Biochem Answers PDF

BIOCHEM Answers 1. What are enzymes? Answer: Biological catalysts that speed up the rate of biochemical reactions Enzymes are proteins that act as catalysts in biological reactions. They accelerate the rate of these reactions without being consumed in the process. 2. What is the region that b...

BIOCHEM Answers 1. What are enzymes? Answer: Biological catalysts that speed up the rate of biochemical reactions Enzymes are proteins that act as catalysts in biological reactions. They accelerate the rate of these reactions without being consumed in the process. 2. What is the region that binds substrates, cofactors and prosthetic groups in enzymes called? Answer: Active site The active site is a specific region on an enzyme that binds to substrates and facilitates the catalytic reaction. 3. Most enzymes are 3D globular proteins. A. True B. False Answer: True (A) The tertiary structure of proteins enables enzymes to have a specific shape and function. 4. What are the two parts of the active site? Answer: Binding site and catalytic site The binding site specifically binds to the substrate, while the catalytic site performs the actual chemical reaction. 5. What is the function of a co-factor? Answer: Carries out chemical reactions that cannot be performed by standard 20 amino acids. Co-factors are non-protein molecules that assist enzymes in their catalytic activity. They often provide essential atoms or chemical groups needed for the reaction. 6. Which of these is NOT a characteristic of enzymes? A. Highly specific B. Sensitive to change C. Affect the nature and properties of end products D. Speed up reaction Answer: Affect the nature and properties of end products (C) Enzymes are highly specific catalysts, meaning they only speed up specific reactions. They do not affect the chemical nature or properties of the products formed. 7. What is turnover number in relation to enzymes? Answer: Number of substrate transformed per minute, by one enzyme The turnover number represents the efficiency of an enzyme. It quantifies how many substrate molecules a single enzyme molecule can convert into product per unit of time. 8. Match the following enzyme classes with their reaction types: 1. A. Non-hydrolytic bond cleavage Isomerases 2. B. Move chemical group Transferases 3. C. Hydrolysis, bond cleavage with Ligases transfer of functional group of water 4. D. Intramolecular group transfer Oxidoreductases (isomerization) E. Synthesis of new covalent bond 5. between substrates using ATP Hydrolases hydrolysis 6. F. Reduction-oxidation (redox) Lysases Answer: Oxidoreductases = Reduction-oxidation (redox) Transferases = Move chemical group Hydrolases = Hydrolysis, bond cleavage with transfer of functional group of water Lysases = Non-hydrolytic bond cleavage Isomerases = Intramolecular group transfer (isomerization) Ligases = Synthesis of new covalent bond between substrates using ATP hydrolysis The International Enzyme Commission classifies enzymes into six major classes based on the type of chemical reaction they catalyze. 9. What are the two perspectives on how enzymes function? Answer: Thermodynamic changes and processes of the active site The thermodynamic changes involve the energy barriers between reactants and products, while the active site processes focus on the specific interactions and mechanisms at the active site. 10. Which of these is NOT one of the ways enzymes catalyze reactions? A. Acid-base catalysis B. Catalysis by proximity C. Catalysis by bond strain D. Transitional state E. Covalent catalysis Answer: Transitional state (D) Enzymes employ various mechanisms to catalyze reactions, including acid-base catalysis, covalent catalysis, proximity effects, and bond strain. The transitional state is a concept related to the energy profile of the reaction, not a specific mechanism of enzyme action. 11. The lock-and-key model by Emil Fischer accurately depicts the dynamic nature of enzyme-substrate interactions. A. True B. False Answer: False (B) The lock-and-key model suggests a rigid interaction between enzyme and substrate, while the induced-fit model, proposed by Daniel Koshland, better reflects the flexible nature of enzyme-substrate binding. In the induced-fit model, the enzyme's active site slightly changes shape upon substrate binding to achieve optimal fit and catalysis. 