NAME Chem 351 Exam 2

Transcription

1 Multiple hoice For Problems 1-15, pick the BEST answer. Write the letter corresponding to your choice in the box provided at the end of this section. 1) almodulin is a(n): A) allosteric activator of calcium-dependent enzymes. B) calcium-dependent enzyme. ) allosteric inhibitor of calcium-dependent enzymes. D) regulatory subunit of calcium-dependent enzymes. E) cell-surface calcium receptor. 2) Sphingosine is not a component of: A) cardiolipin B) ceramide ) cerebrosides D) gangliosides E) sphingomyelin 3) Which of these is a general feature of the lipid bilayer in all biological membranes? A) Polar, but uncharged, compound readily diffuse across the bilayer B) Polar head groups of lipids face toward the inside of the bilayer ) Individual lipid molecules are free to diffuse laterally in the surface of the bilayer D) The bilayer is stabilized by covalent bonds between neighboring phospholipids E) Individual lipid molecules readily flip from the outer to the inner monolayer 4) A particular reaction A + B + D has a ΔG = kj/mol. This reaction as written: A) can never occur in a cell. B) can occur in cells at some concentrations of substrate and product. ) cannot occur because of its large activation energy. D) can occur in a cell only if it is coupled to another reaction for which ΔG is positive. E) A and are both correct. F) B and D are both correct. 5) Facilitated diffusion through a biological membrane is A) driven by a difference in solute concentrations B) driven by ATP ) endergonic (ΔG > 0) D) generally irreversible E) not specific with respect to the solute moving

2 6) The β-adrenergic receptor could be best isolated in its native form using: A) a solution of buffer with alkaline or acid p B) a solution containing a chelating agent that removes divalent cations. ) a solution of high ionic strength. D) a solution containing detergent. E) a solution of hot/boiling water. 7) holera and pertussis toxins are: A) enzyme inhibitors B) enzyme modifiers. ) enzymes. D) G-protein signal transduction disrupters. E) all of the above. 8) Which of these statements about the composition of biological membranes is FALSE? A) In a given eukaryotic cell type, all intracellular membranes have essentially the same complement of lipids and proteins. B) Triacylglycerols are not commonly found in membranes. ) The ratio of lipid to protein varies widely among cell types in a single organism. D) The carbohydrate found in membranes is virtually all part of glycolipids and glycoproteins. E) The plasma membranes of vertebrate animal cells contain more cholesterol than mitochondrial membranes. 9) Guanylyl cyclase receptor enzymes: A) are all membrane-spanning proteins. B) are examples of ligand-gated ion channels. ) specifically hydrolyze cgmp. D) require hydrolysis of ATP in addition to GTP E) catalyze synthesis of a phosphate ester bond. 10) A polysaccharide having the same number of reducing and non-reducing ends is: A) A branched carbohydrate structure B) A peptidoglycan ) A linear carbohydrate like amylose D) A typical glycogen structure E) ot able to reduce copper ions

3 11) All of the following may contribute to the large negative free energy change that occurs upon hydrolysis of high-energy ATP molecules except: A) electrostatic repulsion in the reactant B) low activation energy for the hydrolysis reaction ) resonance stabilization of the resulting products D) increased ionization of products E) increased interaction (solvation) with the aqueous environment 12) ormone-activated phospholipase can convert phosphatidylinositol-4,5- bisphosphate to: A) phosphatidyl glycerol + inositol triphosphate B) diacylglycerol + phosophate + inositol ) inositol triphosphate + diacylglycerol D) inositol + phosphate + glycerol E) phosphatidyl glycerol + inositol + phosphate 13) The immediate precursors (building blocks) of DA and RA synthesis in the cell all contain: A) 3 triphosphate groups B) phosphorylated adenine ) deoxyribose D) pentoses containing a 5 triphosphate activating group E) 2 triphosphate groups 14) In Sanger ( dideoxy ) sequencing, the chain-terminating sequence nucleotide: A) lacks an group at its 2' carbon position. B) lacks an group at its 3' carbon position. ) is in molar excess of normal deoxyribonucleotide triphosphate precursors. D) A and B are both correct. E) B and are both correct. 15) A DA oligonucleotide (short polymer of single stranded DA) is abbreviated patga. What statement describes the structure of this sequence best? A) contains 7 phosphate groups. B) has a free hydroxyl group on its 5 end. ) has a free hydroxyl group on its 3 end. D) violates hargaff s rule. E) contains 1 phosphodiester bond linkage

