Viruses & Bacteriophages
What do host range, tissue tropism, and zoonotic mean?
Host range: The types of hosts a virus can infect.
Tissue tropism: The specific cells or tissues a virus infects.
Zoonotic: An infection that spreads from animals to humans.
What are the three stages of CRISPR defense?
Foreign DNA acquisition: The cell saves a piece of foreign DNA.
CRISPR RNA processing: The saved DNA information is used to make guide RNA.
RNA-guided targeting: The guide RNA directs proteins to recognize and destroy matching foreign genetic material.
Define metabolism, catabolism, and anabolism.
Metabolism: All chemical reactions in a cell.
Catabolism: Breaks molecules down and releases energy.
Anabolism: Builds molecules and requires energy.
What starts glycolysis, what does it produce, and does it require oxygen?
One glucose molecule is broken into two pyruvate molecules. Glycolysis produces a net 2 ATP and 2 NADH and does not require oxygen.
Define sterilization, disinfection, sanitization, antisepsis, and degermining.
Sterilization: Destroys all microbial life, including endospores.
Disinfection: Eliminates or reduces microbes on nonliving surfaces; it may not destroy endospores.
Sanitization: Reduces microbes to levels considered safe by public-health standards.
Antisepsis: Reduces or inhibits microbes on living tissue.
Degermining: Physically removes microbes from a surface, usually skin.
What is a bacteriophage, and what are its main structures and functions?
A bacteriophage is a virus that infects bacteria. Its head contains genetic material, and its tail helps it attach to bacteria and deliver its genetic material.
What is the difference between +sense and −sense single-stranded RNA viruses?
+sense RNA can be translated directly into proteins. −sense RNA must first be copied into +sense RNA by RNA-dependent RNA polymerase.
What is the difference between endergonic and exergonic reactions, and how does ATP help cells?
Exergonic reactions release energy; endergonic reactions require energy. ATP stores and transfers energy. When ATP loses a phosphate and becomes ADP, energy is released for cellular work. Energy is needed to convert ADP back into ATP.
What happens when pyruvate is converted into acetyl-CoA?
Pyruvate is converted into acetyl-CoA, releasing CO₂ and producing NADH. Acetyl-CoA then enters the Krebs cycle.
How can tonicity be used to prevent microbial growth?
High-solute environments, such as concentrated salt or sugar, draw water out of microbial cells by osmosis. This can cause plasmolysis, preventing growth or causing cells to die.
What are the five steps of the lytic bacteriophage cycle?
Attachment → penetration → biosynthesis → assembly/maturation → release by lysis.
What are the major steps of influenza virus infection?
Attachment → entry → uncoating → viral RNA replication and protein production → assembly → release.
What do enzymes do to activation energy, and what are cofactors, coenzymes, and holoenzymes?
Enzymes lower activation energy and speed up reactions. A cofactor is an inorganic helper, a coenzyme is an organic helper, and a holoenzyme is an enzyme combined with its required helper.
What are the main products of one turn of the Krebs cycle per acetyl-CoA?
2 CO₂, 3 NADH, 1 FADH₂, and 1 ATP (or equivalent GTP).
How does UV light kill or inhibit bacteria? What happens to their DNA, and what can this lead to?
UV light causes thymine dimers to form in DNA. This interferes with DNA replication and transcription and can cause mutations or cell death.
What happens during the lysogenic cycle, and what is a prophage?
Viral DNA integrates into the bacterial chromosome and is copied when the bacterium reproduces. The integrated viral DNA is called a prophage. It can later enter the lytic cycle.
What is the difference between antigenic drift and antigenic shift, and which is more likely to cause a pandemic?
Antigenic drift: Small, gradual mutations that change viral surface antigens.
Antigenic shift: A major change that can occur when influenza viruses exchange genome segments through reassortment.
Antigenic shift is more likely to cause a pandemic because many people may have little immunity to the new virus.
What is the difference between competitive inhibition, noncompetitive inhibition, allosteric inhibition, and allosteric activation?
Competitive inhibition: An inhibitor competes for the active site.
Noncompetitive inhibition: An inhibitor binds elsewhere and reduces enzyme activity.
Allosteric inhibition: Binding at another site decreases enzyme activity.
Allosteric activation: Binding at another site increases enzyme activity.
Explain how the electron transport chain uses NADH, FADH₂, electron carriers, an H⁺ gradient, and ATP synthase to produce ATP.
In bacteria, the ETC is located in the plasma membrane. NADH donates electrons to NADH dehydrogenase, while FADH₂ contributes electrons through the respiratory chain. Electrons pass through Q (ubiquinone), Cytochrome B-C1, Cyt c (cytochrome c), and Cytochrome oxidase. Energy released as electrons move through the chain pumps H⁺ from the intracellular side to the extracellular side, creating an H⁺ gradient. H⁺ flows back across the membrane through ATP synthase, which uses the gradient to make ATP from ADP and phosphate. O₂ is the final electron acceptor and combines with electrons and H⁺ to form H₂O.
Name two heavy metals that inhibit microbial growth, explain how they work, and describe why soap is effective at degermining.
Silver and copper can inhibit microbes by damaging proteins and interfering with cellular functions. Soap has a hydrophilic (water-attracting) end and a hydrophobic (oil-attracting) end. This helps loosen oils, dirt, and microbes so they can be washed away.
What is transduction, and how can it spread antibiotic resistance?
Transduction occurs when a bacteriophage transfers bacterial DNA from one bacterium to another. It can transfer genes that provide antibiotic resistance.
What are the major steps of HIV replication, and what do reverse transcriptase, integrase, and protease do?
Reverse transcriptase: Makes DNA from viral RNA.
Integrase: Inserts viral DNA into the host chromosome.
Protease: Cuts viral proteins so new viruses can mature.
What is feedback inhibition, and which of these are oxidized or reduced: NAD⁺, NADH, FAD, and FADH₂?
Feedback inhibition happens when the final product of a pathway inhibits an earlier enzyme.
NAD⁺: Oxidized
NADH: Reduced
FAD: Oxidized
FADH₂: Reduced
Why is fermentation necessary, and how can lipids and proteins be used to make ATP?
Fermentation regenerates NAD⁺, allowing glycolysis to continue when the ETC cannot operate normally. Lipids can be broken down into acetyl-CoA and molecules that produce NADH and FADH₂. Proteins are broken into amino acids, and their carbon skeletons can enter cellular respiration pathways.
How does alcohol kill microbes, and how does catalase protect bacteria from hydrogen peroxide?
Alcohol denatures proteins and disrupts cell membranes. Catalase breaks down toxic hydrogen peroxide into water and oxygen: