BIO 201
What is ∆G°' for the hydrolysis of ATP?
-7.3 kcal/mol
The protein:lipid ratio in a typical membrane (e.g. red blood cells) is approximately:
1:1
Cholesterol generally makes up what percentage of the lipid mass of the plasma membrane?
25%
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
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.
If it were injected directly into liver cells, cAMP would have the effect of:
Activating Protein Kinase A and, therefore, glycogen breakdown
Protons (H+) are moved up their concentration gradients into the lysosome in order to activate lysosomal enzymes. This is an example of:
Active transport
Pyrimidines are synthesized through a long series of reactions beginning with the amino acid aspartate. The ribonucleotide CTP is the final compound in this pathway, and when there is enough CTP, it binds to and inhibits the enzyme that catalyzes the first reaction in the pathway, aspartate transcarbamoylase (ATCase). Because CTP is structurally and chemically different from the enzyme's natural substrates, this type of regulation must be:
Allosteric inhibition
Which of the following is true for both GPCR signaling and steroid hormone signaling?
An extracellular signal is transduced to an intracellular response. They may have widespread effects because they may be secreted into the bloodstream. Both of the above They involve enzyme cascades
Which of the following is/are likely to elicit a rapid, reversible response?
An odorant that binds to a G protein-coupled receptor
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
As we learned in Lecture 15, protein phosphatases catalyze removal of phosphate groups from proteins. How would the activity of a protein phosphatase affect a cell's response to growth factors?
Decrease proliferation
Which of the following is a disadvantage of being a multicellular organism?
Decreased structural stability
Which of the following is NOT consistent with the fluid mosaic model of cell membranes?
Different types of phospholipids are distributed equally between the inner and outer leaflets of the membrane.
The H+ ATPase (a.k.a. "proton pump") creates electrochemical gradients across the membranes of many protists. This is an example of:
Direct active transport.
"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
After you eat, insulin is secreted by pancreatic Beta cells into the bloodstream, where it diffuses throughout the body to bind to receptors on target cells, telling them to take up glucose. This mode of signaling is referred to as:
Endocrine
Which of the following is a mechanism by which cells ensure a strong response to a small amount of ligand?
Enzyme cascades
True or false: Only mutations that alter amino acid residues in the active sites of enzymes affect the function of the enzyme.
FALSE
True or false: if ΔS > 0, the reaction is definitely exergonic.
FALSE
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
Ca++ flowing down its concentration gradient through a Ca++ channel is an example of:
Facilitated diffusion.
True or False: The concentration of Ca++ in the cytoplasm is higher than it is in the smooth ER.
False
Which of the following is a disadvantage of being multicellular?
Greater energy needs More difficult to absorb nutrients Reproduction more complicated All of the above
Factors that increase membrane fluidity have the effect of _______ membrane permeability:
Increase
Even though the blood glucose concentration may drop below the intracellular glucose concentration - for example, during a long fast - brain cells can still absorb glucose from the bloodstream. Under these circumstances, how does glucose get into the cells?
Indirect active transport
Unlike in animals, in which the Na+ gradient is used, it is the H+ gradient in some other species that fuels transport of other compounds up their concentration gradients. This type of transport is:
Indirect active transport
Which of the following never uses simple diffusion to pass through the cell membrane?
Ions
Cells shrink when you place them in a solution with a high concentration of the amino acid glycine. This indicates that the cell membrane:
Is NOT permeable to glycine but IS permeable to water
Which of the following is an advantage of endocrine signaling?
It affects large numbers of cells.
Which of the following is a DISadvantage of paracrine signaling?
It affects only a small number of cells.
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.
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 and then epinephrine. You observe that the cells fail to produce glucose. Which of the following could be how the compound acts?
It could inhibit the GTPase activity of Gα. It could increase the affinity of Gα for GTP. It could cause Gα to bind more tightly to adenylate cyclase. None of the above
Dr. Hutson really likes coffee. Caffeine is a xanthine, a class of molecules that are similar to purines. One of the mechanisms by which caffeine acts is to inhibit the enzyme cAMP phosphodiesterase, which converts cAMP to plain old AMP, which is inactive. How does caffeine alter liver cell responses to epinephrine?
It increases glucose production.
Which of the following is NOT TRUE of a second messenger in signal transduction?
It is diffusible It is produced when the "first messenger" binds to its receptor It may activate enzymes All are TRUE
G-alpha is not only an activator of Adenylate cyclase, but it is a GTPase. How does mutation in G-alpha that decreases its GTPase activity affect liver cell responses to epinephrine?
It would increase glycogen phosphorylase activity.
Chloride ion (Cl-) concentrations must be maintained much higher outside of cells than inside of cells. How this gradient is maintained is complex, but a key transporter co-transports Cl- along with K+ ions. The name of this transport protein could be ____ and its mode of transport would be ____.
K+/Cl- symporter; indirect active transport
Which of the following enzymes catalyzes phosphorylation of proteins using a phosphate group from ATP?
Kinases
Which of the following is an advantage of multicellularity?
Larger size Greater mobility Functional specialization of cells/tissues All of above
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. This suggests that the Cl- transport protein is a:
Na+/Cl- antiporter
Which of the following should be able to diffuse most easily through a cell's plasma membrane?
O2(nonpolar/small)
Which of the following enzymes catalyzes dephosphorylation of proteins?
Phosphatases
If you wanted to decrease liver cell responses to epinephrine, which of the following classes of enzymes would you want to increase in activity?
Protein phosphatase (catalyzes dephosphorylation)
Where in the cell would you expect to see a Ca++ ATPase?
Smooth ER
True or False: The concentration of Na+ outside the cell is higher than it is inside.
TRUE
Which of the following statements is NOT true?
The entropy of a closed system always tends to increase. The enthalpy of a closed system ALWAYS increases An exergonic reaction releases energy. In order to decrease entropy, energy must be provided from somewhere.
The reaction below, phosphorylation of glucose, is exergonic because it is coupled to ATP hydrolysis. The enzyme hexokinase catalyzes this reaction. Which of the following best describes how an enzyme for this reaction works? glucose + ATP <=> glucose-6-P + ADP
The enzyme alters the mechanism of the reaction by altering the transition state.
If the graph below is a free energy diagram for a reaction, what is C?
The free energy of the products
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.
What is the second messenger in the receptor tyrosine kinase signaling pathway?
The receptor The small GTPase ras The enzyme MAPK that gets transported into the nucleus to activate gene transcription None of the above
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.
A major function of the epithelium in animals is to prevent entry of pathogens and toxins from the environment. Which of the following is common to all epithelial cells?
They are held together by tight junctions.
Cell adhesion molecules are important components of:
Tight junctions
True or False: The concentration of Ca++ outside the cell is higher than it is inside.
True
Liver cells respond to epinephrine by breaking down glycogen. What is the second messenger in this pathway?
cyclic AMP
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?
decrease glucose production
Which of the following is an advantage of juxtacrine signaling?
fast
Which of the following is a DISADVANTAGE of endocrine signaling?
slow
True or False: The concentration of K+ inside the cell is higher than it is outside.
true
