choose the correct answer 18. Avtrain of yeast translates mRNA into protein nacc
ID: 266447 • Letter: C
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18. Avtrain of yeast translates mRNA into protein naccurately Individual molecules of a particular protein isolated from this yeast have variations in the first 11 amino at compared with the sequence of the same protein isolated from normal yeast cells, a tested in the figure below. What is the most likely cause of this variation in protein ieds varients Met The Ala Ala Val Ber Aan Thr Gin tleLy Het Thr Ala 1 Val Ber Aan The Gin Ie LY Thr Ala ne Val Ser Ann Thr Gln Ala Met Thr Ala tle Val Ber Aan Thr G1n alr Y Het Thr Ala Ile Val ser Asn Thr Gin Val Ly a. a mutation in the DNA coding for the protein b. a mutation in the anticodon of the isoleucine-tRNA (tRNAe) c a mutation in the isoleucyl-tRNA synthetase that decreases its ability to distinguish between different amino acids a mutation in the isoleucyl-tRNA synthetase that decreases its ability to distinguish between different tRNA molecules d. 19. RNA in cells differs from DNA in that a. it contains the base uracil, which pairs with cyt b. it is single-stranded and cannot form base pairs c. it is single-stranded and can fold up into a variety of structures d. the sugar ribose contains fewer oxygen atoms than does deoxyribose 20. Transcription is similar to DNA replication in that a. an RNA transcript is synthesized discontinuousy and the pieces are then jo together it uses the same enzyme as that used to synthesize RNA primers during DNA replication the newly synthesized RNA remains paired to the template DNA nucleotide polymerization occurs only in the 5'-to-3' direction b. c. d. 21. Which of the following might decrease the transcription of only one specific gene in a bacterial cell? a decrease in the amount of sigma factor a decrease in the amount of RNA polymerase a mutation that introduced a stop codon into the DNA that precedes the gene's coding sequence a mutation that introduced extensive sequence changes into the DNA that precedes the gene's transcription start site a. b. c. d.Explanation / Answer
19. The answer is c. RNA is single stranded and in nature appears as ss foldes on itself. It consists of bases A,U,G and C but uracil pairs with Adenine. It has one oxygen moiety more than DNA (deoxy-, hence the name).
20. The answer is d. In replication, DNA polymerase and during transcription, RNA polymerase add nucleotides at the 3' end to extend the chain length. Polymerases can add nucleotides ONLY at the hydroxyl end which is at 3'. On addition of a base, the DNA helix is reformed and RNA chain separates off from the DNA template, however the concept of base-pairing is common to both processes.
21. The answer is a. Sigma factor is specific for a gene and varies with gene, environmental signals etc. The RNA polymerase that starts initiation is alsi dependent on the sigma factor. Decreased sigma factor leads to reduced RNA and decresed protein synthesis. Stop codon or any other mutation will not reduce, but mostly result in a different gene product. However, we have been asked for reduction in a specific type of gene expression, which should ideally be affected by the availability of sigma factor that initiates the process.
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