Cell Structure and Function: Eukaryotic Nucleus
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Questions and Answers

What is a characteristic of the nucleus in prokaryotes?

  • No nuclear membrane (correct)
  • Has a nuclear membrane
  • Has nuclear elements
  • Has a nucleolus

    • Which cell component is responsible for cell respiration in higher eukaryotes?

  • Golgi apparatus
  • Endoplasmic reticulum
  • Mitochondria (correct)
  • Cytoplasmic membrane

    • What type of cell wall do fungi have?

  • Cellulose
  • Glycans
  • Peptidoglycan
  • Chitin (correct)

    • Which organelle is responsible for protein synthesis in eukaryotes?

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

    What is the function of the endoplasmic reticulum in eukaryotes?

    <p>Protein modification and transport</p> Signup and view all the answers

    Which type of flagella do prokaryotes have?

    <p>Rotating flagella</p> Signup and view all the answers

    What is the function of lysosomes in eukaryotes?

    <p>Digestion and recycling of cellular waste</p> Signup and view all the answers

    Which organelle is responsible for protein modification in eukaryotes?

    <p>Golgi apparatus</p> Signup and view all the answers

    What is the difference between the ribosomes of prokaryotes and eukaryotes?

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

    What is unique about the cell wall of archaebacteria?

    <p>Does not produce a cell wall peptidoglycan comparable to that produced by eubacteria</p> Signup and view all the answers

    What is the main difference between prokaryotic and eukaryotic cells?

    <p>Eukaryotic cells have a distinct nucleus, while prokaryotic cells do not</p> Signup and view all the answers

    What is the function of the nucleus in eukaryotic cells?

    <p>To organize and regulate biochemical and hereditary processes</p> Signup and view all the answers

    What is the structural feature of the eukaryotic nuclear membrane?

    <p>It has a double layer with pores</p> Signup and view all the answers

    Which of the following eukaryotic cells lacks a discrete membrane-bound nucleus?

    <p>Prokaryotic cells</p> Signup and view all the answers

    What is the term for the domain of eukaryotic cells?

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

    What is the characteristic feature of the myxomycete Acyria cinerea nuclear membrane?

    <p>It has a double-layered nuclear membrane that exhibits pores</p> Signup and view all the answers

    What is the primary difference between eubacteria and archaebacteria?

    <p>The characteristics not included in the table</p> Signup and view all the answers

    What is the significance of recent investigations with highly improved techniques and equipment?

    <p>They have shown that there may be a closer similarity between eukaryotes and prokaryotes than previously thought</p> Signup and view all the answers

    What is the function of the nucleolus?

    <p>Not visible in the electron micrograph</p> Signup and view all the answers

    What is the term for the lower eukaryotes that lack some of the distinguishing features of metazoan cells?

    <p>Lower eukaryotes</p> Signup and view all the answers

    What is the term used to describe the DNA-containing region of the cell in bacteria?

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

    What is the structure that appears as small black dots in the electron micrograph?

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

    What is the purpose of the pores in the nuclear membrane?

    <p>To allow for the exchange of materials</p> Signup and view all the answers

    What is the term used to describe the region of the cell between the nucleus and the plasmalemma?

    <p>Not specified in the content</p> Signup and view all the answers

    What is the structure that appears as a distinct region with pores in the electron micrograph of a lower eukaryote?

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

    What is the unit of measurement used in the electron micrograph of Fig. 7-1?

    <p>Micrometer (µm)</p> Signup and view all the answers

    What is a characteristic of the eukaryotic nucleus?

    <p>Presence of a distinct nuclear membrane with pores</p> Signup and view all the answers

    What is a notable feature of the nuclear membrane in eukaryotes?

    <p>Presence of pores with tubules</p> Signup and view all the answers

    Which of the following is a common feature of eukaryotic cells?

    <p>Presence of a discrete membrane-bound nucleus</p> Signup and view all the answers

    What is a notable difference between archaebacteria and eubacteria?

    <p>Structural differences in their cells</p> Signup and view all the answers

    What is the significance of recent investigations with highly improved techniques and equipment?

    <p>To demonstrate a closer similarity between eukaryotes and prokaryotes</p> Signup and view all the answers

    What is a characteristic of the myxomycete Acyria cinerea nuclear membrane?

    <p>Double-layered structure with pores</p> Signup and view all the answers

    What is a common feature of lower eukaryotes?

    <p>Lack of some of the distinguishing features of metazoan cells</p> Signup and view all the answers

    What can be said about the cells of archaebacteria?

    <p>They display important structural differences from the cells of eubacteria</p> Signup and view all the answers

    What is the primary function of the cytoplasmic membrane in bacterial cells?

    <p>To prevent most solutes from entering the cytoplasm</p> Signup and view all the answers

    What is the arrangement of phospholipid molecules in the cytoplasmic membrane?

    <p>A bilayer with hydrophobic ends facing outside</p> Signup and view all the answers

    What type of proteins are embedded in the cytoplasmic membrane?

    <p>Various proteins, including transport proteins</p> Signup and view all the answers

    What is the orientation of the polar phospholipids in the cytoplasmic membrane?

    <p>Facing towards the external and internal sides of the membrane</p> Signup and view all the answers

    What is the function of specific transport proteins in the cytoplasmic membrane?

    <p>To allow solutes to enter the cytoplasm</p> Signup and view all the answers

    What is the composition of the cytoplasmic membrane?

    <p>A phospholipid layer with embedded proteins</p> Signup and view all the answers

    What is the significance of the hydrophilic and hydrophobic ends of phospholipid molecules in the cytoplasmic membrane?

    <p>The hydrophilic ends face towards the external and internal sides of the membrane</p> Signup and view all the answers

    What is the consequence of the cytoplasmic membrane being a permeability barrier?

    <p>Most solutes are prevented from entering the cytoplasm</p> Signup and view all the answers

    What can be observed in the region of the pancreatic exocrine cell between the nucleus and the plasmalemma?

