Bacterial Cell Structure Flashcards

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.

It is made of alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). The NAMs have a peptide tail that covalently links to other tails on other strands, forming a 3D multilayered net which is porous. Signup and view all the answers

What is the function of Peptidoglycan?

It protects against osmotic lysis, provides shape, helps in chemical protection, and anchors important proteins. Signup and view all the answers

What are the biological effects of a peptidoglycan?

It is unique to each bacteria and serves as a PAMP in the body, causing the induction of IL-1, IL-6, GCSF, and TNF-a. Specific fragments can serve as cytotoxin, and it can cause arthritis while also protecting the bacteria from the innate response. Signup and view all the answers

What are Teichoic and Lipoteichoic acids?

Polymers of negatively charged sugars in Gram+ cells. Lipoteichoic Acids have a lipid anchor, both are anchored to different parts of the cell envelope, serving in autolysis protection and providing strength to the Peptidoglycan Layer. Signup and view all the answers

What is the Outer Membrane?

In Gram- cells, it provides asymmetry and contains a phospholipid inner leaflet and an LPS/LOS outer leaflet, containing many proteins including OMPs and outer membrane porins. Signup and view all the answers

What is the function of the Outer Membrane?

It acts as a selective barrier impermeable to aqueous molecules, contains porins/transporters, protects against lysis, and has antigenic variation. Signup and view all the answers

What are the biological effects of LPS?

It can directly bind to TLR or have a LBP-mediated LPS transfer to CD14, causing the release of IL-1 and TNF, which can lead to septic shock. Signup and view all the answers

What is the Periplasm?

It is a viscous solution of proteins and solutes that sits between the plasma membrane and the Outer Membrane/Peptidoglycan Layer. Signup and view all the answers

What is the function of Periplasm?

To protect against osmotic lysis; it allows for the synthesis of peptidoglycan and various other functions such as nutrient binding, macromolecule degradation, detoxification, and housing chemotactic receptors. Signup and view all the answers

What are Exopolysaccharides?

They make up the Capsule and Slime Layer, composed of long chains of sugar, also called Glycocalyx. Signup and view all the answers

What is the difference between Capsule and Slime?

Capsule is an organized, cell-associated exopolysaccharide layer attached to phospholipid, while slime is disorganized and loosely associated. Signup and view all the answers

What is the function of the capsule?

It protects bacteria against phagocytosis, helps reduce complement-mediated opsonization, aids in host mimicry, and can be a target for vaccines. Signup and view all the answers

What is the function of Slime?

It is for adhesion to surfaces or cells and forms biofilms. Signup and view all the answers

What are the S-Layers?

These layers are made of protein and are a crystallized array made from single protein types, bound to either LPS or Peptidoglycan. Signup and view all the answers

What is the function of the S Layers?

They provide protection against enzymes, metals, complement, phagocytosis, and bacteriophages and can aid in adhesion. Signup and view all the answers

What are Pili/Fimbriae?

Short protein strands that cover the cell surface. Signup and view all the answers

What are the functions of Pili/Fimbriae?

They function in adhesion, antiphagocytic action, and twitching motility. Signup and view all the answers

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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Description

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.