18. An allosteric protein is (A) a protein that binds to DNA (B) a protein that

Question

18. An allosteric protein is (A) a protein that binds to DNA (B) a protein that changes shape when it binds a small molecule (C) a protein that cannot carry out an enzyme reaction (D) a protein that generates a colored product that can be casily measured E) a protein that carries nutrient molecules across membranes 19. An E. coli cell that has the genotype r'O ZITO Z would (A) repress ?-galactosidase synthesis upon the addition of lactose (B) constitutively synthesize P-galactosidase (C) be unable to synthesize p-galactosidase (D) only induce B-galactosidase synthesis upon the addition of lactose (E) none of the above 20. In the formation of an aminoacyl tRNA (A) the amino terminus of the amino acid is directly attached to the 5' end of the tRNA (B) the carboxyl terminus of the amino acid is directly attached to the 5' end of the tRNA (C) the amino terminus of the amino acid is directly attached to the 3' end of the tRNA (D) the carboxyl terminus of the amino acid is directly attached to the 3' end of the tRNA E) the side chain group of the amino acid is directly attached to the anticodon loop of the tRNA 21. The enzyme (made of proteins and RNA) that elongates chromosomes by adding TTAGGG sequences to the end of existing chromosomes is (A) endonuclease (B) exonuclease (C) telomerase (D) amylase(E) kinases 22. The enzyme responsible for forming the final phosphodiester bond between two DNA fragments during DNA replication is (A) DNA ligase (D) DNA-directed RNA polymerase (E) reverse transcriptase (B) DNA polymerase I (C) DNA polymerase III 23. Which of the following agents causes DNA damage by forming pyrimidine dimmers? (A) X-rays (B) gamma radiation (C) UV radiation(D) alkylating agents (E) ethidium bromide 24. In the E. coli RecBCD pathway, in order for homologous recombination, which of the following proteins coats the single stranded DNA tail produced by exonuclease activity? (A) RecA (B)RecB (C) RecCRecD(E) RuvB

Explanation / Answer

18) B. An allosteric protein is a protein that changes shape when it binds a small molecule.

19) D. Only induce beta-galactosidase synthesis upon the addition of lactose.

In the genotype, I+ Oc Z-/ I- O+ Z+, will cause gene expression

20) D. The carboxyl terminus of the amino acid is directly attached to the 3' end of the tRNA.

Amino acyl tRNA synthetase catalyzes the charging of tRNA with amino acid, by forming a bond between the carboxyl group of the amino acid and the -OH group attached to either 2' or 3' carbon on the adenine of tRNA

21) C. Telomerase

Telomerase is a ribonucleoprotein cintains RNA and protein.The enzyme replicates the extreme 5' end of each chromosome strand that is independent of normal DNA replication.

22) A. DNA ligase

The enzyme catalyzes the joining of the ends of two DNA chains, this catalyzes the formation of a phosphodiester bnond between the 3'-OH group at the end of one DNA cahin and the 5'-phosphate group at the end of the other.

23) C. UV radiation

UV radiation causes formation of pyrimidine dimers, which is repaired by phoreactivation,catlyzed by DNA photolyase

24) A. Rec A

RecA protein binds to the single stranded end and forms a protein coated DNA filament that invades the inttact double helix and forms D-loop.

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