    <p>Cisternae of the rough endoplasmic reticulum and mitochondria</p> Signup and view all the answers

    What is the characteristic feature of the bacterial nucleoid?

    <p>A cytologically distinct region without a nuclear membrane</p> Signup and view all the answers

    What is the purpose of the pores in the nuclear membrane?

    <p>To regulate the movement of molecules</p> Signup and view all the answers

    What can be observed in the electron micrograph of a lower eukaryote?

    <p>A distinct region with pores</p> Signup and view all the answers

    What appears as small black dots in the electron micrograph?

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

    What is the term used to describe the DNA-containing region of the cell in bacteria?

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

    What is the structural feature of the eukaryotic nuclear membrane?

    <p>Porous membrane</p> Signup and view all the answers

    What organelle is responsible for cell respiration in eukaryotes?

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

    What is the main component of the cell wall of both gram-positive and gram-negative bacteria?

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

    What is unique about the cell wall of archaebacteria?

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

    What is the outermost component of the cell in gram-negative bacteria such as E.coli?

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

    What is the name of the surface layer found in many archaebacteria?

    <p>S-layer</p> Signup and view all the answers

    What is the main component of the peptidoglycan in bacterial cell walls?

    <p>β-1,4-N-acetylglucosamine (NAG) and N-acetyl-muramic acid (NAM)</p> Signup and view all the answers

    What type of linkage is uniform in all bacteria in the peptidoglycan?

    <p>Glycan linkages</p> Signup and view all the answers

    What is the characteristic feature of the cell wall of fungi?

    <p>It contains chitin</p> Signup and view all the answers

    What is the composition of the S-layer in archaebacteria?

    <p>Protein or glycoprotein</p> Signup and view all the answers

    What terminates the short tetrapeptide units in peptidoglycan?

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

    What is the region between the outer and plasma membranes called in gram-negative bacteria?

    <p>Periplasmic space</p> Signup and view all the answers

    What is the term used to describe the DNA-containing region of the cell in bacteria?

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

    What is the main function of the cytoplasmic membrane in bacterial cells?

    <p>To prevent most solutes from entering the cytoplasm</p> Signup and view all the answers

    What is the hallmark of the eubacteria?

    <p>Production of peptidoglycan</p> Signup and view all the answers

    What is characteristic of the cell wall of archaebacteria?

    <p>Thin S-layer as the sole wall layer</p> Signup and view all the answers

    What is the arrangement of phospholipid molecules in the cytoplasmic membrane?

    <p>A bimolecular lipid leaflet with hydrophobic ends aligned</p> Signup and view all the answers

    What is the feature of the peptidoglycan layer in gram-positive bacteria?

    <p>Thick layer</p> Signup and view all the answers

    What is the feature of the peptidoglycan layer in gram-negative bacteria?

    <p>Thin layer</p> Signup and view all the answers

    What type of proteins are embedded in the cytoplasmic membrane?

    <p>Specific transport proteins</p> Signup and view all the answers

    What is the orientation of the polar phospholipids in the cytoplasmic membrane?

    <p>Facing outwards on one side and inwards on the other side</p> Signup and view all the answers

    What is intermediate between the gram-positive and gram-negative formats?

    <p>Clostridium thermosaccharolyticum</p> Signup and view all the answers

    What is the consequence of the cytoplasmic membrane being a permeability barrier?

    <p>Some solutes can enter the cytoplasm through specific transport proteins</p> Signup and view all the answers

    What is the composition of the cytoplasmic membrane?

    <p>Phospholipid molecules and proteins</p> Signup and view all the answers

    What is the significance of the hydrophilic and hydrophobic ends of phospholipid molecules in the cytoplasmic membrane?

    <p>They enable the formation of a permeability barrier</p> Signup and view all the answers

    What can be observed in Fig. 7-17?

    <p>The arrangement of phospholipid molecules in the cytoplasmic membrane</p> Signup and view all the answers

    What is the primary composition of the external layer of the outer membrane in gram-negative bacteria?

    <p>Lipopolysaccharides (LPS)</p> Signup and view all the answers

    What is the function of porin proteins in the outer membrane of gram-negative bacteria?

    <p>To facilitate the diffusion of small molecules</p> Signup and view all the answers

    What is the location of lipoproteins in gram-negative bacteria?

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

    What is the core region of LPS composed of?

    <p>GlcNAc, heptose, and KDO</p> Signup and view all the answers

    What is the purpose of the KDO molecule in the LPS core?

    <p>To form a hydrophobic interaction with lipid A</p> Signup and view all the answers

    What is the function of the peptidoglycan layer in gram-negative bacteria?

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

    What is the periplasmic space located between?

    <p>The outer membrane and the peptidoglycan layer</p> Signup and view all the answers

    What is the role of membrane-derived oligosaccharides (MDO) in gram-negative bacteria?

    <p>To regulate the osmotic balance</p> Signup and view all the answers

    Which protein is responsible for stabilization of outer membrane and mating aggregates in F-dependent conjugation?

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

    What is the function of LamB (maltoporin)?

    <p>Specific porin for maltose and maltodextrin</p> Signup and view all the answers

    Which protein is involved in siderophore-mediated iron transport and B12 transport?

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

    What is the function of Murein lipoprotein (Braun's lipoprotein)?

    <p>Major structural protein</p> Signup and view all the answers

    Which protein is an anion-selective diffusion channel induced under phosphate limitation?

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

    What is the function of OmpC (porin)?

    <p>Diffusion channel for small molecules</p> Signup and view all the answers

    Which protein is involved in ferrichrome siderophore uptake and is a receptor for phages T1, T5, 80, and colicin M?

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

    What is the function of Tsx protein?

    <p>Nucleoside-specific channel</p> Signup and view all the answers

    What is the primary function of the cytoplasmic membrane in bacterial cells?

    <p>To serve as a permeability barrier, preventing most solutes from entering the cytoplasm</p> Signup and view all the answers

    What is the arrangement of phospholipid molecules in the cytoplasmic membrane?

