S13 - S1.The first amino acid in a certain bacterial...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
S1.The first amino acid in a certain bacterial polypeptide chain is methionine. The start codon in the mRNA is GUG, which codes for valine. Why isn t the first amino acid formylmethionine or valine? Answer: The first amino acid in a polypeptide chain is carried by the initiator tRNA, which always carries formylmethionine. This occurs even when the start codon is GUG (valine) or UUG (leucine). The formyl group can be later removed to yield methionine as the first amino acid. S2. A tRNA has the anticodon sequence 3 –CAG–5 . What amino acid does it carry? Answer: Since the anticodon is 3 –CAG–5 , it would be complementary to a codon with the sequence 5 –GUC–3 . According to the genetic code, this codon specifies the amino acid valine. Therefore, this tRNA must carry valine at its acceptor site. S3. In eukaryotic cells, the assembly of ribosomal subunits occurs in the nucleolus. As discussed in chapter 12, the 5.8S, 18S, and 28S rRNAs are actually synthesized as a single 45S rRNA precursor that is processed by cleavage to produce the three rRNAs. The genes that encode the 45S precursor are found in multiple copies (i.e., they are moderately repetitive). Within the nucleus, the segments of chromosomes that contain the 45S rRNA genes align
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 04/07/2009 for the course BIO 325 taught by Professor Saxena during the Spring '08 term at University of Texas.

Page1 / 2

S13 - S1.The first amino acid in a certain bacterial...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online