厦门大学《生物化学》课程试卷Please give the explanations of the terms below: (2 scores per term)1.Hydrogen bondThe hydrogen on one molecule attached to O or N that is attracted to an O or N of a different molecule.2.ZwitterionA zwitterion is a dipolar ion that is capable of carrying both a positive and negative charge simultaneously.3.Quaternary structureThe arrangement of multiple folded protein molecules in a multi-subunit complex.4.Salting outA method of separating proteins based on the principle that proteins are less soluble at high saltconcentrations.5.Induced fitThe change in shape of the active site of an enzyme so that it binds more snugly to the substrate, induced by entry of the substrate.Please fill in the blanks with proper words: (1.5 score per blank)1.Two major elements of secondary structure are the ( α helix) and the ( β strand).2.Polypeptide chains can be synthesized by automated solid-phase methods in which the( carboxyl ) end of the growing chain is linked to an insoluble support.3.Three-dimensional protein structure can be determined by ( NMR Spectroscopy ) and ( X-RayCrystallography ).4.The cleavage of peptide bonds by chymotrypsin is initiated by the attack of a serine residue onthe peptide carbonyl group. The attacking hydroxyl group is activated by interaction with the a ( histidine) residue, a ( aspartate) residue. This catalytic triad generates a powerful nucleophile.5.Three amino acids ( Tyr ), ( Trp ) and ( Phe ) contribute to most of the ultraviolet(UV) absorbance of proteins, which absorb maximally at 280nm.Multiple choices: (1.5 score per choice)1.The roles of carbohydrates are ( e )(i)Structural components (ii) component of nucleic acids (iii) Energy source(iv)Protein modificationa.(i) onlyb.(iii) onlyc.(i), (iii)d.(i), (iii), and (iv)e.All of above2.Which of the following are disaccharides ( a )(i) Galactose (ii) Maltose (iii) Sucrose (iv) Lactosea.(i), (ii)b.(i), (iii)c.(ii), (iii)d.(ii), (iii), (iv)e.(i), (ii), (iii), (iv)3.The difference between D-glucose and L-glucose lies in ( d )a.Carbon 1b.Carbon 2c.Carbon 4d.Carbon 5e.Carbon 64.Which form is the most reducing one for a given monosaccharide ( b )a.Hemiacetalb.Aldosec.Acetald.Alditole.All are equally difficult5.Cellulose and glycogen differ from each other mainly in ( b )a.Chemical compositionb.Glycosidic bond linkagec.Side chain modificationd.None of the abovee.All of the above6.Carbohydrates can be linked to proteins via ( c )(i) Tyrosine (ii) Threonine (iii) Aspartic acid (iv) Asparagine (v) Serinea.(i), (ii), (iii), (iv)b.(i), (iii), (iv), (v)c.(ii), (iv), (v)d.(i), (ii), (iv), (v)e.(i), (ii), (v)7. Starch contains ( e )(i) Amylopectin (ii) Amylose (iii) D-glucosea(i) onlyb(ii) onlyc(iii) onlyd(i) and (ii)e all of the above8. Which of the following statements is false ( a )a.Amylopectin is linear.b.Amylopectin is homopolysaccharides.c.Amylopectin contains glucose.d.Amylopectin is present in plants.e.None of the above9. The significance of the Hershay-Chase experiment is ( c )a.The discovery of messenger RNAb.Phosphate is present in DNAc.DNA replication is semiconservatived.The genetic material is DNAe.The genetic code10. The melting temperature of a fragment of DNA duplex is determined by ( d )(i) The length of fragment (ii) The ratio of GC: AT (iii) The ratio of purines: pyrimidines(iv) The salt concentration in the solutiona.(i), (ii), (iii)b.(iii) onlyc.(i) and (ii)d.(i), (ii), and (iv)e.(i), (iii), and (iv)11.DNA duplex can exist in the following forms except ( c )a. A formb. B formc. C formd.Z forme.H form12.Cholesterol is a precursor of the following hormones except ( b )(i)Testosterone (ii) estradiol (iii) prostaglandin (iv) cortisol (v)progesteronea.(i) and (ii)b.(iii)c.(iv)d.(v)e. None of above13．