    <p>A bilayer with hydrophobic ends facing inward and hydrophilic ends facing outward</p> Signup and view all the answers

    What is the orientation of the polar phospholipids in the cytoplasmic membrane?

    <p>Facing outward, towards the external environment</p> Signup and view all the answers

    What is the role of specific transport proteins in the cytoplasmic membrane?

    <p>To allow specific solutes to enter the cytoplasm</p> Signup and view all the answers

    What is the composition of the cytoplasmic membrane?

    <p>A bilayer of phospholipid molecules with embedded proteins</p> Signup and view all the answers

    What is the significance of the hydrophilic and hydrophobic ends of phospholipid molecules in the cytoplasmic membrane?

    <p>They create a barrier that prevents most solutes from entering the cytoplasm</p> Signup and view all the answers

    What is the consequence of the cytoplasmic membrane being a permeability barrier?

    <p>Specific solutes can enter the cytoplasm through specific transport proteins</p> Signup and view all the answers

    What type of proteins are embedded in the cytoplasmic membrane?

    <p>All of the above</p> Signup and view all the answers

    What is the primary function of lipoteichoic acids (LTAs) in gram-positive bacteria?

    <p>Regulation of autolysin activity and scavenging of divalent cations</p> Signup and view all the answers

    What is the membrane anchor in S. aureus lipoteichoic acids (LTAs)?

    <p>Diglucosyldiacylglycerol moiety</p> Signup and view all the answers

    What is the consequence of YpfP-deficient mutants in S. aureus?

    <p>Pleomorphic cells and replacement of glycolipid anchor with diacylglycerol</p> Signup and view all the answers

    What is the role of the gene ypfP in S. aureus?

    <p>Encoding diglucosyldiacylglycerol synthase</p> Signup and view all the answers

    What is the structure of lipoteichoic acids (LTAs) in gram-positive bacteria?

    <p>Linear polymers of 16 to 40 phosphodiester-linked glycerol phosphate residues</p> Signup and view all the answers

    What is the proposed pathway for the synthesis of lipoteichoic acids (LTAs)?

    <p>Three phases: glycolipid anchor, poly(glycerophosphate) component, and D-alanyl esters linked to poly(glycerophosphate)</p> Signup and view all the answers

    What is the function of the porins in the outer membrane?

    <p>To regulate the access of hydrophilic solutes to the cytoplasmic membrane</p> Signup and view all the answers

    What is the primary function of the O-antigen region of lipopolysaccharides?

    <p>To determine the immunological specificity of the bacterium</p> Signup and view all the answers

    Which region of the lipopolysaccharides shows high-to-moderate structural variability?

    <p>The outer core</p> Signup and view all the answers

    What is the term for the repeating carbohydrate units found in the O-antigen region of lipopolysaccharides?

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

    What is the function of the lipid A component of lipopolysaccharides?

    <p>To anchor the lipopolysaccharides to the outer membrane</p> Signup and view all the answers

    What is the consequence of the alteration in the sugar composition of the O-antigen region?

    <p>A change in the immunological specificity of the bacterium</p> Signup and view all the answers

    What is the common component of the core region of most gram-negative organisms?

    <p>2-keto-3-deoxyoctulosonic acid (KDO)</p> Signup and view all the answers

    What is the function of OmpA in the outer membrane?

    <p>It plays a role in conjugation and the action of colicins K and L</p> Signup and view all the answers

    What are the substituents of the hydroxyl groups in Lipid A?

    <p>Long-chain fatty acids and the core polysaccharide units</p> Signup and view all the answers

    What is the structure of Lipid A in Salmonella?

    <p>A chain of D-glucosamine disaccharide units with all hydroxyl groups substituted</p> Signup and view all the answers

    What is the role of OmpA in relation to the outer membrane?

    <p>It is exposed at the surface and contributes to the stability of the outer membrane</p> Signup and view all the answers

    What is the link between the lipid A molecules in LPS?

    <p>Pyrophosphate bridges</p> Signup and view all the answers

    What is the function of porins in the outer membrane?

    <p>They are involved in various overlapping roles in the physiology of the cell</p> Signup and view all the answers

    What is the most commonly observed fatty acid in Lipid A?

    <p>β-hydroxymyristic acid</p> Signup and view all the answers

    What is the function of the O-antigen region in lipopolysaccharides?

    <p>To account for the tremendous antigenic diversity in Enterobacteriaceae</p> Signup and view all the answers

    What sugar is a common component of the core region of most gram-negative organisms?

    <p>2-keto-3-deoxyoctulosonic acid (KDO)</p> Signup and view all the answers

    What is the most commonly observed fatty acid in Lipid A of Salmonella?

    <p>β-hydroxymyristic acid</p> Signup and view all the answers

    What is the composition of the outermost portion of lipopolysaccharides?

    <p>Repeating carbohydrate units</p> Signup and view all the answers

    What is the characteristic of the inner core region of lipopolysaccharides?

    <p>Low structural variability</p> Signup and view all the answers

    What is the purpose of OmpA in the outer membrane of gram-negative bacteria?

    <p>To contribute to the stability of the outer membrane</p> Signup and view all the answers

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

    <p>To regulate the access of hydrophilic solutes to the cytoplasmic membrane</p> Signup and view all the answers

    How are the LPS subunits linked together?

    <p>Through pyrophosphate bridges between the lipid A molecules</p> Signup and view all the answers

    What is the role of OmpA at the surface of the outer membrane?

    <p>To serve as a receptor for T-even phage and play a role in conjugation and the action of colicins K and L</p> Signup and view all the answers

    What is the component of lipopolysaccharides that shows high-to-moderate structural variability?

    <p>Outer core</p> Signup and view all the answers

    What is the term used to describe the region of lipopolysaccharides that consists of an outer and an inner core?

    <p>Region II</p> Signup and view all the answers

    What is the function of porins in the outer membrane of gram-negative bacteria?

    <p>To form channels for the passage of small molecules</p> Signup and view all the answers

    What is Lipid A composed of?

