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1. Using the following mRNA sequence: 5'-ACAAUCCUGCAUGCCGAUGCGAGCCGAAUAAGCACGUGUU-3'
complete the following:
a. Indicate the start codon.
b. Indicate the stop codon.
c. Give the proper sequence of amino acids if this sequence was translated.
2. For each of the following, give a brief description:
a. initiation complex
b. Shine-Delgarno sequence
c. activation and charging of an amino acid
3. Describe what is meant by the degeneracy of the genetic code, and how this is dealt with in the cell. Include in your answer isoaccepting tRNAs and the wooble hypothesis.
a. Describe in detail the molecular mechanisms involved in termination of translation.
b. What is the proposed mechanism of action of some antibiotics? Give an example.
5. Describe the following:
a. What is meant by the "almost universal genetic code"?
b. How do we know that there is no punctuation in the genetic code?
c. How can we predict the number of genes in an organism's genome?
d. What is meant by the C-value paradox?
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These five questions deal with translation of an mRNA sequence. This solution answers all five questions completely and provides some background to explain the responses in approximately 1000 words.
1a. The start codon is TAC and AUG of DNA and RNA respectively. The start codon or initiation codon encodes the amino acid methionine (Met or M) in eukaryotes. It is inidicated by an asterisk (*) in the sequence as follows:
5'-A CAA UCC UGC *AUG* CCG AUG CGA GCC GAA UAA GCA CGU GUU-3'
1b. If we proceed from your start codon then the stop codon is UAA
1c. The protein sequence starting from the first start codon is: M P M R A E
2a. The initiation complex is a group of proteins that bind the DNA sequence allowing transcription to occur. In eukaryotes this includes proteins which position RNA polymerase II (Pol II) at transcription-initiation sites, and are called general transcription factors, because they are thought to be required for transcription of most genes that are transcribed by this type of polymerase.
2b. The Shine-Delgarno sequence proposed by Australian scientists John Shine and Lynn Dalgarno, is a ribosomal binding site in the mRNA, generally located 16 nucleotides upstream of the start codon AUG. The Shine-Dalgarno sequence exists only in prokaryotes. This sequence helps recruit the ribosome to the mRNA to initiate protein synthesis by aligning it with the start codon.
2c. The correct amino acid is added to its tRNA by a specific enzyme called an aminoacyl-tRNA synthetase. The process is called aminoacylation, or activation and charging.
2d. This question may be referring to either protein or chromosomal translocation. The translocation of proteins across membranes involves the signal sequence, that is, a short amino acid sequence at one end that functions like a postal or zip code for the ...
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