Bacterial Shapes and Structures
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Questions and Answers

What are the three basic shapes of bacteria?

  • Cocci, bacilli, spirochetes (correct)
  • Spirilla, bacilli, filamentous
  • Cocci, spirilla, vibrio
  • Bacilli, vibrio, cocci

    • Which of the following is NOT a type of cocci morphology?

  • Neisseria
  • Staphylococcus
  • Salmonella (correct)
  • Streptococcus

    • What structural component provides rigidity and maintains the shape of bacterial cells?

  • Cell membrane
  • Capsule
  • Cytoplasm
  • Peptidoglycan (correct)

    • What unique characteristic distinguishes gram-negative bacteria from gram-positive bacteria?

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

    Which type of bacterial structure is primarily involved in adhesion and locomotion?

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

    What is a defining feature of pleomorphic bacteria?

    <p>Variable shapes</p> Signup and view all the answers

    Which of the following terms refers specifically to the outermost component of bacteria, excluding Mycoplasma?

    <p>Cell wall</p> Signup and view all the answers

    What is the primary function of the peptidoglycan layer in bacterial cells?

    <p>Providing rigid support</p> Signup and view all the answers

    What constitutes the majority of dry weight in the cell wall of Gram positive bacteria?

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

    Which of the following is a characteristic feature of Gram negative bacterial cell walls?

    <p>Presence of an outer membrane</p> Signup and view all the answers

    What are the two main components of the glycan chains in the peptidoglycan layer?

    <p>N-acetyl-muramic acid and N-acetyl-glucosamine</p> Signup and view all the answers

    How do lysozymes aid in bacterial cell wall degradation?

    <p>By cleaving glycosyl bonds</p> Signup and view all the answers

    What is the primary function of teichoic acids in Gram positive bacteria?

    <p>Cell wall rigidity</p> Signup and view all the answers

    What percentage of the dry weight in Gram negative bacterial cell walls is accounted for by peptidoglycan?

    <p>5-10%</p> Signup and view all the answers

    What role does hyaluronidase play in the bacterial context?

    <p>It degrades host tissues</p> Signup and view all the answers

    Which enzyme is notably active against Gram positive bacteria and is found in human secretions?

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

    What is the primary role of penicillin binding proteins (PBPs)?

    <p>Bind to beta-lactam antibiotics</p> Signup and view all the answers

    Which of the following best describes how beta-lactam antibiotics affect transpeptidase?

    <p>They irreversibly bind to the active site</p> Signup and view all the answers

    What consequence occurs when penicillin binds to transpeptidases?

    <p>Cell wall synthesis is inhibited</p> Signup and view all the answers

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

    <p>Induce septic shock and mediate attachment</p> Signup and view all the answers

    Which of the following correctly describes the composition of the outer membrane in gram-negative bacteria?

    <p>Rich in lipopolysaccharides</p> Signup and view all the answers

    What is the significance of lipopolysaccharides (LPS) in gram-negative bacteria?

    <p>They act as endotoxins causing symptoms of disease</p> Signup and view all the answers

    What mechanism is common between teichoic acids in gram-positive bacteria and lipopolysaccharides in gram-negative bacteria?

    <p>Both induce septic shock</p> Signup and view all the answers

    How does the structure of the cell wall in gram-negative bacteria differ from gram-positive bacteria?

    <p>Gram-negative bacteria possess a bilayered membrane</p> Signup and view all the answers

    What component is the anthrax bacillus capsule primarily made of?

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

    How do the sugar components of polysaccharide capsules affect bacteria?

    <p>They determine the serologic type.</p> Signup and view all the answers

    Which mechanism does the capsule use to limit phagocyte activity?

    <p>Disguising the bacteria as self</p> Signup and view all the answers

    Which of the following bacterial structures is associated with chemotaxis?

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

    What type of bacteria predominantly possesses flagella?

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

    What role do flagella play in urinary tract infections caused by certain bacteria?

    <p>Propelling bacteria up the urethra</p> Signup and view all the answers

    What unique feature do spirochetes use for movement?

    <p>Flagellum-like structure</p> Signup and view all the answers

    What specific reaction indicates the presence of a capsular polysaccharide in bacteria?

    <p>Quellung reaction</p> Signup and view all the answers

    What is the primary function of mesosomes during cell division?

    <p>To serve as the origin of the transverse septum</p> Signup and view all the answers

    Which of the following correctly describes bacterial ribosomes?

    <p>They consist of 50S and 30S subunits</p> Signup and view all the answers

    What is a key characteristic of the nucleoid in prokaryotic cells?

    <p>It has no histones associated with the DNA</p> Signup and view all the answers

    What role do plasmids play in bacteria?

