أسئلة الثانية ميكرو دمياط (قبل التعديل)
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Questions and Answers

What is one function of the bacterial cell wall?

  • Conducts cellular respiration
  • Transports nutrients
  • Provides structure and shape (correct)
  • Stores genetic information

Which component is NOT found in prokaryotic cells?

  • Ribosomes
  • Cytoskeleton
  • Plasmid
  • Nuclear membrane (correct)

What happens to bacteria when they face unfavorable conditions like starvation?

  • They increase metabolic activity
  • They undergo mitosis
  • They enter a dormant phase
  • They form endospores (correct)

What type of DNA do prokaryotic cells primarily contain?

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

Which of the following statements is true regarding metachromatic granules?

<p>They represent stored nutrients (D)</p> Signup and view all the answers

What is the primary component of the bacterial cell wall?

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

Which structure is responsible for the motility of bacteria?

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

What defines a monomorphic bacterium?

<p>It has a single, consistent shape. (D)</p> Signup and view all the answers

What role does lipopolysaccharide (LPS) play in Gram-negative bacteria?

<p>It acts as an endotoxin. (A)</p> Signup and view all the answers

Which of the following structures is found in all bacteria except Mycoplasma species?

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

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

<p>They provide structural support. (B)</p> Signup and view all the answers

What happens to bacteria that lose their cell walls?

<p>They transform into L forms and can still divide. (D)</p> Signup and view all the answers

What is the main characteristic of acid-fast bacteria during staining?

<p>They stain pink. (A)</p> Signup and view all the answers

What is referred to as the glycocalyx when it is firmly attached to the cell wall?

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

What is the primary function of the flagella in bacteria?

<p>Movement towards nutrients (A)</p> Signup and view all the answers

Which component of bacterial ribosomes is not present in eukaryotic ribosomes?

<p>70S ribosome structure (C)</p> Signup and view all the answers

What structure protects bacterial cells from phagocytosis?

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

Which of the following is a characteristic of Gram-negative bacteria?

<p>Presence of pilin (D)</p> Signup and view all the answers

What role does the slime layer play in bacterial adhesion?

<p>Promotes attachment to surfaces (D)</p> Signup and view all the answers

Which of the following describes the composition of the bacterial plasma membrane?

<p>Phospholipid bilayer and proteins (C)</p> Signup and view all the answers

What is the size of bacterial ribosomes?

<p>70S (D)</p> Signup and view all the answers

What characteristic distinguishes Gram-positive bacteria from Gram-negative bacteria?

<p>Presence of a thicker peptidoglycan layer (C)</p> Signup and view all the answers

Which of the following accurately describes the cytoskeleton in prokaryotic cells?

<p>Play a role in maintaining cell shape and division (A)</p> Signup and view all the answers

Which nutrient reserves can be found in bacterial inclusions?

<p>Carbohydrates like glycogen (C)</p> Signup and view all the answers

What is the significance of metachromatic granules in certain bacteria?

<p>They serve as energy reserves, particularly phosphates (D)</p> Signup and view all the answers

Under which conditions do certain bacteria form endospores?

<p>When faced with unfavorable environmental conditions (C)</p> Signup and view all the answers

What type of glycocalyx structure is loosely attached to the bacterial cell wall?

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

Which of the following components is NOT involved in the composition of bacterial ribosomes?

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

What term describes the layer that protects bacteria from phagocytosis?

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

Which structure in bacteria serves as the primary site of protein synthesis?

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

What characteristic distinguishes the flagella of Gram-negative bacteria?

<p>More numerous than in Gram-positive (C)</p> Signup and view all the answers

Which type of antigen is associated with the glycocalyx of bacteria?

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

What distinguishes Mycoplasma from other bacteria regarding cell membrane components?

<p>Presence of sterols (B)</p> Signup and view all the answers

Which of these structures is essential for bacterial motility?

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

What is the function of lipopolysaccharide (LPS) in the bacterial cell wall?

<p>Serves as an endotoxin and triggers immune responses (B)</p> Signup and view all the answers

Which of the following is NOT a feature of the bacterial cell wall?

<p>Composed entirely of phospholipids (D)</p> Signup and view all the answers

What distinguishes monomorphic bacteria from pleomorphic bacteria?

<p>Monomorphic bacteria have a consistent shape (D)</p> Signup and view all the answers

Which structure is crucial for the bacterial cell to maintain its shape?

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

What is the immediate consequence for bacteria that lose their cell wall?

