Questions and Answers
Describe the structure of the bacterial plasma membrane.
It is made of proteins within a phospholipid bilayer. There are no sterols except mycoplasmas. It contains cardiolipin.
What is the function of the bacterial plasma membrane?
It acts as a barrier against aqueous ions that allows gradients to control osmotic balance. It is involved in metabolite and nutrient transport and biosynthesis of lipids, polysaccharides, and peptidoglycan.
What is the Cell Wall made of?
Peptidoglycan
Describe the structure of Peptidoglycan.
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What is the function of Peptidoglycan?
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What are the biological effects of a peptidoglycan?
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What are Teichoic and Lipoteichoic acids?
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What is the Outer Membrane?
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What is the function of the Outer Membrane?
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What are the biological effects of LPS?
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What is the Periplasm?
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What is the function of Periplasm?
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What are Exopolysaccharides?
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What is the difference between Capsule and Slime?
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What is the function of the capsule?
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What is the function of Slime?
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What are the S-Layers?
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What is the function of the S Layers?
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What are Pili/Fimbriae?
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What are the functions of Pili/Fimbriae?
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Study Notes
Bacterial Plasma Membrane
- Composed of proteins embedded in a phospholipid bilayer.
- Lacks sterols, except in mycoplasmas.
- Contains cardiolipin, contributing to membrane integrity.
Functions of the Plasma Membrane
- Acts as a barrier against ions, essential for osmotic balance.
- Involved in transport of metabolites and nutrients.
- Plays a role in biosynthesis of lipids, polysaccharides, and peptidoglycan.
Bacterial Cell Wall Composition
- Primarily made of peptidoglycan.
Structure of Peptidoglycan
- Alternating units of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM).
- NAM includes a peptide tail for cross-linking, forming a 3D multilayered net that is porous.
Functions of Peptidoglycan
- Protects bacteria from osmotic lysis.
- Maintains cell shape and provides chemical protection.
- Acts as an anchor for vital proteins.
Biological Effects of Peptidoglycan
- Unique to each bacterial species, acts as a PAMP (Pathogen-Associated Molecular Pattern).
- Induces cytokines IL-1, IL-6, GCSF, and TNF-alpha.
- Certain fragments can serve as cytotoxins, linking to diseases like arthritis and evasion of the innate immune response.
Teichoic and Lipoteichoic Acids
- Found in Gram-positive cells, composed of negatively charged sugar polymers.
- Lipoteichoic acids have lipid anchors, while teichoic acids are bound at different cell envelope regions.
- These aid in autolysis protection and strengthen the peptidoglycan layer, acting as virulence factors.
Outer Membrane in Gram-negative Cells
- Provides asymmetry with a phospholipid inner leaflet and LPS (lipopolysaccharide) outer leaflet.
- Contains proteins such as OMPs (outer membrane proteins) and porins.
Function of the Outer Membrane
- Serves as a selective barrier, impermeable to aqueous molecules.
- Allows selective transport via porins/transporters.
- Provides protection against lysis and facilitates antigenic variation.
Biological Effects of LPS (Lipopolysaccharide)
- Can directly activate TLR (Toll-like receptors) or be transferred via LBP (LPS-binding protein) to CD14.
- Triggers cytokine release, leading to conditions like septic shock.
Periplasm Structure
- A viscous solution between the plasma membrane and the outer membrane/peptidoglycan layer, containing proteins and solutes.
Function of Periplasm
- Provides protection against osmotic lysis.
- Site of peptidoglycan synthesis, nutrient binding, macromolecule degradation, detoxification, and housing chemotactic receptors.
Exopolysaccharides
- Comprise the capsule and slime layer, consisting of long sugar chains, also referred to as glycocalyx.
Difference between Capsule and Slime Layer
- Capsule: Organized, cell-associated layer, firmly attached to the cell membrane.
- Slime: Disorganized, loosely associated layer; may appear like capsule in large quantities.
Functions of the Capsule
- Protects against phagocytosis and reduces complement-mediated opsonization.
- Assists in host mimicry and is recognized as "K" antigen in serotyping.
- Potential target for vaccine development.
Function of Slime Layer
- Facilitates adhesion to surfaces or cells and contributes to biofilm formation.
S-Layers (Surface Layers)
- Made of protein, forming a crystallized array of single protein types.
- Bound to peptidoglycan or LPS, functioning as a protective mesh with small pores.
Functions of S-Layers
- Protects against various threats including enzymes, metals, phagocytosis, and bacteriophages.
- Can be useful in vaccine development and aid in bacterial adhesion.
Pili/Fimbriae
- Short protein strands that cover bacterial cell surfaces.
Functions of Pili/Fimbriae
- Essential for adhesion, providing antiphagocytic properties.
- Contribute to twitching motility and facilitate genetic exchange (conjugation).
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Explore the essential components of bacterial cell structure with these flashcards. Learn about the bacterial plasma membrane's structure and function in detail, enhancing your understanding of microbiology. Perfect for students and enthusiasts alike.