Part 1: Please choose the ONE correct MOST APPROPRIATE answer on the ANSWER SHEE

Question

Part 1: Please choose the ONE correct MOST APPROPRIATE answer on the ANSWER SHEET (last page). (1.5 point each, 75 pts) 1. Which of the follovwing most likely best describe the 3D structure of a tRNA? a. It has the shape of a cloverleat b. The CCA terminus containing the amino acid attachment site and the anti-codon loop extend from the same side of the molecule e. The molecule is L-shaped. d. All of the hydrogen bonded base pairs follow a strict Watson and Crick base pairing rule. 2. Amino-Acyl tRNA synthetases are divided into two groups. The main differences between theses 2 goups is: a. Class I enzymes acylate the 2' -hydroxyl group of the terminal adenosine of tRNA, whereas class Il enzymes (except the enzyme for Phe-tRNA) acylate the 3" -hydroxyl group. b. The two classes hinds ATP in different configurations. Most class I enzymes are monomeric, whereas most class II enzymes are dimerie c. d. All of the ahbove are true. 3. If we use the syntbetic polynucleotide 5' AAA (AAA AAC 3' (giving that AAA encod for a lys and AAC encodes for an Asn). the polypeptide synthesized would be NH, -Ly (Lys)n-Asn-COOH. This proves that: a. The genetic code is degenerate b. The mRNA is read from 3 to 5 direction. c. The direction of the translation is from 5 to 3 d. The proteins synthesis occur from C-terminal to N-terminal. 4. In prokaryotes, protein synthesis starts when: a. Simply the first three nucleotides in the mRNA serves as the first codon. b. The 30S subunit recognizes a purine rich region of the mRNA called the Shine-Dalg sequence and binds to it. c. The 30S slides off the mRNA and starts the translation when it hit the first AUG in it. d. The protein synthesis in prokaryotes starts randomly 5. All aminoacyl tRNA synthetase specifically recognizes their corresponding tRNA a. Exclusively on the basis of the acceptor stem . Exclusively on the basis of the variable loop The aminoacyl-tRNA-synthetase is not specific for a tRNA pair,TRNA In general, tRNA recognition by the synthetase is different for each synthetase and Which of the following statement about elongation is FALSE? The aminoacyl-tRNA leaves the synthetase and diffuse freely to the A site. The elongation factor Tu (EF-Tu) protects the delicate ester linkage in aminoacyl-4RN hydrolysis. Page

Explanation / Answer

1)d- all the molecules follow watson and crick rule for hydrogen bonding

2)a

3)d

4)b

5)a

6) a

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