Bacterial Cell Structure and Function
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Questions and Answers

Which of the following characteristics distinguishes plasmids from the nucleoid genome in bacteria?

  • Plasmids are composed of flagellin protein.
  • Plasmids often carry genes that contribute to virulence or antibiotic resistance. (correct)
  • Plasmids always carry genes essential for bacterial survival.
  • Plasmids are typically larger in size.

A bacterial capsule is considered a virulence factor because it impairs the ability of bacteria to cause disease.

False (B)

How does the presence of water within a bacterial capsule contribute to the bacterium's survival?

It protects against desiccation.

Bacteria that possess flagella distributed all over their cell surface are described as having a ___________ arrangement.

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

Match the type of bacterial flagellar arrangement with its correct description:

<p>Monotrichous = Single flagellum at one pole Lophotrichous = Tuft of flagella at one or both poles Amphitrichous = Single flagellum at both poles Peritrichous = Flagella distributed over the entire cell surface</p> Signup and view all the answers

What is the primary differentiating factor between Gram-positive and Gram-negative bacteria?

<p>The structure and composition of their cell walls (D)</p> Signup and view all the answers

Teichoic acids are a characteristic component of Gram-negative bacterial cell walls.

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

What is the primary function of the bacterial cell wall in relation to osmotic pressure?

<p>Counteracting the effects of osmotic pressure</p> Signup and view all the answers

The outer membrane of Gram-negative bacteria contains a significant amount of ______, which contributes to its structural integrity.

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

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

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

Match the component to the cell type:

<p>Thick peptidoglycan layer = Gram-positive bacteria Lipopolysaccharides (LPS) = Gram-negative bacteria Teichoic acids = Gram-positive bacteria Outer membrane = Gram-negative bacteria</p> Signup and view all the answers

What cellular structure is the site of protein synthesis in bacterial cells and is sensitive to antibiotics like streptomycin?

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

Plasmids are essential for bacterial survival under all environmental conditions.

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

Which of the following bacterial arrangements describes cocci in a cluster formation?

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

All cells, including bacteria, protozoa and fungi, have a well-defined nucleus.

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

What is the primary function of the bacterial cell membrane?

<p>Acts as a permeability barrier</p> Signup and view all the answers

The cell wall of bacteria primarily consists of a substance called ________.

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

Match the following bacterial shapes with their descriptions:

<p>Coccus = Spherical Bacillus = Rod-shaped Vibrio = Curved Spirillum = Spiral-shaped</p> Signup and view all the answers

If a microbiologist is examining a bacterium under a microscope and observes flagella, what can they infer about the bacterium?

<p>It is capable of movement. (C)</p> Signup and view all the answers

Which of the following best describes the bacterial cell envelope?

<p>All structures external to and enclosing the cytoplasm. (B)</p> Signup and view all the answers

What two monosaccharides make up peptidoglycan?

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

What is the primary function of an endospore in bacteria?

<p>Providing a protective structure that allows survival during harsh conditions. (A)</p> Signup and view all the answers

Viral capsids are composed of diverse types of proteins arranged asymmetrically to maximize variability in host cell recognition.

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

Describe two key functions of viral capsids.

<p>packaging and protecting nucleic acid, host cell recognition and genomic material delivery</p> Signup and view all the answers

A _ is a hardened mass of mycelium that generally serves as an overwintering stage for fungi.

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

Match the fungal structure with its description:

<p>Hyphae = Tube-like strands that make up the body of a fungus Mycelium = An aggregate of hyphae Sclerotium = Hardened mass of mycelium for overwintering</p> Signup and view all the answers

What is the correct sequence of steps when using a light microscope?

<p>Place the slide, start with the lowest magnification, adjust the light, then increase magnification gradually. (D)</p> Signup and view all the answers

After adding oil to a slide when using a microscope, it is acceptable to return to lower magnification powers without cleaning the objective lens.

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

In a light microscope, which lens initially magnifies the image of the specimen?

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

What is the primary reason Gram-positive bacteria retain the crystal violet-iodine complex during Gram staining?

