Bacterial Classification and Cell Walls
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Questions and Answers

What is the primary function of the peptide cross-links in the gram-positive cell wall?

  • Provide energy storage
  • Facilitate nutrient uptake
  • Stabilize peptidoglycan structure (correct)
  • Enhance motility

Teichoic acids are solely made of glycerol phosphate.

False (B)

What enzyme destroys preexisting peptidoglycan in bacteria?

Lysozyme

Lysozyme is found in human ______ and helps defend against bacterial infection.

<p>secretions</p> Signup and view all the answers

What distinguishes lipoteichoic acids from regular teichoic acids?

<p>They are covalently bonded to membrane lipids. (B)</p> Signup and view all the answers

In Staphylococcus aureus, the interbridge often consists of ______ glycines.

<p>five</p> Signup and view all the answers

Match the following terms with their descriptions:

<p>Lysozyme = Enzyme that cleaves peptidoglycan Penicillin = Antibiotic that blocks peptide cross-link formation Teichoic acids = Acidic molecules in gram-positive cell walls Phosphatidylethanolamine = Type of phospholipid found in bacterial membranes</p> Signup and view all the answers

Penicillin can cause cell lysis by destroying preexisting peptidoglycan.

<p>False (B)</p> Signup and view all the answers

What is the primary classification system used by microbiologists?

<p>Bergey’s Manual of Systematics of Archaea and Bacteria (A)</p> Signup and view all the answers

The cell envelope of a gram-negative bacterium is thicker than that of a gram-positive bacterium.

<p>False (B)</p> Signup and view all the answers

What is the process called when the cell membrane bursts due to osmotic pressure?

<p>cell lysis</p> Signup and view all the answers

The cytoplasm of prokaryotic cells maintains a high concentration of dissolved solutes creating about ____ atm of osmotic pressure.

<p>2</p> Signup and view all the answers

Match the following bacteria with their classification based on Gram staining:

<p>Staphylococcus aureus = Gram-positive Escherichia coli = Gram-negative Bacillus subtilis = Gram-positive Salmonella enterica = Gram-negative</p> Signup and view all the answers

Which component is found in the cell envelope of gram-negative bacteria but not in gram-positive bacteria?

<p>Outer membrane (A)</p> Signup and view all the answers

The Prokaryotes provides information on the ecology and physiology of Bacteria and Archaea.

<p>True (A)</p> Signup and view all the answers

A ____ is a compartment located between the cytoplasmic and outer membranes of gram-negative cells.

<p>periplasm</p> Signup and view all the answers

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

<p>To prevent osmotic lysis (C)</p> Signup and view all the answers

All Archaea possess cell walls made of peptidoglycan.

<p>False (B)</p> Signup and view all the answers

Name the polysaccharide found in the cell walls of certain methanogens.

<p>pseudomurein</p> Signup and view all the answers

The amino acids in pseudomurein are all of the _____ stereoisomer.

<p>l</p> Signup and view all the answers

In what way does pseudomurein differ from peptidoglycan?

<p>By having b-1,3 glycosidic bonds (A)</p> Signup and view all the answers

Pseudomurein is susceptible to destruction by penicillin.

<p>False (B)</p> Signup and view all the answers

What are the main components of the hydrophobic portions of archaeal lipids?

<p>isoprenoid chains</p> Signup and view all the answers

What is a key function of the cytoplasmic membrane in cells?

<p>Maintaining selective permeability (A)</p> Signup and view all the answers

Archaea only form lipid bilayers in their membrane structure.

<p>False (B)</p> Signup and view all the answers

What are the two types of outer layers secreted by bacteria and archaea called?

<p>capsule and slime layer</p> Signup and view all the answers

If the polysaccharide layer is tightly attached to the cell and excludes small particles, it is classified as a ______.

<p>capsule</p> Signup and view all the answers

Match the following organisms with their corresponding features:

<p>Vibrio cholerae = Classic gram-negative type cell envelope Caulobacter crescentus = Gram-negative with S-layer Nitrosopumilus maritimus = Typical archaeal cell envelope Mycoplasma pneumoniae = No cell wall, only CM</p> Signup and view all the answers

Which of the following statements about S-layers is true?

<p>They can vary considerably in molecular structure. (C)</p> Signup and view all the answers

Slime layers are tightly attached and always exclude small particles.

<p>False (B)</p> Signup and view all the answers

What microscopy technique can be used to make capsules visible?

<p>India ink staining</p> Signup and view all the answers

What is the primary function of surface polysaccharides in microorganisms?

