23 public questions tagged with this topic.
Peptidoglycan is a structural component of bacterial ll walls. This follows from NCERT principle where relation explains outcome clearly for students.
Ref: NCERT Biology Textbook for Class XI and XII (Zoology section), Chapter: Biology - Zoology portion covering relevant system and function, Topic: Structural organization and physiology.
Polygalacturonase is a major pectinase induced during tomato ripening, leaf abscission and pod dehiscence, directly responsible for fruit softening. Primary cell wall and middle lamella contain homogalacturonan composed of α-1,4-linked D-galacturonic acid residues partially methylesterified. During breaker to red stage, ethylene upregulates endo-polygalacturonase, pectin methylesterase and cellulase synergistically. Endo-PG hydrolyzes internal glycosidic bonds, reducing polymer length, increasing water solubility, decreasing cell-to-cell adhesion, facilitating separation of cells and access fo
Ref: Alberts Molecular Biology of the Cell 6th ed Chapter 20 Plant Cell Walls; Taiz & Zeiger Plant Physiology, PG pectin degradation.
Wall teichoic acids covalently attached to peptidoglycan via phosphodiester to N-acetylmuramic acid and lipoteichoic acids anchored to membrane diacylglycerol through glycolipid are hallmark anionic glycopolymers of Gram-positive envelope, comprising up to 60 percent of wall dry weight. Their polyanionic phosphate backbone creates high density of negative charge at surface, enabling binding of divalent cations like magnesium and calcium, concentrating them near membrane for activity of enzymes and protection against cationic antimicrobial peptides. By controlling local ionic environment, teich
Ref: Brown et al., Ann Rev Microbiol 2013, Teichoic Acids; Percy & Grundling, Ann Rev Microbiol 2014, LTA Functions.
Gram-negative cell wall is thin but complex, optimized for protection while maintaining permeability for nutrients. It comprises inner plasma membrane, narrow periplasmic space containing single or few layers of peptidoglycan only about 2 to 6 nanometers thick, and outer membrane distinguished by asymmetry. Outer membrane outer leaflet consists of lipopolysaccharide anchored by lipid A, while inner leaflet contains phospholipids; integral outer membrane proteins such as porins, TonB-dependent receptors, and OmpA form beta-barrels. Lipopolysaccharide confers negative charge, stabilizes outer me
Ref: Silhavy et al., The Bacterial Cell Envelope, 2nd ed.; Vollmer & Seligman, Trends Microbiol 2010, Gram-Negative Wall.
Distribution of pseudomurein within Archaea is limited to certain methanogenic euryarchaeota that build rigid wall sacculus, whereas many other archaea rely solely on proteinaceous S-layers. Methanobrevibacter species, including human commensal Methanobrevibacter smithii and rumen isolate Methanobrevibacter ruminantium within order Methanobacteriales, synthesize pseudomurein composed of N-acetylglucosamine and N-acetyltalosaminuronic acid linked beta-1,3 and crosslinked with tetrapeptides containing L-amino acids. Related genera like Methanobacterium and Methanothermobacter share this trait, d
Ref: Kandler, Microbiol Sci 1982, Pseudomurein Distribution; Doddema et al., Int J Syst Bacteriol 1982, Methanobrevibacter.
In many archaea, particularly those lacking pseudomurein or outer proteinaceous sheath, envelope consists of cytoplasmic membrane plus outermost crystalline surface layer that serves as cell wall equivalent. This S-layer is not composed of peptidoglycan, lipids, or teichoic acids characteristic of bacteria; it is assembled from one or two species of proteins or glycoproteins that self-organize into hexagonal or tetragonal lattice with nanometer-scale pores. Subunits are often heavily glycosylated with sulfated or branched oligosaccharides that confer additional stability against proteases and
Ref: Sleytr et al., FEMS Microbiol Rev 2014, S-layers; Fagan & Fairweather, Nature Rev Microbiol 2014, S-layer Proteins.
Hypertonic surroundings draw water out of bacterial cytoplasm through semipermeable inner membrane, generating inward osmotic pressure that tends to detach inner membrane from wall and shrink cytoplasm, a process termed plasmolysis. Survival depends on mechanical resistance supplied by peptidoglycan, a covalently crosslinked heteropolymer forming a single macromolecule sacculus surrounding entire cell, often described as exoskeleton. Its glycan strands crosslinked via peptide bonds possess high tensile strength, allowing it to withstand internal turgor of 2 to5 atmospheres in Gram-negatives an
Ref: Rojas et al., PNAS 2014, Stiffness of Bacterial Cell Wall; Alberts et al., Molecular Biology Cell, Cell Wall Mechanics.
Gram positive wall comprises thick peptidoglycan crosslinked peptides providing rigidity against internal turgor up to 20 atmospheres. Embedded anionic polymers wall teichoic acids covalently linked phosphodiester to C6 hydroxyl N acetylmuramic acid and lipoteichoic acids anchored diacylglycerol into membrane extending outward. Structure polyglycerol phosphate or polyribitol phosphate modified D alanylation introducing positive charge modulating autolytic enzymes. Physiological roles encompass providing cell wall integrity by controlling autolysin Atl Atl mediated remodeling preventing prematu
Ref: Brown et al., Nat Rev Microbiol 2013, Teichoic acids provide cell wall integrity in Gram-positive.
In the maturation phase, cells attain their maximal size with thickened walls and fully developed structures.
Ref: NCERT Class 11 Biology Chapter 13: Plant Growth and Development Growth - Phases Differentiation Dedifferentiation Redifferentiation
During the elongation phase, cells increase in size due to vacuolation, enlargement, and new cell wall deposition.
Ref: NCERT Class 11 Biology Chapter 13: Plant Growth and Development Growth - Phases Differentiation Dedifferentiation Redifferentiation
Algal walls may contain cellulose, galactans, mannans and minerals such as calcium carbonate. In other plants, the wall is composed of cellulose, hemicellulose, pectins and proteins.
Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Eukaryotic Cell - Cell Wall and Cell Membrane - Fluid Mosaic Model
Prokaryotes generally possess a cell wall surrounding the plasma membrane, but Mycoplasma is an exception and lacks a cell wall.
Ref: NCERT Class 11 Biology Chapter 8: Cell: The Unit of Life Eukaryotic Cell - Cell Wall and Cell Membrane - Fluid Mosaic Model