    <p>They replicate independently of the bacterial chromosome</p> Signup and view all the answers

    Which component is NOT typically found in the cytoplasm of prokaryotic cells?

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

    What distinguishes bacterial DNA from eukaryotic DNA?

    <p>Bacterial DNA is a single circular molecule</p> Signup and view all the answers

    How do antibiotics selectively target bacterial protein synthesis?

    <p>Due to differences in ribosomal size and composition</p> Signup and view all the answers

    What type of genetic material is primarily stored in ribosomes during protein synthesis?

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

    What is the primary function of pili in bacteria?

    <p>Mediating attachment to human cell receptors</p> Signup and view all the answers

    Which genus of bacteria is known for forming spores in response to nutrient depletion?

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

    What specific role does the glycocalyx play in bacterial adhesion?

    <p>It allows bacteria to adhere to surfaces like skin and teeth</p> Signup and view all the answers

    What type of pilus is involved in the conjugation process between donor and recipient bacteria?

    <p>Sex pilus</p> Signup and view all the answers

    What can be inferred about Neisseria gonorrhoeae mutants that lack pili?

    <p>They are considered nonpathogens</p> Signup and view all the answers

    What is a distinguishing feature of the spores formed by Bacillus and Clostridium?

    <p>They have a thick, keratin-like coat</p> Signup and view all the answers

    Which of the following best describes the structure of the glycocalyx?

    <p>It is a polysaccharide coating</p> Signup and view all the answers

    What triggers the process of spore formation (sporulation) in certain bacteria?

    <p>Depletion of nutrients such as carbon and nitrogen</p> Signup and view all the answers

    Study Notes

    Bacterial Structure

    • Bacteria are categorized by shape into cocci (round), bacilli (rod-shaped), and spirochetes (spiral-shaped).
    • Some bacteria can change shape, described as pleomorphic.
    • Cocci can form clusters, chains, pairs, or pairs with pointed ends.
    • Rods can have square, rounded, club, fusiform, or comma shapes.
    • Spirochetes can be relaxed or tightly coiled.

    Learning Objectives

    • Students should be able to define typical bacteria.
    • Bacteria possess morphology with typical appearances.
    • Cell wall structure, including peptidoglycans, is a key component.
    • Gram-positive and gram-negative bacteria have distinct cell wall structures.
    • Cell membranes, mesosomes, ribosomes, and genetic material are components of bacteria.
    • Specialized structures (capsule, pili, flagella, glycocalyx) are outside the cell wall.

    Structure of Bacterial Cells

    • Peptidoglycan is a rigid structural component of bacterial cell walls.
    • Peptidoglycan is composed of glycan chains and peptide bonds.
    • It provides shape and prevents lysis from osmotic pressure.
    • In gram-positive bacteria, peptidoglycan forms a thick layer.
    • In gram-negative bacteria, peptidoglycan forms a thinner layer.

    Bacterial Morphology

    • Gram-positive cocci come in clusters (e.g., Staphylococcus) and chains (e.g., Streptococcus).
    • Gram-positive rods include Bacillus and Salmonella.
    • Gram-negative rods include Vibrio and Fusobacterium.
    • Spirochetes, such as Borrelia, have relaxed or tightly coiled shapes.

    Bacterial Cell Wall

    • Cell walls are the outermost component of most bacteria, with exceptions like Mycoplasma.
    • They are a rigid structure made up of peptidoglycans.
    • Gram-positive cell walls have a thicker peptidoglycan layer compared to gram-negative.
    • The cell wall is composed of an inner layer of peptidoglycan and an outer membrane, with varying thickness and composition depending on the bacterial type.

    Peptidoglycan

    • Also known as murein or mucopeptide, it is found only in bacterial cell walls.
    • It is crucial in maintaining the bacteria's shape.
    • Peptidoglycan is constructed of glycan chains bound together by peptide bonds.
    • N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG) form the repeating sugars, connected by a beta 1,4 glycoside bond.
    • Lysozyme, an enzyme found in human secretions, targets these bonds.

    Cell Wall Differences in Gram-Positive and Gram-Negative Bacteria

    • Gram-positive walls are thicker, stronger, contain teichoic acids, and have a high peptidoglycan content.
    • Gram-negative walls are thinner, contain lipopolysaccharide (LPS), and have a lower peptidoglycan content.

    Cytoplasmic Membrane

    • The cytoplasmic membrane is composed of a phospholipid bilayer.
    • It contains hopanoids, similar to eukaryotic sterols, but not all bacteria.
    • It's important for functions like transporting molecules into and out of the cell, generating energy, synthesizing cell wall precursors, and secreting enzymes and toxins.

    Mesosome

    • Invaginations of the cytoplasmic membrane.
    • Important during bacterial cell division.
    • They help divide DNA and form cross-walls.

