WGU Biochem Mod 2 Questions

WGU Biochem Mod 2 Questions. Unit 2 Quiz 1. Which level of protein structure is disrupted through the hydrolysis of peptide bonds? a. Primary b. Tertiary c. Secondary d. Quaternary Answer: A. The primary structure of a protein is the sequence of amino acids held together by peptide bonds. Peptide bonds are formed by dehydration reactions and disrupted by hydrolysis. 2. A mutation in the beta-hemoglobin gene, which results in the replacement of the amino acid glutamate in position 6 with the amino acid valine, leads to the development of sickle cell anemia. The structures of glutamate and valine are shown below. Amino acid structures of glutamate and valine If the beta hemoglobin gene in a patient with sickle-cell anemia were to be edited so that the valine in position 6 wasreplaced with a different amino acid, which replacement for valine would be expected to have the best clinical outcome, in theory, for the patient? (Assume the valine can potentially be replaced with any amino acid other than glutamate.) A. b. c. d. Answer: B. The original amino acid in a healthy patient is glutamate, which is negatively charged. The mutated amino acid is valine, which is non-polar. Valine is causing sickle cell anemia. The best amino acid to replace valine so that the patient is healthy again would be the one most like glutamate, so any negatively charged amino acid. Amino acid structure C is non-polar, not charged. 3. Secondary, tertiary, and quaternary levels of protein structure can all be impacted by exposing a protein to which treatment? a. Increase in the concentration of the protein in solution b. Placement of the protein in a solution with a low pH c. Addition of a reducing agent d. Change of a hydrophobic amino acid to a different hydrophobic amino acid Answer: B. The correct answer is “Placement of the protein in a solution with a low pH”. The addition of a reducing agent would only affect disulfide bonds in the side chains of polar amino acids containing SH. These types of bonds are only found in the tertiary and quaternary structure, not secondary structure. 4. An increase in beta-pleated sheet structure in some brain proteins can lead to an increase in amyloid deposit formation, characteristic ofsome neurodegenerative diseases. What isthe primary biochemical process that follows the increase in beta-pleated sheet structure that leads to the development of the amyloid deposits? a. An increase in anaerobic metabolism of glucose in the brain b. Aggregation of the proteinsin the brain c. An increase in glycogen formation in the brain cells d. Secretion of glucagon, leading to excessive ketogenesis Answer: B. The correct answer is “Aggregation of the proteins in the brain”. This question is describing changes in protein structure. Glycogen is a carbohydrate, not a protein, and is stored in the liver and muscles, not the brain. See Unit 6 for more information on glycogen. 5. Which level of protein structure is determined by the sequence of amino acids? a. Secondary structure b. Tertiary structure c. Primary structure d. Quaternary structure Answer: C. The correct answer is “Primary structure”. The primary structure of a protein is simply the sequence of amino acids held together by peptide bonds. The quaternary structure of a protein is when two or more polypeptide chains(“subunits”) work together to perform the function of the protein. The two or more polypeptide chains are held together by side chain interactions, including the hydrophobic effect, ionic bonds, disulfide bonds, and hydrogen bonds. 6. Which force is most influential in determining the secondary structure of a protein? a. Disulfide bonding b. Hydrophobic effect c. Hydrogen bonding d. Electrostatic interactions Answer: C. The secondary structure of a protein is built by hydrogen bonds between the carboxyl groups and amino groups on the backbones of the amino acids. 7. Which amino acid would most likely participate in hydrogen bonds? a. b. c. d. Answer: C. This is a polar, uncharged amino acid due to the OH group on the side chain. Polar, uncharged amino acids containing oxygen or NH groups make hydrogen bonds. 8. Which portion of the amino acid isinside the box? a. Amino group b. Alpha carbon c. Side chain d. Carboxyl group Answer: C. The side chain is the variable group of the amino acid, also called the R group. Every amino acid has the same amino group, carboxylic acid group, and an alpha carbon, but the side chain is different. 9. Which pair of amino acids will most likely interact through hydrophobic forces between their side chains? a. b. c. d. Answer: D. “Pair of amino acids (3)”. In “Pair of amino acids (4)” the left is non-polar and therefore can make hydrophobic interactions, but it must do this with another non-polar amino acid. The amino acid on the right is polar, uncharged due to the SH group. Please note that the “S” in the amino acid on the left is non-polar, while the “SH” group is polar. The S must have an H to be polar and is otherwise non-polar. SH groups make disulfide bonds with other SH groups. 10. Which portion of the amino acid is inside the box? a. Alpha carbon b. Amino group c. Carboxyl group d. Side chain Answer: A. The alpha carbon is the central carbon on an amino acid that holds together the other groups of the amino acid. It is always attached to the amino group, the carboxyl group, the side chain, and a single hydrogen. It is part of the backbone of the amino acid and is found in every amino acid. 11. Given the following amino acid structure, what isthe strongest intermolecular force it would participate in to stabilize a protein structure? a. Hydrogen bond b. Hydrophobic interaction c. Disulfide bond d. Ionic bond Answer: B. The correct answer is “Hydrophobic interaction”. The amino acid pictured only has CH groups in its side chain, and therefore is non-polar. Non-polar amino acids make hydrophobic interactions. Hydrogen bonds occur between polar, uncharged amino acids containing oxygen or NH groups in their side chains. 