<p>They swell into irregular shapes (C)</p> Signup and view all the answers

What role do fimbriae/pili play in bacterial physiology?

<p>Aiding in adherence to surfaces (C)</p> Signup and view all the answers

Which of the following components is responsible for the Gram staining reaction?

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

Flashcards

Medical Microbiology

The scientific study of microbes and their interactions with hosts, leading to infectious diseases.

Cocci

Round-shaped bacteria.

Rod-shaped Bacilli

Bacteria with a rod-like shape, may have tapered ends like cigars or resemble cocci.

Spiral Bacteria

Bacteria with one or more twists in their shape.

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Monomorphic Bacteria

Bacteria that maintain a single, consistent shape.

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Pleomorphic Bacteria

Bacteria that exhibit multiple shapes.

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Glycocalyx

A sticky, sugary outer layer that surrounds some bacteria, protecting them and helping them attach to surfaces.

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Fimbriae/Pili

Tiny hair-like structures on the surface of bacteria, used for attachment and sometimes for transferring genetic material.

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Osmotic lysis

The bursting of a bacterial cell due to rapid water influx, causing it to swell and rupture.

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Capsule

A tightly bound glycocalyx firmly attached to the cell wall, offering protection against phagocytosis.

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Slime layer

A loosely bound glycocalyx attached to the cell wall, providing protection and adhesion.

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Flagella

Long, helical, tubular structures composed of flagellin protein, used for bacterial movement.

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Pili

Short, numerous, thinner structures than flagella, used for bacterial attachment.

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Plasma membrane

A thin, flexible membrane inside the cell wall, responsible for controlling the passage of molecules in and out of the cell.

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Ribosomes

Tiny organelles involved in protein synthesis, composed of two subunits (30S and 50S).

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What is the function of peptidoglycan?

Peptidoglycan is a unique structural component found in bacterial cell walls. It provides structural support, helps maintain the shape of the cell, and serves as a target for certain antibiotics.

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Gram-Positive vs. Gram-Negative

Gram-positive bacteria have a thick layer of peptidoglycan in their cell wall, while Gram-negative bacteria have a thinner layer and an outer membrane.

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What is an endotoxin?

Endotoxin is part of the outer membrane of Gram-negative bacteria, specifically Lipopolysaccharide (LPS). It is released when the bacteria die, causing harmful effects in the host.

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What are protoplasts?

Protoplasts are bacteria that have lost their cell wall, usually due to the action of lysozyme. They are typically formed from Gram-positive bacteria.

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What are spheroplasts?

Spheroplasts are bacteria that have lost most of their cell wall, usually due to the action of lysozyme. They are typically formed from Gram-negative bacteria.

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What are L forms?

L forms are bacteria that can survive and replicate without a complete cell wall. They are often resistant to antibiotics that target the cell wall.

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What are acid-fast bacteria?

Acid-fast bacteria have a waxy outer layer called mycolic acid that makes them resistant to staining with traditional methods. They require special staining techniques to be visualized.

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What are Mycoplasma?

Mycoplasma are bacteria that lack a cell wall and are therefore resistant to antibiotics that target cell wall synthesis.

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What is the difference between Gram-positive and Gram-negative bacteria?

The key difference lies in the structure of their cell wall. Gram-positive bacteria have a thick peptidoglycan layer, while Gram-negative bacteria have a thinner peptidoglycan layer with an outer membrane.

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Name 3 functions of the cell wall.

The cell wall provides structural support, maintains cell shape, and protects the cell from osmotic lysis (bursting).

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What are metachromatic granules?

These are granules found in some bacteria that stain red with methylene blue dye. They primarily consist of inorganic phosphate (PO4) and represent stored nutrients.

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What is a nucleoid?

The nucleoid is the region in a bacterial cell where the single, circular DNA molecule is located. It's not enclosed by a membrane like a nucleus in eukaryotic cells.

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What are endospores?

Endospores are highly resistant structures formed by some bacteria under unfavorable conditions. They can survive harsh environments and germinate into new bacterial cells when conditions improve.

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What does osmotic lysis do to bacteria?

Osmotic lysis causes bacteria to swell and burst due to rapid water uptake into the cell.

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How does a capsule protect bacteria?

A capsule is a tightly bound glycocalyx that protects bacteria from phagocytosis, a process where immune cells engulf and destroy bacteria.

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What's the role of the flagella?

Flagella are long, helical structures used for bacterial movement, propelling them towards nutrients and favorable environments.

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What are pili used for?

Pili are short, numerous, and thinner structures, used for bacterial attachment to surfaces and sometimes for transferring genetic material.

