生物化学试题及参考答案.docx

1、生物化学试题及参考答案生物化学试题及参考答案1. Explanation of Terms (30)1) Edman DegradationA procedure used to determine the sequence of amino acid residues from a free N-terminus of a polypeptide chain. The N-terminal residue is chemically modified, cleaved from the chain, and identified by chromatographic procedures,

2、and the rest of the polypeptide is recovered. Multiple reaction cycles allow identification of the new N-terminal residue generated by each cleavage step.2) Protein KinaseAny of a number of enzymes that phosphorylate one or more hydroxyl or phenolic groups in proteins, ATP being the phosphoryl-group

3、 donor. The attachment of phosphoryl groups to specific amino acid residues of a protein is catalyzed by protein kinases, and removal of phosphoryl groups is catalyzed by protein phosphatase.3) Western Blotting1. Separation of proteins by gel electrophoresis2. Transfer the separated proteins to a me

4、mbrane3. Membrane blocking with nonspecific protein4. Incubate with primary and secondary antibody (antibody-enzyme complex)5. Add substrate6. Formation of colored4) Immunoglobulin G (IgG)Immunoglobulin G (IgG) is the major class of antibody molecule and one of the most abundant proteins in the bloo

5、d serum. IgG has four polypeptide chains: two large ones, called heavy chains, and two light chains, linked by noncovalent and disulfide bonds into a complex of Mr 150,000.5) G ProteinGuanine nucleotide binding protein; any a family of heterotrimeric GTP-binding and hydrolysing proteins, they are a

6、component of receptor mediated activation or inhibition of adenylate cyclase and other second messenger systems such as phosphatidylinositol cycle. They mediate the intracellular actions of many hormones, growth factors and cytokines. The system is widely distributed but unique to eukaryotes.6) Dena

7、turation of Protein and DNAProtein denaturation: A loss of three-dimensional structure sufficient to cause loss of function is called protein denaturation (by heat, extremes of pH, organic solvents, urea, guanidine hydrochloride, or detergents).DNA denaturation: The complete unwinding and separation

8、 of complementary strands of DNA.7) Genome and ProteomeGenome: The whole of the genetic information of an organism. It is contained as DNA in eukaryoties and prokaryotes, and as either DNA or RNA in viruses. A given organism has only one genome regardless of whether the organism is haploid, diploid,

9、 or polyploid.Proteome: The complete expression profile of the proteins of an organism.8) Helix and Conformation Helix: Conformation of a polypeptide chain in which successive turns of the helix are held together by hydrogen bonds between the amid (peptide) links. Conformation: An extended, zigzag a

10、rrangement of a polypeptide chain in which the chain is almost fully extended but slightly puckered. sheet; The zigzag peptide chains can be arranged side by side to form a structure resembling a series of plates. turns; A type of secondary structure in polypeptides consisting of four amino acid res

11、idues arranged in a tight turn (180 ) so that the polypeptide turn back on itself.9) Transcription and TranslationTranscription: The synthesis of either RNA on a template of DNA or DNA on a template of RNA.Translation: The synthesis of a polypeptide whose sequence reflects the nucleotides sequence o

12、f an mRNA molecule.10) DNA Polymerase and RNA PolymeraseDNA Polymerase: The enzymes catalyse the synthesis of DNA from deoxyribonucleoside triphosphates in the presence of a nucleic-acid primer.RNA Polymerase: The enzyme that directs transcription, or synthesis of RNA.2. Description (30)1) Three maj

13、or RNA processing.Capping: The cap is a structural feature present at the 5 end of mRNA molecules. It consists of 7-methylguanosine and a triphasphate bridge linking it 5-5 to the end of polynucleotide chain. Capping is the process of forming or placing a cap on an mRNA molecule. Functions: (a) Prot

14、ect mRNAs from degradation. (b) Enhance the translatability. (c) Enhance the transport of mRNAs from the nucleus into cytoplasm. (d) Enhance the efficiency of splicing of mRNAs.Polyadenylation: Poly (A) is a sequence of adenylyl residues at the 3 end of eukayotic mRNA. Almost all mature mRNAs have 4

15、0-200 nucleotides of poly (A) tail. Addition of poly (A) to the 3 end of mRNA is called polyadenylation. Functions: (a) Protection of mRNA. (b) Translatability of mRNA.Splicing: The enzymic process in eukaryotic cells by which introns are excised from heterogeneous nuclear RNA (hnRNA) following its

16、transcription from DNA, and the cut ends are rejoned to form messenger RNA.2) Three classes of genetic recombination and their major functions.Homologous recombination involves genetic exchanges between any two DNA molecules that share an extended region of nearly identical sequence. Functions: (a)

