Terminology and Principles of Microbial Control
What is the process of removing or destroying all microbial life on an object?
Sterilization
How does moist heat kill microorganisms?
Denaturing enzymes
What are chemical agents used on inanimate objects called?
Disinfectants
What kind of bond forms between complementary nitrogenous bases in DNA, and what specific base pairs are formed? How many bonds are formed between the different pairs?
Hydrogen bonds form between A-T (2) and C-G (3)
What is the main difference between constitutive and inducible genes?
Constitutive genes are always expressed, while inducible genes are expressed only in response to specific environmental signals.
What is a type of sterilization that uses heat treatment of canned foods to destroy C. botulinum endospores? Bonus points if you name the process
Commercial sterilization (12D canning process)
What is the lowest temperature at which all microbes in a liquid culture are killed in 10 minutes?
Thermal death point (TDP)
How do phenolic compounds exert their antimicrobial effect?
Injuring the plasma membrane
Why does DNA polymerase require an RNA primer during replication?
DNA polymerase can only add nucleotides to an existing 3′-OH group — RNA primase provides that starting point.
How does the lac operon simultaneously integrate both positive and negative regulatory mechanisms in response to glucose and lactose availability? What does it ensure?
The lac operon is negatively regulated by the lac repressor (which blocks transcription in the absence of lactose) and positively regulated by the cAMP–CRP complex (which enhances transcription when glucose is low). This dual control ensures expression only when lactose is available and glucose is scarce.
What is a process that inhibits microbial growth on living tissue?
Antisepsis
Why is autoclaving the most effective method of moist heat sterilization?
Steam must directly contact the material being sterilized
Why does iodine have germicidal properties?
Combines with amino acids to inactivate enzymes and cellular proteins
How does the antiparallel arrangement of DNA strands affect replication on the leading and lagging strands?
Leading strand can be synthesized continuously toward the fork
The lagging strand is synthesized in Okazaki fragments
What molecular mechanism allows cAMP and CAP to enhance transcription at the lac promoter?
High cAMP levels, caused by low glucose, enables cAMP to bind to CAP, forming a complex that attaches upstream of the lac promoter. This complex bends DNA and facilitates RNA polymerase binding, increasing transcription efficiency.
What is a suffix that means "to kill", as opposed to a suffix that means "to inhibit"?
-cide and -stat, respectively
What type of radiation causes thymine dimers in DNA and is most effective at 260 nanometers?
Ultraviolet (UV) radiation
How do heavy metals like silver, copper, and mercury exert antimicrobial action?
Act through oligodynamic action, denaturing proteins by binding to sulfhydryl (SH) groups
What role does the enzyme DNA ligase play in replication, and why is it essential for the lagging strand?
DNA ligase seals nicks between Okazaki fragments, joining discontinuous pieces into one continuous DNA strand.
How does a missense mutation and a nonsense mutation differently affect enzyme structure and function? Give an example of when a missense mutation might not be harmful.
A missense mutation substitutes one amino acid, which might maintain protein function if the new residue has similar properties (a conservative change). A nonsense mutation introduces a premature stop codon, usually producing a truncated, nonfunctional protein. For example, a missense in a non-critical site may be neutral.
What is the rate of microbial death plotted as?
Logarithmic plot
What method of sterilization kills microbes by oxidation and includes direct flaming and hot-air sterilization?
Dry heat sterilization
How do quaternary ammonium compounds (“quats”) kill microorganisms?
Disrupt plasma membranes
What is the central dogma? Why is it disproved by retroviruses?
They produce reverse transcriptase mRNA --> cDNA
How does exposure to UV light induce a specific type of DNA lesion? Describe the enzymatic steps bacteria use to repair this damage through photoreactivation and nucleotide excision repair?
UV light causes covalent bonds between adjacent thymines (thymine dimers), distorting the DNA helix. In photoreactivation, photolyase uses visible light energy to directly break these bonds. In nucleotide excision repair, endonucleases remove the damaged section, DNA polymerase fills in the gap using the undamaged strand as a template, and DNA ligase seals the backbone.