4 Short Answer 1) Fill in the missing information (11 points) A) i) Label each side appropriately: Lungs or deep tissue ii) omplete the reaction arrows to show direction iii) ame the two proteins in the boxes Enzyme: B) The following figure represents the regulation of a particular kinase in the b- adrenergic cascade. Label everything and tell which protein it is. This represents the protein:

5 2) onsider the following system of transporters (A-F). Assume that each transporter acts independently, moving solute(s) in the direction shown. Also note that [solute] indicates that the higher concentration of that solute is in the compartment indicated (i.e. glucose is higher outside, chloride is higher inside, etc.) and the membrane potential is -25mV (inside negative). Provide the letters for the transporters as appropriate ( none if none apply) and answer other questions. (2 points each) a + l - F E K + A l - D Glucose a 2+ + B a 2+ P 4 2- [a 2+ ] [ + ] [l - ] [K + ] [P 2-4 ] [a + ] [Glucose] A) Which transporter(s) is/are electrogenic? B) Which transporter(s) is/are antiporters? ) Which transporter(s) is/are only moving solute(s) down their chemical gradient? D) Which uniporters are moving solute(s) spontaneously considering only the membrane potential (electrical gradient)? E) onsidering only concentration (chemical) gradients, which uniporter(s) must be primary active transport system(s)? F) Which co-transporter(s) must be part of a secondary active transport system? 3) What statement(s) could be used to describe the a + /K + pump (write all that apply) (3 points): A) It is a P-type pump. B) It is a uniporter. ) It is electrogenic. D) It generally transports 3a + into the cell. E) It uses a downhill movement of K + to move a +. F) When it is phosphorylated, its affinity for K + is lower than its affinity for a +. G) Phosphorylation of the protein favors a + release. ) It is the main reason that cells have a transmembrane potential. I) It is a passive transporter.

6 4) The following problems are about the transport of solutes across a red blood cell membrane as it moves through the bloodstream. The following might be useful information: R = 8.3 J/molK T= 298K F (Faraday constant) = 96,500 J/Vmol onsider the following solute concentrations and answer the questions regarding the energy required or gained due to transport of these individual species across the membrane, ΔG t. The transmembrane potential of this cell is -63 mv (inside negative) under these conditions. Watch your sign for these questions and make sure you have units. A) TRASPRT SYSTEM 1 (5 points) Solute Inside the Red Blood ell utside (plasma) Glucose 1.2 mm 0.23 mm 1) What is the total ΔG t for glucose transport into the cell? 2) Assume that this transporter has been observed to follow Michaelis-Menten kinetics with a K t of 2 mm and a V max of 50 mmoles/s. If the red blood cell moves into an area where the glucose concentration in the bloodstream is negligible (0), and the concentration of glucose inside the red blood cell is still 1.2 mm, at what initial rate will the glucose be transported out of the cell? 3) Transport system 1 is likely to be taking place in (circle one): liver muscle B) TRASPRT SYSTEM 2 (5 points) Solute Inside the Red Blood ell utside (plasma) l - a mm 3.2 mm 2.3 mm 2.2 mm 1) What is the total ΔG t for chloride transport into the cell? 2) What is the total ΔG t for calcium transport into the cell? 3) Will an a l-/a 2+ antiporter work under these conditions, assuming passive transport and a 1 l - out for 1 a +2 in activity? 5) Specific Transport Activity (8 points): hoose the letter from each of the following categories (the best one from each column) that describes the transporter named. Energy requirement Electrical Type of transport A. Passive transport D. Electrogenic F. Uniport B. 1 active transport E. on-electrogenic G. Symport. 2 active transport. Antiport A) Acetylcholine receptor B) SERA ) Intestinal sodium/glucose transporter D) AQP (porins)

7 6) alculations of energy! Each problem is worth 2 points, show your work. R = 8.3 J/molK T= 298K F (Faraday constant) = 96,500 J/Vmol Reaction Standard ΔG (kcal/mol) Sucrose + 2 glucose + fructose Glucose-1-phosphate + 2 glucose + P i A) Sucrose phosphorylase catalyzes the phosphorylitic cleavage of sucrose in some microorganisms: Sucrose + Pi glucose-1-phosphate + fructose i) Using the information in the table above, calculate ΔG for the reaction: ii) alculate the K eq for this reaction at 25. Reactions Standard reduction potential (E ) (volts) FAD e - FAD Dihydroxyacetone phosphate e - glycerol-3-phopshate B) For the following reaction: Glycerol-3-phosphate + FAD FAD 2 + dihydroxyacetone phosphate a) alculate ΔE for the reaction. b) alculate ΔG for the reaction. c) Is this reaction thermodynamically favorable under standard conditions? 7) ompare the effects of these two channels by picking the description(s) that apply (not every description must be used, some may be used more than once) (2 pts each) The K + channels that respond in the recovery stage after a neuronal stimulus (action potential). The a +2 (cation) channels involved in visual response in rod cells A) The channel is regulated by ligand binding B) The channel is regulated by a voltage gate ) The channel opens at the signal D) The channel closes at the signal E) The membrane potential of the cell hyperpolarizes F) The membrane potential of the cell depolarizes.