<p>They have a thick peptidoglycan layer that resists decolorization. (B)</p> Signup and view all the answers

Gram-negative bacteria appear blue to purple after Gram staining due to their thick peptidoglycan layer retaining the crystal violet stain.

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

What decolorizing agent is typically used in the Gram staining procedure to differentiate between Gram-positive and Gram-negative bacteria?

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

In acid-fast staining, acid-fast bacteria resist ______ by acid once stained.

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

Match the following bacteria with their Gram stain reaction and morphology:

<p>Gram-positive cocci = Purple/blue spherical cells Gram-negative rods = Pink/red rod-shaped cells</p> Signup and view all the answers

What happens if you use the coarse adjustment knob on a microscope with high magnification?

<p>The slide will likely break. (C)</p> Signup and view all the answers

If a microscope has an ocular lens of 10x and an objective lens of 60x, what is the total magnification?

<p>600x (A)</p> Signup and view all the answers

Microbial staining is unnecessary when using a light microscope because microbial cytoplasm is easily visible.

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

Which of the following is NOT a purpose of microbial staining?

<p>To make the cytoplasm transparent (C)</p> Signup and view all the answers

In ___________ staining, only one dye is used to stain a microorganism.

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

Which type of dye carries a positive electrical charge and is used in direct staining methods?

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

Why do acidic dyes not stain bacterial cells in an indirect staining method?

<p>Acidic dyes are repelled by the negative charge on bacterial cell surfaces. (A)</p> Signup and view all the answers

What is the purpose of a counterstain in differential staining?

<p>To stain unstained cells after the primary stain is applied. (C)</p> Signup and view all the answers

Flashcards

Eukaryotic Cells

Cells with a well-defined nucleus.

Prokaryotic Cells

Cells lacking a nucleus.

Coccus Bacteria

Spherical-shaped bacteria.

Bacillus Bacteria

Rod-shaped bacteria.

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Streptococcus

Chain arrangement of coccus bacteria.

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Staphylococcus

Cluster arrangement of coccus bacteria.

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Cell Envelope

The outer layer enclosing the cytoplasm, including the cell wall and membrane.

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Cytoplasmic Membrane

A structure composed of a lipid bilayer that regulates what enters and exits the cell.

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Bacterial Cell Walls

Bacterial cell walls are mainly Gram-positive or Gram-negative, determined by Gram staining.

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Cell Wall Functions

Provides shape, resists osmotic pressure, facilitates gas/water movement, anchors appendages, aids cell division, and contains antigenic sites.

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Gram-Positive Cell Wall

Thick peptidoglycan layer that retains crystal violet dye during Gram staining.

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Teichoic Acids

Polysaccharides found in Gram-positive cell walls, including teichoic and lipoteichoic acids.

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Gram-Negative Cell Wall

A thin peptidoglycan layer with an outer membrane of lipids, lipoproteins, and lipopolysaccharide (LPS).

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Lipopolysaccharide (LPS)

Outer membrane component of Gram-negative bacteria contributing to structural integrity.

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Cytoplasm

Water-based substance with proteins, nucleic acids, lipids, enzymes, and solutes.

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Plasmids

Small, circular, self-replicating DNA outside the nucleoid, often carrying advantageous genes.

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Capsule (Glycocalyx)

A sharply defined, organized layer, usually polysaccharide-based, that protects bacteria and enhances its ability to cause disease.

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Flagella

Long, helical filaments composed of flagellin that enable bacteria to move in a directed manner; also highly antigenic.

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Monotrichous

Having a single flagellum.

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Pili

Attachment structures shorter and thinner than flagella, promoting specific cell-to-cell contact.

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Gram Stain

A staining technique that differentiates bacteria based on their cell wall structure. Gram-positive bacteria stain purple/blue, while Gram-negative bacteria stain pink/red.

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Gram-Positive Bacteria

Bacteria with a thick peptidoglycan layer in their cell wall, which retains the crystal violet stain during Gram staining, resulting in a purple/blue appearance.