    <p>A chain of D-glucosamine disaccharide units</p> Signup and view all the answers

    What is the significance of the hydroxyl groups in Lipid A?

    <p>They are substituted with long-chain fatty acids</p> Signup and view all the answers

    What is the primary function of lipoteichoic acids in gram-positive bacteria?

    <p>To regulate autolysin activity</p> Signup and view all the answers

    What is the composition of the poly(glycerophosphate) component of lipoteichoic acids?

    <p>16-40 phosphodiester-linked glycerol phosphate residues</p> Signup and view all the answers

    What is the function of the diglucosyldiacylglycerol synthase enzyme in lipoteichoic acid synthesis?

    <p>To synthesize the glycolipid anchor</p> Signup and view all the answers

    What is the consequence of YpfP deficiency in S. aureus?

    <p>Pleomorphic cells and replacement of the glycolipid anchor with diacylglycerol</p> Signup and view all the answers

    What is the role of lipoteichoic acids in the interaction of bacteria with host cells?

    <p>To promote the adhesion of bacteria to host cells</p> Signup and view all the answers

    What is the structural feature of lipoteichoic acids that allows them to interact with divalent cations?

    <p>The presence of negatively charged phosphate groups</p> Signup and view all the answers

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

    <p>To regulate the access of hydrophilic solutes to the cytoplasmic membrane</p> Signup and view all the answers

    What is the significance of the O-antigen region of lipopolysaccharides?

    <p>It determines the immunological specificity of the bacteria</p> Signup and view all the answers

    What is the composition of the core region of lipopolysaccharides?

    <p>An outer and an inner core with low structural variability</p> Signup and view all the answers

    What is the function of the lipid A component of lipopolysaccharides?

    <p>To anchor the lipopolysaccharides to the outer membrane</p> Signup and view all the answers

    What is the significance of the repeating carbohydrate units in the O-antigen region of lipopolysaccharides?

    <p>They determine the immunological specificity of the bacteria</p> Signup and view all the answers

    What is the characteristic feature of the O-antigen region of lipopolysaccharides in Salmonella, Shigella, and other Enterobacteriaceae?

    <p>It accounts for tremendous antigenic diversity and many hundreds of chemical types or serotypes</p> Signup and view all the answers

    What is the primary function of the glycolipid anchor in lipoteichoic acids?

    <p>Covalent linkage to the membrane</p> Signup and view all the answers

    What is the number of phosphodiester-linked glycerol phosphate residues in lipoteichoic acids?

    <p>16-40</p> Signup and view all the answers

    What is the role of the YpfP enzyme in lipoteichoic acid synthesis?

    <p>Synthesis of the glycolipid anchor</p> Signup and view all the answers

    What is the consequence of YpfP-deficient mutants of S. aureus?

    <p>Formation of pleomorphic cells</p> Signup and view all the answers

    What is the function of lipoteichoic acids in gram-positive bacteria?

    <p>All of the above</p> Signup and view all the answers

    What is the characteristic of the carbohydrate group antigen of streptococci?

    <p>Based on the relative amounts of N-acetylglucosamine or N-acetylgalactosamine present</p> Signup and view all the answers

    What is a unique component of the core region in most gram-negative organisms?

    <p>2-keto-3-deoxyoctulosonic acid (KDO)</p> Signup and view all the answers

    What is the most commonly observed fatty acid in Lipid A of Salmonella?

    <p>β-hydroxymyristic acid</p> Signup and view all the answers

    How are the LPS subunits linked together?

    <p>Through pyrophosphate bridges</p> Signup and view all the answers

    What is the role of OmpA in the outer membrane?

    <p>All of the above</p> Signup and view all the answers

    What is the function of porins in the outer membrane?

    <p>They allow passage of small molecules through the membrane</p> Signup and view all the answers

    What is the structure of lipid A in Salmonella?

    <p>A chain of D-glucosamine disaccharide units with all hydroxyl groups substituted</p> Signup and view all the answers

    What is the relationship between LPS and OMPs in the outer membrane?

    <p>LPS is tightly associated with OMPs, particularly OmpA</p> Signup and view all the answers

    What is the function of OmpA in addition to its role in the outer membrane?

    <p>It plays a role in conjugation and the action of colicins K and L</p> Signup and view all the answers

    What is the structure of the cytoplasmic membrane in bacterial cells?

    <p>A bimolecular lipid leaflet</p> Signup and view all the answers

    What is the orientation of the polar phospholipids in the cytoplasmic membrane?

    <p>Facing both the internal or cytoplasmic side and the external or outside of the membrane</p> Signup and view all the answers

    What is the function of specific transport proteins in the cytoplasmic membrane?

    <p>To mediate the transport of solutes across the membrane</p> Signup and view all the answers

    What is the consequence of the cytoplasmic membrane being a permeability barrier?

    <p>Most solutes cannot enter the cytoplasm except through specific transport proteins</p> Signup and view all the answers

    What is embedded in the cytoplasmic membrane?

    <p>Various proteins and other components of the cell</p> Signup and view all the answers

    What is the arrangement of phospholipid molecules in the cytoplasmic membrane?

    <p>Aligned at their hydrophobic ends</p> Signup and view all the answers

    What is the function of the cytoplasmic membrane?

    <p>To serve as a permeability barrier</p> Signup and view all the answers

    What is the significance of the hydrophilic and hydrophobic ends of phospholipid molecules in the cytoplasmic membrane?

    <p>They facilitate the interaction between phospholipid molecules and other cellular components</p> Signup and view all the answers

    What is the major component of the cell wall of both gram-positive and gram-negative bacteria?

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

    Which polymer is present in small amounts in vegetative cells of yeast?

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

    What is the outermost component of the cell wall of many archaebacteria?

    <p>S-layer</p> Signup and view all the answers

    What is the primary component of the cell wall of fungi?

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

    What is the characteristic of the cell wall of yeast?

    <p>It contains a high proportion of mannan</p> Signup and view all the answers

    What is the function of the S-layer in bacteria?