    Cytoplasm

    • Divided into an amorphous matrix and a nucleoid region.
    • The matrix contains ribosomes, nutrients, metabolites, and plasmids.
    • The nucleoid region houses the bacterial DNA.

    Ribosomes

    • Sites of protein synthesis.
    • Differ from eukaryotic ribosomes in size with 70S bacterial ribosomes compared to 80S in eukaryotes.
    • Contain 50S and 30S subunits.
    • Antibiotics that target bacterial ribosomes can inhibit protein synthesis.

    Granules

    • Storage areas within the cytoplasm.
    • Contain nutrients and stain with various dyes.

    Nucleoid

    • Area of cytoplasm where bacterial DNA is located.
    • DNA is a single circular molecule with approximately 2,000 genes.
    • Unlike eukaryotic DNA, lacks a nuclear membrane, nucleolus, mitotic spindle, and histones.
    • Bacterial DNA has no introns.

    Plasmids

    • Extra-chromosomal double stranded circular DNA.
    • Replicate independently of the bacterial chromosome.
    • Some plasmids can integrate into the bacterial chromosomes.
    • Common in both gram-positive and gram-negative bacteria.
    • Types include transmissible plasmids for conjugation, and non-transmissible plasmids.

    Transmissible Plasmids

    • Can be transferred between bacteria via conjugation.
    • Relatively large with several genes encoding sex pilus and transfer mechanisms.
    • Typically present in a few copies per cell.

    Non-transmissible Plasmids

    • Small and lack conjugation transfer genes.
    • Usually present in multiple copies (10–60) per cell.
    • Often carry genes for antibiotic resistance, heavy metal resistance, toxins, and other beneficial traits for the bacteria.

    Transposons (Jumping Genes)

    • Pieces of DNA that move easily within or between bacterial genomes, plasmids, and bacteriophages.
    • Often carry genes coding for drug resistance, toxins, and other metabolic enzymes.
    • Not capable of independent replication.

    Specialized Structures Outside the Cell Wall

    • Capsule: Gel-like outer layer, aiding in bacterial attachment and masking antigens from host immune systems.
    • Flagella: Whip-like appendages, permitting chemotaxis which is movement towards or away from stimuli.
    • Pili/Fimbriae: Hair-like structures which facilitate attachment to surfaces.
    • Glycocalyx/Slime Layer: Polysaccharide layer covering surfaces enabling adhesion.

    Spores

    • Highly resistant structures formed by Bacillus and Clostridium in response to adverse conditions.
    • Contain the bacterial DNA, cytoplasm, and a protective outer layer.
    • Formed due to exhaustion of nutrients.
    • Resistant to harsh environmental factors.

    Endospores

    • Dormant, resistant forms of some bacteria.
    • Location (Central, Terminal, Subterminal)
    • High resistance to heat, chemicals, and radiation.

    Endo/Exotoxins

    • Endotoxins are part of the gram-negative outer membrane and induce toxic responses.
    • Exotoxins are proteins secreted by bacteria and cause a variety of effects.

    Lipopolysaccharide (LPS)

    • Component of Gram-negative outer membranes.
    • Known as endotoxin due to its link to toxic responses in the body.
    • Has three distinct parts: lipid A (toxic portion), core polysaccharide, and O-antigen (variable portion).

    Porin Proteins

    • Protein channels in the outer membrane of Gram-negative bacteria.
    • Allow passage of various molecules.

    Acid-Fast and Associated Cell Walls

    • Mycobacteria have thick cell walls rich in lipids (Waxy substances) containing mycolic acid.
    • Cell walls resist gram staining and decolorization, leading to the term "acid-fast".

    L-form Bacteria

    • Lack the rigid structure of the cell wall.
    • Formed when exposed to antibiotics or lysozyme.

    Teichoic Acid

    • Found in gram-positive cell walls in the peptidoglycan layer.
    • Helps with cell wall maintenance.
    • Plays a role in septic shock, bacterial attachment, and virulence mechanisms.

    Important Note

    • Differences exist between the ribosomes of bacteria and humans which is the basis for antibiotics that target protein synthesis in bacteria but not in humans.

    Cell Structure summary

    • The diagram of the cell wall shows the layers are different for Gram (+) and Gram (-) bacteria.
    • Essential components are the components that a bacteria ALWAYS use.
    • Non-essential components are the components that one type of bacteria have, but not the other type.

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    Bacterial Structure PDF

    Description

    Test your knowledge on the basic shapes of bacteria and their structural components. This quiz covers topics such as cocci morphology, rigidity, gram-positive vs gram-negative differentiation, and bacterial locomotion. Perfect for students of microbiology or anyone interested in bacterial characteristics.

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