12. What is the study of the rate of enzyme-catalyzed reactions called? Answer: Enzyme kinetics Enzyme kinetics is a crucial field in biochemistry that investigates how enzymes catalyze reactions and how factors such as temperature, pH, and substrate concentration affect the reaction rate. 13. What are the three main factors that affect the rate of enzyme- catalyzed reactions? Answer: Temperature, hydrogen ion concentration (pH), and substrate concentration These factors influence enzyme activity and reaction rate by affecting the enzyme's structure, substrate binding affinity, and overall catalytic efficiency. 14. What is inhibition in the context of enzymes? Answer: Prevention of an enzyme process as a result of interaction of inhibitors with the enzyme. Inhibition can dramatically reduce or even halt enzyme activity by interfering with the enzyme's catalytic mechanism through various mechanisms. 15. Which type of inhibition involves a molecule competing with the substrate for the active site? A. Noncompetitive inhibition B. Mixed inhibition C. Uncompetitive inhibition D. Competitive inhibition Answer: Competitive inhibition (D) Competitive inhibition occurs when a molecule similar in structure to the substrate binds to the active site, blocking the substrate from accessing it. 16. What type of inhibition involves the covalent attachment of an inhibitor to the enzyme, completely eliminating its catalytic activity? Answer: Irreversible inhibition Irreversible inhibitors permanently modify the enzyme, often through covalent bonds, making the enzyme non-functional and requiring new enzyme synthesis for recovery of activity. 17. Which of these is NOT a way enzymes can be activated? A. Activation by temperature increase B. Activation by phosphorylation C. Activation by cofactors D. Activation by allosteric regulation E. Activation by proteolytic cleavage Answer: Activation by temperature increase (A) Temperature can influence enzyme activity, but it generally does not act as a specific mechanism for enzyme activation. Activation typically involves specific molecular events, such as binding of cofactors, proteolytic cleavage, phosphorylation, or allosteric regulation. 18. Pepsin is an example of an enzyme activated by proteolytic cleavage. A. True B. False Answer: True (A) Pepsin is initially synthesized as an inactive zymogen called pepsinogen. It is activated by proteolytic cleavage in the stomach, revealing its active catalytic site. 19. What are the four main types of enzymes specificity? Answer: Bond specificity, group specificity, substrate specificity, and optical/stereo-specificity These specificities define the specific types of substrates that enzymes can interact with and catalyze reactions. 20. Enzymes can function on multiple substrates with different reaction types. A. True B. False Answer: False (B) Enzymes are highly specific catalysts, meaning they usually act on one or a very limited number of substrates and perform one or very few specific reactions. While some enzymes might exhibit broader specificity, their activity is still generally restricted. 21. What is the common backbone structure of lipids? Answer: Glycerol Glycerol is a three-carbon alcohol that forms the backbone for many types of lipids, including fats, oils, and phospholipids. 22. What is the basic structural unit of lipids that contains a carboxylic acid group? Answer: Fatty acid Fatty acids are long-chain carboxylic acids that are essential components of various lipid types. Based on their structure, they are categorized as saturated or unsaturated. 23. Which of these is NOT a characteristic of saturated fatty acids? A. Solid at room temperature B. Contain only single carbon-carbon bonds C. Closely packed D. Low melting points E. Strong attractions between their chains Answer: Low melting points (D) Saturated fatty acids have high melting points due to their closely packed structures, making them solid at room temperature. In contrast, unsaturated fatty acids have lower melting points. 24. What are triacylglycerols? Answer: Storage form of fatty acids in organisms, typically found as fats or oils Triacylglycerols or triglycerides are the main storage form of fatty acids in living organisms. They are composed of three fatty acid chains esterified to a glycerol molecule. 25. Which of these is NOT a function of triglycerides? A. Storage form of energy B. Insulation and protection C. Carriers of fat-soluble compounds D. Sensory qualities (flavor and texture) E. Structural component of cell membranes Answer: Structural component of cell membranes (E) While lipids play crucial roles in cell membranes, triglycerides are primarily responsible for energy storage and insulation. Their unique properties also contribute to the flavor and texture of foods. 