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Questions and Answers
What is the primary function of the peptide cross-links in the gram-positive cell wall?
What is the primary function of the peptide cross-links in the gram-positive cell wall?
Teichoic acids are solely made of glycerol phosphate.
Teichoic acids are solely made of glycerol phosphate.
False
What enzyme destroys preexisting peptidoglycan in bacteria?
What enzyme destroys preexisting peptidoglycan in bacteria?
Lysozyme
Lysozyme is found in human ______ and helps defend against bacterial infection.
Lysozyme is found in human ______ and helps defend against bacterial infection.
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What distinguishes lipoteichoic acids from regular teichoic acids?
What distinguishes lipoteichoic acids from regular teichoic acids?
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In Staphylococcus aureus, the interbridge often consists of ______ glycines.
In Staphylococcus aureus, the interbridge often consists of ______ glycines.
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Match the following terms with their descriptions:
Match the following terms with their descriptions:
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Penicillin can cause cell lysis by destroying preexisting peptidoglycan.
Penicillin can cause cell lysis by destroying preexisting peptidoglycan.
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What is the primary classification system used by microbiologists?
What is the primary classification system used by microbiologists?
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The cell envelope of a gram-negative bacterium is thicker than that of a gram-positive bacterium.
The cell envelope of a gram-negative bacterium is thicker than that of a gram-positive bacterium.
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What is the process called when the cell membrane bursts due to osmotic pressure?
What is the process called when the cell membrane bursts due to osmotic pressure?
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The cytoplasm of prokaryotic cells maintains a high concentration of dissolved solutes creating about ____ atm of osmotic pressure.
The cytoplasm of prokaryotic cells maintains a high concentration of dissolved solutes creating about ____ atm of osmotic pressure.
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Match the following bacteria with their classification based on Gram staining:
Match the following bacteria with their classification based on Gram staining:
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Which component is found in the cell envelope of gram-negative bacteria but not in gram-positive bacteria?
Which component is found in the cell envelope of gram-negative bacteria but not in gram-positive bacteria?
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The Prokaryotes provides information on the ecology and physiology of Bacteria and Archaea.
The Prokaryotes provides information on the ecology and physiology of Bacteria and Archaea.
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A ____ is a compartment located between the cytoplasmic and outer membranes of gram-negative cells.
A ____ is a compartment located between the cytoplasmic and outer membranes of gram-negative cells.
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What is the primary function of the S-layer in most Archaea?
What is the primary function of the S-layer in most Archaea?
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All Archaea possess cell walls made of peptidoglycan.
All Archaea possess cell walls made of peptidoglycan.
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Name the polysaccharide found in the cell walls of certain methanogens.
Name the polysaccharide found in the cell walls of certain methanogens.
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The amino acids in pseudomurein are all of the _____ stereoisomer.
The amino acids in pseudomurein are all of the _____ stereoisomer.
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In what way does pseudomurein differ from peptidoglycan?
In what way does pseudomurein differ from peptidoglycan?
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Pseudomurein is susceptible to destruction by penicillin.
Pseudomurein is susceptible to destruction by penicillin.
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What are the main components of the hydrophobic portions of archaeal lipids?
What are the main components of the hydrophobic portions of archaeal lipids?
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What is a key function of the cytoplasmic membrane in cells?
What is a key function of the cytoplasmic membrane in cells?
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Archaea only form lipid bilayers in their membrane structure.
Archaea only form lipid bilayers in their membrane structure.
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What are the two types of outer layers secreted by bacteria and archaea called?
What are the two types of outer layers secreted by bacteria and archaea called?
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If the polysaccharide layer is tightly attached to the cell and excludes small particles, it is classified as a ______.
If the polysaccharide layer is tightly attached to the cell and excludes small particles, it is classified as a ______.
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Match the following organisms with their corresponding features:
Match the following organisms with their corresponding features:
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Which of the following statements about S-layers is true?
Which of the following statements about S-layers is true?
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Slime layers are tightly attached and always exclude small particles.
Slime layers are tightly attached and always exclude small particles.
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What microscopy technique can be used to make capsules visible?
What microscopy technique can be used to make capsules visible?
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What is the primary function of surface polysaccharides in microorganisms?
What is the primary function of surface polysaccharides in microorganisms?
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Capsules of bacteria can help them avoid detection by the host's immune system.
Capsules of bacteria can help them avoid detection by the host's immune system.
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Name one bacterium that has a polysaccharide capsule.
Name one bacterium that has a polysaccharide capsule.
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Bacterial ________ are involved in the formation of biofilms by helping bacteria adhere to surfaces.
Bacterial ________ are involved in the formation of biofilms by helping bacteria adhere to surfaces.
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Match each bacterium with its corresponding feature:
Match each bacterium with its corresponding feature:
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What role do extracellular polysaccharides play in bacteria?
What role do extracellular polysaccharides play in bacteria?
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Fimbriae are also known as pili and are thicker structures compared to regular pili.
Fimbriae are also known as pili and are thicker structures compared to regular pili.
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Bacterial capsules help prevent ________ by binding water during dry conditions.
Bacterial capsules help prevent ________ by binding water during dry conditions.
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What is one primary function of pili in bacteria?
What is one primary function of pili in bacteria?
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All bacteria have pili.
All bacteria have pili.
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What process do conjugative pili facilitate in bacteria?
What process do conjugative pili facilitate in bacteria?
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Pili can contribute to the ________ of pathogens by enabling them to adhere to specific host tissues.
Pili can contribute to the ________ of pathogens by enabling them to adhere to specific host tissues.
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Match the type of pili with their respective functions:
Match the type of pili with their respective functions:
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Which type of pili is known for facilitating an unusual form of movement in bacteria?
Which type of pili is known for facilitating an unusual form of movement in bacteria?
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Pili only serve to allow bacteria to attach to surfaces without any additional functions.
Pili only serve to allow bacteria to attach to surfaces without any additional functions.
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What energy source is required for the extension and retraction of pili during twitching motility?
What energy source is required for the extension and retraction of pili during twitching motility?
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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.
Bacterial Cell Walls: Cross-Links in Peptidoglycan
- 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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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.
