Biology Exam 2 Practice
The lipid:protein ratio in a typical membrane (e.g. red blood cells) is approximately:
1:1
Protein makes up what percentage of the mass of the plasma membrane in a typical cell (e.g. red blood cells)?
50%
The enzyme phenylalanine hydroxylase (PAH) catalyzes the conversion of the amino acid phenylalanine to tyrosine. If for this reaction, Keq' = 18.1, ∆G°' is ____ and the reaction is ____.
<0; Exergonic
Consider the reaction: A <=> B. Under standard conditions at equiliubrium, the concentrations of the compounds are [A] = 0.1 M, and [B] = 1.1 M. Keq' for this reaction is ____ and ∆G°' is _____. (You do not need a calculator for this.)
> 1; < 0
The Krebs cycle involves the aerobic breakdown of glucose for energy. In the first reaction of the Krebs Cycle, the enzyme Aconitase converts Citric acid to its isomer, the molecule isocitrate. The Keq' for this reaction is approximately 0.1. ∆G°' for this reaction is therefore ____ and the reaction is ____.
>0; Endergonic
Imagine you are a drug developer aiming to inhibit epinephrine responses specifically in liver cells. Which of the following would accomplish this?
A kinase inhibitor
Collagen, an extremely important extracellular matrix protein, is constitutively secreted by fibroblast cells, a type of connective tissue cell. If you had a patient in which collagen is synthesized normally, but fails to be secreted into the extracellular matrix, which of the following would you examine as the likely cause of this problem? (Think very carefully before answering this question!)
A kinesin disorder
If you had a patient in which the lung epithelium was leaking fluids from the bloodstream into the lumen of the lung, which of the following is the most likely cause?
A mutation in a cell adhesion molecule
Which of the following correctly describes a second messenger?
A soluble cytoplasmic molecule produced in response to ligand binding that activates a cellular response.
Depletion of ATP causes rigor (don't worry - I don't think this is cat is actually dead!). Why?
ATP is required for myosin to release from actin.
If it were injected directly into liver cells, cAMP would have the effect of:
Activating Protein Kinase A and, therefore, glycogen breakdown
Based on our model for evolution of the nucleus, which of the following organelles is likely evolved from plasma membrane infoldings?
All of the above
The active and inactive forms of a hypothetical enzyme are shown below. (The polypeptide is represented by the colored rectangles and grey lines holding them together.) The middle rectangle is the catalytic domain, and the reaction it is catalyzing is also shown. This form of enzyme regulation is _______.
Allosteric activation
The enzyme phosphofructokinase-1 (PFK-1) catalyzes the 3rd reaction in glycolysis. When AMP concentrations are very high, AMP binds to a location outside the active site PFK-1, which promotes catalysis. This is an example of:
Allosteric activation
Shown below is a branched reaction pathway, in which either D or E can be made from C, depending on which enzyme(s) are active. Imagine that D is necessary for the cell, but that it is beneficial to stop production of D when it reaches a certain threshold concentration in order to preserve A and C for other things (e.g. production of E). Which of the following is the best way to ensure this? E1-E4 are the enzymes that catalyze each of the reactions.
Allosteric inhibition of Enzyme 3 by D
hown below is a branched reaction pathway, in which either D or E can be made from C, depending on which enzyme(s) are active. Imagine that D is necessary for the cell, but that it is beneficial to stop production of D when it reaches a certain threshold concentration in order to preserve A and C for other things (e.g. production of E). Which of the following is the best way to ensure this? E1-E4 are the enzymes that catalyze each of the reactions.
Allosteric inhibition of Enzyme 3 by D
Why did Palade and his colleagues use pancreatic acinar cells in their original Pulse-Chase experiment?
Almost all of the proteins produced by pancreatic acinar cells are secreted.
If you were attempting to identify natural product inhibitors of kinesin activity, which of the following would be a good assay for screening them?
Anterograde transport in cells
Which adaptation specific to becoming multicellular compensates for the destabilizing effect of increased size?
Both ECM and tight junctions
Which adaptation specific to becoming multicellular compensates for the destabilizing effect of increased size? (Think carefully about answer choices!)
Both ECM and tight junctions
Which of the following is/are likely to elicit a slow, but long-lasting or even permanent cellular response?
Both growth factor signaling and steroid hormone signaling
Consuming very large amounts of certain foods/drinks can affect the digestive system in profound ways. Which of the following would LEAST likely cause some sort of osmotic shock to your stomach and intestinal cells if you consumed a very large amount of it in a short period of time?
Butter
The enzyme Succinate dehydrogenase (SDH) catalyzes the reaction succinate --> fumarate in the Citric Acid Cycle (structures shown below). If fumarate binds to the active site of SDH, thereby preventing succinate from binding, this is an example of:
Competitive inhibition
Loss of peptidoglycan, combined with increased cell size during evolution of eukaryotes led to a less stable cell. Which of the following evolutionary adaptations compensated for this decreased structural stability?
