أسئلة ريتين الثانية ميكرو دمياط (قبل التعديل)
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Questions and Answers

What structure in bacteria is primarily responsible for energy production in the form of ATP?

The plasma membrane is responsible for energy production via ATP synthesis.

Identify two types of stored nutrients found in bacterial cells.

Stored nutrients in bacterial cells may include glycogen and lipids.

What are the roles of the cytoskeleton in bacterial cells?

The cytoskeleton helps in cell division and maintaining cell shape.

What occurs when bacteria encounter unfavorable conditions, such as starvation or heat?

<p>Bacteria can form endospores under unfavorable conditions.</p> Signup and view all the answers

List three functions of the bacterial cell wall.

<p>The bacterial cell wall provides shape, protects against osmotic pressure, and serves as a barrier to certain substances.</p> Signup and view all the answers

What is the difference between a capsule and a slime layer in bacterial cells?

<p>A capsule is firmly attached to the cell wall, while a slime layer is loosely attached.</p> Signup and view all the answers

What role does the glycocalyx play in bacteria?

<p>The glycocalyx protects bacterial cells from phagocytosis and aids in adherence to human tissues.</p> Signup and view all the answers

What is the composition of bacterial ribosomes, and why are they significant?

<p>Bacterial ribosomes are composed of two subunits: a small 30S and a large 50S, which are essential for protein synthesis.</p> Signup and view all the answers

Describe the primary function of the plasma membrane in bacterial cells.

<p>The plasma membrane regulates the passage of certain molecules and ions, allowing some to enter while blocking others.</p> Signup and view all the answers

What is the significance of H antigens in bacteria?

<p>H antigens are used in serodiagnosis and play a role in the identification of bacterial strains.</p> Signup and view all the answers

How do antibiotics that cause osmotic lysis affect bacterial cells?

<p>These antibiotics allow water to enter the bacterial cells rapidly, leading to cell enlargement and rupture.</p> Signup and view all the answers

What are the main components of the bacterial cell wall?

<p>The bacterial cell wall is primarily composed of a polysaccharide layer, which can include peptidoglycan.</p> Signup and view all the answers

What are the functions of sex pili in bacteria?

<p>Sex pili facilitate attachment between bacterial cells and can enable the transfer of genetic material.</p> Signup and view all the answers

What are the key differences between Gram-positive and Gram-negative bacteria regarding their cell wall structure?

<p>Gram-positive bacteria have a thick multilayered peptidoglycan cell wall, while Gram-negative bacteria have a thinner single-layered peptidoglycan and outer membrane.</p> Signup and view all the answers

What role does peptidoglycan play in bacterial cells?

<p>Peptidoglycan provides structural support, maintains the shape of the cell, and serves as a target for certain antibiotics.</p> Signup and view all the answers

Describe the characteristics of cocci and bacilli bacteria.

<p>Cocci are round-shaped bacteria, while bacilli are rod-shaped, which can vary in appearance, including tapered ends or being oval (coccobacilli).</p> Signup and view all the answers

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

<p>LPS serves as an endotoxin, contributes to the bacterial cell's toxicity, and plays a role in the Gram staining reaction.</p> Signup and view all the answers

Explain the concept of monomorphic and pleomorphic bacteria.

<p>Monomorphic bacteria maintain a single shape, while pleomorphic bacteria can exhibit multiple shapes.</p> Signup and view all the answers

What is the function of flagella in bacterial cells?

<p>Flagella facilitate movement by acting as a propeller, allowing bacteria to swim towards favorable environments.</p> Signup and view all the answers

What is the difference between protoplasts and spheroplasts?

<p>Protoplasts are formed from Gram-positive bacteria that lose their cell walls, while spheroplasts are from Gram-negative bacteria that retain their outer membrane.</p> Signup and view all the answers

How do lysozyme and the presence of L-forms relate to bacterial cell walls?

<p>Lysozyme can damage bacterial cell walls, leading to the formation of L-forms, which are wall-less bacteria that can still replicate.</p> Signup and view all the answers

What type of bacteria are known for forming endospores in response to unfavorable conditions?

<p>Genus Clostridium and Genus Bacillus.</p> Signup and view all the answers

What structures are contained within bacterial cells that help with cell division and maintaining shape?

<p>The cytoskeleton, which consists of a series of fibers.</p> Signup and view all the answers

What is the main characteristic that separates Gram-positive bacteria from Gram-negative bacteria?

