Cell Walls of Bacteria and Archaea

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Questions and Answers

What is the primary structural component of peptidoglycan in bacterial cell walls?

N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) (correct)

Amino acids and proteins

Chitin and cellulose

Lipid A and O-antigen

Which characteristic is NOT typical of gram-positive bacteria cell walls?

Outer membrane with lipopolysaccharides (correct)

Thick peptidoglycan layer

Multi-layered peptidoglycan structure

Presence of teichoic acids

What role do teichoic acids play in gram-positive bacteria?

They provide additional structural support. (correct)

They serve as receptors for viruses.

They inhibit the growth of nearby bacteria.

They facilitate the transport of nutrients.

What are the two main components of lipopolysaccharide (LPS) in gram-negative bacteria?

Core polysaccharide and O-specific polysaccharide Signup and view all the answers

Which of the following statements about gram-negative bacteria is accurate?

They possess an outer membrane rich in lipopolysaccharides. Signup and view all the answers

What is the primary function of peptidoglycan in bacterial cells?

To provide rigidity and shape Signup and view all the answers

How do some bacteria survive without cell walls?

By utilizing tough membranes or protective environments Signup and view all the answers

What component connects Lipid A to the O-antigen in the lipopolysaccharide structure?

Core polysaccharide Signup and view all the answers

What sugar molecule is uniquely found in pseudomurein as opposed to peptidoglycan?

N-acetyltalosaminuronic (TalaNAcA) Signup and view all the answers

Which type of glycosidic bond is present in pseudomurein?

β (1→3) Signup and view all the answers

What is the primary function of the S-layer in Archaea?

To act as a selective sieve Signup and view all the answers

Which statement is true about the evolutionary origin of peptidoglycan and pseudomurein?

They emerged independently after Archaea and Bacteria diverged. Signup and view all the answers

What component typically makes up the most common type of cell wall in Archaea?

S-layer Signup and view all the answers

Which organism is noted for consisting only of an S-layer?

Methanocaldococcus jannaschii Signup and view all the answers

What characteristic of the amino acids in pseudomurein is highlighted?

They are all levo-rotatory stereoisomers. Signup and view all the answers

Which cell wall structure is not found in all Archaea?

Pseudomurein Signup and view all the answers

What distinguishes the periplasm in Gram-negative bacteria?

It is filled with enzymes and proteins. Signup and view all the answers

What is the primary function of porins in Gram-negative bacteria?

To form channels for small molecules and nutrients. Signup and view all the answers

How do porins and the periplasm work together in Gram-negative bacteria?

Porins enable nutrient entry, while the periplasm manages those nutrients. Signup and view all the answers

What appearance do gram-negative bacteria typically exhibit after Gram staining?

They appear red or pink. Signup and view all the answers

What is the role of crystal violet in the Gram staining process?

It is the primary stain that colors the cells. Signup and view all the answers

Which of the following best describes the peptidoglycan layer in Gram-positive bacteria?

It is thick and retains the crystal violet dye. Signup and view all the answers

What happens to the crystal violet dye during the Gram staining of Gram-negative bacteria?

It is washed away during the decolorization step. Signup and view all the answers

Which chemical serves as a counterstain in the Gram staining process?

Safranin Signup and view all the answers

Study Notes

Peptidoglycan Structure

Peptidoglycan is a polymer made from alternating units of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM).
Provides structural integrity, rigidity, and shape to bacterial cells.

Gram-Positive vs. Gram-Negative Bacteria

Gram-positive bacteria have a thick, multi-layered peptidoglycan wall and contain teichoic acids, contributing to their structural strength.
Gram-negative bacteria possess a thinner peptidoglycan layer and have an outer membrane that includes lipopolysaccharides (LPS).

Lipopolysaccharide (LPS) Composition

LPS consists of Lipid A, a core polysaccharide, and O-specific polysaccharide (O-antigen).
Lipid A anchors LPS to the outer membrane of Gram-negative bacteria, with core polysaccharides linking it to O-antigens.

Periplasm and Porins

The periplasm is the gel-like space between the inner and outer membranes of Gram-negative bacteria, filled with enzymes and proteins.
Porins are specialized proteins in the outer membrane that allow passage of small molecules and nutrients into the periplasm; they can be specific or nonspecific.

Gram Staining Process

Crystal violet serves as the primary stain, followed by iodine treatment, and alcohol for decolorization; safranin is used as a counterstain.
Thick peptidoglycan in Gram-positive bacteria retains crystal violet, appearing purple; Gram-negative bacteria lose the violet stain and take up the counterstain, appearing pink or red.

Archbial Cell Walls

Archaea may feature pseudomurein, which includes N-acetylglucosamine and N-acetyltalosaminuronic acid (replacing N-acetylmuramic acid).
Pseudomurein's glycosidic bonds differ (β(1→3) versus β(1→4) in peptidoglycan) and vary in stereochemistry.

S-Layers

Archaea commonly have an S-layer, a paracrystalline layer of interlocking proteins or glycoproteins that can withstand osmotic pressures.
The S-layer serves as the outermost wall layer, acting as a selective sieve that retains proteins close to the cell surface.

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Description

Explore the structure and chemistry of bacterial and archaeal cell walls in this quiz. Focus on the peptidoglycan structure and its significance in Gram-positive cell walls. Test your knowledge on the composition and functions of cell walls in these microorganisms.