26. What are complex lipids? Answer: Lipids containing additional components besides fatty acids and alcohol, such as proteins, carbohydrates, phosphates, sulfates, and nitrogen Complex lipids, unlike simple lipids, incorporate diverse molecules beyond fatty acids and glycerol, making them more structurally and functionally diverse. 27. What are the main functions of phospholipids? Answer: Structural and regulatory functions in cell membranes as well as absorption of fats and transport of lipids Phospholipids create the phospholipid bilayer, forming the structural basis of cell membranes. Their role in transport and absorption is also essential for various biological processes. 28. Glycolipids are made up of fatty acids, an alcohol, and some carbohydrates. A. True B. False Answer: True (A) Glycolipids are a class of complex lipids characterized by their unique combination of fatty acids, an alcohol (such as sphingosine), and carbohydrate components. 29. What are lipoproteins? Answer: Lipids combined with specific proteins, crucial for the transport of lipids around the body Lipoproteins play a vital role in lipid metabolism by enabling the efficient transport of lipids through the bloodstream, both for storage and delivery to various tissues. 30. Steroids are lipids containing a steroid nucleus, which consists of four fused rings. A. True B. False Answer: True (A) Steroids are a distinct class of lipids characterized by their unique fused ring system, which is made up of three cyclohexane rings and one cyclopentane ring. 31. Cholesterol is the most common steroid in the body. A. True B. False Answer: True (A) Cholesterol is a crucial steroid molecule in the body. It serves as a precursor for various hormones and is a key component of cell membranes, contributing to their structural integrity and fluidity. 32. What are the major reactions that lipids undergo? Answer: Hydrolysis, saponification, hydrogenation, iodination, and oxidation These reactions involve breaking or modifying the chemical bonds within lipids, altering their structure and properties, leading to diverse biological roles and transformations. 33. What is the main function of lipids in terms of energy? Answer: Serving as a storage form of energy in the body Lipids, particularly triglycerides, are the primary energy storage molecules in the body. When energy is needed, these stored lipids can be broken down to release energy. 34. Cholesterol plays a role in stabilizing the fluidity of cell membranes. A. True B. False Answer: True (A) Cholesterol has a unique structure that can influence membrane fluidity. At higher temperatures, it can restrict movement, reducing fluidity, while at lower temperatures, it can prevent excessive packing of phospholipids, increasing fluidity. 35. Which of these is NOT a type of membrane protein? A. Integral proteins B. Surface proteins C. Transmembrane proteins D. Peripheral proteins Answer: Surface proteins (A) Membrane proteins play various roles in cellular processes. Peripheral, integral, and transmembrane proteins are common categories. Surface proteins are not a recognized category of membrane proteins. 36. What are the two main types of membrane transport? Answer: Passive and active transport Passive transport relies on the concentration gradient of molecules, and active transport utilizes energy to move molecules against their concentration gradients. 37. Simple diffusion is a type of active transport. A. True B. False Answer: False (B) Simple diffusion is a type of passive transport. It does not require energy and is driven by the movement of molecules from areas of high concentration to areas of low concentration. 38. What are the two main categories of vitamins? Answer: Fat-soluble and water-soluble vitamins Vitamins are essential organic compounds that our bodies cannot synthesize themselves. They are classified based on their solubility properties: fat-soluble vitamins can be stored in the body, while water-soluble vitamins are not stored and are easily excreted in urine. 39. Vitamin A is important for vision. A. True B. False Answer: True (A) Vitamin A plays a vital role in vision by participating in the process of light absorption. It is essential for the production of rhodopsin, a pigment responsible for low-light vision. 40. What is the primary role of vitamin D in the body? Answer: Regulating calcium and phosphorus metabolism Vitamin D is crucial for maintaining proper levels of calcium and phosphorus in the body. It promotes calcium absorption from the gut, and it also plays a role in bone formation and maintenance. 