Bacterial Cell Walls: Structure and Function
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Questions and Answers

Which component of the Gram-negative bacterial cell envelope is responsible for causing fever and potentially fatal endotoxic shock in humans?

  • Core polysaccharide
  • Cell membrane
  • Lipid A (correct)
  • Superoxide radicals

Mycoplasma can be classified as either gram-positive or gram-negative based on their thick cell wall.

False (B)

What is the primary structural difference that prevents Mycoplasma from being classified as either gram-positive or gram-negative?

lack of a cell wall

When molecular oxygen gains electrons, it can form byproducts like hydrogen peroxide, superoxide radicals, and a ______ radical.

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

Match each of the following radicals with their potential effects and/or bacterial defenses:

<p>Lipid A = Gram-negative endotoxin Superoxide radicals = Molecular oxygen byproduct Cell membrane fragments = Lysed bacterial cells</p> Signup and view all the answers

Which of the following components are covalently linked in Lipopolysaccharide (LPS)?

<p>O-specific side chain, Lipid A, and core oligosaccharide (A)</p> Signup and view all the answers

Mycobacteria are strongly gram-positive bacteria.

<p>False (B)</p> Signup and view all the answers

The bacterium Treponema pallidum belongs to the group of spiral-shaped organisms known as ________.

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

Which of the following pairs of Gram-positive rods are spore-forming?

<p>Bacillus and Clostridium (A)</p> Signup and view all the answers

What is the name of the group of gram-negative cocci that appear as diplococci?

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

Which of the following accurately describes the role of teichoic acid in Gram-positive bacteria?

<p>It provides structural support and rigidity to the cell wall. (B)</p> Signup and view all the answers

The outer lipopolysaccharide-containing cell membrane in Gram-negative bacteria facilitates the easy passage of antibiotics to the peptidoglycan layer.

<p>False (B)</p> Signup and view all the answers

What is the primary difference between the cytoplasmic membrane of bacteria and that of animal cells concerning sterols?

<p>Bacterial cytoplasmic membranes lack cholesterol or other sterols, unlike animal cells.</p> Signup and view all the answers

The enzyme also known as __________ interacts with substances that can pass through the cytoplasmic membrane.

<p>penicillin binding protein</p> Signup and view all the answers

Why is the presence of an outer membrane significant in Gram-negative bacteria regarding antibiotic resistance?

<p>It blocks the passage of antibiotics to the peptidoglycan layer. (C)</p> Signup and view all the answers

What is the function of charge regulation in bacteria?

<p>Maintaining the cell's negative surface charge. (C)</p> Signup and view all the answers

What is the space between the cytoplasmic membrane and the peptidoglycan layer in Gram-negative bacteria called?

<p>The periplasmic space. (A)</p> Signup and view all the answers

What is the arrangement of Streptococcus and Enterococcus?

<p>Strips of cocci. (C)</p> Signup and view all the answers

What structure protects a dormant bacterium from harsh environmental conditions?

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

What do antibiotics that target the peptidoglycan cell wall, such as penicillins, have difficulty doing?

<p>Passing through the cell’s outer structures (B)</p> Signup and view all the answers

What is the primary function of transpeptidase in bacteria?

<p>Catalyzing the cross-linking of amino-acid chains in peptidoglycan (A)</p> Signup and view all the answers

Which of the following describes the location of transpeptidase?

<p>Inner cytoplasmic membrane (D)</p> Signup and view all the answers

What is the first step in the Gram stain procedure?

<p>Pouring on crystal violet stain (C)</p> Signup and view all the answers

Which dye is used as a counter-stain in the Gram stain procedure?

<p>Safranin (B)</p> Signup and view all the answers

What is the function of the iodine solution in the Gram stain procedure?

<p>To act as a mordant and form a complex with crystal violet (B)</p> Signup and view all the answers

Which of the following is the decolorizing agent used in the gram-staining procedure?

<p>95% alcohol (C)</p> Signup and view all the answers

What energy source do phototrophs utilize?

<p>Light (B)</p> Signup and view all the answers

Medically important bacteria are classified as what, based on their carbon and energy sources?

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

What is the primary structural component of the bacterial cell wall?

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

Which antibiotic inhibits transpeptidase?

<p>Penicillin (B)</p> Signup and view all the answers

Which process is used by aerobic organisms to produce ATP?

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

What is the end product of glycolysis in fermentation?

<p>Pyruvic acid (A)</p> Signup and view all the answers

Which of the following pathways describes the Embden-Meyerhof pathway?

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

What is the function of the electron transport chain?