<p>Facilitating attachment to solid surfaces (A)</p> Signup and view all the answers

Capsules of bacteria can help them avoid detection by the host's immune system.

<p>True (A)</p> Signup and view all the answers

Name one bacterium that has a polysaccharide capsule.

<p>Streptococcus pneumoniae</p> Signup and view all the answers

Bacterial ________ are involved in the formation of biofilms by helping bacteria adhere to surfaces.

<p>capsules</p> Signup and view all the answers

Match each bacterium with its corresponding feature:

<p>Bacillus anthracis = Protein capsule Streptococcus pneumoniae = Polysaccharide capsule Leuconostoc mesenteroides = Dextran slime layer Acinetobacter = Negative staining with India ink</p> Signup and view all the answers

What role do extracellular polysaccharides play in bacteria?

<p>They are involved in the development and maintenance of biofilms. (A)</p> Signup and view all the answers

Fimbriae are also known as pili and are thicker structures compared to regular pili.

<p>False (B)</p> Signup and view all the answers

Bacterial capsules help prevent ________ by binding water during dry conditions.

<p>desiccation</p> Signup and view all the answers

What is one primary function of pili in bacteria?

<p>Enable attachment to surfaces (D)</p> Signup and view all the answers

All bacteria have pili.

<p>False (B)</p> Signup and view all the answers

What process do conjugative pili facilitate in bacteria?

<p>Genetic exchange</p> Signup and view all the answers

Pili can contribute to the ________ of pathogens by enabling them to adhere to specific host tissues.

<p>virulence</p> Signup and view all the answers

Match the type of pili with their respective functions:

<p>Conjugative pili = Facilitate genetic exchange Type IV pili = Support twitching motility Electrical conductive pili = Conduct electrons in energy metabolism Fimbriae = Enable adhesion to surfaces</p> Signup and view all the answers

Which type of pili is known for facilitating an unusual form of movement in bacteria?

<p>Type IV pili (B)</p> Signup and view all the answers

Pili only serve to allow bacteria to attach to surfaces without any additional functions.

<p>False (B)</p> Signup and view all the answers

What energy source is required for the extension and retraction of pili during twitching motility?

<p>ATP</p> Signup and view all the answers

Flashcards

Prokaryotic Cell Wall

A protective layer that surrounds the cytoplasmic membrane in most Bacteria and Archaea.

Osmotic Pressure

The pressure created by a high concentration of dissolved solutes inside a cell.

Cell Lysis

The bursting of a cell due to excess internal pressure.

Gram-positive Cell Envelope

A bacterial cell envelope with a thick cell wall and a single membrane.

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Gram-negative Cell Envelope

A bacterial cell envelope with a thin cell wall, and an outer membrane along with a periplasmic space.

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Cell Wall Function

Maintains cell shape, rigidity, and prevents osmotic lysis.

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Bergey's Manual

The primary taxonomic resource for bacteria and archaea.

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The Prokaryotes

A second major source on prokaryotic biology.

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Archaea cell wall

Archaea cell walls differ from bacterial cell walls, and some lack cell walls altogether (employing S-layers). Instead of peptidoglycan, some Archaea use pseudomurein.

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Pseudomurein

A polysaccharide found in some Archaea cell walls, similar to peptidoglycan but with different structural components and bonds.

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Peptidoglycan

A polysaccharide polymer in bacterial cell walls, forming mesh-like layers.

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S-layer

A rigid protein shell found in some Archaea, acting as a cell wall to protect from osmotic lysis.

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Isoprenoid chains

Chains synthesized from repeated isoprene units, forming the hydrophobic portions of archaeal lipids.

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Archaeal lipids

Lipids in archaeal membranes, often composed of isoprenoid chains and formed with ether linkages.

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Osmotic lysis

The rupturing of a cell due to differences in water pressure exerted on the cell

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Methanogens

Methane-producing Archaea which have distinctive cell walls made from pseudomurein

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Peptidoglycan cross-links

Three-dimensional connections between peptidoglycan strands that provide structural strength to the gram-positive cell wall.

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Gram-positive interbridge

A short peptide sequence embedded in the peptidoglycan cross-links of gram-positive bacteria, varying in amino acid sequence and length between different species.

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Teichoic acids

Acidic molecules embedded in the cell walls of gram-positive bacteria, composed of glycerol phosphate or ribitol phosphate with attached sugars.

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Lipoteichoic acids

Teichoic acids covalently bonded to membrane lipids rather than peptidoglycan.

