Microbial Growth (Ch. 6)
What type of microbes thrive above 80 degrees celsius and live in hydrothermal vents?
Hyperthermophiles are microbes that grow best at extremely high temperatures, often above 80 degrees
What type of media has ingredients that are fully known?
Chemically defined media have exact amounts of every ingredient listed, which makes them useful for precise experiments.
What is the lowest temperature that kills all microbes in 10 minutes?
The thermal death point (TDP) is the lowest temperature that kills all microbes in a sample within 10 minutes.
What enzyme sticks Okazaki fragments together during DNA replication?
DNA ligase joins together the short DNA fragments made on the lagging strand during replication.
What sugar molecule turns on the lac operon by inactivating the repressor?
Allolactose binds to the repressor, causing it to fall off the DNA so the lac genes can be turned on.
What phase shows no net population change because growth = death?
In the stationary phase, the number of new cells equals the number of dying cells, so the population stays the same.
What kind of media helps certain microbes grow more while others don’t?
Enrichment media promote the growth of a specific microbe while giving it an advantage over others in the sample.
What moist heat method uses 121 degrees celsius at 15 psi for 15 minutes to sterilize?
Autoclaving uses steam under pressure to kill all bacteria, viruses, and spores. It's the most effective heat method.
What kind of mutation makes a stop codon too early and cuts the protein short?
A nonsense mutation changes a codon to a stop signal, which causes the protein to be cut off too soon and likely nonfunctional.
What happens in a repressible operon when the corepressor binds the repressor?
When the corepressor binds to the repressor, the repressor becomes active and shuts off the operon.
Which microbes are harmed by oxygen and can’t use it at all?
Obligate anaerobes are bacteria that are killed by oxygen and can only grow in oxygen-free environments.
Which biosafety level requires full protective suits and sealed labs?
BSL-4 labs are the highest safety level and are used when working with deadly and unknown pathogens like Ebola.
What kind of radiation causes thymine bases in DNA to stick together?
UV light causes thymine dimers to form in DNA, which blocks proper replication and can kill the cell.
How does UV damage DNA and what does it create?
UV light causes two thymines next to each other to stick together, forming a thymine dimer that interferes with DNA copying.
What do cAMP and CAP do when glucose is low?
When glucose is low, cAMP builds up and helps CAP bind to the DNA, which boosts transcription of the lac operon.
What kind of environment causes plasmolysis and which microbes like it?
Hypertonic environments, like those with high salt or sugar, pull water out of cells and cause plasmolysis. Halophiles are microbes that can survive in these conditions.
What lab method lets you isolate pure colonies on solid agar?
The streak plate method spreads bacteria out on a solid surface to grow separate colonies from a single cell.
What test uses bacteria-covered rings dipped into disinfectants to see what kills them?
The use-dilution test checks how well a disinfectant works by seeing if it kills bacteria on metal rings after soaking.
In the Ames test, what is counted to see if a chemical is a mutagen?
The number of colonies that regain the ability to grow without histidine is counted. more colonies means more mutations.
What’s the difference between inducible and constitutive genes?
Inducible genes are only turned on when needed; constitutive genes are always active.
What do we call needed compounds that bacteria must get from the environment because they can't make them?
Organic growth factors are essential molecules like vitamins or amino acids that some bacteria cannot produce on their own and must absorb from their surroundings.
What is the job of sodium thioglycolate in a culture medium?
Sodium thioglycolate removes oxygen from the medium, making it suitable for growing anaerobic bacteria.
What method passes liquids through a membrane to remove bacteria, especially for heat-sensitive things?
Filtration uses special filters with tiny pores to physically remove microbes from solutions that can’t be heated.
What are the three ways bacteria can exchange genes with each other? explain
Bacteria share genes through transformation (DNA from the environment), conjugation (direct contact), and transduction (viruses).
What are the 3 parts of an operon and what do they do?
The promoter is where RNA polymerase binds, the operator controls access to the genes, and the structural genes code for proteins.