Bacterial Structure and Morphology
48 Questions
1 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What primarily constitutes the dry weight of Gram positive bacterial cell walls?

  • Outer membrane
  • Teichoic acid
  • Peptidoglycan (correct)
  • Proteins

    • Which statement correctly describes the structure of the Gram negative bacterial cell wall?

  • It is more rigid compared to Gram positive bacterial cell walls.
  • It lacks a periplasmic space.
  • It contains a thin peptidoglycan layer between an outer and inner membrane. (correct)
  • It has a thick peptidoglycan layer with no outer membrane.

    • Which component connects glycan chains in the peptidoglycan layer?

  • Beta 1,4-glycoside bond (correct)
  • Disulfide bridges
  • Hydrogen bonds
  • Peptide bonds

    • What is the role of lysozyme in relation to bacterial cells?

    <p>It cleaves glycosyl bonds in peptidoglycan. (C)</p> Signup and view all the answers

    Which type of bacteria is more resistant to lysozyme?

    <p>Gram negative bacteria (C)</p> Signup and view all the answers

    Which of the following statements is true about teichoic acids?

    <p>They play a role in tightening glycan strings in Gram positive bacteria. (C)</p> Signup and view all the answers

    What percentage of dry weight does the Gram positive bacterial cell wall contribute to?

    <p>40-80% (D)</p> Signup and view all the answers

    Which enzyme is particularly active against Gram positive bacteria?

    <p>Lysozyme (C)</p> Signup and view all the answers

    Which of the following is true about transmissible plasmids?

    <p>They can be transferred to other cells by conjugation. (C)</p> Signup and view all the answers

    What is a characteristic feature of non-transmissible plasmids?

    <p>They are often present in many copies per cell. (C)</p> Signup and view all the answers

    What role do plasmids play in antibiotic resistance?

    <p>They carry genes for resistance enzymes. (A)</p> Signup and view all the answers

    Which statement about transposons is correct?

    <p>They can move between plasmids, bacteriophages, and bacterial DNA. (A)</p> Signup and view all the answers

    What is the primary component of lipid A in LPS responsible for its toxic effects?

    <p>Phospholipid (D)</p> Signup and view all the answers

    What is one function provided by plasmids that is of medical significance?

    <p>Resistance to toxins and heavy metals. (D)</p> Signup and view all the answers

    What role do porin proteins play in the outer membrane of gram-negative bacteria?

    <p>Channels for transporting substances (B)</p> Signup and view all the answers

    Which characteristic differentiates acid-fast bacteria like Mycobacterium tuberculosis from other bacteria?

    <p>Rich in mycolic acid (A)</p> Signup and view all the answers

    What is the primary function of pili (fimbriae) in bacteria?

    <p>To mediate adherence to epithelial cells. (D)</p> Signup and view all the answers

    What does the capsule of a bacterium do?

    <p>It protects the bacterium from desiccation and immune responses. (D)</p> Signup and view all the answers

    What causes bacteria to become cell wall-deficient (CWD)?

    <p>Exposure to lysozyme or certain antibiotics (A)</p> Signup and view all the answers

    Ultraviolet light resistance in bacteria is mediated by which of the following?

    <p>DNA repair enzymes. (D)</p> Signup and view all the answers

    Which of the following is NOT a function of the cytoplasmic membrane in prokaryotic cells?

    <p>Defense against phagocytosis (C)</p> Signup and view all the answers

    What is the size range of the outer polysaccharide in LPS that contributes to O antigen?

    <p>Up to 25 repeating units (C)</p> Signup and view all the answers

    What is the primary function of the capsule in bacteria?

    <p>Limit phagocyte engulfment (A)</p> Signup and view all the answers

    What common feature distinguishes the cytoplasmic membranes of prokaryotes from those of eukaryotes?

    <p>Lack of sterols in most prokaryotes (D)</p> Signup and view all the answers

    Which of the following statements about bacterial capsules is false?

    <p>They are consistent across all bacterial species (A)</p> Signup and view all the answers

    Which function is NOT typically associated with the cytoplasmic membrane of prokaryotes?

    <p>Regulating water balance (C)</p> Signup and view all the answers

    What role do flagella play in bacteria?

    <p>They enable movement toward nutrients (B)</p> Signup and view all the answers

    Which of the following bacteria is known to utilize flagella for movement?

    <p>Escherichia coli (D)</p> Signup and view all the answers

    How are different serologic types of Streptococcus pneumoniae distinguished?

    <p>By antigenic differences of their polysaccharide capsule (C)</p> Signup and view all the answers

    What is the undulating motion of spirochetes produced by?

    <p>Axial filament (D)</p> Signup and view all the answers

    Which of the following statements about flagella is true?

