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Questions and Answers
Which structural component is responsible for providing rigidity to bacterial cells?
Which structural component is responsible for providing rigidity to bacterial cells?
What component differentiates Gram-positive bacteria from Gram-negative bacteria?
What component differentiates Gram-positive bacteria from Gram-negative bacteria?
Which of the following structures are considered non-essential for eubacteria?
Which of the following structures are considered non-essential for eubacteria?
Which of the following is not part of the internal structure of eubacteria?
Which of the following is not part of the internal structure of eubacteria?
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Which structures are responsible for bacterial movement?
Which structures are responsible for bacterial movement?
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What is the primary function of teichoic acids in Gram-positive bacteria?
What is the primary function of teichoic acids in Gram-positive bacteria?
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The slime layer is a type of what bacterial structure?
The slime layer is a type of what bacterial structure?
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Which component of the bacterial cell wall varies in thickness and chemical composition?
Which component of the bacterial cell wall varies in thickness and chemical composition?
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Which of the following is an essential internal structure of eubacteria?
Which of the following is an essential internal structure of eubacteria?
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What role do spores serve in bacteria?
What role do spores serve in bacteria?
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What is the role of OmpA in bacteria?
What is the role of OmpA in bacteria?
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Which of the following structures is responsible for maintaining the shape of bacteria?
Which of the following structures is responsible for maintaining the shape of bacteria?
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What is the primary component that confers the negative charge to Gram-negative bacteria?
What is the primary component that confers the negative charge to Gram-negative bacteria?
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What type of bond connects the N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) in peptidoglycan?
What type of bond connects the N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) in peptidoglycan?
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Which component confers a negative charge to the bacterial cell?
Which component confers a negative charge to the bacterial cell?
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Which component of the Gram-negative cell wall is missing in Gram-positive bacteria?
Which component of the Gram-negative cell wall is missing in Gram-positive bacteria?
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What triggers the innate immune response in relation to the outer membrane?
What triggers the innate immune response in relation to the outer membrane?
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Which of the following accurately describes the structure of the Gram-negative cell wall?
Which of the following accurately describes the structure of the Gram-negative cell wall?
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Which amino acids are typically found in the tetrapeptide attached to NAM in peptidoglycan?
Which amino acids are typically found in the tetrapeptide attached to NAM in peptidoglycan?
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What is the function of porin proteins in the Gram-negative outer membrane?
What is the function of porin proteins in the Gram-negative outer membrane?
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What characterizes the lipid A component of lipopolysaccharides (LPS) in Gram-negative bacteria?
What characterizes the lipid A component of lipopolysaccharides (LPS) in Gram-negative bacteria?
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What is one of the main functions of lipoproteins in the outer membrane?
What is one of the main functions of lipoproteins in the outer membrane?
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What is the role of the OmpC and OmpF proteins?
What is the role of the OmpC and OmpF proteins?
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In Gram-negative cell walls, what percentage of the total structure is constituted by peptidoglycan?
In Gram-negative cell walls, what percentage of the total structure is constituted by peptidoglycan?
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How many rings are present in the basal body of flagella in Gram-negative bacteria?
How many rings are present in the basal body of flagella in Gram-negative bacteria?
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Which amino acid is critical for the cross-linking of the peptidoglycan chain?
Which amino acid is critical for the cross-linking of the peptidoglycan chain?
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Which of the following is NOT a characteristic of the Gram-positive cell wall compared to the Gram-negative cell wall?
Which of the following is NOT a characteristic of the Gram-positive cell wall compared to the Gram-negative cell wall?
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Which structural component is located at the inner leaflet of the outer membrane and resembles the cytoplasmic membrane?
Which structural component is located at the inner leaflet of the outer membrane and resembles the cytoplasmic membrane?
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Which component is found in the outer leaflet of the Gram-negative outer membrane?
Which component is found in the outer leaflet of the Gram-negative outer membrane?
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What role does the middle core of lipopolysaccharides play in Gram-negative bacteria?
What role does the middle core of lipopolysaccharides play in Gram-negative bacteria?
