Microbial Physiology: Cell Structure and Function Part-2
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Microbial Physiology: Cell Structure and Function Part-2

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Questions and Answers

What are the three stages of peptidoglycan synthesis?

  • Cytoplasmic stage, Membrane stage, Extracellular stage (correct)
  • Cytoplasmic stage, Extracellular stage, Transport stage
  • Membrane stage, Transport stage, Crosslinking stage
  • Cytoplasmic stage, Cytosol stage, Membrane stage
  • Which gene is NOT involved in the pathway of peptidoglycan synthesis in E.coli?

  • murD
  • murZ (correct)
  • murC
  • murF
  • What is the role of phosphonomycin in peptidoglycan synthesis?

  • Inhibits transport of precursors
  • Inhibits UDP muramic acid biosynthesis (correct)
  • Inhibits crosslinking of peptidoglycan
  • Inhibits synthesis of crosslinking enzymes
  • Which of the following statements is NOT a general step in peptidoglycan biosynthesis?

    <p>Formation of antibiotic resistance</p> Signup and view all the answers

    Which two antibiotics act at the first step of the peptidoglycan synthesis cascade?

    <p>Phosphonomycin and Cycloserine</p> Signup and view all the answers

    What is the primary component of the cell walls in vascular plants?

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

    Which polymer is predominantly found in the cell walls of fungi?

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

    What is the composition percentage of β-glycans in the yeast cell wall of S.cerevisiae?

    <p>29%</p> Signup and view all the answers

    What is the term used for the rigid structure that forms the major backbone of bacterial cell walls?

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

    What type of cell wall structure is unique to archaea as compared to bacteria?

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

    What characterizes the cell wall of gram-negative bacteria such as E.coli?

    <p>Presence of an outer membrane</p> Signup and view all the answers

    Which of the following components is found in smaller percentages in the yeast cell wall?

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

    What primary role do the cell walls of microorganisms serve?

    <p>Protection and structural support</p> Signup and view all the answers

    What is one key function of the bacterial cell wall?

    <p>It maintains the characteristic shape of the cell.</p> Signup and view all the answers

    Which component is primarily responsible for the strength of the bacterial cell wall?

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

    What are the two sugar derivatives that form peptidoglycan?

    <p>N-acetylglucosamine and N-acetylmuramic acid</p> Signup and view all the answers

    How does the bacterial cell wall prevent bursting due to osmosis?

    <p>By maintaining turgor pressure</p> Signup and view all the answers

    What kind of amino acids are connected in peptidoglycan to form the glycan tetrapeptide?

    <p>L-alanine and D-glutamic acid</p> Signup and view all the answers

    Why are glycosidic bonds formed in peptidoglycan important?

    <p>They connect sugars but do not provide rigidity.</p> Signup and view all the answers

    In Gram-negative bacteria, how does cross-linking usually occur?

    <p>By direct peptide linkage of the amino group of diaminopimelic acid to the carboxyl group of D-alanine</p> Signup and view all the answers

    What characteristic does the cell wall contribute to regarding bacterial pathogenicity?

    <p>It helps bacteria resist the host's immune system.</p> Signup and view all the answers

    Which amino acids are never found in the interbridge of peptidoglycan?

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

    What role does peptidoglycan play in bacteria?

    <p>It serves as a protective cell wall component.</p> Signup and view all the answers

    Which antibacterial drug inhibits the synthesis of peptidoglycan?

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

    What triggers programmed cell death in bacteria?

    <p>Activation of murein hydrolases</p> Signup and view all the answers

    What is the function of glycan-strand hydrolyzing peptidoglycan hydrolases?

    <p>To hydrolyze bonds within glycan strands</p> Signup and view all the answers

    Which of the following enzymes is classified as an endopeptidase hydrolyzing?

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

    What is N-acetylmuramic acid's significance in bacteria?

    <p>It is a sugar component of peptidoglycan.</p> Signup and view all the answers

    What important role do peptidoglycan hydrolases play during cell growth?

    <p>Promoting cell wall extension</p> Signup and view all the answers

    What primarily makes up the cell wall of gram-positive bacteria?

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

    Which amino acid is found in the interbridge of the peptidoglycan structure in Staphylococcus aureus?

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

    What is the predominant sugar component found in the glycan portion of peptidoglycan?

    <p>N-acetylglucosamine</p> Signup and view all the answers

    Which component is typically absent in the cell walls of Archaea?

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

    What percentage of the cell wall in gram-negative bacteria consist of peptidoglycan?

    <p>10%</p> Signup and view all the answers

    What type of linkage connects the sugars in the glycan portion of peptidoglycan?

    <p>β-1,4 linkage</p> Signup and view all the answers

    Which amino acid is involved in the lysine-diaminopimelic acid alternation within the tetrapeptide of peptidoglycan?

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

    How many different peptidoglycan types are known?

    <p>More than 100</p> Signup and view all the answers

    Study Notes

    Cell Wall Structure and Functions

    • The cell wall exists outside the cell membrane in organisms like plants, fungi, bacteria, algae, and archaea.
    • In vascular plants, cell walls are primarily made of cellulose, a β-1,4-linked polymer of glucose.
    • Yeast cell walls exhibit a layered structure; they contain 29% β-glycans, 31% mannan, and 13% protein.

    Prokaryotic Cell Surfaces

    • Peptidoglycan serves as the main structural component of bacterial cell walls, providing rigidity.
    • Archaea have a unique structure called pseudomurein along with protein or glycoprotein-based S-layer.
    • Gram-positive bacteria may have up to 90% of their cell walls composed of peptidoglycan, while in gram-negative bacteria, it is about 10%.

    Peptidoglycan Structure

    • Peptidoglycan is composed of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM), along with certain amino acids.
    • Glycosidic bonds between sugars in glycan chains provide strength, but rigidity is enhanced by amino acid cross-linking.
    • Cross-linking varies between species; Gram-positive bacteria typically have peptide interbridges, while Gram-negative exhibit direct linkage.

    Peptidoglycan Synthesis and Antibiotic Targets

    • Peptidoglycan synthesis has three main stages: cytoplasmic (precursor synthesis), membrane (precursor transport), and extracellular (cross-linking).
    • Important genes in E. coli for peptidoglycan synthesis include murC, murD, murE, ddl, murF, mraY, and murG.
    • Antibiotics like penicillin and vancomycin inhibit transpeptidase, preventing cross-link formation.

    Peptidoglycan Hydrolases

    • Almost all bacteria produce peptidoglycan hydrolases, essential for various cellular activities such as cell growth and wall turnover.
    • These enzymes include endo-N-acetylmuramidases, endo-N-acetylglucosaminidases, and endopeptidases, critical in maintaining cell integrity.
    • Activation of hydrolases under stress can lead to programmed cell death, also known as apoptosis.

    Antibiotic Mechanisms

    • Phosphonomycin and cycloserine inhibit the first step in peptidoglycan synthesis by blocking the biosynthesis of UDP muramic acid.
    • These antibiotics target the synthesis pathway at different stages, making peptidoglycan a viable target for treatment.

    Important Concepts

    • The characteristic cell shape and osmotic resilience of bacteria are largely determined by peptidoglycan structure.
    • Peptidoglycan is unique to bacteria, making it an effective target for antibacterial agents, posing no harm to human cells.

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    Description

    This quiz focuses on the structure and properties of the cell wall, particularly the peptidoglycan cell wall synthesis, function, and its importance in microbial physiology. It also highlights how the bacterial cell wall serves as a target for antibiotic treatments. Test your understanding of these critical concepts in biology.

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