<p>Generates ATP. (C)</p> Signup and view all the answers

Which of the following use inorganic sources?

<p>Autotrophs (B)</p> Signup and view all the answers

Which of the following require a host cell to replicate?

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

What is one function of teichoic acid in Gram-positive bacteria?

<p>Providing structural support and stability to the cell wall. (A)</p> Signup and view all the answers

Which of the following is a characteristic of the bacterial cytoplasmic membrane, unlike that of animal cells?

<p>Absence of sterols like cholesterol. (D)</p> Signup and view all the answers

Why does the Gram-negative outer membrane provide antibiotic resistance?

<p>It blocks the passage of many substances, including antibiotics, to the peptidoglycan layer. (D)</p> Signup and view all the answers

What is another name for the enzyme which interacts with substances that can pass through the cytoplasmic membrane?

<p>Penicillin binding protein (A)</p> Signup and view all the answers

Which of the following is NOT a key function of teichoic acid?

<p>Aiding in cell division (B)</p> Signup and view all the answers

What is a primary function of the bacterial cytoplasmic membrane?

<p>Controlling the movement of substances into and out of the cell. (D)</p> Signup and view all the answers

What type of substances can pass through the cytoplasmic membrane?

<p>Antibiotics, dyes, and detergents (D)</p> Signup and view all the answers

Which component is present in Gram-positive cell walls but not in Gram-negative cell walls?

<p>Teichoic Acid (B)</p> Signup and view all the answers

What is the direct source of ATP for bacteria that are energy parasites?

<p>Host cells (B)</p> Signup and view all the answers

What happens to pyruvate following fermentation?

<p>Pyruvate is broken down into different end products (B)</p> Signup and view all the answers

What is the MOST accurate description of bacteria classified as energy parasites?

<p>They cannot survive without a host because they steal ATP. (C)</p> Signup and view all the answers

Which of the following is a potential end product of bacterial fermentation?

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

What allows energy parasite bacteria to steal ATP?

<p>A special cell membrane transport system (C)</p> Signup and view all the answers

Which ribosomal subunit does erythromycin target to inhibit protein synthesis?

<p>50S subunit (D)</p> Signup and view all the answers

What enzyme catalyzes the breakdown of hydrogen peroxide?

<p>Catalase (A)</p> Signup and view all the answers

What is the function of superoxide dismutase?

<p>Breaks down the superoxide radical (D)</p> Signup and view all the answers

Where are the axial flagella located in spirochetes?

<p>Along the spirochete under the outer membrane sheath. (A)</p> Signup and view all the answers

Which type of microscope is required to visualize spirochetes?

<p>Dark field microscope (C)</p> Signup and view all the answers

What is a key characteristic of aerotolerant anaerobes?

<p>They can grow in the presence or absence of oxygen. (B)</p> Signup and view all the answers

What cellular process does tetracycline affect?

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

Which of the following requires oxygen to survive?

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

Flashcards

Bacillus

Gram-positive, spore-forming rod-shaped bacteria.

Clostridium

Gram-positive, spore-forming anaerobic rod-shaped bacteria.

Corynebacterium

Gram-positive rods that do not form spores.

Listeria

Gram-positive rods that do not form spores; causes listeriosis.

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Mycobacteria

Weakly gram-positive bacteria identified using acid-fast stain.

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Bacterial Cytoplasmic Membrane Target

Enzyme targeted by some antibiotics, dyes, and detergents in bacteria; also known as penicillin binding protein.

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Gram-Negative Outer Membrane

The outer membrane in Gram-negative bacteria that blocks certain substances from reaching the peptidoglycan layer and cytoplasmic membrane.

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Teichoic Acid

A polysaccharide in Gram-positive cell walls providing rigidity and stability.

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Bacterial Membrane Composition

Unlike animal cells, bacterial cytoplasmic membranes lack cholesterol or other sterols.

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Structural Support (Teichoic Acid)

Provide rigidity and stability to the cell wall of gram-positive bacteria.

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Core Polysaccharide

Water-soluble component found in the central region of a structure.

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Lipid A

A disaccharide with multiple fatty acid tails located interior to the core polysaccharide. Known as the gram-negative endotoxin.

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Endotoxic (Septic) Shock

Severe reaction caused by the release of Lipid A into the circulation, leading to fever, diarrhea, and potential shock.

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Mycoplasma

Bacteria lacking a cell wall, thus not gram-positive or gram-negative.

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Superoxide Radicals, Hydrogen Peroxide and Hydroxyl Radical

Unstable molecules formed when oxygen gains electrons, damaging cells.