<p>The composition of their cell wall.</p> Signup and view all the answers

What cellular structure in bacteria contains nucleoid and ribosomes but lacks a true nucleus?

<p>The cytoplasm.</p> Signup and view all the answers

What is the purpose of the metachromatic granules found in certain bacterial cells?

<p>They serve as storage for nutrients, particularly polyphosphate.</p> Signup and view all the answers

What is the role of the glycocalyx in bacterial adhesion to human tissues?

<p>The glycocalyx facilitates adherence by promoting attachment between bacterial cells and human tissues.</p> Signup and view all the answers

How do flagella contribute to bacterial motility?

<p>Flagella move bacteria toward nutrients and attractants through a mechanism called chemotaxis.</p> Signup and view all the answers

Describe the composition of bacterial ribosomes and their significance in protein synthesis.

<p>Bacterial ribosomes consist of a small 30S subunit and a large 50S subunit, made of rRNA and proteins, playing a vital role in translating mRNA into proteins.</p> Signup and view all the answers

What distinguishes an encapsulated bacterium from a non-encapsulated one, particularly in relation to phagocytosis?

<p>Encapsulated bacteria have a protective layer that helps them evade phagocytosis, unlike non-encapsulated ones which are more susceptible to immune response.</p> Signup and view all the answers

Explain the function and composition of the plasma membrane in bacterial cells.

<p>The plasma membrane is a phospholipid bilayer with proteins that regulates the passage of molecules and ions, ensuring semipermeability.</p> Signup and view all the answers

What is the significance of antigenic properties such as K and H antigens in bacteria?

<p>K antigens, associated with the glycocalyx, are important for serodiagnosis and vaccine preparation, while H antigens help in bacterial identification based on flagellar structure.</p> Signup and view all the answers

How does the structure of the bacterial cell wall contribute to its function?

<p>The bacterial cell wall provides structural support and protection, maintaining cell shape and integrity against osmotic pressure.</p> Signup and view all the answers

What are the unique features of Mycoplasma that differentiate them from other bacteria regarding their plasma membrane?

<p>Mycoplasma lack sterols in their plasma membrane, differentiating them from other bacteria that typically possess these components.</p> Signup and view all the answers

What defines acid-fast bacteria, and how do they stain compared to non-acid-fast bacteria?

<p>Acid-fast bacteria stain pink due to mycolic acid in their cell walls, while non-acid-fast bacteria stain purple.</p> Signup and view all the answers

How does the structure of Gram-positive bacteria differ from that of Gram-negative bacteria regarding peptidoglycan?

<p>Gram-positive bacteria have a thick multilayer of peptidoglycan, while Gram-negative bacteria have a thinner single layer sandwiched between outer and cytoplasmic membranes.</p> Signup and view all the answers

What role do teichoic acids play in the structure of Gram-positive bacteria?

<p>Teichoic acids provide structural support and are antigenic, protruding from the peptidoglycan layer.</p> Signup and view all the answers

Explain the consequences of lysozyme's action on bacterial cells.

<p>Lysozyme breaks down peptidoglycan, leading to the formation of protoplasts in Gram-positive bacteria and spheroplasts in Gram-negative bacteria.</p> Signup and view all the answers

What are the primary components of lipopolysaccharides (LPS) in Gram-negative bacteria, and why are they significant?

<p>LPS consists of lipid A (toxic component) and O-polysaccharide, and they are significant for their role as endotoxins and in inducing immune responses.</p> Signup and view all the answers

Describe the implications of bacterial size variability, particularly in the context of pathogenicity.

<p>Bacteria range in size from 0.2 to 5 μm, and smaller sizes may enhance their ability to invade host cells, impacting pathogenicity.</p> Signup and view all the answers

What distinguishes monomorphic bacteria from pleomorphic bacteria?

<p>Monomorphic bacteria maintain a single shape, while pleomorphic bacteria can adopt multiple shapes under varying conditions.</p> Signup and view all the answers

How does the presence of a glycocalyx influence bacterial virulence?

<p>The glycocalyx aids in adherence to surfaces and evasion of the host immune response, thus enhancing bacterial virulence.</p> Signup and view all the answers

Flashcards

Medical Microbiology

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

Cocci

Round-shaped bacteria.

Rod-shaped Bacilli

Rod-shaped bacteria. May have tapered ends like cigars or be oval, resembling cocci.

Spiral Bacteria

Bacteria with one or more twists in their shape.

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Monomorphic Bacteria

Bacteria that maintain a single, defined shape.