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What's the function of the plasma membrane?

The plasma membrane is a thin, flexible layer that controls the passage of molecules in and out of bacterial cells, ensuring only necessary nutrients enter and waste products exit.

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What are ribosomes responsible for?

Ribosomes are tiny organelles within bacteria responsible for protein synthesis, the process of making proteins essential for various cell functions.

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What is the function of the cell wall?

The cell wall is a rigid outer layer that provides structural support and protection to bacterial cells, maintaining their shape and preventing bursting.

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What is the glycocalyx composed of and what are its functions?

The glycocalyx is a sticky layer composed of polysaccharides and proteins that provides protection from engulfment by immune cells and helps in the adhesion of bacteria to surfaces.

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Study Notes

Bacterial Cell Structure

  • Medical microbiology studies microbes and their interactions with hosts, leading to infectious diseases.
  • Cocci: Round-shaped bacteria. Bacilli are rod-shaped, which may have tapered ends. Coccobacilli are short rod-shaped. Spirals have one or more twists.
  • Shape and arrangement: Cocci, coccobacilli, vibrio, bacilli, spirillum, and spirochete are examples of bacterial shapes.
  • Size: Bacteria range in size from 0.2 to 5 micrometers (μm).
  • Monomorphic: Have a single shape.
  • Pleomorphic: Have various shapes.
  • Light and electron microscopes are used in microbiology to view bacteria.
  • Examples of bacterial shapes include coccus, coccobacillus, vibrio, bacillus, spirillum, and spirochete.

Bacterial Cell Structures (External)

  • Glycocalyx: Gelatinous layer of polysaccharide or polypeptide.
    • Capsule: Firmly attached to the cell wall, protects the bacteria from phagocytosis, aids in attachment to surfaces.
    • Slime layer: Loosely attached, aids in attachment to surfaces.
    • Protects bacteria from phagocytosis. Involves bacterial adhesion to surfaces.
  • Flagella: Long helical structures composed of flagellin, anchored by a basal body, move the bacteria towards nutrients.
  • Fimbriae/pili: Hair-like appendages formed of pilin. They are more numerous, shorter, and thinner than flagella. They promote attachment.

Bacterial Cell Structures (Internal)

  • Cell wall: Located outside the cytoplasmic membrane, composed of peptidoglycan (in nearly all bacteria, except Mycoplasma). Peptidoglycan is composed of N-acetylglucosamine and N-acetylmuramic acid.
    • Provides support and rigidity to the cell.
  • Cytoplasmic membrane: Thin, elastic membrane below the cell wall; composed of phospholipids and proteins. Functions in semipermeability, energy production (ATP), and biosynthesis.
  • Cytoplasm: Semi-transparent substance within the membrane; contains nucleoid, ribosomes, and inclusions. 
  • Nucleoid: Region containing a single, circular DNA molecule (no nucleus).
  • Ribosomes: Structures for protein synthesis (70S ribosomes). Made up of large and small subunits (50S and 30S).
  • Inclusions: Stored nutrients like protein, lipids, or glycogen, visible under a microscope.

Gram-Positive and Gram-Negative Cell Walls

  • Gram-positive: Thick peptidoglycan layer, with teichoic acids outside.
  • Gram-negative: Thinner peptidoglycan layer; have an outer membrane containing lipopolysaccharide (LPS). This layer contains lipoprotein and phospholipids. The periplasmic space is between the outer membrane and the peptidoglycan layer. It contains enzymes like beta-lactamases.

Atypical Cell Walls

  • Acid-fast bacteria: Resist staining by Gram stain, retain a dye (e.g., carbol fuchsin) under acid wash.
  • Cell wall deficient bacteria:
    • Mycoplasma: Lacks a cell wall.
    • L-forms: Bacteria that lose their cell walls and swell, forming irregular shapes. 
    • Protoplasts and spheroplasts:  Gram-positive and Gram-negative cells with a cell wall removed.

Bacterial Spores

  • Some bacteria form endospores in unfavorable conditions (starvation, desiccation, heat).
  • Genus Clostridium and Bacillus.
  • Spores are highly resistant to environmental stress.
  • Spores germinate into active bacterial cells upon exposure to nutrients.

Cell Wall Function

  • Structural support: Maintains the shape of the bacterium.
  • Toxicity: Lipopolysaccharide (LPS) acts as an endotoxin.
  • Antigenic: Cell wall components act as antigens.
  • Gram staining reaction: Determined by cell wall structure.

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