Microbiology 101: Types of Microbes

Questions and Answers

What is the minimum number of subunits in an icosahedral capsid?

120

60 (correct)

Which of the following viral symmetries is characterized by a continuous cylinder surrounded by a lipid layer and complex proteinaceous core wall?

Complex (correct)

Icosahedral

Helical

Oblong

What is the function of the viral matrix protein in the viral envelope?

To determine the tropism of the virus

To mediate the interaction between the capsid and envelope (correct)

To attach to membrane proteins in the host cell

To transcribe the viral genome

Which of the following statements is true about enveloped viruses?

They often survive only transiently outside the host Signup and view all the answers

What is the term for the repeating units of protein that make up the helical capsid?

Capsomeres Signup and view all the answers

Which of the following viruses has an icosahedral capsid?

Adenovirus Signup and view all the answers

What is the term for the viral genome enclosed by the capsid protein coat?

Nucleocapsid Signup and view all the answers

What is the function of the HA protein in the influenza virion?

To attach to membrane proteins in the host cell Signup and view all the answers

Which bacterial structure is responsible for attachment and conjugation?

Pili Signup and view all the answers

Which of the following is NOT a characteristic of Gram-positive bacteria?

Presence of lipopolysaccharide (LPS) Signup and view all the answers

What is the primary function of the capsule in bacteria?

Resistance to phagocytosis Signup and view all the answers

Which staining technique is used to visualize Mycobacterium tuberculosis?

Ziehl-Neelsen (ZN) stain Signup and view all the answers

What is the primary role of plasmids in bacteria?

Carrying antibiotic resistance genes Signup and view all the answers

Which of the following bacteria cannot be visualized with the Gram stain?

Mycobacterium tuberculosis Signup and view all the answers

What is the main component of the bacterial capsule?

Polysaccharides Signup and view all the answers

Which of the following statements about spores is TRUE?

They are highly resistant to heat, chemicals, and drying. Signup and view all the answers

Which of the following is NOT a characteristic of Gram-negative bacteria?

Presence of teichoic acids Signup and view all the answers

What is the function of the mordant in the Gram stain?

Fix the dye to the bacterial cell wall Signup and view all the answers

What is the primary function of viral mRNA?

To express the viral proteins Signup and view all the answers

Which type of virus encodes many of the enzymes they need, such as DNA-dependent RNA polymerase?

Large viruses, e.g., pox-, herpes- Signup and view all the answers

What is a critical step in the viral replication process that involves the use of host cell machinery?

Translation of viral proteins Signup and view all the answers

What is the primary difference between large and small viruses in terms of gene expression and replication?

Small viruses use host cell enzymes, while large viruses encode their own enzymes Signup and view all the answers

What is the role of the viral genome structure in determining the route to produce viral mRNA?

It determines the route to produce viral mRNA Signup and view all the answers

What is the correct sequence of gene expression and replication?

DNA, mRNA, protein Signup and view all the answers

Which type of virus has a genome structure that involves the use of host or viral RNA polymerase to produce mRNA?

All of the above Signup and view all the answers

What is the correct description of the attachment step in viral replication?

The process by which the virus attaches to the host cell surface Signup and view all the answers

What is a key distinguishing characteristic of viruses compared to bacteria and fungi?

Require host cell machinery for replication Signup and view all the answers

Which group of microbes is characterized by having eukaryotic cells?

Fungi Signup and view all the answers

What is the typical generation time for macroparasites compared to microparasites?

Relatively long for macroparasites and short for microparasites Signup and view all the answers

What is the primary role of RNA-dependent RNA polymerase in RNA genomes?

To synthesize RNA using complementary RNA as template Signup and view all the answers

How are organisms classified in taxonomy?

Based on similar characteristics into related groups Signup and view all the answers

Which of the following accurately describes prions?

Protein-based infectious agents without nucleic acids Signup and view all the answers

In the context of retroviruses, what enzyme is responsible for converting +ve ssRNA into dsDNA?

Reverse transcriptase Signup and view all the answers

What characteristic is unique to bacteria in comparison to viruses and fungi?

Reproductive method of binary fission Signup and view all the answers

What characteristic distinguishes prion diseases from other infectious diseases?

They are caused by misfolded proteins Signup and view all the answers

Which microbial group has a flexible outer membrane?

Protozoa Signup and view all the answers

Which of the following is a common symptom of toxoplasmosis in most cases?

No symptoms typically Signup and view all the answers

Which of the following statements is true regarding ribosomes in different groups of microbes?

Fungi have 80S ribosomes Signup and view all the answers

What type of organism is Taenia solium, which is mentioned along with prion diseases?

