Bacterial Cell Structure Quiz

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Questions and Answers

What is the primary function of flagella in bacteria?

Formation of a capsule

Motility or locomotion (correct)

Adherence to host cells

Gene transfer by conjugation

Which structure is present in spirochetes and contributes to their motility?

Pili

Axial filaments (endoflagella) (correct)

Capsule

Fimbriae

What type of pili is involved in gene transfer by conjugation?

Fimbriae

Sex pili (correct)

Capsular pili

Common pili

Which of the following is NOT a component of the bacterial cell envelope?

Nucleic acid Signup and view all the answers

What is the structure of common pili in bacteria?

Short and thin Signup and view all the answers

In which type of bacteria are sex pili commonly found?

Only in Gram-negative bacteria Signup and view all the answers

What is the primary composition of the capsule found in pathogenic bacteria?

Polysaccharides Signup and view all the answers

What is the primary function of ribosomes in bacterial cells?

Protein synthesis Signup and view all the answers

Which type of antibiotic can inhibit bacterial growth but does not necessarily kill the bacteria?

Bacteriostatic antibiotics Signup and view all the answers

Which of the following antibiotic types target protein synthesis by binding to the ribosome?

Macrolides Signup and view all the answers

What is a key characteristic of bacterial spores?

They can remain dormant for many years. Signup and view all the answers

Which of the following is classified as a cell wall synthesis inhibitor?

Vancomycin Signup and view all the answers

What is the primary role of the capsule in bacteria?

Acts as a virulence factor Signup and view all the answers

Which method is used to demonstrate the capsule of Bacillus anthracis?

India ink wet mount Signup and view all the answers

What component of the bacterial cell wall is responsible for determining its shape?

Peptidoglycan backbone Signup and view all the answers

Which component is typically found in Gram-positive bacteria cell walls but not in Gram-negative bacteria?

Lipoteichoic acid Signup and view all the answers

What is the function of transpeptidase enzymes in bacterial cells?

Cross-linking the peptidoglycan chains Signup and view all the answers

What does the cytoplasmic membrane primarily consist of?

Phospholipid bilayer and proteins Signup and view all the answers

What is one function of mesosomes in bacterial cells?

Facilitating cell division Signup and view all the answers

Which of the following describes the type of peptidoglycan layer in Gram-negative bacteria?

Thin and located in the periplasmic space Signup and view all the answers

What is the primary role of lipopolysaccharide (LPS) in Gram-negative bacteria?

Contributes to virulence and can act as an endotoxin Signup and view all the answers

What is the main purpose of a plasmid in bacterial cells?

Carries genes for antibiotic resistance Signup and view all the answers

Study Notes

Bacterial Cell Structure

Structure of bacterial cells, from outside to inside:
- Cell appendages (flagella, fimbriae, axial filaments)
- Cell envelope (capsule, cell wall, cytoplasmic membrane)
- Cytoplasmic contents (nucleic acid, plasmids, ribosomes)

Cell Appendages

Flagella:
- Origin: cytoplasm
- Structure: protein
- Shape: long, thick, and twisted
- Gram-positive and Gram-negative bacteria
- Number: one, two, numerous per cell
- Function: motility (locomotion)
- Examples: Salmonella, Vibrio cholerae, Escherichia coli
Axial Filaments (Endoflagella):
- Location: periplasmic space
- In spirochetes (like Treponema)
- Function: rotation motility
Pili & Fimbriae:
- Origin: cytoplasmic membrane
- Structure: protein
- Common pili:
  - Shape: short, thin
  - Presence: all gram-negative bacteria and some gram-positive
  - Number: numerous (up to 1000 per cell)
  - Function: adherence to host cells and other bacteria
- Sex pili:
  - Shape: long, thick
  - Presence: only in gram-negative bacteria
  - Number: 1-10 per cell
  - Function: gene transfer by conjugation

Cell Envelope

Capsule:
- Location: outermost layer
- Formed mainly in vivo conditions
- Presence: most pathogenic bacteria
- Composition: polysaccharides (e.g., Streptococcus pneumoniae, Neisseria meningitides); exception: Bacillus anthracis (polypeptides)
- Function: important virulence factor (enhances infection by preventing the immune cells from engulfing the bacteria); also important for identification/diagnosis, and vaccine preparation.
Cell Wall:
- Location: outside the cytoplasmic membrane, determines the shape of the cell
- Structure: Peptidoglycan backbone (chains of two alternating sugars, NAM, and NAG, with peptide chains attached, forming cross-links.)
- Gram-positive cell wall: thick peptidoglycan layer, contains lipoteichoic acid for attachment
- Gram-negative cell wall: thin peptidoglycan layer in periplasmic space; additional outer membrane contains lipopolysaccharides (LPS) and Lipid A

Cytoplasmic membrane

Structure: phospholipid bilayers and proteins
Function:
- Selective permeability and transport of solutes
- Energy production (electron transport chain)
- Excretion of hydrolytic exoenzymes and toxic waste
- Biosynthesis of cell wall
Mesosomes: invaginations of the cytoplasmic membrane into the cytoplasm.
- Increase surface area and function of the cytoplasmic membrane.
- Role in cell division

Cytoplasm

Chromosome:
- One DNA, double-stranded (helix)
Plasmid:
- Circular extra DNA segment
- In some bacteria
- Capable of autonomous replication
- Function: carry genes of antibiotic resistance
Ribosomes (70S):
- Composed of rRNA and protein
- Function: protein synthesis

Bacterial Spores

Spores: resistant structures formed under adverse conditions (chemicals, radiations, freezing, heat).
- Can remain viable for many years in dormant state
- Fomred by certain bacterial types (like Bacillus and Clostridium).
Sporulation: process of producing inactive bacterial form from active vegetative cells.
- Spores contain DNA, encased in a multi-layered rigid envelope, strengthened by keratin + calcium dipicolinate
Spore Germination: In suitable environment(like in "vivo", the spore coat is disintegrated, the bacteria form vegetative cells by binary fission.

Antimicrobial Chemotherapy

Antimicrobials: Chemicals that kill or inhibit microbes (bacteria, fungi, viruses, parasites)
Classification:
- Source: natural, synthetic, semisynthetic
- Action: bactericidal (lethal), bacteriostatic (inhibit bacterial growth).
  - Broad spectrum: active against many bacteria types
  - Narrow spectrum: active against limited types of bacteria
Classification according to the targets of antibiotics: -Cell wall inhibitors (Beta-lactams, Penicillins, Cephalosporins, Glycopeptides, e.g,. Vancomycin)
- Cell membrane inhibitors (Polymyxins)
- Protein synthesis inhibitors (Macrolides, Aminoglycosides, Tetracyclines)
- Nucleic acid inhibitors (Sulfonamides, Quinolones, Rifampicin)

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Description

Test your knowledge on the structure of bacterial cells, including cell appendages and the cell envelope. This quiz covers essential components like flagella, axial filaments, and the cytoplasmic contents of bacteria. Perfect for students studying microbiology.