomurein cell walls.

  • Divide by binary fission.

Eukaryotes

  • Paired chromosomes within a nuclear membrane.

  • Contains histones.

  • Contains organelles.

  • Polysaccharide cell walls when present.

  • Divides by mitosis.

Basic Shapes of Bacteria (Learning Objective 2)

  • Bacillus: Rod-shaped.

  • Coccus: Spherical.

  • Spiral: Includes vibrio, spirillum, and spirochete.

Glycocalyx (Learning Objective 3)

  • Sugary substances covering the cell are made of polysaccharides and/or polypeptides.

  • Types:

    • Capsule: Neatly organized and firmly attached.

    • Slime layer: Unorganized and loose.

  • Functions include:

    • Protecting bacteria from phagocytosis.

    • Enabling adherence.

    • Preventing dehydration.

    • Serving as a nutrient source.

Structures: Flagella, Axial Filaments, Fimbriae, and Pili (Learning Objective 4)

Flagella

  • Outside cell wall, made of flagellin (protein)

  • Attached to a hook, anchored by the basal body.

  • Movement toward or away from stimuli (taxis).

  • Functions as an antigen (H protein).

Fimbriae

  • Hairlike appendages allow attachment.

  • Involved in biofilm formation.

  • Enable adherence to body surfaces.

Pili

  • Involved in motility (gliding and twitching).

  • Conjugation pili facilitate DNA transfer between cells.

Axial Filaments (Endoflagella)

  • Also known as endoflagella, it is found in spirochetes.

  • Anchored at one end, causing corkscrew movement.

Gram-Positive vs Gram-Negative Cell Walls (Learning Objective 5)

Gram-Negative Cell Wall

  • Peptidoglycan sandwiched between two lipid bilayer membranes.

  • Composed of:

    • Few peptidoglycan layers.

    • Outer membrane with LPS, lipoproteins, and phospholipids.

Gram-Positive Cell Wall

  • Composed of many layers of peptidoglycan.

  • Contains teichoic acid (an alcohol molecule + phosphate group).

Acid-Fast, Archaea, and Mycoplasma Cell Walls (Learning Objectives 5/6)

Acid-Fast Cell Walls

  • Similar to gram-positive cell walls, with thick peptidoglycan and waxy lipids (mycolic acid).

Archaea Cell Walls

  • Composed of pseudomurein (lacks NAM and D-amino acids).

Mycoplasma Cell Walls

  • Have little or no cell wall.

  • It may be protected by sterols in the plasma membrane.

Protoplast, Spheroplast, and L Forms (Learning Objective 7)

Protoplast

  • Formed by completely removing the cell wall.

  • Has one membrane and is round/oval.

  • Removal typically involves enzymatic and mechanical methods.

Spheroplast

  • Formed by partially removing the cell wall.

  • Retains some cell wall structure and has two membranes.

  • Typically round or spherical in shape.

L Forms

  • Irregular in shape.

  • Cell-wall deficient bacteria that grow as protoplasts or spheroplasts.

Plasma Membrane Structure and Function (Learning Objective 8)

Structure

  • Phospholipid bilayer enclosing cytoplasm.

  • Contains peripheral proteins on inner/outer surfaces and integral/transmembrane proteins.

  • Includes glycoproteins and glycolipids.

  • Fluid mosaic model: the membrane is as viscous as olive oil, with freely moving proteins and laterally rotating phospholipids.

Function

  • Selective Permeability: Allows passage of some molecules but not others.

  • Contains enzymes for ATP synthesis.

  • It may have photosynthetic pigments on foldings (chromatophores).

Definitions (Learning Objective 9)

  • Simple Diffusion: Movement of solute from high to low concentration; equal distribution achieved.

  • Facilitated Diffusion: Movement of ions or larger molecules across the membrane facilitated by integral membrane proteins.

  • Active Transport: Requires transporter protein and ATP; moves substances against their gradient.

  • Group Translocation: Requires transporter protein and phosphoenolpyruvic acid (PEP); substance is altered during crossing.

  • Osmosis: Net movement of water across a semipermeable membrane from higher to lower water concentration.

Nucleoid and Ribosomes (Learning Objective 10)

Nucleoid

  • Bacterial chromosome: Circular double-stranded DNA, not enclosed in a nuclear envelope, with no associated histones.

Ribosomes

  • Sites of protein synthesis are made of protein and ribosomal RNA; prokaryotic ribosomes are 70S (50S + 30S).

Inclusions (Learning Objective 11)

  • Contains reserve deposits of nutrients:

    • Metachromatic granules (volutin) for phosphate reserves.