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Gram-Negative Bacteria

Bacteria with a thin peptidoglycan layer in their cell wall, which does not retain the crystal violet stain during Gram staining, but stains pink/red with safranin.

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Acid-Fast Stain

A differential staining method used to identify bacteria with mycolic acid in their cell walls, such as Mycobacterium. Acid-fast bacteria resist decolorization by acid after staining.

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Non-Acid-Fast Bacteria

Bacteria that do not retain the primary stain after acid decolorization in the acid-fast staining procedure.

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High Magnification Knob

Use the fine adjustment knob on high magnification to prevent breaking the slide.

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Total Magnification

Multiply the ocular lens magnification by the objective lens magnification.

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Ocular Lens Magnification

Ocular lenses typically magnify by 10x.

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Microbial Staining

To visualize microorganisms, since their cytoplasm is transparent.

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Simple Staining

A staining technique using only one dye to observe basic microbial structures.

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Direct Staining

Uses basic dyes with positive charges to directly stain cells.

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Indirect Staining

Uses acidic dyes with negative charges that don't stain cells due to charge repulsion.

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Differential Stains

Uses two types of dyes to differentiate between different groups of bacteria, such as Gram-positive and Gram-negative.

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Endospore

A thick-coated, resistant structure formed by some bacteria, containing bacterial DNA.

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Capsid

A virus's protective outer shell made of protein subunits.

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Capsid Function

Packaging/protecting nucleic acid, host cell recognition, and genomic material delivery.

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Fungal Body Forms

Unicellular, filamentous (hyphae), or multicellular; mycelium is an aggregate of hyphae.

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Sclerotium

Hardened mass of mycelium that generally serves as an overwintering stage.

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Mycelium

Aggregate of hyphae

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Microscope Lenses

Objective lens gathers light/magnifies; ocular lens magnifies image further.

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Microscopy Procedure

Low to high magnification; focus at each step; don't go back after adding oil.

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Study Notes

  • Lecture is about Microbial Structure and Microscopy.
  • The lecture aims to provide knowledge on bacterial shapes, arrangements, structures, and their functions.
  • The lecture will cover the differences between Gram-positive and Gram-negative bacteria.
  • The lecture will focus on differences between bacterial, viral, and fungal structures.
  • In the lecture, how to use a light microscope will be explained.
  • Microbial staining types will be mentioned.

Introduction

  • The cellular world is divided into two major groups based on the presence of a nucleus.
  • Eukaryotic cells have a well-defined nucleus.
  • Prokaryotic cells lack a nucleus.
  • Bacteria are prokaryotes.
  • Fungi and protozoa are eukaryotes.

Bacterial Structure & Arrangements

  • Coccus: Spherical shape; can form chains (Streptococcus) or clusters (Staphylococcus).
  • Bacillus: Rod shape; can form chains (Streptobacillus).
  • Coccobacillus: An oval shape, between coccus and bacillus.
  • Vibrio: Curved shape.
  • Spirillum: Spiral shape.
  • Spirochete: Flexible, spiral shape.

Essential Structures

  • Cell Wall: Provides structure and protection.
  • Cell Membrane: Regulates passage of substances in and out of the cell.
  • Cytoplasm: Gel-like substance inside the cell containing various structures.
  • Nuclear Material: Includes DNA, which carries genetic information.

Particular Structures

  • Capsule: Provides protection and aids in attachment.
  • Flagella: Facilitates movement.
  • Pili: Involved in attachment and genetic exchange.
  • Spores: Dormant structures that allow survival in harsh conditions.

Cell Envelope

  • It consists of all the material external to, and enclosing the cytoplasm of a bacterial cell.
  • It consists of the cell wall, and the cytoplasmic membrane.
  • Capsules and pili are also included in the cell envelope when present.

Cytoplasmic Membrane

  • Also known as the cell membrane.
  • It is composed of phospholipids arranged in a lipid bilayer.
  • It is flexible and easily ruptured.
  • It acts as a permeability barrier, controlling the entry and exit of molecules.