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Lysozyme function

An enzyme that cleaves the glycosidic bonds in peptidoglycan.

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Lysozyme role in defense

A major component of human defense mechanisms against infections, found in tears and saliva.

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Penicillin's mechanism

Antibiotic that blocks the formation of peptide cross-links in peptidoglycan.

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Phospholipid Bilayer

A key component of cell membranes, with hydrophilic heads and hydrophobic tails.

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Archaea membrane structure

Archaea can have lipid bilayers, lipid monolayers, or a mix of both.

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Cytoplasmic membrane function

The cytoplasmic membrane controls selective permeability, protein anchoring, and energy conservation.

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Cell envelope structures

Bacterial and archaeal cells have cell walls, outer membranes, cytoplasmic membranes, and S-layers.

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Gram-negative cell envelope example

Vibrio cholerae has a gram-negative cell envelope.

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Archaeal cell envelope example

Nitrosopumilus maritimus has a typical archaeal cell envelope with a cytoplasmic membrane and an S-layer.

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Capsule vs. slime layer

Capsules are organized tightly, exclude particles, and are attached to the cell; slime layers are loosely attached and don't exclude particles.

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Capsule detection

Capsules are visible with India ink staining.

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Slime layer detection

Slime layers are more difficult to see microscopically.

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Surface Polysaccharides

Sugars on the outside of bacteria that help them stick to surfaces, including host tissues.

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Biofilm

A thick layer of bacteria that forms on a surface, often held together by extracellular polysaccharides.

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Capsule

A protective layer around some bacteria that can be made of protein or polysaccharide, helping them evade the immune system.

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Slime Layer

A loose, sticky layer of polysaccharide that surrounds some bacteria, aiding in attachment and protection.

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Fimbriae

Short, hair-like structures on bacteria, made of protein, that help with attachment.

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Pili

Longer, filamentous structures on bacteria, made of protein, with various functions including attachment and DNA transfer.

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Hami

Hook-shaped structures on some bacteria, involved in attachment to surfaces and forming biofilms.

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How do bacterial capsules help the cell survive?

Capsules help bacteria evade the host's immune system and protect against dehydration.

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What are pili?

Hair-like appendages on the surface of bacteria that help them stick to surfaces, form biofilms, and exchange genetic material.

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How do pili contribute to virulence?

Pili allow bacteria to adhere to host cells, which can help them invade tissues and cause disease.

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What are conjugative pili?

Special pili that facilitate genetic exchange between bacteria through a process called conjugation.

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What are electrically conductive pili?

Pili that can conduct electrons, playing a role in the energy metabolism of microbes.

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What is twitching motility?

A type of bacterial movement where pili extend, attach to a surface, retract, and pull the cell forward.

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What are fimbriae?

Short, numerous pili that help bacteria adhere to surfaces.

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How do hami contribute to biofilm formation?

Hami are grappling hook-like structures in Archaea that connect cells, forming a network that holds the biofilm together.

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What is the role of ATP in twitching motility?

ATP provides the energy for extending and retracting pili, driving the movement of the bacteria.

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Study Notes

Bacterial Classification

  • Bergey's Manual of Systematics of Archaea and Bacteria is the most widely accepted classification system for microbiologists.
  • It's been used since 1923 as a comprehensive resource on known prokaryotic species.
  • The Prokaryotes is another crucial source, detailing the physiology, ecology, phylogeny, isolation, and cultivation of Bacteria and Archaea.
  • Both Bergey's Manual and The Prokaryotes provide microbiologists with the necessary knowledge and details of bacterial and archaeal biology to characterize newly isolated organisms.

The Cell Wall

  • Prokaryotic cytoplasm maintains a high solute concentration ( ~ 2 atm).
  • This osmotic pressure is enough to cause the cell membrane to burst (cell lysis.)
  • To withstand the pressure, Bacteria and Archaea have a cell wall outside the cytoplasmic membrane.
  • Cell walls maintain cell shape and rigidity.
  • Gram-positive and gram-negative cell envelopes differ structurally.
  • Gram-positive cells have a thick cell wall and a cytoplasmic membrane.
  • Gram-negative cells have a thin cell wall, an outer membrane, and a periplasm.

Gram-Positive and Gram-Negative Cell Envelopes

  • Gram staining determines the classification of bacterial cell envelopes as either gram-positive or gram-negative, based on differences in their cell wall structure.
  • The Gram stain reaction is primarily determined by the thickness of the cell wall, not the number of layers.
  • Gram stain reactions, though predictive of structure, don't always correlate with it.