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Study Notes
Pathogenic Microorganisms 222 PHARM
- Course offered at King Saud University
- Focuses on pathogenic microorganisms
- Slides cover bacterial structures and function
Bacterial Structures and Function
- Objectives include:
- Detailed microscopic bacterial structure (intra cytoplasmic structures)
- Bacterial cell wall structure
- Surface structures (outside the cell wall)
- Differentiating between Gram-positive and Gram-negative cell walls
- Describing bacterial movement
- Describing spore formation
Bacterial Structure (Diagram)
- Shows Gram-positive and Gram-negative bacteria
- Labels various components:
- Peptidoglycan layer
- Capsule
- Cytoplasmic membrane
- Ribosomes
- Surface proteins
- Chromosome
- Inclusion bodies
- Mesosome
- Outer membrane
- Pili
- Flagella
- Porin proteins
- Periplasmic space
Structure of Eubacteria
- I. Essential structures
- Cell wall
- Cell membrane
- Cytoplasm
- Ribosomes
- Nuclear material
- II. Additional (non-essential) structures
- Capsule
- Slime layer
- Flagella
- Pili
- Fimbriae
- Inclusions
- Spores
- Plasmids
Structure of Eubacteria (Alternative Diagram)
- I. External structure (extracytoplasmic)
- Glycocalyx
- Flagella
- Pili
- Fimbriae
- II. Cell envelope
- Outer membrane
- Cell wall
- Cell membrane
- III. Internal structure (intra cytoplasmic)
- Cytoplasm
- Ribosomes
- Nuclear material
- Inclusions
- Spores
- Plasmids
Cell Wall Structures
- Outer membrane (OM)
- Peptidoglycan
- Teichoic acids
- Periplasm
- Cytoplasmic membrane (CM)
Cell Wall (CW)
- Outermost component of bacteria, external to cytoplasmic membrane
- Highly rigid structure providing cell shape
- Varies in thickness and chemical composition, depending on the bacterial type
- Two types: Gram-positive and Gram-negative
Gram-positive and Gram-negative Cell Walls
-
Gram-positive
- Outer membrane: Absent
- Peptidoglycan (PDG): Present, thin (7-8 nm), 2 layers; 5-10% of cell wall
- Teichoic acids: Present
- Periplasm: Present
- Mesosome: Less prominent
- Flagella structure: 4 rings in basal body
-
Gram-negative
- Outer membrane: Present
- Peptidoglycan (PDG): Present, thick (20-80 nm), 40 layers; 50% of cell wall
- Teichoic acids: Absent
- Periplasm: Present
- Mesosome: More prominent
- Flagella structure: 2 rings in basal body
Outer Membrane (OM)
- Present only in Gram-negative bacteria
- Outside the peptidoglycan (PDG) layer
- Asymmetric lipid bilayer
- Components:
- Lipopolysaccharides (LPS)
- Porin proteins
- Phospholipids
- Lipoproteins
Lipopolysaccharides (LPS)
- Hydrophilic, located in outer leaflet of OM
- Confers negative charge to the cell
- Consists of polysaccharides extending into the cell exterior
- O-antigen (O-specific polysaccharides)
- Immunogenic (e.g., E. coli O157:H7)
- Up to 40 repeating units of 3-5 sugars
- Highly varied among species
- O-antigen (O-specific polysaccharides)
- Middle core: Oligosaccharide (five sugars); Sugars (heptose and ketodeoxy-octonate (KDO)).
- Lipid A (hydrophobic): Endotoxin (pyrogen); Composed of phosphorylated glucosamine disaccharide unit (β-1,6); Decorated with multiple fatty acids inserted in OM outer leaflet; Antigenic (PAMP) initiates innate immune response
Porin Proteins
- Also called outer membrane proteins (Omp)
- Form channels (pores) located in both halves of outer membrane
- Responsible for passage of hydrophilic molecules (like sugars)
- Loss of porins can lead to antibiotic resistance
- PDG-associated proteins (OmpC & OmpF)
- PDG-non-associated proteins (OmpA)
- Provides receptors for some viruses and bacteriocins.
- Stabilizes mating cells.
Lipoproteins (Braun)
- Play a role in stabilizing the outer membrane (OM) structure
- Covalently bound to the peptidoglycan (PDG) layer
- Anchor the inner leaflet of OM to PDG
- Determine and maintain the shape of bacteria
Phospholipids
- Inner leaflet of OM resembles cytoplasmic membrane (CM).
- Outer leaflet contains lipopolysaccharides (LPS).
Functions of OM
- Confers negative charge to the cell
- Maintains bacterial structure
- Provides protection from adverse conditions
- OmpC & OmpF are pores for entrance of hydrophilic molecules
- OmpA provides receptor for some viruses; stabilizes mating cells
- Initiates innate immune response and activates macrophages to secrete cytokines (e.g., IL-1, TNF-α)
Peptidoglycan (PDG)
- All eubacteria possess a PDG layer surrounding the cytoplasmic membrane (CM)
- Highly rigid structure preventing osmotic lysis
- Maintains the shape of bacteria
- Fully permeable to ions, amino acids, and sugars
- Made up of rope-like linear polysaccharide chains cross-linked by short peptides
- Composed of repeating disaccharides of N-acetylglucosamine (NAG) & N-acetylmuramic acid (NAM)
Additional Notes on Peptidoglycan
- NAG and NAM connected by β-(1,4)-glycosidic bond
- Tetrapeptide attached to NAM
- Usually composed of amino acids (AAs): L-Ala, D-Glu, L-Lys, D-Ala (1st & 2nd AA vary)
- 3rd AA is either lysine or diaminopimelic acid
- 4th AA is D-alanine
- Cross-linking between 2 different layers occurs between tetrapeptides
- Peptide cross-link formed between NH₂ of di-amino acid and COOH of D-alanine. Cross-linking can also occur directly or by a pentaglycine peptide.
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Description
Test your knowledge on pathogenic microorganisms by exploring their structures and functions. This quiz focuses on the intricacies of bacterial anatomy, including a comparison of Gram-positive and Gram-negative bacteria, as well as the different components essential for bacterial survival and movement.
