3.In the lactose operon model, the repressor protein binds to
(A) An enhancer
(B) An operator
(C) A promoter
(D) A TATA box
(E) A start codon

39. The eukaryotic transcription factor CREB is active when it is phosphorylated and it binds cAMP response elements (CREs) in the promoters of genes, activating transcription. The mechanism of transcription activation is best described by the following statements. (A) CREB binds the CREs and recruits a complex of proteins that acetylates histones in nucleosomes at the promoter; thereby displacing nucleosomes and facilitating the assembly of basal transcription factors on the promoter. (B) CREB binds the CREs and recruits nucleosome assembly proteins that increase the amount of DNA assembled into nucleosomes in the promotere; thereby increasing the rate of basal transcription factor binding. (C) CREB binds to the CREs and prevents the repressor form binding; thereby increasing the rate of basal transcription factor binding. (D) CREB binds the CREs and directly recruits the basal transcription factors to bind the promoter.

40. What is aminoacyl t-RNA synthetase? (A) The protein that adds amino acids to the growing peptide chain. (B) The protein that recruits the initiator tRNA. (C) The protein that matches the anti-codon of the tRNA and the codon of the mRNA. (D) The protein that adds the appropriate amino acid to the tRNA, matching anti-codon to amino acid. II. Essay questions (20%): Please answer the following question as sufficient as you can.

1. Common lesion found in DNA after exposure to ultraviolet light are not able to be repaired by (A) Nucleotide excision repair system (B) Recombinational repair system (C) DNA photolyase (D) Base excision repair system (E) Alkyltransferase

2.Which of the following types of bonds or interaction are likely to be involved in stabilizing the three-dimensional folding of most proteins (A) Electrostatic bonds (B) Phosphodiester bonds (C) Ester bonds (D) Peptide bonds (E) None

4."Leucine zippers" are important in cellular regulation because they are (A) Structures with high redox potential (B) A unique DNA sequences for protein binding (C) A domain in many growth factor receptors (D) A motif in many DNA-binding proteins (E) At the catalytic site of many kinases

5.Which of the following is most likely to lead to a loss of gene function? (A) A change from a TGA codon to a TAA codon in the coding region (B) A change from C to T in an enhancer region (C) A change from A to G in the open reading frame (D) A frameshift mutation in promoter region (E) A single nucleotide polymorphism in coding region

6. Which of the following columns are used in purification of eukaryotic mRNA? (A) Ni-NTA-column (B) Oligo-dT column (C) Oligo-dG column (D) GST column (E) IgG column

7.Which of the following enzyme abnormalities result in hyperuricermia and gout? (A) Нурохanthine-guanine phosphoribosyltransferase (B) PRPP amidotransferase (C) PRPP synthetase (D) All above (E)None

8. Which of the following protein responds to damage DNA and induces activation of SOS regulon? (A) Lex A9. (B) Rec A (C) Sul A (D) Uvr A (E) Dna A

9.The peptide bond formation between two amino acids is catalyzed by (A) The large subunit of a ribosome (B) The small subunit of a ribosome (C) Aminoacyl tRNA synthetase (D) EF-Tu (E) 16S rRNA