12. Which change would most likely result in a permanent modification of an expressed protein’s function? a. An increase in the pH of a solution in which a protein is dissolved from 6.5 to 8.0, when it is known that the protein has an optimal activity of pH 7.8 b. A mutation of the gene for a protein that leads to the substitution of a hydrophobic amino acid with a nonpolar amino acid c. A mutation of the gene for a protein that leads to the substitution of a nonpolar amino acid with a charged amino acid d. The mutation of a gene for an enzyme involved in protein synthesisfollowing exposure to X-rays, causing the protein not to be synthesized Answer: C. The correct answer is “Mutation of the gene for a protein that leads to the substitution of a nonpolar amino acid with a charged amino acid”. A “hydrophobic amino acid” is the same thing as a “non-polar amino acid”. Therefore, the protein’s function will not be disrupted. Additional Practice Questions – Unit 2 1. Which kind of interaction can the following pair of amino acids form between their side chains (Rgroups)? a. Disulfide bond b. Hydrogen bond c. Ionic bond d. Hydrophobic interaction Answer: The correct answer is ‘hydrogen bonds’. Hydrogen bonds are made between R groups that have polar bonds within them N-H, O-H, C-O or C-N but do not display a visible charge (+/-) on their R group. The disulfide bond is a very specific interaction between two cysteine amino acids where their sulfur atoms (S) bond to each other covalently (S-S). 2. Which bond or interaction can the R group of this amino acid form to stabilize tertiary structure? a. Disulfide bond b. Hydrophobic interaction c. Ionic bond d. Van der Waalsinteraction Answer: Cysteine can also form a disulfide bond with its terminal S-H. van der Waals interactions form when atoms are close together, such as when hydrophobic interactions form in the core of the protein. Hydrophobic interactions are formed by non-polar amino acids that have R groups with C-H bonds. 3. A missense mutation resulting in a change from asparagine to leucine at a specific position on an enzyme leads to a neurodegenerative disease. Isthere an alternate amino acid substitution of a missense mutation listed below that would have less of an impact on the protein structure and consequently its function than the proposed leucine substitution would? a. b. c. d. Answer: The correct answer is ‘Glutamine’. Glutamine is a polar amino acid and the amino acid asparagine is a polar amino acid, which contain C-N, C-O, O-H or N-H bonds on the outside surface of their R groups. The most likely replacement for a polar amino acid that would have less of an impact on protein structure would be another polar amino acid. Glutamate is a charged amino acid. 4. Choose the answer that correctly labels the amino group, the carboxyl group, and the variable group on the amino acid from the image: a. A-carboxyl group, B-variable group, D-amino group b. A-amino group, B-carboxyl group, D-variable group c. A-variable group, B-amino group, C-carboxyl group Answer: C. A is a variable group and can be any one of 20 different things, B is an amine group that contains one nitrogen and three hydrogens, C is a carbonyl group consisting of one carbon and two oxygens and, D is a hydrogen atom found attached to the central carbon (carbon alpha). 5. Which characteristic correctly describes the amino acid image? a. Polar b. Charged c. Non-polar Answer: C. Non-polar amino acids have R groups with C-H bonds. 6. Which of the following interactions can occur between two positively charged amino acids? a. none of these b. hydrogen bond c. disulfide bond d. hydrophobic interaction e. ionic bond Answer: The correct answer is‘none of these’. Two positively charged amino acids would repel each other. Only opposite charges attract. Ionic bonds occur between two oppositely charged amino acids. 7. Antibodiesthat enable our body to fight bacterial infections must bind to antigens on the surface of the bacterial cell. If the antigen on the surface of the bacterial cell has several negatively charged amino acids, which of the following amino acids would you expect to find on the portion of the antibody that binds to the antigen? a. b. c. d. Answer: The correct answer is C. Positive charged amino acids will be attracted to the negatively charged amino acids. 8. What category does this amino acid belong to? a. Polar, uncharged b. Nonpolar c. Polar, charged Answer: C. The amino acid depicted is charged. There is a COO- group displayed as the R group of this amino acid with a visible charge. 9. This amino acid is polar. a. True b. False Answer: True. The amino acid depicted in this problem is polar/hydrophilic because the end of the amino acid R group has an oxygen bound to a hydrogen. Other polar amino acids can have nitrogen bound to hydrogen, carbons bound to oxygens or carbons bound to nitrogens. 10. This amino acid would prefer to interact with oil over water. a. True b. False Answer: False. The amino acid depicted in this problem is polar/hydrophilic because the end of the amino acid R group has a nitrogen bound to a hydrogen. Other polar amino acids can have oxygen bound to hydrogen, carbons bound to oxygens or carbons bound to nitrogens. Water is also polar and that is why this amino acid would like to interact with water and why the amino acid is categorized as hydrophilic (water loving). Oils are nonpolar and polar amino acids don't like nonpolar molecules. 