    <p>It protects the cell from external environment</p> Signup and view all the answers

    What is the composition of the cell wall of gram-negative bacteria?

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

    What is the characteristic of the cell wall of archaebacteria?

    <p>It contains a high proportion of pseudomurein</p> Signup and view all the answers

    What is the composition of peptidoglycan in bacterial cell walls?

    <p>Heteropolymer of repeating units of β-1,4-N-acetylglucosamine and N-acetyl-muramic acid</p> Signup and view all the answers

    What is the characteristic of the glycan linkages in peptidoglycan?

    <p>Uniform in all bacteria with every D-lactyl group being peptide substituted</p> Signup and view all the answers

    What is the typical structure of the tetrapeptide units in peptidoglycan?

    <p>Terminating with D-alanine or occasionally tripeptide units lacking the terminal D-alanine</p> Signup and view all the answers

    What is the function of the interpeptide bridges in peptidoglycan?

    <p>Linking peptidoglycan to other peptidoglycan molecules</p> Signup and view all the answers

    What is the characteristic feature of the peptidoglycan layer in gram-positive bacteria?

    <p>Thick and uniform</p> Signup and view all the answers

    What is the characteristic feature of the peptidoglycan layer in gram-negative bacteria?

    <p>Thin and wavy</p> Signup and view all the answers

    What is the characteristic feature of the cell wall in archaebacteria?

    <p>Proteinaceous S-layer</p> Signup and view all the answers

    What is the term for the region between the outer and plasma membranes in gram-negative bacteria?

    <p>Periplasmic space</p> Signup and view all the answers

    What is the main component of peptidoglycan?

    <p>N-acetylglucosamine (NAG) and N-acetyl-muramic acid (NAM)</p> Signup and view all the answers

    What is the function of the D-alanine and glycine in peptidoglycan?

    <p>They terminate the tetrapeptide units</p> Signup and view all the answers

    What is the type of bacteria that has a wall profile intermediate between the gram-positive and gram-negative formats?

    <p>Clostridium thermosaccharolyticum</p> Signup and view all the answers

    What is the main component of the cell wall of fungi?

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

    What is the characteristic of the cell wall of archaebacteria?

    <p>Presence of pseudomurein and S-layer</p> Signup and view all the answers

    What is the name of the region between the outer and plasma membranes in Escherichia coli?

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

    What is the primary component of the outer membrane of Gram-negative bacteria?

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

    What is the characteristic feature of the archaebacterium Methanococcus voltae?

    <p>It has only a thin S-layer as its sole wall layer</p> Signup and view all the answers

    What is the term used to describe the wall layer above the plasma membrane in Escherichia coli?

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

    Which of the following is a characteristic of the cell wall of yeast?

    <p>Presence of β-glycans and mannan</p> Signup and view all the answers

    What is the significance of the waviness of the outer membrane in Escherichia coli?

    <p>It is an artifact of the conventional fixation-embedding technique</p> Signup and view all the answers

    What is the common constituent found in the cell walls of all filamentous fungi?

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

    What is the characteristic of the S-layer in many archaebacteria?

    <p>It represents the only surface component outside the plasma membrane</p> Signup and view all the answers

    What is the characteristic feature of the peptidoglycan layer in Bacillus subtilis?

    <p>It is thick and amorphous</p> Signup and view all the answers

    What is the characteristic of the cell wall of yeast in vegetative cells?

    <p>Presence of chitin in the septum and bud scar</p> Signup and view all the answers

    What is the characteristic of the cell surface layer (S-layer) in bacteria?

    <p>It is composed of protein or glycoprotein</p> Signup and view all the answers

    What is the primary function of the cytoplasmic membrane in bacterial cells?

    <p>To serve as a permeability barrier, controlling the movement of solutes into the cytoplasm</p> Signup and view all the answers

    What is the arrangement of phospholipid molecules in the cytoplasmic membrane?

    <p>A bimolecular lipid leaflet with hydrophobic ends facing inward</p> Signup and view all the answers

    What type of proteins are embedded in the cytoplasmic membrane?

    <p>Transport proteins that facilitate the movement of solutes into the cell</p> Signup and view all the answers

    What is the orientation of the polar phospholipids in the cytoplasmic membrane?

    <p>Facing outward, toward the external environment</p> Signup and view all the answers

    What is the function of specific transport proteins in the cytoplasmic membrane?

    <p>To facilitate the movement of solutes into the cell</p> Signup and view all the answers

    What is the composition of the cytoplasmic membrane?

    <p>A bimolecular lipid leaflet of phospholipid molecules</p> Signup and view all the answers

    What is the significance of the hydrophilic and hydrophobic ends of phospholipid molecules in the cytoplasmic membrane?

    <p>The hydrophobic ends face inward, while the hydrophilic ends face outward</p> Signup and view all the answers

    What is the consequence of the cytoplasmic membrane being a permeability barrier?

    <p>Solutes can enter the cell only through specific transport proteins</p> Signup and view all the answers

    Study Notes

    Cell Structure and Function

    • Eukaryotic cells differ from prokaryotic cells in several ways, with eukaryotes displaying a cytologically distinct nucleus.
    • The nucleus is the organizational and regulatory center for biochemical and hereditary processes in eukaryotes.
    • The eukaryotic nucleus has a double-layered membrane with pores, with the outer surface containing tubules that transcend both membrane layers.

    Eukaryotic Nucleus

    • Eukaryotes, including protozoa, algae, fungi, and metazoans, have a discrete membrane-bound nucleus.
    • Examples of eukaryotic cells with a nuclear membrane include mammalian cells, amoebeae, and myxomycetes.
    • The eukaryotic nucleus has a nucleolus and ribosomes.

    Bacterial Nucleoids

    • In most bacteria, the DNA-containing region is folded into a cytologically distinct region without a nuclear membrane, known as the nucleoid.
    • The nucleoid is not bound by a nuclear membrane and is generally smaller than the eukaryotic nucleus.