41. What are the main functions of prostaglandins? Answer: Signaling molecules involved in various physiological processes, including inflammation, pain, and blood clotting Prostaglandins are a group of lipids that act as signaling molecules in the body, regulating inflammation, pain perception, and blood clotting. 42. What is the primary role of leukotrienes? Answer: Signaling molecules involved in inflammation and immune responses Leukotrienes are a group of lipids that act as signaling molecules, primarily involved in inflammation and allergic responses. They are produced by white blood cells and are important mediators of the immune system. 43. What is a carbohydrate? Answer: A polyhydroxyaldehyde, a polyhydroxyketone, or a substance that gives these compounds on hydrolysis Carbohydrates are a class of organic compounds that are essential for various biological functions, including energy production, structural support, and cell signaling. 44. A monosaccharide can be hydrolyzed into a simpler carbohydrate. A. True B. False Answer: False (B) Monosaccharides, also known as simple sugars, are the simplest forms of carbohydrates. They cannot be further broken down by hydrolysis into simpler carbohydrates. 45. An aldose is a monosaccharide with an aldehyde functional group. A. True B. False Answer: True (A) Aldoses are a type of monosaccharide containing an aldehyde functional group, while ketoses contain a ketone functional group. 46. What are the simplest monosaccharides? Answer: Trioses with three carbon atoms Trioses, such as glyceraldehyde and dihydroxyacetone, are the smallest monosaccharides, having only three carbon atoms. 47. How is the configuration of a monosaccharide determined in the Fischer projection? Answer: The position of the hydroxyl group (-OH) on the penultimate carbon atom The Fischer projection uses a two-dimensional representation to show the configuration of a monosaccharide. If the OH group is on the right, it is a D- sugar; if it's on the left, it's an L-sugar. 48. Epimers are stereoisomers that differ in the position of the hydroxyl group on only ONE chiral center. A. True B. False Answer: True (A) Epimers are a type of isomer that have the same molecular formula but differ in the configuration of only one chiral center. This difference typically involves the position of a hydroxyl group on a carbon atom. 49. Enantiomers are mirror images of each other. A. True B. False Answer: True (A) Enantiomers are a type of stereoisomer that are non-superimposable mirror images of each other. They have the same chemical formula but differ in their three-dimensional arrangement. 50. Diastereomers are stereoisomers that are NOT mirror images of each other. A. True B. False Answer: True (A) Diastereomers are a type of stereoisomer that are not mirror images of each other. They have the same molecular formula but differ in the configuration of at least one chiral center, but not all. 51. What happens when a sugar forms a cyclic molecule? Answer: The carbonyl group reacts with a hydroxyl group on a distant carbon atom, forming either a hemiacetal or hemiketal. Cyclization is a common process for sugars, especially pentoses and hexoses. This reaction creates a cyclic structure where the carbonyl carbon becomes chiral, leading to the formation of anomers. 52. The anomeric carbon is a new chiral center in a cyclic sugar. A. True B. False Answer: True (A) The anomeric carbon is the carbon atom that was originally part of the carbonyl group in the open-chain form of the sugar. Upon cyclization, it becomes a new chiral center due to the formation of a hemiacetal or hemiketal. 53. Haworth projections represent cyclic hemiacetals or hemiketals as planar pentagons or hexagons. A. True B. False Answer: True (A) Haworth projections are a commonly used method for visualizing cyclic forms of sugars. They depict the cyclic structures as simplified planar representations, with the rings represented as pentagons or hexagons. 54. A pyranose is a six-membered ring, while a furanose is a five- membered ring. A. True B. False Answer: True (A) Pyranoses and furanoses are different cyclic forms of sugars named after the heterocyclic compounds pyran and furan. Pyranoses have a six-membered ring, while furanoses have a five-membered ring. 55. In Haworth projections, an alpha anomer has the hydroxyl group on the anomeric carbon pointing up (above the plane of the ring), while a beta anomer has it pointing down (below the plane of the ring). A. True B. False Answer: False (B) The orientation of the hydroxyl group on the anomeric carbon in Haworth projections is reversed. An alpha anomer has the hydroxyl group pointing down (below the plane of the ring), while a beta anomer has it pointing up (above the plane of the ring).