    <p>Some bacteria have multiple flagella located all over their surface (C)</p> Signup and view all the answers

    What is an example of pathogenesis related to flagella?

    <p>Flagella help propel bacteria into the bladder (A)</p> Signup and view all the answers

    What is the primary role of the mesosome during cell division?

    <p>It functions as the origin of the transverse septum. (C)</p> Signup and view all the answers

    How does the size of bacterial ribosomes differ from eukaryotic ribosomes?

    <p>Bacterial ribosomes are smaller, measuring 70S. (B)</p> Signup and view all the answers

    What distinguishes bacterial DNA from eukaryotic DNA?

    <p>Bacterial DNA is a single, circular molecule. (C)</p> Signup and view all the answers

    What are plasmids in bacteria?

    <p>Extrachromosomal, double-stranded circular DNA molecules. (B)</p> Signup and view all the answers

    What structure in the cytoplasm contains ribosomes and metabolites?

    <p>Amorphous matrix. (A)</p> Signup and view all the answers

    Which component of bacterial cells lacks a nuclear membrane and histones?

    <p>Nucleoid. (D)</p> Signup and view all the answers

    What is a significant consequence of the differences in ribosomal composition between bacteria and humans?

    <p>Targeting bacterial protein synthesis specifically with antibiotics. (D)</p> Signup and view all the answers

    What is a characteristic feature of granules found in the cytoplasm?

    <p>They serve as storage areas for nutrients. (A)</p> Signup and view all the answers

    What is the primary function of penicillin in relation to penicillin binding proteins (PBP)?

    <p>It prevents PBP from binding to D-alanine. (B)</p> Signup and view all the answers

    How do teichoic acids influence bacterial behavior?

    <p>They induce septic shock by activating immune pathways. (A)</p> Signup and view all the answers

    What distinguishes endotoxins from exotoxins in bacterial cell walls?

    <p>Endotoxins are part of the cell wall while exotoxins are not. (D)</p> Signup and view all the answers

    Which characteristic is true regarding the cell wall of gram-negative bacteria?

    <p>It has a bilayered membrane with distinct inner and outer layers. (D)</p> Signup and view all the answers

    What happens when beta-lactam antibiotics bind to transpeptidases?

    <p>They irreversibly inhibit the formation of cross-links in peptidoglycan. (D)</p> Signup and view all the answers

    What is a major medical implication of lipopolysaccharides (LPS) in gram-negative bacteria?

    <p>They induce a strong immune response that can lead to shock. (D)</p> Signup and view all the answers

    In terms of structure, what is a key component of teichoic acids found in gram-positive bacteria?

    <p>They consist of polymers of ribitol phosphate or glycerol phosphate. (A)</p> Signup and view all the answers

    Which of the following best describes the role of carboxypeptidases?

    <p>They are involved in the final stages of peptidoglycan synthesis. (C)</p> Signup and view all the answers

    Study Notes

    Bacterial Structure

    • Bacteria are classified by shape into three groups: cocci, bacilli, and spirochetes
    • Cocci are round, bacilli are rod-shaped, spirochetes are spiral-shaped
    • Some bacteria have variable shapes and are called pleomorphic
    • Bacterial morphology includes cocci in clusters (e.g., Staphylococcus), chains (e.g., Streptococcus), pairs, pairs with pointed ends, and pairs with kidney bean shapes
    • Rods (bacilli) can have diverse shapes, including square ends, rounded ends, club-shaped, fusiform, and comma-shaped
    • Spirochetes are relaxed or tightly coiled

    Learning Objectives

    • Students should define typical bacteria, including morphology (appearance), cell wall structure (peptidoglycans), and the cell wall in gram-positive and gram-negative bacteria.
    • Students should also learn about the cell membrane, mesosomes, ribosomes, and genetic material.
    • Specialized structures outside the cell wall include: capsules, pili (fimbriae), flagella, and glycocalyx (slime layer).

    Bacterial Cell Wall

    • The cell wall is the outermost component common to all bacteria (except Mycoplasma)
    • It is composed of an inner layer of peptidoglycan and an outer membrane; the thickness varies based on the bacterial type
    • Peptidoglycan provides structural support and maintains the shape of the cell
    • Peptidoglycan (also called murein or mucopeptide) is only found in bacterial walls
    • It provides rigid support to the cell and maintains its shape
    • Peptidoglycan's structure includes glycan chains connected by peptide bonds. Repeating sugars (N-acetylmuramic acid (NAM) and N-acetyl glucosamine (NAGA)) are connected by a beta 1, 4-glycoside bond
    • The bonds are the target region of lysozyme.
    • Gram-positive cell walls are thicker (50-80% of dry weight), while gram-negative walls are thinner (5-10% of dry weight). Thicker walls result in increased strength
    • Gram-positive cells have a thick peptidoglycan layer with glycan chains strengthened by teichoic acid