Bacterial Cell Walls: Peptidoglycan

  • Bacterial cell walls contain a rigid polysaccharide called peptidoglycan.
  • Peptidoglycan provides structural integrity only to bacteria that have a cell wall.
  • The sugar backbone is composed of alternating repeats of N-acetylglucosamine & N-acetylmuramic acid, linked by b-1,4 linkages.
  • A short peptide side chain is attached to the muramic acid.
  • The amino acid composition of this peptide varies considerably between bacteria.
  • Cross-links happen between adjacent peptide side chains, forming one enormous molecule.
  • Gram-negative bacteria primarily form cross-links between the amino group of DAP (on one glycan strand) and the carboxyl group of d-alanine on the next glycan strand.
  • Gram-positive cell walls' peptidoglycan is stabilized three-dimensionally by peptide cross-links that create a strong mesh.
  • Peptide cross-links in gram-positive cells often include a short peptide interbridge.
  • The interbridge varies between species, for example, the interbridge in S. aureus contains five glycines.

Teichoic Acids

  • In gram-positive bacteria, teichoic acids are embedded in the cell wall; these molecules are glycerol phosphate or ribitol phosphate attached to alcohol and/or glucose or d-alanine.
  • Sometimes teichoic acids are bonded to membrane lipids; these are called lipo-teichoic acids.
  • Lysozyme weakens the peptidoglycan, leading to cell lysis by cleaving the glycosidic bond between N-acetylglucosamine & N-acetylmuramic acid

Cytoplasmic Membrane

  • The cytoplasmic membrane is a phospholipid bilayer embedded with integral membrane proteins, and some peripheral membrane proteins.
  • The inner surface faces the cytoplasm and the outer surface faces the environment.
  • Its molecular structure is generally the same in prokaryotes and eukaryotes but species have differing chemical compositions.
  • Its key functions include maintaining selective permeability, anchoring proteins, and conserving energy.

LPS: The Outer Membrane

  • Gram-negative cell envelope often consists of an outer membrane.
  • The outer membrane is the second lipid bilayer found outside the cell wall and has a different structure and function than the cytoplasmic membrane.
  • It also contains polysaccharide molecules covalently bound to lipids.
  • The outer membrane is called the lipopolysaccharide layer (or LPS)
  • LPS molecules have unique functions; they facilitate surface recognition, function as virulence factors, and contribute to mechanical strength
  • Contains porins, transmembrane proteins, that allow for non-specific transport of solutes.

Archaeal Cell Walls

  • Archaeal cell envelopes differ fundamentally from bacterial ones.
  • Archaeal membranes typically lack peptidoglycan and outer membranes.
  • Most Archaea possess an S-layer, a rigid protein shell, instead of a polysaccharide-containing cell wall. The S layer functions to prevent osmotic lysis.
  • Some archaea have cell walls containing pseudomurein, structurally related to peptidoglycan. Pseudomurein has glycosidic linkages that are β(1,3) instead of β(1,4), and the amino acids are all l-stereoisomers.

Major Lipids of Archaea

  • Archaea can have lipid bilayers composed of phosphoglycerol diethers.
  • Their hydrophobic portions are comprised of isoprenoid chains, unlike bacteria or eukaryotes, which have fatty acid tails.
  • The isoprenoids are attached to glycerol by ether linkages, not ester linkages.. Examples include phytanyl, biphytanyl, and crenarchaeol.

Cell Surface Structures

  • Many bacteria and archaea secrete polysaccharide or protein materials on their cell surfaces.
  • These materials are distinct from the cell envelope and are often referred to as capsules or slime layers.
  • Capsules exclude small particles; slime layers are loosely attached.
  • These outer layers mediate attachment, protecting the cell from attack and environmental stresses, and alter the cell's diffusive environment.

Fimbriae, Pili, and Hami

  • Fimbriae and pili are thin filamentous protein structures that extend from the cell surface and mediate attachment.
  • Pili enable bacterial cells to attach to surfaces, form pellicles or biofilms.
  • Pili are involved in conjugation (genetic transfer). Some pili are electrically conductive, playing a role in energy transfer.
  • Hami are unique attachment structures found in certain archaea.

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Bacterial Cell Walls PDF

Description

This quiz explores the classification systems for bacteria and archaea as detailed in Bergey's Manual and The Prokaryotes. It also examines the structure and significance of prokaryotic cell walls, including differences between gram-positive and gram-negative bacteria. Test your understanding of key microbiological concepts and terminologies.

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