Cell Wall

  • It's primary structure is peptidoglycan, a repeating sugar molecule.
  • Key components include: N-acetyl glucosamine (NAG) and N-acetyl muramic acid (NAM).
  • Meshwork held together by small peptide chains, forming inter-bridge structures.
  • Two main types exist: Gram-positive and Gram-negative, differentiated by Gram staining characteristics.

Functions of the Cell Wall

  • It provides flexibility and maintains cell shape and rigidity.
  • It counters the effects of osmotic pressure.
  • It facilitates the movement of gases and water in and out of cells.
  • Rigid platform for surface appendages (flagella and pili).
  • Cell division (binary fission) is also helped by the cell wall.
  • Major antigenic determinants on the cell surface are also contained.
  • It has antibiotic resistance.

Gram-Positive Bacteria Cell Wall

  • Has a thick peptidoglycan layer.
  • 90% of the cell wall consists of peptidoglycan, retaining crystal violet dye during Gram staining.
  • Composed of polysaccharides, including teichoic acid and lipoteichoic acid.

Gram-Negative Bacteria Cell Wall

  • Has a thin peptidoglycan layer surrounded by an outer membrane.
  • The outer membrane is composed of lipids, lipoproteins, and lipopolysaccharide (LPS).
  • Contains no teichoic acids.
  • The outer membrane is composed of lipopolysaccharides.
  • The Periplasmic space differs from gram-positive cells, containing many enzymes.

Gram-Positive vs. Gram-Negative Bacteria

  • Peptidoglycan Layer: Thick in Gram-positive, thin in Gram-negative.
  • Teichoic Acid: Present in Gram-positive, absent in Gram-negative.
  • Lipids: Very little in Gram-positive, lipopolysaccharide layer in Gram-negative.
  • Outer Membrane: Absent in Gram-positive, present in Gram-negative.
  • Toxins: Exotoxins in Gram-positive, endotoxins in Gram-negative.
  • Antibiotic Sensitivity: Very sensitive in Gram-positive, moderately sensitive in Gram-negative.

Cytoplasm

  • It is composed largely of water, proteins, nucleic acids, lipid enzymes, coenzymes, and organic as well as inorganic solutes, with small amounts of sugars and salts.
  • Ribosomes occur in copious amounts, range from 15-20nm in diameter with 70S; distributed throughout the cytoplasm.
  • Streptomycin and erythromycin are sensitive ribosomes, the site of protein synthesis.

Nuclear Material

  • It is concentrated in a region called the nucleoid within the cytoplasm.
  • This region has no membrane-bound nucleus.
  • Double strand DNA is located within a specialized region of the cytoplasm.
  • Plasmids are small, circular, self-replicating loops of DNA.
  • Plasmids carry the infection-causing gene (Virulence factor).
  • Plasmids provide antibiotic resistance.

Capsule (Glycocalyx)

  • Sharply defined structures that exist around the cell surface.
  • Well-organized layers that doesn't wash off easily.
  • Usually made up of polysaccharides.
  • It is a virulence factor that enhances the ability of bacteria to cause disease.
  • Protects bacteria from desiccation.

Appendages

  • Hair-like parts projecting from the cell wall.
  • Flagella are long, semi-rigid, and helical.
  • Hollow tubular made of protein flagellin.
  • Bacteria move in a directed way through their function,.
  • They are antigenic.
  • Cells may have one or many flagella.
  • Monotrichous flagella has one flagella.
  • Lophotrichous flagella have a tuft at one end.
  • Amphitrichous flagella have on both ends.
  • Peritrichous flagella are all around.
  • Pili are shorter and thinner than flagella.
  • Attachment structures that promote specific cell to cell contact via their function.
  • The bacterial cell and the host eukaryotic cell, or between one bacterial cell and another via attachment.

Endospores

  • Thick-coated, resistant structure,
  • Contains bacterial DNA.
  • Harsh conditions can destroy most of the cell, however the endospore may survive,
  • When favorable conditions return, they give rise to new bacterial cells.