    • Polysaccharide granules for energy reserves.

    • Lipid inclusions for energy reserves.

    • Sulfur granules for energy reserves.

  • Other structures:

    • Carboxysomes: Contain RuBisCO for CO2 fixation in photosynthesis.

    • Gas Vacuoles: Maintain buoyancy.

    • Magnetosomes: Iron oxide inclusions that destroy H2O2.

Endospores (Learning Objective 12)

  • Resting cells are produced when nutrients are depleted.

  • Resistant to desiccation, heat, chemicals, and radiation, it can remain dormant for thousands of years.

  • It is not a reproductive process but a survival mechanism produced by Bacillus and Clostridium.

  • Sporulation: Process of endospore formation.

  • Germination: Endospore returns to vegetative state.

  • Important in the food industry.

Prokaryotic vs Eukaryotic Flagella (Learning Objective 13)

Prokaryotic Flagella

  • Composed of flagellin with three parts: filament, hook, and basal body. Propel bacteria.

Eukaryotic Flagella

  • Long projections made of microtubules organized in a 9 + 2 array.

  • The motion resembles a wave-like manner.

Cell Walls and Glycocalyxes (Learning Objective 14)

Prokaryotic Cell Wall

  • It prevents osmotic lysis, protects cell membranes, and is made of peptidoglycan. Differentiates major groups of bacteria and sites of antibiotic action.

Eukaryotic Cell Wall

  • Found in plants, algae, and fungi, made of carbohydrates

    • Cellulose in plants

    • Chitin in fungi

Prokaryotic Glycocalyx

  • External to the cell wall, viscous and gelatinous, made of polysaccharide/protein.

    • Capsule: Neatly organized and firmly attached.

    • Slime layer: Unorganized and loose.

Eukaryotic Glycocalyx

  • Found in animal cells, bonded to proteins/lipids in the plasma membrane, strengthens cell surface, aids in attachment, and helps in cell recognition.

Prokaryotic vs Eukaryotic Plasma Membrane (Learning Objective 15)

Prokaryotic Plasma Membrane

  • Phospholipid bilayer enclosing cytoplasm with peripheral and integral proteins. Self-sealing and fluid mosaic.

Eukaryotic Plasma Membrane

  • Similar but has sterols and carbohydrates for attachment and cell recognition. Functions similarly to endocytosis mechanisms.

Prokaryotic vs Eukaryotic Cytoplasm (Learning Objective 16)

Prokaryotic Cytoplasm

  • Thick, aqueous, elastic, containing DNA (nucleoid), ribosomes, inclusions, and cytoskeleton for shape maintenance and division.

Eukaryotic Cytoplasm

  • Substances inside the plasma membrane and outside the nucleus contain cytosol and cytoskeleton for shape and support.

Prokaryotic vs Eukaryotic Ribosomes (Learning Objective 17)

Prokaryotic Ribosomes

  • Sites of protein synthesis, 70S structure (50S + 30S).

Eukaryotic Ribosomes

  • Larger 80S structure with 60S (large) + 40S (small), some bound to the endoplasmic reticulum.

Nucleus vs Nucleoid (Learning Objective 18)

Nucleus (Eukaryotic)

  • A double membrane structure (nuclear envelope) encloses DNA and is complex with histones as chromatin.

Nucleoid (Prokaryotic)

  • Circular DNA strands are not enclosed within a nuclear envelope or without histones.

Organelle Definition and Functions (Learning Objective 18 & 19)

Organelle

  • Specialized structures within a cell perform specific functions.

Functions of Organelles

  • Endoplasmic Reticulum: Rough (protein synthesis) and Smooth (lipid synthesis).

  • Nucleus: Encloses genetic material.

  • Golgi Complex: Modifies and transports proteins.

  • Lysosomes: Digestive enzymes.

  • Vacuoles: Storage, providing structure and shape.

  • Mitochondria: ATP production via respiration.

  • Chloroplasts: Photosynthesis.

  • Peroxisomes: Oxidizing fatty acids.

  • Centrosomes: Organizing center for mitotic spindle.

Endosymbiotic Theory (Learning Objective 20)

  • Explains the origins of eukaryotes:

    • Larger prokaryotic cells engulfed smaller ones, leading to eukaryotic evolution.

    • Nucleus formed from plasma membrane infoldings.

    • Ingested photosynthetic bacteria evolved into chloroplasts; aerobic bacteria evolved into mitochondria.

  • Evidence:

    • Double membranes of mitochondria/chloroplasts.

    • Only reproduced via division of pre-existing organelles.

    • Own DNA, circular and naked.

    • Ribosomes size 70S.