Cytoskeleton
Shown below is a free energy diagram for a chemical reaction. An enzyme that catalyzes this reaction acts by ________ the magnitude of _________:
Decreasing; 1
Pancreatic acinar cells produce and secrete digestive enzymes into the duodenum. What would happen if pancreatic acinar cells were treated with a toxin that causes lysis (breakage) of smooth ER membranes?
Digestive enzymes would be immediately secreted into the duodenum.
"He was awakened in the middle of the night by a low growling that sounded as if it was coming from just outside his tent. In response, the cells of his adrenal medulla began to secrete epinephrine, causing his palms to sweat, his heart to race, and his hair to stand on end." Epinephrine is involved in what type of signaling as described in this passage?
Endocrine
If you used Pulse-Chase to follow the path of a protein after endocytosis, what organelle most likely corresponds to X in the graph shown here? X = pink
Endosome
Shown below are the results of two fluorescence recovery after photobleaching (FRAP) experiments. Which of the following could explain the difference between the data represented by the dashed line as compared to that represented by the solid line?
FRAP was performed on the same cell but at a lower temperature.
The hormone glucagon is secreted by the pancreas in response to low blood sugar. Liver cells respond to glucagon by breaking down glycogen to form glucose, which is then release into the bloodstream for the other tissues. Based on this information, what mechanism is most likely used to transport glucose out of the cell into the bloodstream?
Facilitated diffusion
What type of transport brings glucose into cells soon after eating a large meal?
Facilitated diffusion
Ca++ flowing down its concentration gradient through a Ca++ channel is an example of:
Facilitated diffusion.
True or False: The concentration of Na+ inside the cell is higher than it is outside.
False
Which of the following is/are required in order for pancreatic acinar vesicles to be transported to the plasma membrane prior to secretion? (Select all that apply!)
GTP Kinesin Microtubules Myosin ATP Actin
Which of the following is/are required in order for an endosome to be transported from the plasma membrane to the Golgi complex? (Select all that apply!)
GTP Microtubules Dynein ATP
Shown here is a graph illustrating data from the origial Pulse-Chase experiment analyzing protein secretion in pancreatic acinar cells. Trace C corresponds to radioactivity in which structure? C = black line
Golgi
Which of the following is least likely to diffuse through a cell's plasma membrane?
H+
Taxol, derived from the Pacific Yew tree, was one of the first effective anti-cancer compounds discovered. It acts by inhibiting microtubule depolymerization. Which of the following is a likely cellular side effect of treatment with Taxol?
Increased cell size
Which of the following is an advantage of multicellularity?
Increased mobility
ras, a small GTPase, hydrolyzes GTP slowly on its own, but its enzymatic activity is increased significantly in the presence of GTPase activating proteins (GAPs). Imagine you discovered a novel mutation that prevents GAP from binding to ras. This mutation would have the effect of:
Increasing cell proliferation
Which of the following can be considered both an advantage and a disadvantage of juxtacrine signaling?
It affects only one or a very small number of cells.
Which of the following correctly describes why it can be advantageous to have membrane-bound organelles?
It allows for sequestration of reactions that may be damaging to a cell.
Which of the following is an advantage of juxtacrine signaling?
It is fast.
Which of the following is an advantage of paracrine signaling?
It is relatively fast
Whooping cough, also known as pertussis, is caused by the bacterium Bordetella pertussis. Some of its effects result from production of Pertussis toxin, which prevents Gα from binding to G-protein coupled receptors, and thereby "locking" Gα in the GDP-bound state. If you treated liver cells with Pertussis toxin, how would it affect liver cell responses to epinephrine?
It would decrease glucose production.
What would happen if you treated cells with a toxin that inhibits tubulin's enzymatic activity?
It would prevent depolymerization of microtubules.
Which of the following enzymes catalyzes phosphorylation of proteins using a phosphate group from ATP?
Kinases
When doing differential centrifugation, microsomes pellet to the bottom of the tube at faster spin speeds than lysosomes. This indicates that microsomes are ___________ than lysosomes.
Lighter
For solutes that cannot diffuse through the membrane, water moves across the membrane from a region of ______ to a region of ______ solute concentration
Low to high
If you used Pulse-Chase to follow the path of a protein after ENDOCYTOSIS, what organelle most likely corresponds to Y in the graph shown here?
Lysosome
Differential centrifugation separates particles based on _______ by applying different _______.
Mass; Spin speeds
Which of the following is/are found in eukaryotes but not bacteria?
Mitochondria
Which of the following is a disadvantage of being a multicellular organism specifically as opposed to unicellular? (read and think carefully!)
More difficult to absorb nutrients
Based on their differences in cell structure, which of the following would you be more likely to see in bacteria than in Eukaryotes?
More proteins with primary structure changes.
Inhibition of which of the following would prevent indirect active transport of glucose into cells?
Na+/K+ ATPase
Archeological evidence suggests that Neanderthals may have been aware of the medicinal properties of plants over 60,000 years ago. Imagine you are a modern-day ethnobotanist and have identified a compound from fossilized tree pollen that binds to the alpha subunit of the most common G-proteins. To test how the compound affects the activity of Gα, you treat liver cells with the compound alongside epinephrine. You observe that the cells fail to produce glucose. Which of the following could be how the compound acts?