Viral Structure

  • Size varies from 17 nm to 3000 nm in diameter.
  • The basic shape is either rod-like or spherical.
  • The protective shell, or capsid, is made of many identical protein subunits and can be symmetrically organized.
  • The viral genome can be either DNA or RNA, single-stranded or double-stranded.
  • Virus capsids aid in packaging and protecting nucleic acid
  • Virus capsids has role in Host cell recognition
  • Virus capsids delives Genomic material

Fungal Structure

  • Body form can be Unicellular, filamentous (tube-like strands called hyphae).
  • Mycelium = aggregate of hyphae.
  • Sclerotium = hardened mass of mycelium, serves as a stage through winter.
  • Multicellular, mycelial cords, rhizomorphs, and fruit bodies/mushrooms.

Microscopy

  • The body tube of ocular and objective lens focuses the image.
  • The objective (bottom) convex lens magnifies and focuses (bends) the image inside the body tube.
  • The ocular convex (top) lens of a microscope magnifies it again.
  • To use a microscope, put the the slide on a stage and secure by the lock clips.
  • Start with the the lowest magnification power (x4, x10, x40, x100 (with oil).
  • Adjust light source.
  • Don't move to the next magnification power if you can't focus on the previous one.
  • Don't return to the lower magnification power if oil is added.
  • Don't use the coarse adjustment knob on high magnification.
  • To focus a sample, use the fine adjustment.
  • The ocular lens us multiplied with the the objective lens,
  • for example if the ocular is 10x and the objective is 40x the magnification power is 400x.

Microscopy

Microbial Staining

  • It is transparent which it is necessary to stain microorganisms before viewing them using light microscope
  • To study different parts of microbes (Bacteria & Fungi), use different staining techniques.
  • Differential staining (e.g., Gram stain) is the most common, for Classification of Microorganisms.
  • Classification of Microorganisms facilitates successful diagnosis so the cause of infection is determined.
  • Stains are categorized into Simple Staining or Differential Staining
  • Simple Staining Technique employs only one dye (stain).
  • Direct Staining Method uses basic dyes (stains) that carry +ve electrical charges (e.g: crystal violet, safranin, Methylene Blue, malachite green,...etc.
  • Indirect Staining method uses acidic dyes (carrying -ve charges) which do not stain the bacterial cells due to repulsion (e.g,. nigrosin).
  • Differential Stainings includes using 2 types of dyes (stains).
  • In Differential Stainings the first stain is principal stain and the second one is counter stain to stain unstained cells (e.g. Gram and acid fast staining technique).
  • used Differential stains differentiats two different bacteria ( gram-positive or gram-negative) in a sample.

Gram Stain

  • Hans Christian Gram, a Danish physician, developed the Gram stain procedure in 1882, this is done to differentiate between gram positive and gram negative organisms
  • The differentiation is based on cell wall makeup.
  • Exploits the basic differences in the outer layers of bacteria so that other bacterial groups can keep initial stain, losing the dye during the process of decolorization.
  • Bacterial cells that lose color during the step of decolorization will keep the color of the counterstain.
  • gram-positive cells will appear blue/purple while gram-negative cells will apear pink/red.
  • Gram-positive has a very thick peptidoglycan cell wall (a layer of sugars and amino acids) that is able to withhold crystal violet-iodine during staining, while Gram-negative cells have a thin a thin peptidoglycan cell wall.
  • Gram positive cells do not decolorize with a short burst of ethanol.
  • After ethanol, gram negative cells accept counter stain safranin.

Other Differential Staining Methods

  • Acid-fast stain, clinical application to detect members of the Mycobacterium.
  • M. tuberculosis, the etiologic agent of tuberculosis, is the most common pathogen of this group.
  • The Nocardia can be identified by it's acid-fast characteristic.
  • The term acid-fast is derived from the resistance displayed by acid-fast bacteria to decolorization by acid once they have been stained by another dye.

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Description

Explore bacterial cell structures: plasmids vs. nucleoid genome, capsule virulence, flagellar arrangements. Differentiate Gram-positive and Gram-negative bacteria based on cell wall composition and teichoic acids. Understand the role of the cell wall in osmotic pressure regulation.

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