Structural Sabotage
A mutation replaces a nonpolar amino acid in a transmembrane protein with a polar one. Explain why this protein might now get "stuck" in the cytoplasm rather than inserting into the membrane.
The polar amino acid repels the hydrophobic fatty acid tails of the membrane, preventing insertion.
If you heat an enzyme to 80°C, the reaction stops. If you cool it to 0°C, it also stops. Why is the stop at 80°C permanent, while the stop at 0°C is reversible?
Heat breaks bonds/denatures the protein (permanent structural change); Cold just lowers kinetic energy (molecular motion) without destroying structure
Cholera toxin prevents a G-protein from hydrolyzing GTP to GDP. Is the pathway stuck "on" or "off," and why?
Stuck "On." The G-protein is active when bound to GTP; if it can't break it down, it never turns off.
In an experiment, the error bars for the control group and the experimental group overlap. What is the biological conclusion?
The treatment had no statistically significant effect (Null hypothesis cannot be rejected).
What is the purpose of the G1 phase in the cell cycle?
Growth and preparation for DNA synthesis.
Intravenous fluids are isotonic to blood. If a nurse accidentally administers pure distilled water, describe the thermodynamic movement of water and the physical result for the red blood cells.
Water moves from high potential (IV fluid) to low potential (cell interior), causing the cells to swell and lyse (burst).
Dinitrophenol (DNP) makes the inner mitochondrial membrane "leaky" to protons (H+). Predict the effect on Oxygen consumption: does it increase, decrease, or stay the same?
Increases. The cell burns more fuel/oxygen trying to re-establish the gradient that is constantly leaking out
Steroid hormones can influence gene expression in any cell with the right receptor, but they take hours to show an effect. Protein hormones act in seconds. Why the difference?
Steroids require transcription and translation (making new proteins); Protein hormones activate existing proteins via phosphorylation cascades (much faster)
You observe a cell with 2x the normal amount of DNA. Which checkpoint has it likely passed, and which checkpoint is it currently facing?
Passed G1 and S; facing the G2 checkpoint.
Name the stages of mitosis in order.
Prophase, Metaphase, Anaphase, Telophase (PMAT).
Why does the breakdown of the Nuclear Envelope during mitosis suggest that the components of the nucleus and the cytoplasm are chemically compatible?
Because the nuclear contents mix with the cytosol without precipitating or denaturing, implying similar pH and ionic conditions.
In a chloroplast, if the thylakoid membrane is punctured, ATP production stops, but NADPH production continues. Why?
ATP relies on the proton gradient (which requires a sealed membrane); NADPH relies only on the Electron Transport Chain passing electrons (which doesn't strictly need the gradient).
A mutation destroys the phosphatase enzymes in a phosphorylation cascade. What is the consequence for the cell's response to a signal?
The signal cannot be turned off (the proteins stay phosphorylated/active indefinitely).
Differentiate between autocrine and paracrine signaling.
Autocrine signaling affects the same cell, while paracrine signaling affects nearby cells.
What is the significance of meiosis in sexual reproduction?
It produces gametes (sperm and eggs) with half the chromosome number, ensuring genetic diversity.
Explain why a cell with a radius of 1mm metabolizes glucose much slower per unit of volume than a cell with a radius of 0.1mm.
The larger cell has a smaller Surface Area-to-Volume ratio, where nutrients cannot diffuse in fast enough to service the massive volume.
Why does a lack of Oxygen eventually stop the Krebs Cycle, even though Oxygen is not used directly in the Krebs Cycle?
Without Oxygen to accept electrons at the end of the ETC, NADH and FADH2 cannot be oxidized back to NAD+ and FAD. The Krebs cycle runs out of electron carriers.
Differentiate between aerobic and anaerobic respiration.
Aerobic respiration requires oxygen, producing more ATP, while anaerobic respiration occurs in the absence of oxygen, producing less ATP.
Explain how mutations in genes involved in cell signaling can lead to cancer.
Abnormal cell signaling can result in uncontrolled cell division and tumor formation.
Differentiate between a haploid and diploid cell.
Haploid cells have half the chromosome number (n), while diploid cells have the full complement (2n).
These are the four major elements that make up approximately 96% of living matter.
Carbon, hydrogen, nitrogen, oxygen
A competitive inhibitor is added to a reaction. How can you experimentally restore the maximum rate of reaction V{max} without removing the inhibitor?
Add a massive excess of Substrate (to out-compete the inhibitor for the active sites).
Explain how chemiosmosis is involved in ATP production.
Protons move through ATP synthase, driving the production of ATP
Identify the major types of cell junctions in animal cells.
Tight junctions, gap junctions, and desmosomes.
Explain how the cell cycle is regulated.
Checkpoints ensure proper progression through the cell cycle, and cyclins and cyclin-dependent kinases (CDKs) regulate these checkpoints.