Tapeworm Signup and view all the answers

How do macroparasites typically reproduce compared to microparasites?

They replicate outside the host releasing eggs or larvae Signup and view all the answers

Leishmaniasis primarily manifests in which form?

Cutaneous ulcers Signup and view all the answers

Which of the following correctly identifies the cellular structure of bacteria?

Prokaryotic cells with rigid cell walls Signup and view all the answers

Study Notes

Microbial Classification

Organisms that cause infectious diseases can be grouped into:
- Parasites: Helminths and Protozoa
- Fungi
- Bacteria
- Viruses
- Prions
Each group has distinctive characteristics that determine how they interact with hosts and cause disease, including:
- Structural and molecular make-up
- Biochemical and metabolic strategies
- Reproductive processes

Comparison of Microbes

Characteristics of microbes:
- Viruses:
  - No cells
  - DNA or RNA
  - No nucleus
  - No ribosomes
  - No membrane-bound organelles
  - Protein capsid
  - Require host cell machinery for replication
- Bacteria:
  - Cells
  - DNA and RNA
  - Prokaryotic nucleus
  - 70S ribosomes
  - No membrane-bound organelles
  - Rigid cell wall containing peptidoglycan
  - Binary fission replication
- Fungi:
  - Cells
  - DNA and RNA
  - Eukaryotic nucleus
  - 80S ribosomes
  - Membrane-bound organelles
  - Rigid cell wall containing chitin
  - Budding or mitosis replication
- Protozoa and Helminths:
  - Cells
  - DNA and RNA
  - Eukaryotic nucleus
  - 80S ribosomes
  - Membrane-bound organelles
  - Flexible membrane
  - Mitosis replication

Macroparasites vs Microparasites

Characteristics of macroparasites and microparasites:
- Macroparasites:
  - Big (naked eye)
  - Replicate outside host
  - Long generation time
  - Weak and short-lived immunity
- Microparasites:
  - Small (microscope)
  - Replicate within host
  - Short generation time
  - Immunity present

Structure of Bacteria

Cell wall:
- Gram-positive cell wall: thick peptidoglycan layer, no outer membrane, low lipid and lipoprotein content, teichoic and lipoteichoic acids present
- Gram-negative cell wall: thin peptidoglycan layer, outer membrane present, high lipid and lipoprotein content, lipopolysaccharide present
Other components:
- Capsule: gelatinous layer outside cell wall, composed of polysaccharides, determinant of virulence, used for identification and lab diagnosis
- Flagella: organ of motility, fixed number and location, plays a role in pathogenesis, used for identification and lab diagnosis
- Pili (fimbriae): hair-like filaments, attachment and conjugation functions
- Plasmids: extra-chromosomal genetic material, capable of self-replication, can contain antibiotic resistance genes
- Spores: highly resistant structures formed in response to adverse conditions, contain bacterial DNA surrounded by a thick keratin-like coat

Structure of Viruses

Components:
- Capsid: protein coat that surrounds the viral genome
- Genome: viral genetic material, can be DNA or RNA
- Envelope: lipid bilayer derived from the host cell membrane, contains viral glycoproteins
Types of symmetry:
- Icosahedral: 20 solid equilateral triangles arranged around the face of a sphere
- Helical: capsomeres bound in a periodic fashion to the viral genome
- Complex: neither purely helical nor purely icosahedral
Importance of viral surface proteins:
- Attach to membrane proteins (receptors) in host cell, determinants of tropism
- Targets for antibodies, determinants of antibody specificity (serotype)

Basic Steps of Viral Replication

Attachment
Entry
Uncoating
Production of viral proteins and replication of viral genome
Assembly
Release

Gene Expression and Replication

The principle: transcription and translation
The fact: viral protein synthesis is completely dependent on cellular translation machinery
Route to produce viral mRNA depends on genome structure of each virus
Examples:
- DNA genomes: large viruses encode many of the enzymes they need, small viruses use host cell enzymes
- RNA genomes: most examples encode their own RNA-dependent RNA polymerase
- Retroviruses: use reverse transcriptase to copy a +ve ssRNA genome into dsDNA

Prion Diseases

Group of fatal and infectious neurodegenerative diseases
Infectious agent propagates in the absence of nucleic acid
Infectious agent is a misfolded protein that alters folding of the normal host version of the protein

Parasites

Examples:
- Taenia solium (pork tapeworm)
- Schistosomiasis
- Malaria
- Toxoplasmosis
- Leishmaniasis

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Description

Learn about the classification of microbes and the characteristics that distinguish them. From parasites to viruses, understand how these microorganisms interact with their hosts and cause disease.