The proper abbreviation for 5-methyl deoxyuridine diphosphate would be ( b )a. dUDPb. dTDPc. TDPd. UDPe. dCDP14. Which of the following amino acids has positive charge at physiological pH ? ( c )a. Cysb. Gluc. Lysd. Trpe. Ile15. The mass of a protein can be precisely determined by ( c )(i) sedimentation equilibrium (ii) isoelectric focusing (iii) mass spectrometry (iv) massspectrometry chromatography (v) dialysisa (i) onlyb (ii) onlyc (iii) onlyd (i) and (iii) onlye.all of the aboveThe following statements are true (T) or false (F): (1.5 score per choice)1.Vitamin A is a derivative of isoprene. ( T )2.The biological system is an open system, sot living organisms are at equilibrium with theirsurroundings. ( F )3.Activation energy for a chemical reaction is the energy required for a chemical reaction toconvert the reactant to transition state, but does not measure the free energy change between the reactants and products. ( T )4.The Buchners’ discovery of fermentation supported the view that fermentation cannot takeplace outside living cells. ( F )5.Steroids have a common structural motif of three 6-membered rings and one 5-membered ringall fused together. ( T )6.Nonessential fatty acids mean our body does not need them. ( F )7.Biological functions of water can be mostly attributed to its being a small molecule.( F )8.Fructofuranose has an anomeric carbon. ( T )9.In the B form DNA,all bases are in the anti orientation. ( T )10.Fat refers to all water-insoluble compounds. ( F )11.Each core nucleosome contains two subunits of H2A, H2B, H3, and H4. ( T )12. A phospholipid may contain an ether bond. ( T )13.For a DNA polymer to elongate, it must contai n a 3’-OH. ( T )14.The longer the DNA polymer is, the shorter time it takes to renature. ( F )15.Ultraviolet light can cause formation of purine dimers. ( F )16.The ribose in nucleic acid is in beta-furanose conformation. ( T )17. The catalysts in biological systems are enzymes, and all enzymes are proteins. ( F )18. Enzymes serve as catalysts by increasing the free energy of activation of chemical reactions.( F )19. Each amino acid consists of a central tetrahedral carbon atom; all these tetrahedral centers arechiral. ( F )20. Allosteric enzymes are oligomeric enzymes. ( T )Please answer the following questions:1. The following reagents are often used in the protein chemistry: CNBr, Urea, Mercaptoethanol,Trypsin, Performic acid, Dabsyl chloride, 6N HCl, Ninhydrin, Phenyl isothiocyanate and Chymotrypsin. Which one is the best suited for accomplishing each of the following tasks? (6 points)(1) Determination of the amino acid sequence of a small peptide.Phenyl isothiocyanate(2) Identification of the amino-terminal residue of a peptide chain.Dabsyl chloride(3) Reversible denaturation of a protein devoid of disulphide bonds. Which additional reagentwould you need if disulfide bonds were present?Urea, Mercaptoethanol(4) Hydrolysis of peptide bonds on the carboxyl side of aromatic residues.Chymotrypsin(5) Cleavage of peptide bonds on the carboxyl side of methionines.CNBr,(6) Hydrolysis of peptide bonds on the carboxyl side of lysine and arginine residues..Trypsin2. Pyridoxal phosphate (PLP) is a coenzyme for the enzyme ornithine aminotransferase. Theenzyme was purified from cells grown in PLP-deficient media as well as from cells grown in media that contained PLP. The stability of the enzyme was then measured by incubating the enzyme at 37℃and assaying for the amount of enzyme activity remaining. The following results were obtained. (4 points)(1)Why does the amount of active enzyme decrease with the time of incubation?Incubating the enzyme at 37°C leads to a denaturation of enzyme structure and a loss of activity. For this reason, most enzymes must be kept cool if they are not actively catalyzing their reaction.(2)Why does the amount of enzyme from the PLP-deficient cells decline more rapidly?The coenzyme apparently helps to stabilize the enzyme structure, because enzyme from pyridoxal phosphate-deficient cells denatures faster. Cofactors often help stabilize enzyme structure.。
