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.