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Pleomorphic Bacteria

Bacteria that exhibit multiple shapes.

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Cell Wall

A tough outer layer present in all bacteria except Mycoplasma species.

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Peptidoglycan

A complex molecule composed of sugar units (N-acetylglucosamine and N-acetylmuramic acid), found in both Gram-positive and Gram-negative bacteria.

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Gram-positive vs. Gram-negative

A difference in the chemical composition of the cell wall, leading to differing staining reactions with Gram staining.

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Nucleoid

The genetic material of bacteria, circular double-stranded DNA, located in the cytoplasm.

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Plasmid

Small, circular DNA molecules that replicate independently of the bacterial chromosome, often carrying genes for resistance to antibiotics.

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Endospore

A dormant, resistant structure formed by some bacteria under unfavorable conditions, highly resistant to heat, radiation, and chemicals.

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Glycocalyx

A sticky layer that surrounds some bacteria, composed of sugars and proteins. It can be tightly attached (capsule) or loosely attached (slime layer).

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Cell Membrane (Plasma Membrane)

A flexible membrane that lies just beneath the cell wall. It's made of a phospholipid bilayer and proteins. It controls what goes in and out of the cell.

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Osmotic Lysis

The process by which water rushes into a bacterial cell, causing it to swell and burst. This happens when the cell is exposed to certain antibiotics.

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Flagella

Long, whip-like structures that help bacteria move. They are made of a protein called flagellin.

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Pili

Short, hair-like structures that help bacteria attach to surfaces, including host cells.

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Ribosomes

The site of protein synthesis in bacteria. It's made up of two subunits: a small subunit (30S) and a large subunit (50S).

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Pilin

A structural component of bacteria, mainly found in Gram-negative bacteria. It's a helical tube made of pilin protein, which is a type of protein.

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Chemotaxis

The process by which bacteria move towards a food source or other attractants.

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What are bacterial inclusions?

A storage form of nutrients within bacteria, including proteins, lipids, and glycogen.

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What is the nucleoid in a bacterial cell?

A distinct, dense region within the cytoplasm of bacteria, containing a single, circular chromosome of DNA. It's essentially the bacteria's genetic control center.

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What are plasmids in bacteria?

Small, circular DNA molecules found in bacterial cells, separate from the main chromosome. These often carry genes that provide resistance to antibiotics or other advantages.

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What are endospores in bacteria?

A protective, dormant structure formed by certain bacteria under stressful conditions, like starvation or heat. They are highly resistant to harsh environments.

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What is the function of the cell wall in a bacterium?

A thick, rigid outer layer surrounding the cell membrane of bacteria. It provides structural support and protection, and its composition determines whether the bacterium is Gram-positive or Gram-negative.

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What is the glycocalyx?

A sticky layer that surrounds some bacteria, composed of sugars and proteins. It can be tightly attached (capsule) or loosely attached (slime layer).

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What is chemotaxis?

The process by which bacteria move towards food sources or other attractants.

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What are pili?

Short, hair-like structures that help bacteria attach to surfaces, including host cells. They are often made of a protein called pilin.

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What are flagella?

Long, whip-like structures that help bacteria move. They are made of a protein called flagellin.

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What is the cell membrane?

A thin, flexible membrane just inside the cell wall. It controls what goes in and out of the cell.

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What is osmotic lysis?

When a bacterial cell takes in too much water and bursts.

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What is the cell wall?

It's a tough outer layer present in most bacteria. It gives the bacteria its shape and protects it from the environment.

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What are cell wall-inhibiting antibiotics?

A type of antibiotic that targets the cell wall of bacteria, disrupting its structure and causing it to weaken.

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What is the cell wall of a bacterium?

A tough outer layer found in all bacteria except Mycoplasma species. It helps maintain the shape of the cell, provides structural support, and is a target for certain antibiotics.

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What is peptidoglycan?

A complex molecule made of sugar units (N-acetylglucosamine and N-acetylmuramic acid). It's found in both Gram-positive and Gram-negative bacteria.

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What is glycocalyx?

A sticky layer that surrounds some bacteria. It can be tightly attached (capsule) or loosely attached (slime layer). It helps bacteria evade the host's immune system.

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What is a Gram-Positive bacterium?

Bacteria with a thick, multilayered peptidoglycan layer and no outer membrane. They stain purple in a Gram stain.

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What is a Gram-Negative bacterium?

Bacteria with a thin, single-layered peptidoglycan layer and an outer membrane. They stain pink in a Gram stain.