8 ame: hem 351 Exam 2 Structural Analysis 8) onsider the structures shown below. Answer each question with the best word, letter(s) representing the sugar(s), or one, if none of the structures apply (1 point each) A B D E A) What is the stereochemical relationship between A and? B) What is the stereochemical relationship between and D-Glucose? ) Which of the above structure(s) is/are aldoses? D) What is the stereoconfiguration of Sugar B? E) Which of the above sugars is/are pentose(s) F) What is the configuration of the anomeric carbon in sugar E G) D-tagatose is an epimer of D-fructose at carbon-4. Draw the Fischer projection for L-tagatose. (3 points) ) Draw a Fischer projection for sugar D above (3 points) I) Draw the chair conformation (most stable) for the β- pyranose form of sugar above. (3 points) 8

9 ame: hem 351 Exam 2 9) onsider the structures shown below. Answer each question with letters representing the molecule, or one, if none of the structures apply (2 points each). A B 2 P E F P 2 G 2 D 2 (2 points each) Which of the above: A) are or contain ketose sugars? B) are or contain hexose sugars? ) are or contain sugars with an α-anomeric stereochemistry? D) are or contain pyrimidines? E) could be found within a section (polymer) of DA, but is not likely to be found in RA? Full names require numbering the positions of important functional groups, like phosphates on the sugar ring... F) Give the full name of ompound G) Give the full name of ompound D ) Give the full name of ompound E I) Draw UMP (3 points) 9

10 ame: hem 351 Exam 2 10) onsider the structures shown below. Answer each question with letters representing the molecule, or one, if none of the structures apply (2 points each). Rs designate any hydrocarbon chain A B R 1 ( 2 ) D P R 1 R 2 P 3 2 R 1 E R 2 R 1 P F 2 3 ( 2 ) 12 3 A) Which of the above: i) is/are considered glycerophospholipids. ii) contain(s) choline. iii) is/are considered sphingomyelin(s). B) Write the standard systematic abbreviation for ompound A. ) ame ompound D D) ame ompound F E) ame ompound F) For the following set of fatty acids, put them in order of their Tm, from lowest to highest- if any share the same Tm, indicate it by putting parentheses around the letters. a) 24:0 b) 18:1(Δ 9 ) c) 18:2 (Δ 9,11 ) d) 16:2 (Δ 9,11 ) G) Draw the fatty acid whose systematic simple name is 14:2(Δ 9,12 ) (3 points) 10

11 ame: hem 351 Exam 2 11) ompare the function/role of arrestins: True or False (1 point each): A) In the β-adrenergic response (β-adrenergic receptor), arrestins phosphorylate the receptor B) In the β-adrenergic response (β-adrenergic receptor), arrestin binding causes a halt to signal transduction ) In vision signal transduction (rhodopsin activity), arrestin binding to the receptor causes internalization of the receptor (receptor moves into the cell on vesicles) D) In vision signal transduction (rhodopsin activity), arrestin has a higher affinity for the receptor when the receptor is phosphorylated 12) General True or False (1 point each): A) Membrane transporters would show distinct regions of high hydropathy in a hydropathy plot. B) The bilayer is commonly stabilized by covalent bonds between neighboring fatty acids in eukaryotes. ) In the olfactory response, adenylyl cyclase makes camp to open calcium channels D) ovalent regulation by phosphorylation can directly inhibit the K + channel in the gustatory response (taste). E) The all trans form of retinal (in rhodopsin) absorbs incoming light to initiate a vision response. Extra redit: omplete the curved arrow mechanism in which a sugar is attached to a serine residue of a protein, with the help of the + transfer activity of a nearby aspartate residue and a resonance stabilized anomeric carbocation intermediate (you may abbreviate AY structure, as long as the important site(s) are clearly drawn) enzyme active site 2 Asp Protein 2 Ser enzyme active site Asp 2 2 Ser Protein Multiple hoice: 30 Page 4 11 Page 5 15 Page 6 18 Page 7 14 Page 8 15 Page 9 19 Page Page Total: 150 (+4) 11