    Comparison of Cell Components

    • Eukaryotes have a true nucleus, nuclear membrane, nucleolus, and 40S, 60S/80S ribosomes.
    • Prokaryotes lack a true nucleus, nuclear membrane, and nucleolus, and have 30S, 50S/70S ribosomes.
    • Archaebacteria have characteristics distinct from both eukaryotes and eubacteria, including a lack of a cell wall peptidoglycan.

    Cellular Structure and Function

    • Eubacteria and archaebacteria differ in several characteristics beyond those listed in the table.
    • Some species of eubacteria and archaebacteria have been shown to have a nuclear membrane.

    Bacterial Nucleoids

    • In most bacteria, the DNA-containing region (chromosome) is folded into a cytologically distinct region called the nucleoid.
    • The nucleoid is not bound by a nuclear membrane.

    Eukaryotic Cells

    • Eukaryotic cells differ from prokaryotic cells in several major ways (Table 7-1).
    • Lower eukaryotes (protozoa, algae, and fungi) lack some distinguishing features of metazoan cells.
    • All eukaryotic cells appear to be similar versions of the same overall plan.

    The Eukaryotic Nucleus

    • Eukaryotes (Eukarya) display a cytologically distinct nucleus, which is the organizational and regulatory center for biochemical and hereditary processes.
    • The eukaryotic nucleus has a well-defined nuclear membrane composed of at least two distinct layers.
    • The outer surface of the nuclear membrane contains pores with tubules that transcend both membrane layers.

    Cytoplasmic Membranes

    • The cytoplasmic membrane of bacterial cells is a bimolecular lipid leaflet of phospholipid molecules aligned at their hydrophobic ends.
    • The phospholipids are hydrophilic and face the external or outside of the membrane and the internal or cytoplasmic side of the membrane.
    • The cell membrane serves as a permeability barrier, preventing most solutes from gaining entrance to the cytoplasm except through specific transport proteins present in the membrane layer.

    Peptidoglycans of Bacterial Cell Walls

    • Peptidoglycan is a heteropolymer of repeating units of β-1,4-N-acetylglucosamine (NAG) and N-acetyl-muramic acid (NAM).
    • The glycan linkages of peptidoglycan are uniform in all bacteria, with every D-lactyl group of NAM being peptide-substituted.
    • Glycans have short tetrapeptide units terminating with D-alanine or occasionally tripeptide units lacking the terminal D-alanine.
    • The L-alanine at the N-terminus can be replaced by glycine.
    • Interpeptide bridges linking peptidoglycans are of four major types.

    Structure of Bacterial Cell Walls

    • B. subtilis 168 has an amorphous wall fabric above the plasma membrane.
    • E. coli has a thin peptidoglycan murein layer above the plasma membrane, over which lays a wavy outer membrane.
    • Clostridium thermosaccharolyticum has a wall profile intermediate between gram-positive and gram-negative formats.
    • Methanococcus voltae, an archaebacterium, has only a thin S-layer above the plasma membrane as its sole wall layer.

    Yeast Cell Walls

    • Yeast cell walls contain 29% β-glycans, 31% mannan, and 13% protein.
    • The mannan-rich outer layer of the wall contains a higher proportion of 1,6-β-glycan.
    • Yeast cell walls also contain small percentages of lipids and other materials.
    • Chitin is present in small amounts in vegetative cells of yeast, being confined almost entirely to the ring encircling the septum of budding yeast.

    Prokaryotic Cell Surfaces

    • Peptidoglycan is the major backbone of the murein sacculus of the cell wall of both gram-positive and gram-negative bacteria.
    • Archaea produce a pseudomurein and an associated surface layer (S-layer) composed of protein or glycoprotein.
    • In many archaebacteria, the S-layer may represent the only surface component outside the plasma membrane.

    Surface Layers of Bacteria

    • Bacteria from all major phylogenetic groups produce a crystalline cell surface layer (S-layer) as the outermost component of the cell.

    Cytoplasmic Membranes

    • The cytoplasmic membrane of bacterial cells is a bimolecular lipid leaflet of phospholipid molecules aligned at their hydrophobic ends.
    • The polar phospholipids are hydrophilic and face the external or outside of the membrane and the internal or cytoplasmic side of the membrane.
    • The cell membrane serves as a permeability barrier, preventing most solutes from gaining entrance to the cytoplasm except through specific transport proteins present in the membrane layer.

    Outer Membrane Structure

    • The outer membrane of gram-negative bacteria appears as an asymmetric bilayer.
    • The external layer is primarily composed of Lipopolysaccharides (LPS).
    • LPS is composed of:
      • O-Antigen repeat
      • Core region (including GlcNAc, Glucose, Galactose, Heptose, and KDO)
      • Lipid A
    • The inner layer is composed of phospholipids.

    Outer Membrane Proteins

    • OmpA:
      • Stabilizes outer membrane and mating aggregates in F-dependent conjugation.
      • Receptor for phage TuII.
    • Murein lipoprotein (Braun's lipoprotein):
      • Most abundant surface protein in E. coli and S. enterica.
      • Major structural protein.
      • Stabilizes cell surface in conjunction with OmpA.
    • Porins:
      • OmpB (porin): diffusion channel for various metabolites including maltose.
      • LamB (maltoporin): specific porin for maltose and maltodextrin; receptor for bacteriophage λ.
      • OmpC (porin): diffusion channel for small molecules; receptor for phages TuIb and T4.
      • OmpF (porin): diffusion channel for small molecules; receptor for phages TuIa and T2.
    • Other proteins:
      • OmpT: protease.
      • PhoE (protein E): anion-selective diffusion channel induced under phosphate limitation.
      • Protein P: anion-selective diffusion channel in Pseudomonas aeruginosa; induced under phosphate limitation.
      • TolA: maintenance of OM integrity; activity of group A colicins.
      • TonA: ferrichrome siderophore uptake; receptor for phages T1, T5, 80, and colicin M.
      • TonB: siderophore-mediated iron transport; B12 transport.
      • Tsx: nucleoside-specific channel; receptor for T-even phages and colicin K.