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What is lipopolysaccharide (LPS)?

The substance found in the outer membrane of Gram-negative bacteria. It's toxic (endotoxin) and can cause fever and shock in humans.

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What is L-form formation?

The process by which bacteria lose their cell walls and swell into irregular shapes. This can occur when bacteria are exposed to certain antibiotics.

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What is a protoplast?

A bacterial cell that has lost its cell wall. They are highly susceptible to osmotic lysis.

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Study Notes

Bacterial Cell Structure

  • Medical microbiology studies microbes and their interactions with hosts, leading to infectious diseases.
  • Cocci are round.
  • Rod-shaped bacilli may have tapered ends, like cigars or be oval. Coccobacilli are cocci-shaped bacilli.
  • Spiral bacteria have one or more twists.
  • Bacteria have diverse shapes: Cocci, Coccobacilli, Vibrio, Bacillus, Spirillum, Spirochete.
  • Monomorphic bacteria have a single shape.
  • Pleomorphic bacteria have many shapes.
  • Bacterial sizes range from 0.2 to 5 micrometers (µm).
  • A micron (µm) is one-thousandth of a millimeter.

Bacterial Cell Shape and Arrangement

  • Diagrams displaying various arrangements of bacteria (diplococci, streptococci, tetrads, sarcinae, staphylococci, diplobacilli, streptobacilli, vibrio, spirillum, spirochete) are shown.
  • SEM (Scanning Electron Micrographs) images are also included showing different arrangements.

Structures External to the Cell Wall

  • Glycocalyx (capsule/slime layer) is a gelatinous polysaccharide or polypeptide layer surrounding the cell wall.
    • Capsule is firmly attached.
    • Slime layer is loosely attached.
    • Functions include protection from phagocytosis, antigenicity (K antigen), and adherence to surfaces.
  • Flagella are long helical structures made of protein flagellin. They anchor in the cell membranes. They are organs of motility, allowing bacteria to move towards nutrients and other attractants (chemotaxis). They are also antigenic (H antigen).
  • Fimbriae and pili help bacteria adhere to surfaces or other bacteria.

Structures Internal to the Cell Wall

  • Cytoplasm is a thick, transparent substance within the plasma membrane.
  • Nucleoid is the area containing the circular DNA.
  • Cytoplasmic membrane is a thin, elastic membrane beneath the cell wall; it is composed of phospholipids and proteins.
  • Ribosomes are the primary sites for protein synthesis (translation).
  • Inclusions are stored nutrients (proteins, lipids, glycogen), and include structures like metachromatic granules (in C. diphtheriae). These are observed using a methylene blue stain.

Cell Wall

  • The cell wall is external to the cytoplasmic membrane and provides support and rigidity to the cell. It's composed of peptidoglycan in all bacteria except Mycoplasma.
  • Peptidoglycan is composed of N-acetylglucosamine and N-acetylmuramic acid. It is found in both Gram-positive and Gram-negative bacteria.
  • Gram-positive bacteria have a thick peptidoglycan layer with teichoic acids located outside the layer.
  • Gram-negative bacteria have a thin peptidoglycan layer situated between the outer and cytoplasmic membranes. The outer membrane contains lipopolysaccharides (LPS, endotoxin), lipoproteins, and phospholipids. The periplasmic space is between the outer and cytoplasmic membranes. Enzymes like β-lactamases are present in this space.

Gram-Positive and Gram-Negative Cell Walls: Key Differences

  • Gram-positive cell walls (thick): teichoic acids are outside the peptidoglycan layer.
  • Gram-negative cell walls (thin): an outer membrane with lipopolysaccharides (LPS) and lipoproteins surrounds the peptidoglycan layer. Periplasmic space is between the outer and cell membranes.

Cell Wall Function

  • Supports and maintains cell shape.
  • Is involved in the gram staining reaction.
  • Responsible for bacterial toxicity due to LPS.
  • Serves as a target for many antibiotics.

Atypical Cell Walls

  • Acid-fast bacteria are resistant to some dyes due to a waxy lipid layer surrounding peptidoglycans.
  • Mycoplasmas lack cell walls and are resistant to antibiotics that target cell walls.
  • L-forms of some bacteria lose cell walls and maintain some functions.

Bacterial Endospores

  • Some bacteria form endospores during conditions like starvation, desiccation, and heat.
  • Endospores are extremely resistant structures.
  • Endospores function in survival and reproduction under harsh conditions.

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