11. Which of the following best describes the nature of protein primary structure? a. Amino acids linked together in a specific order by peptide bonds b. Two or more polypeptide chains coming together to form the final functional protein c. The overall three-dimensional shape of a chain of amino acids d. Structural elements such as alpha helices and beta-pleated sheets Answer: A. The correct answer is ‘Amino acids linked together in a specific order by peptide bonds’. The sequence of amino acids connected by peptide bonds in a specific order defines the protein primary structure. Two or more polypeptide chains coming together to form the final functional protein refers to a quaternary structure. 12. Which of the following statements about the different levels of protein structure istrue? a. The interactions between the side chains of the amino acids make up the secondary level structure of a protein b. Peptide bonds between amino acids make up the secondary structure of a protein c. The interactions between the side chains of the amino acids make up the tertiary level structure of a protein d. Two or more polypeptides each with their own secondary structures come together to form a single larger tertiary structure of a protein Answer: The correct answer is ‘The interactions between the side chains of the amino acids make up the tertiary level structure of a protein’. Two or more polypeptides each with their own tertiary structures come together to form a single larger quaternary structure of a protein. 13. Which type of bonding or interaction is correctly paired with a chemical or change in environment that will disrupt/break the interaction or bond? a. Hydrogen bonds/ionic bonds: Change in pH b. Hydrophobic interactions: Change in pH c. Peptide bonds: Reducing agents d. Peptide bonds: Change in pH Answer: A. Changes in pH instead disrupt hydrogen bonds and ionic bonds. 14. Which of the following statements about protein structure and stability istrue? a. Ionic bonds between the side chains of the charged amino acids stabilize the protein structure b. Protein structure is notstabilized by the hydrophobic effect c. Denaturation isthe loss of primary,secondary, and tertiary structure d. Denatured proteinsretain their tertiary structure Answer: A. Ionic bonds help stabilize both the tertiary structure of a protein chain and the quaternary structure of a protein with multiple subunits. 15. The negatively charged amino acid, Glutamate, isreplaced with the negatively charged amino acid Aspartate. Which level of protein structure is most significantly impacted by this change? a. Tertiary structure b. Secondary structure c. Quaternary structure d. Primary structure Answer: D. The correct answer is ‘primary structure’. The original and substitute amino acid both have a negative charge and can both form an ionic bond with a positively charged amino acid. The amino acid sequence, however, has been altered, and so the primary structure has certainly been changed. The secondary structure of a protein depends on backbone interactions, and these are probably unaffected. 16. Which of the following pairs of amino acids are NOT likely to interact with one another to stabilize tertiary structure? a. b. c. d. Answer: B (option 4). This is correct because the side-chains of aspartate and glutamate are both negatively charged, they will repel each other. Opposite charges attract and like charges repel. 17.17. Which portion of the amino acid above islikely to engage in a hydrogen bond with an oxygen in the carboxyl group of another amino acid as part of a beta pleated sheet? C D A B Answer: The correct answer is ‘A’. Secondary structures arise from hydrogen bonding between backbone atoms. The H attached to the more electronegative N can form a hydrogen bond to the carboxyl O. This H atom is attached to a C atom, which leads to a non-polarized bond and no capability for hydrogen bonding 18. Primary structure consists of the order of in a protein. These are held together with bonds that are formed by a reaction. a. Amino acids, peptide, dehydration b. Nucleotides, phosphodiester, dehydration c. Nucleotides, peptide, dehydration d. Amino acids, peptide, hydrolysis Answer: A. Protein primary structure is defined by the order of amino acids that make up the protein. The amino acids are linked together by peptide bonds, which are formed via dehydration reactions. 19. Which of the following statements describes the tertiary structure of a protein? a. It involves hydrogen bonding between the backbone atoms. b. It includes beta pleated sheets as a common form. c. It involves hydrogen bonding between amino acid side- chains. d. It includes alpha helices as a common form. Answer: C. The correct answer is‘It involves hydrogen bonding between amino acid side- chains’. Secondary structures arise from hydrogen bonding patterns between backbone atoms. The most common secondary structures are alpha-helices and beta sheets. 20. What type of reaction breaks peptide bonds apart? a. Oxidation/Reduction Reaction b. Condensation Reaction c. Methylation Reaction d. Hydrolysis Reaction Answer: D. The correct answer is‘hydrolysisreaction’. Peptide bonds are formed by dehydration reactions(named for the loss of water that occurs) and broken via hydrolysis (named for the addition of water). To break this down further, hydro- meaning water, and -lysis meaning cutting, the water cuts the peptide bond. For an oxidation/reduction, this reaction transfers electrons from one molecule to another. 21. A toddler mistakenly swallows a bathroom cleaning solution, containing a strong reducing agent. Which interaction is most likely to be disrupted within a glycoprotein in the lining of the toddler’s esophagus? a. Disulfide Bond b. Ionic Bonds c. Hydrogen Bond d. Hydrophobic interactions Answer: A. Reducing agents disrupt disulfide bonds