BIOL 2051 - Final Exam - Panopto Questions

You are a researcher exploring a deep-sea hydrothermal vent where temperatures exceed. You isolate a novel microorganism and analyze its cellular structure. Which of the following characteristics would you most likely find in this organism's cell membrane to ensure it remains functional at such extreme temperatures?

a.) Branched-chain fatty acids to increase membrane fluidity.

b.) High concentrations of polyunsaturated fatty acids to prevent solidification.

c.) A balanced ratio of saturated and unsaturated fatty acids using ester

linkages.

d.) Tetraether lipids and saturated straight-chain fatty acids provide the necessary rigidity and stability.

d.) Tetraether lipids and saturated straight-chain fatty acids provide the necessary rigidity and stability.

An industrial plant accidentally leaks a chemical into a nearby pond that inhibits the enzymes responsible for creating ether linkages and stops saturated fatty acid synthesis, forcing all resident microorganisms to use ester linkages and unsaturated fatty acids instead.

Question: Which group of organisms would be most negatively impacted by this change, and why does the type of chemical bond matter for their survival?

Thermophiles because ether linkages and saturated fatty acids are needed in their cell wall for more stability; losing them would cause the membranes to become too fluid and break down at higher temperatures.

A laboratory accident causes a culture of E. coli (a mesophile) to be moved from a 37°C incubator to a refrigerator set at 4°C. To survive the sudden drop in temperature, the bacteria must quickly alter their membrane composition.

Question: Would you expect the bacteria to increase the production of saturated or unsaturated fatty acids, and how does this change prevent the membrane from "freezing"?

Unsaturated fatty acids; they increase membrane fluidity by preventing fatty acid tails from packing tightly and solidifying in the cold.

T or F: Salt bridges are electrostatic interactions between oppositely charged amino acid residues that help protect against thermal stress

True

T or F: Psychrophiles produce cryoprotectants to help prevent ice formation and maintain cellular processes.

True

T or F: Heat shock proteins (HSPs) like Hsp70 help thermophiles refold denatured proteins.

True

T or F: Psychrophiles require a higher activation energy (Ea) for catalysis than thermophiles.

False

T or F: Thermophilic proteins often feature an enrichment of hydrophobic amino acid residues example lysine and arginine.

False

T or F: Mesophiles maintain a balance of non-covalent interactions to allow for optimal flexibility within a moderate temperature range.

True

T or F: To increase stability, thermophile proteins may form more stable oligomers with additional subunits in their quaternary structure.

True

T or F: The amino acid glycine is more common in thermophiles because it adds structural rigidity.

False

T or F: Psychrophile proteins have a higher number of stabilizing bonds to prevent them from freezing

False

T or F: Bacteria use the proton motive force (PMF), an electrochemical gradient of protons H+, primarily powers their flagella

True

T or F: During fermentation, bacteria can use an F1F0-ATPase to pump protons out of the cell by hydrolyzing ATP.

True

T or F: When exposed to acidic environments, bacteria can use the antiporter proteins to export a proton out of the cell while simultaneously importing another ion, which helps neutralize the cytoplasm.

T or F: Helicobacter pylori survives acidic stomach conditions by sensing low pH, importing urea via the UreI channel, and hydrolyzing it into ammonia to neutralize its periplasm.

True

Acidithiobacillus ferrooxidans flourishes in extreme acid mine drainage (pH < 3). In these conditions, it must generate ATP to survive. How does its specific environment naturally assist its method of ATP synthesis?

a.) The naturally massive gradient of protons (H+) outside the cell provides a ready-made Proton Motive Force (PMF) that the bacteria can harness to drive chemiosmosis.

b.) The acidic environment prevents the formation of thymine dimers, conserving cellular energy usually spent on extensive DNA repair.

a.) The naturally massive gradient of protons (H+) outside the cell provides a ready-made Proton Motive Force (PMF) that the bacteria can harness to drive chemiosmosis.

In Escherichia coli K-12, the potassium transporters TrkG and TrkH have different regulatory mechanisms. If a chemical inhibitor completely deactivated the repressor (H-NS) in the cell, how would potassium uptake be affected?

a.) Na+-dependent K+ uptake would likely increase due to the derepression of the trkG gene.

b.) Both TrkG and TrkH would be permanently deactivated, starving the cell of potassium.

c.) Na+-independent K+ uptake would cease completely because TrkH requires H-NS for activation.

a.) Na+-dependent K+ uptake would likely increase due to the derepression of the trkG gene.

An Escherichia coli population is subjected to long-term hypertonic stress in a high-salinity environment. To prevent plasmolysis while maintaining cellular function, what strategy is the bacteria most likely to employ?

a.) Rapidly synthesizing or importing organic 'compatible solutes' like glycine betaine that do not disrupt protein function.

b.) Shedding its rigid cell wall to allow the cell membrane to freely shrink and expand with the water potential.

a.) Rapidly synthesizing or importing organic 'compatible solutes' like glycine betaine that do not disrupt protein function.

Streptomyces alkaliphilus thrives in environments with a pH above 10.5. If these bacteria are experimentally transferred to a highly alkaline medium completely lacking sodium ions (Na+), what is the most immediate threat to their survival?

a.) They will be unable to power their Na+/H+ antiporters to bring protons into the cell, causing the cytoplasm to become lethally alkaline.

b.) Their internal environment will become hypertonic, causing water to rapidly rush into the cell and lyse it.

a.) They will be unable to power their Na+/H+ antiporters to bring protons into the cell, causing the cytoplasm to become lethally alkaline.