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Peptidoglycan Layer

The layer just outside the bacterial cytoplasmic membrane.

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Peptidoglycan Composition

Repeating disaccharides with 4 amino acids in a side chain.

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Amino Acids in Peptidoglycan

L-alanine, D-glutamic acid, meso-diaminopimelic acid (DAP) or L-lysine, and D-alanine.

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Transpeptidase

Catalyzes the formation of linkages between amino acid chains in peptidoglycan.

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Penicillin's Target

It binds to and inhibits transpeptidase.

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Gram Stain

A staining technique to differentiate bacteria based on cell wall structure.

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Gram Stain Steps

Crystal violet (blue dye), iodine solution, decolorization with 95% alcohol, and safranin (red dye).

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Gram-Positive Permeability

The gram-positive layer does not block diffusion of low molecular weight compounds.

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Periplasmic Space

A gel-filled space between the cytoplasmic membrane and the thin peptidoglycan layer in Gram-negative bacteria.

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Charge Regulation (Cell Wall)

Help maintain the cell's negative surface charge, important for cellular processes.

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Cell Division (Cell Wall)

Plays a role in cell growth and division for bacteria.

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Antigenicity (Cell Wall)

Can act as an antigen, stimulating the immune system to produce antibodies.

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Streptococcus and Enterococcus

Form strips of cocci.

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Lipopolysaccharide (LPS)

A component of the gram negative outer membrane; triggers strong immune responses.

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Phototrophs

Organisms that use light as their energy source.

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Chemotrophs

Organisms that use chemical compounds as their energy source.

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Autotrophs

The use of inorganic sources (ammonium and sulfide) as a carbon source.

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Heterotrophs

The use of organic carbon sources.

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Chemoheterotrophs

Bacteria that use chemical and organic compounds, such as glucose, for energy.

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Respiration

A metabolic process that includes glycolysis, the Krebs cycle, and the electron transport chain, coupled with oxidative phosphorylation, to produce ATP.

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Fermentation

A metabolic process (glycolysis) where glucose is broken down to pyruvic acid, yielding ATP directly.

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Embden-Meyerhof Pathway

The most common pathway for the breakdown of glucose to pyruvate.

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Erythromycin's Mechanism

Inhibits protein synthesis by binding to the 50S ribosomal subunit.

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Tetracycline's Mechanism

Inhibits protein synthesis by binding to the 30S ribosomal subunit.

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Catalase Function

Breaks down hydrogen peroxide into water and oxygen, neutralizing its toxicity.

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Peroxidase Function

Breaks down hydrogen peroxide, neutralizing its toxicity.

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Superoxide Dismutase

Breaks down the superoxide radical, a toxic free radical.

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Aerotolerant Anaerobes

Bacteria that can tolerate the presence of oxygen but do not use it for growth.

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Obligate Aerobes

Bacteria that require oxygen for growth.

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Spirochetes

Bacteria with a gram-negative-like cell wall and axial flagella running under the outer membrane, visualized using dark field microscopy.

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Energy Parasites

Parasitic bacteria that live inside a host cell, needing the host's ATP to survive.

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ATP Stealing System

A special system that parasitic bacteria use to transport and steal ATP from their host cells.

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ATP Synthesis Pathways

Metabolic routes for ATP synthesis studied in biochemistry that parasitic bacteria utilize, obtaining ATP from a host rather than producing it themselves.

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Bacterial Fermentation

Process in which pyruvate is not fully broken down. Different acids and alcohols produced can be used to classify bacteria.

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Fermentation End-Products

Examples are lactic acid, ethanol, propionic acid, butyric acid and acetone. These end products are made during fermentation and can be used to classify bacteria.

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Study Notes

  • Gram stain involves staining the bacterial sample with crystal violet (a blue dye) for 60 seconds, then flooding with iodine solution for 60 seconds, then "decolorizing" with 95% alcohol, followed by counterstaining with safranin (a red dye), and then rinsing off with water.
  • The skin and mucous membranes of the external genitalia have spirochetes, which are too small to be seen with a light microscope and must be visualized with a special dark field microscope.
  • An anaerobic growth media with no oxygen is used for blood cultures in hospital settings.
  • The bacteria Rickettsia causes Rocky Mountain Spotted Fever.
  • Chlamydia causes chlamydia infections.

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Description

The bacterial cytoplasmic membrane differs from animal cells, lacking cholesterol. The peptidoglycan layer, external to this membrane, is crucial in both Gram-positive and Gram-negative bacteria. Penicillin inhibits transpeptidase, vital for peptidoglycan synthesis.

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