    Gram-Negative Cell Wall

    • Gram-negative cell walls are composed of an outer membrane, a thin peptidoglycan layer, and a periplasmic space
    • The outer membrane contains lipopolysaccharide (LPS)
    • Porins are proteins in the outer membrane that serve as channels for substances
    • LPS is an important somatic (O antigen)

    Bacterial Cytoplasmic Membrane

    • Found just inside the peptidoglycan layer
    • Composed of a phospholipid bilayer similar to eukaryotic cells (except Mycoplasma)
    • Maintains the cell's shape, maintains selective permeability, site for metabolic enzymes, transport of molecules
    • Functions include active transport of molecules into the cell, energy generation through oxidative phosphorylation, synthesis of precursors for cell wall components, and secretion of enzymes and toxins

    Mesosome

    • Invagination of the cytoplasmic membrane
    • Important during cell division where it functions as the origin of transverse septum that splits the cell
    • Acts as the binding site for DNA, becoming genetic material for daughter cells

    Cytoplasm

    • The cytoplasm has two distinct areas: a matrix containing ribosomes, nutrient granules, metabolites, and plasmids; and a nucleoid region made up of DNA
    • The DNA in prokaryotes is a single, circular molecule (compared to human DNA, which consists of approximately 100,000 genes)

    ribosomes

    • Bacterial ribosomes are 70S in size, (with 50S and 30S subunits) which gives them different properties from eukaryotic ribosomes (80S with 60S and 40S subunits)
    • Site of protein synthesis
    • Differences in the ribosomes' composition are the basis of the selective action of several antibiotics

    Granules

    • The cytoplasm has granules that serve as storage areas for nutrients They usually stain characteristically with dyes.

    Nucleoid

    • The nucleoid is the area where DNA is located in the cytoplasm
    • Prokaryotic DNA is a single, circular molecule
    • Contains approximately 2000 genes

    Plasmids

    • Small, extrachromosomal, double-stranded, circular DNA molecules.
    • Can replicate independently of the bacterial chromosome
    • Can integrate into the bacterial chromosome
    • Found in gram-positive and gram-negative bacteria
    • Various types can exist in a single cell
    • Transmissible plasmids can be transferred from cell to cell
    • Non-transmissible plasmids are small (MW 3-20 million), do not contain transfer genes, and are present in many copies

    Transposons(jumping genes)

    • Pieces of DNA that readily move within or between bacterial DNA, plasmids, or bacteriophages.
    • Can code for drug-resistant enzymes, toxins, or metabolic enzymes
    • Not capable of independent replication

    Specialized Structures Outside the Cell Wall

    • Capsule
    • Flagella
    • Pili/Fimbriae
    • Glycocalyx (slime layer)

    Capsule

    • Gelatinous layer surrounding the entire bacterium (with few exceptions)
    • Composed mainly of polysaccharide, but can also be polymerized D-glutamic acid in some species
    • Variation in sugar components of the polysaccharide differentiates bacterial species
    • Capsule aids in bacterial virulence (resistance to phagocytosis). It helps with identification (e.g., quellung reaction)
    • Capsular polysaccharides are components of vaccines

    Flagella

    • Long, whip-like appendages aiding in chemotaxis, moving bacteria toward nutrients or away from harmful substances
    • Vary in structure and location. Some have one at an end, others have numerous, covering the entire outer surface
    • Some bacteria don't have flagella
    • Spirochetes use the axial filament for motility.

    Pili/Fimbriae

    • Hairlike, short, and straighter than flagella
    • Mainly present in gram-negative bacteria
    • Important in attachment to surfaces and in conjugation

    Glycocalyx (Slime Layer)

    • Polysaccharide coating that surrounds some bacteria, like a film
    • Helps bacteria adhere to various surfaces like skin, heart valves, and catheters
    • Plays a role in the formation of plaque (the precursor to dental caries)

    Spores

    • Highly resistant structures formed in response to adverse conditions by certain gram-positive rods (Bacillus and Clostridium species)
    • Contains bacterial DNA, reduced cytoplasm, cell membrane, peptidoglycan/outer coat
    • Significantly reduces water content
    • Contributes to bacterial resistance.

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    Bacterial Structure PDF

    Description

    This quiz covers the classification and structure of bacteria, focusing on their various shapes: cocci, bacilli, and spirochetes. Students will learn about bacterial morphology, cell wall structure, and specialized structures such as capsules and flagella. Test your knowledge on these essential aspects of microbiology!

    More Like This

    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser