Microbiology: Bacteria & Viruses

What are the defining characteristics of prokaryotic cells?

Prokaryotic cells, like bacteria, lack a membrane-bound nucleus and other membrane-bound organelles. Their genetic material is located in a nucleoid region.

Describe the primary difference between Gram-positive and Gram-negative bacterial cell walls.

Gram-positive bacteria have a thick peptidoglycan layer and no outer membrane, while Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane containing lipopolysaccharides.

What is the main method of reproduction for bacteria?

Bacteria primarily reproduce asexually through binary fission, a process where one cell divides into two identical daughter cells.

Name three common bacterial shapes and provide an example for each.

Three common shapes are cocci (spherical, e.g., Staphylococcus), bacilli (rod-shaped, e.g., Escherichia coli), and spirilla (spiral, e.g., Treponema pallidum).

Explain the function of bacterial flagella and pili.

Flagella are whip-like appendages used for motility, enabling bacteria to move. Pili (or fimbriae) are hair-like structures used for attachment to surfaces and other cells, and sex pili are involved in conjugation.

How do exotoxins differ from endotoxins produced by bacteria?

Exotoxins are proteins secreted by bacteria, often highly toxic, while endotoxins are lipopolysaccharides released only upon lysis of Gram-negative bacterial cells.

What are the three main mechanisms of horizontal gene transfer in bacteria?

The three mechanisms are transformation (uptake of naked DNA), transduction (gene transfer via bacteriophages), and conjugation (direct transfer of DNA via cell-to-cell contact).

What is a virus composed of and how does it replicate?

A virus consists of genetic material (DNA or RNA) enclosed in a protein coat called a capsid. They replicate by infecting host cells and using the host's cellular machinery to produce new viral particles.

Describe the key difference between the lytic and lysogenic cycles of bacteriophages.

In the lytic cycle, the virus replicates and lyses the host cell. In the lysogenic cycle, the viral DNA integrates into the host genome (as a prophage) and replicates with it without immediately killing the cell.

Why are viruses considered obligate intracellular parasites?

Viruses are considered obligate intracellular parasites because they lack the cellular machinery for metabolism and reproduction, requiring them to infect and utilize host cells to replicate.

How do antibiotics primarily work against bacteria, and why are they ineffective against viruses?

Antibiotics target specific bacterial structures or processes (e.g., cell wall synthesis, protein synthesis). They are ineffective against viruses because viruses lack these bacterial targets and use host cell machinery instead.

What is the purpose of a viral envelope, and where does it originate?

A viral envelope is an outer lipid bilayer derived from the host cell membrane during budding. It helps the virus evade the host's immune system and facilitate entry into new host cells.

What is meant by the term 'host range' in virology?

Host range refers to the specific types of cells, tissues, or organisms that a particular virus can infect. It is determined by the virus's ability to bind to specific receptors on the host cell surface.

Briefly explain the concept of bacterial resistance to antibiotics.

Bacterial resistance occurs when bacteria evolve mechanisms to withstand the effects of antibiotics, such as altering drug targets, producing enzymes that inactivate drugs, or pumping drugs out of the cell.

What role do beneficial bacteria (microbiota) play in the human body?

Beneficial bacteria, or microbiota, colonize various parts of the human body, aiding in digestion, synthesizing vitamins, protecting against pathogens by competing for resources, and modulating the immune system.