None of the above
What is the second messenger in the receptor tyrosine kinase signaling pathway?
None of the above
Which of the following do eukaryotes have that bacteria do not?
Nuclei
Which of the following pellets at the slowest speeds during differential centrifugation?
Nuclei
Which of the following can diffuse most easily through the cell membrane?
O2
Which of the following should be able to diffuse most easily through a cell's plasma membrane?
O2
"During embryonic development red blood cells begin to develop in patches called blood islands. The blood cells secrete growth factors that diffuse only to nearby cells, signaling differentiation into endothelial cells. The endothelial cells eventually form the linings of the blood vessels." The growth factor described in the passage is involved in what type of signaling?
Paracrine
Which of the following is/are found in bacteria but not eukaryotes?
Peptidoglycan
All living organisms, including both bacteria and Eukaryotes have: (Select all that apply; you may want to review Lecture 7 in addition to the current material for this one)
REST BUT Exclude: Peptidoglycan Robust cytoskeleton, including actin and microtubules Nuclei
All living organisms, including both bacteria and Eukaryotes have: (Select all that apply; you may want to review Lecture 7 in addition to the current material for this one)
Ribosomes Peptidoglycan Robust cytoskeleton, including actin and microtubules double stranded DNA Nuclei the ability to extract energy from the environment to do work D-monosaccharides L-amino acids Plasma membranes made of phospholipids
If you used Pulse-Chase to follow the path of a protein after endocytosis, what organelle most likely corresponds to X in the graph shown here? X = Pink Line
Rough ER
Pancreatic acinar cells were selected for the original original Pulse-Chase experiment of Dr. Palade and his colleagues because almost all of the proteins they produce are:
Secreted
Pancreatic acinar cells were selected for the original original Pulse-Chase experiment of Dr. Palade and his colleagues because they wanted to better understand how _________ were transported through the cell.
Secreted proteins
You are most likely to find Ca++ channels in the membranes of what organelle?
Smooth ER
Imagine you walk into lab after spring break, and your TA hands you a beaker containing a solution of A, B, and C in water represented by the equilibrium shown below. If the solution has reached equilibrium, and the beaker is at pH 7.0, 25°C, and 1 atm pressure, what other information do you need to obtain in order to calculate ∆G°' for this reaction?
The concentrations of A, B, and C
Which of the following would likely result from infection with a virus that causes lysis (breakage) of lysosome membranes? Consider that the total volume of the lysosomes is approximately 50 cubic microns and the total volume of the cell is approximately 500 cubic microns.
The lysosomal enzymes would be inactivated due to an increase in pH.
Shown below are the results of two fluorescence recovery after photobleaching (FRAP) experiments. Which of the following could explain the difference between the data represented by the dashed line as compared to the data represented by the solid line?
The membrane of the cell indicated by the dashed line contains longer fatty acid chains in its phosopholipids.
Which of the following is true of steroid hormones but not a signaling molecule such as a ligand for G-protein coupled receptors?
Their receptors regulate gene transcription.
Which of the following is true for all enzymes?
They alter the transition state.
Which of the following is true for all enzymes?
They increase the reaction rate.
Which of the following is never true of enzymes?
They lower ΔG of a reaction.
Which of the following statements is TRUE?
Tubulin and actin are both enzymes.
Which of the following statements is TRUE?
Tubulin is an enzyme.
The Na+/K+ ATPase transports Na+ up its concentration gradient and K + ______ its concentration gradient. This is an example of ______ .
Up; Direct active transport
Chymotrypsin is a pancreatic digestive enzyme that is inactive until it is secreted into the intestines, where it is hydrolyzed by the protease Trypsin. One of the fragments that results from this hydrolysis is the active form. This form of enzyme regulation is:
Zymogen activation
The active and inactive forms of a hypothetical enzyme are shown below. (The polypeptide is represented by the colored rectangles and grey lines holding them together.) The middle rectangle is the catalytic domain and the reaction it catalyzes is also shown. This form of enzyme regulation is _______.
Zymogen activation
Chloride ion (Cl-) concentrations are approximately 10x higher outside of cells than inside. Imagine you discovered a novel protein that is required in liver cells for transporting Cl- out of the cell up its concentration gradient, and further found that this protein only functions if the Na+/K+ ATPase is active. Which of the following might you reasonably conclude about the Cl- transport protein?
a Na+/Cl- antiporter
Fill in the blank: The name of the cytoskeleton fiber that polymerizes to form pseudopods during amoeboid cell migration is called ___. (one word; spelling matters!)
actin
Liver cells respond to epinephrine by breaking down glycogen. What is the second messenger in this pathway?
cyclic AMP
∆G°' for the hydrolysis of ATP is considered to be:
highly exergonic
Fill in the blank: The cytoskeleton "railroad tracks" used by motor proteins to transport vesicles and other organelles to and from the plasma membrane is called ___.
microtubules
Fill in the blank: The name of the motor protein that uses actin as its cytoskeletal partner is called ___. (one word; spelling matters!)
myosin
If the graph below is a free energy diagram for a reaction, what is number 3?
ΔG of the reaction