    Cytoplasmic Membrane

    • The cytoplasmic membrane is a bimolecular lipid leaflet of phospholipid molecules.
    • The polar phospholipids are hydrophilic and face the external or outside of the membrane and the internal or cytoplasmic side of the membrane.
    • The cell membrane serves as a permeability barrier, preventing most solutes from gaining entrance to the cytoplasm except through specific transport proteins present in the membrane layer.

    Cell Membrane Structure

    • The outer membrane of gram-negative bacteria contains phospholipids and outer membrane proteins (OMPs), such as porins, which form large water-filled pores with diameters of 1-2 nm.
    • The pores regulate the access of hydrophilic solutes to the cytoplasmic membrane.

    Lipopolysaccharides (LPS)

    • LPS consists of three basic components: O-antigen (region I), core region (region II), and lipid A (region III).
    • The O-antigen region contains repeating carbohydrate units that determine the immunological specificity of the bacterium.
    • The core region consists of an outer and an inner core, with the outer core showing high-to-moderate structural variability and the inner core showing very low variability.
    • Lipid A is embedded in the outer membrane and consists of a chain of D-glucosamine disaccharide units with all hydroxyl groups substituted.
    • The substituents on lipid A include core polysaccharide units and long-chain fatty acids, such as β-hydroxymyristic acid.

    Lipopolysaccharide Structure

    • The oligosaccharide subunits of the core region of E. coli and Shigella differ only slightly from those of Salmonella.
    • The unique octose sugar, 2-keto-3-deoxyoctulosonic acid (KDO), is a common component of the core region of most gram-negative organisms.
    • An average of three LPS subunits are linked together through pyrophosphate bridges between the lipid A molecules.

    Outer Membrane Proteins (OMPs)

    • OMPs, such as OmpA, are tightly associated with LPS and contribute to the stability of the outer membrane.
    • OmpA spans the membrane and is cross-linked to the underlying peptidoglycan layer.
    • OmpA is exposed at the surface, where it serves as a receptor for T-even phage and plays a role in conjugation and the action of colicins K and L.

    Lipoteichoic Acids (LTAs)

    • LTAs are membrane-associated polymers characteristic of gram-positive bacteria.
    • LTAs are linear polymers of 16-40 phosphodiester-linked glycerol phosphate residues covalently linked to a membrane anchor.
    • Physiological roles postulated for LTA include regulation of autolysin activity, scavenging of divalent cations, and interaction of bacteria with cells of infected hosts.

    Lipoteichoic Acid Synthesis

    • The synthesis of LTA occurs in three phases: the glycolipid anchor, the poly(glycerophosphate) component, and the D-alanyl esters linked to poly(glycerophosphate).
    • The diglucosyldiacylglycerol moiety of LTA functions as the membrane anchor in S. aureus.

    Cell Membrane Structure

    • The outer membrane of gram-negative bacteria contains phospholipids and outer membrane proteins (OMPs), such as porins, which form large water-filled pores with diameters of 1-2 nm.
    • The pores regulate the access of hydrophilic solutes to the cytoplasmic membrane.

    Lipopolysaccharides (LPS)

    • LPS consists of three basic components: O-antigen (region I), core region (region II), and lipid A (region III).
    • The O-antigen region contains repeating carbohydrate units that determine the immunological specificity of the bacterium.
    • The core region consists of an outer and an inner core, with the outer core showing high-to-moderate structural variability and the inner core showing very low variability.
    • Lipid A is embedded in the outer membrane and consists of a chain of D-glucosamine disaccharide units with all hydroxyl groups substituted.
    • The substituents on lipid A include core polysaccharide units and long-chain fatty acids, such as β-hydroxymyristic acid.

    Lipopolysaccharide Structure

    • The oligosaccharide subunits of the core region of E. coli and Shigella differ only slightly from those of Salmonella.
    • The unique octose sugar, 2-keto-3-deoxyoctulosonic acid (KDO), is a common component of the core region of most gram-negative organisms.
    • An average of three LPS subunits are linked together through pyrophosphate bridges between the lipid A molecules.

    Outer Membrane Proteins (OMPs)

    • OMPs, such as OmpA, are tightly associated with LPS and contribute to the stability of the outer membrane.
    • OmpA spans the membrane and is cross-linked to the underlying peptidoglycan layer.
    • OmpA is exposed at the surface, where it serves as a receptor for T-even phage and plays a role in conjugation and the action of colicins K and L.

    Lipoteichoic Acids (LTAs)

    • LTAs are membrane-associated polymers characteristic of gram-positive bacteria.
    • LTAs are linear polymers of 16-40 phosphodiester-linked glycerol phosphate residues covalently linked to a membrane anchor.
    • Physiological roles postulated for LTA include regulation of autolysin activity, scavenging of divalent cations, and interaction of bacteria with cells of infected hosts.

    Lipoteichoic Acid Synthesis

    • The synthesis of LTA occurs in three phases: the glycolipid anchor, the poly(glycerophosphate) component, and the D-alanyl esters linked to poly(glycerophosphate).
    • The diglucosyldiacylglycerol moiety of LTA functions as the membrane anchor in S. aureus.

    Outer Membrane Structure

    • The outer membrane of Gram-negative bacteria consists of an outer layer containing lipopolysaccharides (LPS) and an inner layer containing primarily phospholipids.
    • Outer membrane proteins (OMPs), called porins, form large water-filled pores with diameters of 1 to 2 nm that traverse the membrane and regulate the access of hydrophilic solutes to the cytoplasmic membrane.

    Lipopolysaccharides (LPS)

    • LPS consists of three basic components or regions: the O-antigen region, the core region, and lipid A.
    • The O-antigen region (Region I) contains repeating carbohydrate units that represent the “O” antigen, which determines the immunological specificity of the bacterium.
    • The core region (Region II) consists of an outer and an inner core, with the inner core showing very low structural variability.
    • Lipid A (Region III) is embedded in the outer membrane and has been extensively studied in Salmonella.
    • The chemical composition of lipid A consists of a chain of D-glucosamine disaccharide units with all of the hydroxyl groups substituted with long-chain fatty acids.

