Microbial Death, Sterilization, and Genetic Mechanisms in Microbiology

Q: What is the rate of microbial death?

: Microbes die at a constant percentage over time, not all at once, creating a logarithmic death curve.

Q: What is thermal death time (TDT)?

: The total time required to kill all microorganisms at a specific temperature.

Q: What is decimal reduction time (D-value)?

: The time it takes to kill 90% of a microbial population.

Q: What factors affect microbial death?

: Temperature, type of microbe (like endospores), environment, and presence of organic matter.

Q: What is moist heat sterilization?

: A method using steam to denature proteins and kill microbes quickly.

Q: Why is moist heat more effective than dry heat?

: Because water transfers heat better, allowing faster protein denaturation.

Q: Give an example of moist heat sterilization.

: Autoclaving surgical tools.

Q: What is dry heat sterilization?

: A method that kills microbes by oxidizing cell components using high heat.

Q: Give an example of dry heat sterilization.

: Sterilizing glassware in a hot air oven.

Q: How does radiation kill microbes?

: By damaging DNA so the cell cannot replicate.

Q: What is the difference between UV and ionizing radiation?

: UV causes thymine dimers, while ionizing radiation breaks DNA strands.

Q: What is filtration used for?

: Removing microbes from liquids or air without heat.

Q: Difference between disinfectants and antiseptics?

: Disinfectants are for surfaces; antiseptics are safe for skin.

Q: What is the structure of DN

?

A: Double helix with a sugar-phosphate backbone and base pairs (A-T, C-G).

Q: What is the structure of RN

?

A: Single-stranded with bases A, U, C, G.

Q: What is replication?

: The process of copying DNA; it is semi-conservative.

Q: What is transcription?

: DNA is copied into mRNA.

Q: What is translation?

: mRNA is used to build proteins at the ribosome.

Q: What provides energy for replication, transcription, and translation?

: ATP.

Q: What is an operon?

: A group of genes controlled together under one promoter.

Q: What is the lac operon?

: An inducible operon that turns ON when lactose is present.

Q: What is the trp operon?

: A repressible operon that turns OFF when tryptophan is present.

Q: What is vertical gene transfer?

: Transfer of DNA from parent to offspring.

Q: What is horizontal gene transfer?

: Transfer of DNA between bacteria.

Q: What is transformation?

: Uptake of naked DNA from the environment.

Q: What is transduction?

: Transfer of DNA by a bacteriophage (virus).

Q: What is conjugation?

: Transfer of DNA through direct contact using a sex pilus.

Q: What are plasmids?

: Small circular DNA molecules that often carry antibiotic resistance genes.

Q: What are transposons?

: Jumping genes that move within DNA.

Q: How are viruses different from bacteria?

: Viruses are not living and need a host, while bacteria are living cells.

Q: What are the main parts of a virus?

: Capsid, nucleic acid, and sometimes an envelope.

Q: What are the main virus shapes?

: Helical, icosahedral, complex, and enveloped.

Q: What is the lytic cycle?

: Virus replicates and destroys the host cell.

Q: What is the lysogenic cycle?

: Viral DNA integrates into host DNA and stays dormant.

Q: Where do DN

viruses replicate?

A: Usually in the nucleus.

Q: Where do RNA viruses replicate?

A: Usually in the cytoplasm.

Q: How can viruses cause cancer?

: By inserting DNA that disrupts normal cell regulation.

Q: What are prions?

: Infectious proteins with no DNA.

Q: What is infection?

: The invasion of microbes into the body.

Q: What is disease?

: Damage caused by infection.

Q: What is normal microbiota?

: Beneficial microbes that live on

in the body.

Q: What are opportunistic pathogens?

: Microbes that cause disease when the immune system is weak.

Q: What are healthcare-associated infections (H

Is)?

A: Infections acquired in hospitals.

Q: What are predisposing factors?

: Conditions that make someone more likely to get sick.

Q: What is the chain of infection?

: A sequence: pathogen → host → transmission → infection.

Q: What are portals of entry?

: Ways microbes enter the body (skin, mucous membranes, cuts).

Q: What are adhesins?

: Molecules that help microbes attach to host cells.

Q: How do microbes evade the immune system?

: Capsules, antigenic variation, and enzymes.

Q: What are siderophores?

: Molecules that steal iron from the host.

Q: What are exotoxins?

: Proteins secreted by bacteria that damage cells.

Q: What are endotoxins?

: Toxins from Gram-negative cell walls.

Q: What is direct damage?

: When microbes use host nutrients or destroy cells.

Q: What are cytopathic effects?

: Visible changes in infected cells (lysis, fusion, inclusion bodies).

Q: What are portals of exit?

: Ways pathogens leave the body (respiratory, feces, blood, skin).