Bio 151 Exam 2 Review Questions And Answers

Which of the following statements best describes the mechanism by which the ced-9 protein in the nematode C. elegans prevents apoptosis in normal cells? - ANS Active Ced9 prevents activation of Ced3 A loss of function of Apaf1, the human equivalent of ced-4 in C. elegans, is most likely to result in which of the following? - ANS a form of cancer in which normal apoptosis fails As mentioned in the lecture, both excessive and insufficient apoptosis can cause problems. If scientists wanted to develop a drug to inhibit apoptosis in C. elegans, which of the following would be likely to produce that effect? (Select ALL correct answers) - ANS - A drug that inhibits Ced-4 - A drug that inhibits Ced-3 - A drug that interferes with death-signaling receptors Which of the following may occur as a result of cross-talk? (Select ALL correct answers) - ANS - A cell may have a stronger response to a ligand than usual - A cell may have a weaker response to a ligand than usual In the example of acetylcholine signaling, how is it that the same signal causes heart muscle cells to contract less frequently, but skeletal muscle cells to contract MORE frequently? - ANS The two cell types express different acetylcholine receptor types An antagonist is a chemical that - ANS Binds to a receptor and prevents the ligand from activating it Which of the following statements best describes scaffolding proteins? - ANS Large molecules to which several relay proteins attach to facilitate cascade effects Second messengers are needed because - ANS Most ligands cannot enter the cell so they help transmit messages to the cell interior The name of the enzyme that catalyzes the conversion of ATP to cAMP is - ANS Adenylyl cyclase The steps of IP3 signaling - ANS 1. The ligand binds to the receptor 2. The G protein swaps out GDP for GTP 3. Phospholipase C is activated 4. Phospholipase C catalyzes the synthesis of IP3 5. IP3 binds to ligand-gated calcium channels on the ER membrane 6. Calcium is released into the cytosol 7. Calcium activates calcium-binding proteins The best definition of the word ligand is - ANS Any type of signaling molecule that binds to another molecule Which of the following is the best description of how a G protein coupled receptor responds to a ligand binding? - ANS Binding of ligand to the receptor causes the G protein to become activated, then the G protein travels through the plasma membrane to activate an enzyme Which of the following receptors are activated by phosphorylation after binding to a ligand? - ANS receptor tyrosine kinases Which of the following statements describes a likely effect of a drug that enhances testosterone (a steroid) binding to its receptor in human cells? - ANS The production of particular proteins would begin Which of the following activities would be inhibited by a drug that specifically blocks the addition of phosphate groups to proteins? - ANS receptor tyrosine kinase activity Which of the following is NOT a mechanism by which a cell can send a signal to another cell? - ANS - Sending the signal directly from the cytoplasm of one cell to the cytoplasm of another through junctions - Attaching two cells together with cell-surface proteins - Releasing the signal into the extracellular fluid/intracellular space - Releasing the signal into the blood When you step on something sharp, a sensory receptor called a nociceptor, involved in the transmission of painful signals to the brain, generates an electrical signal that leads to the release of a neurotransmitter called glutamate into the extracellular fluid. This is an example of: - ANS Synaptic signaling You have discovered a new human genetic disorder that affects a relay molecule involved in the cellular response to the neurotransmitter dopamine. Which step in cell signaling would be most directly affected in this disorder? - ANS Signal transduction Sucrase is a molecule that catalyzes the reaction that breaks the disaccharide sucrose down into the monosaccharides glucose and fructose. Sucrase is a(n): - ANS enzyme What happens when an enzyme is denatured? - ANS Its shape is altered, making it nonfunctional How does an allosteric inhibitor decrease the rate of an enzyme-catalyzed reaction? - ANS By binding to a regulatory site, separate from the active site, and changing the shape of the active site All enzymes that function in the human body have the same optimum pH. - ANS False Which of the following is a characteristic feature of anabolic pathways? - ANS They consume energy to build up polymers from monomers Which of the following is an example of feedback inhibition? - ANS Isoleucine acting as an allosteric inhibitor of one of the enzymes involved in its own synthesis A series of enzymes catalyze the reactions in the metabolic pathway X → Y → Z → A. Product A binds to the enzyme that coverts X to Y at a position remote from its active site. What does substance X represent in this pathway? - ANS A substrate Which of the following is a step in the Calvin cycle? - ANS Carbon from CO2 molecules is added to RuBP Which of the following does NOT happen during the Calvin cycle - ANS Glucose is produced Of the 6 molecules of G3P produced during the Calvin cycle _____ of them are used to regenerate _____. - ANS 5; RuBP Chloroplasts and mitochondria both perform cellular respiration. - ANS False The Order of the Light Reactions - ANS 1. A photon of light excites a pigment molecule in phtosystem II 2. Energy is transferred to the photosystem II reaction center chlorophyll 3. The photosystem II electron is replaced by the splitting of water 4. The photosystem II reaction center chlorophyll donates an electron to photosystem I via an electron transport chain 5. A photon of light excites a pigment molecule in photosystem I 6. Energy is transferred to the photosystem I reaction center chlorophyll 7. An electron is donated to NADP+