    Lipid A Structure

    • The most commonly observed fatty acid in lipid A is β-hydroxymyristic acid (3-hydroxy-tetradecanoic acid), a C14 saturated fatty acid.
    • The hydroxyl groups of lipid A are also esterified with other long-chain fatty acids such as lauric, myristic, and palmitic acids.
    • An average of three lipid A subunits are linked together through pyrophosphate bridges.

    Outer Membrane Proteins (OMPs)

    • OMPs play a variety of overlapping roles in the physiology of the cell, including regulation of the access of hydrophilic solutes to the cytoplasmic membrane.
    • OmpA is a major OMP that contributes to the stability of the outer membrane, spans the membrane, and is cross-linked to the underlying peptidoglycan layer.
    • OmpA is exposed at the surface, where it serves as a receptor for T-even phage and plays a role in conjugation and the action of colicins K and L.

    Lipoteichoic Acids (LTAs)

    • LTAs are membrane-associated polymers characteristic of Gram-positive bacteria.
    • LTAs are linear polymers of 16 to 40 phosphodiester-linked glycerol phosphate residues covalently linked to a membrane anchor (generally a glycolipid or glycophospholipid).
    • Physiological roles postulated for LTA include regulation of autolysin activity, scavenging of divalent cations, electromechanical properties of the cell wall, and interaction of bacteria with cells of infected hosts.

    Peptidoglycan Structure

    • Peptidoglycan is a heteropolymer composed of repeating units of β-1,4-N-acetylglucosamine (NAG) and N-acetyl-muramic acid (NAM)
    • Glycan linkages of peptidoglycan are uniform in all bacteria
    • Every D-lactyl group of NAM is peptide-substituted
    • Glycans have short tetrapeptide units terminating with D-alanine or occasionally tripeptide units lacking the terminal D-alanine

    Peptidoglycan Interpeptide Bridges

    • Interpeptide bridges linking peptidoglycans are of four major types
    • The proportion of peptide cross-linking varies between bacteria

    Bacterial Cell Walls

    • The cell wall of B. subtilis 168 has an amorphous wall fabric that lies directly above the plasma membrane
    • E. coli has a thin peptidoglycan murein layer above the plasma membrane, with a wavy outer membrane above it
    • The region between the outer and plasma membranes is called the periplasm or periplasmic space

    Cytoplasmic Membranes

    • The cytoplasmic membrane is a bimolecular lipid leaflet of phospholipid molecules aligned at their hydrophobic ends
    • The polar phospholipids are hydrophilic and face the external and internal sides of the membrane
    • Various proteins and other components of the cell may be partially or wholly embedded in the membrane layer
    • The cell membrane serves as a permeability barrier, preventing most solutes from entering the cytoplasm except through specific transport proteins

    Cell Wall Polymers

    • Chemical structures of cell wall polymers include cellulose, chitin, glucan, and mannan
    • Yeast cell walls contain 29% β-glycans, 31% mannan, and 13% protein

    Prokaryotic Cell Surfaces

    • Peptidoglycan is the major backbone of the murein sacculus of the cell wall of both gram-positive and gram-negative bacteria
    • Archaea produce a pseudomurein and an associated surface layer (S-layer) composed of protein or glycoprotein
    • The S-layer may represent the only surface component outside the plasma membrane in many archaebacteria

    Surface Layers of Bacteria

    • Bacteria from all major phylogenetic groups produce a crystalline cell surface layer (S-layer) as the outermost component of the cell
    • The S-layer can be attached to the peptidoglycan-containing sacculus or the outer membrane in different bacteria

    Peptidoglycans of Bacterial Cell Walls

    • Peptidoglycan is a heteropolymer of repeating units of β-1,4-N-acetylglucosamine (NAG) and N-acetyl-muramic acid (NAM).
    • Glycan linkages of peptidoglycan are uniform in all bacteria with every D-lactyl group of the NAM being peptide substituted.
    • All glycans have short tetrapeptide units terminating with D-alanine or occasionally tripeptide units lacking the terminal D-alanine.
    • L-alanine at the N-terminus can be replaced by glycine.
    • Interpeptide bridges linking peptidoglycans are of four major types.

    Cell Wall Structure

    • Cell wall profile of B. subtilis 168 shows amorphous wall fabric directly above the plasma membrane.
    • Escherichia coli has a thin peptidoglycan murein layer above the plasma membrane, overlaid by a wavy outer membrane.
    • Clostridium thermosaccharolyticum has a wall profile intermediate between gram-positive and gram-negative formats, with a peptidoglycan layer and a proteinaceous S-layer.
    • Methanococcus voltae has a thin S-layer as its sole wall layer.

    Cytoplasmic Membranes

    • Cytoplasmic membrane is a bimolecular lipid leaflet of phospholipid molecules aligned at their hydrophobic ends.
    • Polar phospholipids are hydrophilic and face the external and internal sides of the membrane.
    • Various proteins and components may be embedded in the membrane layer.
    • Cell membrane serves as a permeability barrier, preventing most solutes from entering the cytoplasm except through specific transport proteins.

    Cell Wall Polymers

    • Chemical structures of cell wall polymers include cellulose, chitin, glucan, and mannan.
    • Yeast cell walls contain 29% β-glycans, 31% mannan, 13% protein, and small percentages of lipids and other materials.

    Prokaryotic Cell Surfaces

    • Peptidoglycan is the hallmark of eubacteria, forming the major backbone of the murein sacculus of the cell wall.
    • Archaea produce a pseudomurein and an associated surface layer (S-layer) composed of protein or glycoprotein.
    • In many archaebacteria, the S-layer may represent the only surface component outside the plasma membrane.

    Surface Layers of Bacteria

    • Bacteria from all major phylogenetic groups produce a crystalline cell surface layer (S-layer) as the outermost component of the cell.
    • S-layer may be attached to the peptidoglycan-containing sacculus or the outer membrane.

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