17、Contributes to the repair of several types of DNA damage. (b) In eukaryotic cells, it provides a transient physical link between chromatides that promotes the orderly segregation of chromosomes at the first meiotic cell division. (c) It enhances the genetic diversity in a population.Site-specific re

18、combination differs from homologous recombination in that the exchanges occur only at a particular DNA sequence. Functions: (a) Regulating the expression of certain genes. (b) Promoting programmed DNA rearrangements during embryonic development. (c) Complete chromosome replicationDNA transposition i

19、s distinct from both other classes in that it usually involves a short segment of DNA with the remarkable capacity to move from one location in a chromosome to another. Functions: (a) Complete chromosome replication. (b) Move one genetic elements from one location to another and maintenance of genet

20、ic diversity.3) Four types of weak interactions (noncovalent bonds) within and between biomolecules.4) Eight major protein functions.1. Catalysis2. Structure3. Movement4. Defense5. Regulation6. Transport7. Storage8. Stress Response5) The biological functions of the lipids.1. Energy storage (fats and

21、 oils).2. Major structural elements of biological membrane (phospholipids and sterols).3. Others (enzyme cofactors, light-absorbing pigments, hormone, electron carrier).6) DNA repair systems.Mismatch repair: A system for the correction of errors introduced during DNA replication when an incorrect ba

22、se, which cannot form hydrogen bonds with the corresponding base in the parent strand, is incorporated into the daughter strand.Base-excision repair: A damage base is recognized by an enzyme called DNA glycosylase, which breaks the glycosidic bond between the damaged base and its sugar. This leaves

23、an apurinic or apyrimidinic site (AP site), which is a sugar without its purine or pyrimidine base. Once the AP site is created, it is recognized by an AP endonuclease that cuts or nikes the DNA strand on the 5 side of the AP site.Nucleotide-excision repair: Bulky base damage can be removed directly

24、, without help from a DNA glycosylase. In this pathway, the incising enzyme (excinuclease) system recognizes the strand with the bulky damage and makes cuts on either side of the damage, removing an oligonucleotide with the damage.Direct repair: One type of DNA damage repair system without removing

25、a base or nucleotide.DNA recombination3. Enzymes are extraordinary catalysts. The rate enhancements brought about by enzyme are in the range of 5 to 17 orders of magnitude enzymes are also very specific, readily discriminating between substrates with quite similar structures. How can these enormous

26、and highly selective rate enhancements be explained? Where do the energies come from for the dramatic lowing of the activation energies for specific reactions?Binding energy is a major source of free energy used by enzymes to lower the activation energies of reactions.1. Much of the catalytic power

27、of enzymes is ultimately derived from the free energy released in forming multiple weak bonds and interactions between an enzyme and its substrate. This binding energy contributes to specificity as well as catalysis.2. Weak interactions are optimized in the reaction transition state; enzyme active s

28、ites are complementary not to the substrates per se, but to the transition states through which substrates pass as they are converted into products during the course of an enzymatic reaction.4. DNA sequencing is readily automated using a variation of Sangers sequencing method in which the dideoxynuc

29、leotides used for each reaction are labeled with a differently colored fluorescent tag. Describe the strategy of automating DNA sequencing reactions.5. Describe the separation principles of proteins on the basis of size (size-exclusion chromatography), charge (ion-exchange chromatography), and bindi

30、ng specificity (affinity chromatography).size-exclusion chromatography ion-exchange chromatography affinity chromatography6. Write three-letter and one-letter abbreviations for the 20 standard amino acids. The topic can be simplified by grouping the amino acids into five main classes based on the pr

31、operties of their R groups. Describe the five groups and their properties.Amino acids can be classified by R group:Nonpolar, aliphatic groups: Gly(G) Ala(A) Pro(P) Val(V) Leu(L) Ile(I) Met(M)Aromatic R groups: Phe(F) Tyr(Y) Trp(W)Polar, uncharged R groups: Ser(S) Thr(T) Cys(C) Asp(D) Glu(E)Negativel

32、y charged R groups: Asn(N) Gln(Q)Positively charged R groups: Lys(K) Arg(R) His(H)生物化学试题及参考答案1. Explanation of Terms (1) Apolipoproteins: Apolipoproteins are lipid-binding proteins in the blood, responsible for the transport of triacylglycerols, phospholipids, cholesterol, and cholesteryl esters between organs.(2) Photorespiration: A light-dependent catabolic process occurring concomitantly with photosynthesis in plants (especially C3 plants) whereby