Question

The following sequence contains the open reading frame of a polypeptide. How many amino acids will the polypeptide consist of?
5’ AGCATATGATCGTTTCTCTGCTTTGAACT- 3’
A. 4
B.6
C. 10
D. 7

Answer 1

Hint: Protein synthesis always starts with a start codon.
The start codon is ATG. protein synthesis will start form ATG and will end on CTT, which means the polypeptide will contain 6 amino acids.

Complete answer: Now starting from the ATG, if we read in triplets, the codons are ATG, ATC, GTT, TCT, CTG, CTT, and TGA. Triplet TGA (UGA in RNA) is a STOP codon. Thus the A genome sequence is not an end in itself. A major challenge still has to be met in understanding what the genome contains and how the genome functions.
1. The former is addressed by a combination of computer analysis and experimentation, with the primary aim of locating the genes and their control regions. These methods can be divided into those that involve simply inspecting the sequence, by eye or more frequently by computer, to look for the special sequence features associated with genes, and those methods that locate genes by experimental analysis of the DNA sequence.
2. Sequence inspection can be used to locate genes because genes are not a random series of nucleotides but instead have distinctive features. These features determine whether a sequence is a gene or not, and so by definition are not possessed by non-coding DNA.
3. At present we do not fully understand the nature of these specific features, and sequence inspection is not a foolproof way of locating genes, but it is still a powerful tool and is usually the first method that is applied to the analysis of a new genome sequence.
4. Most of the various software programs available for gene location can identify up to 95% of the coding regions in a eukaryotic genome, but even the best ones tend to make frequent mistakes in their positioning of the exon-intron boundaries.
5. These limitations can be offset to a certain extent by the use of a homology search to test whether a series of triplets is a real exon or a chance sequence. In this analysis, the DNA databases are searched to determine if the test sequence is identical or similar to any genes that have already been sequenced.

So, the correct answer is “Option A”.

Note: Drosophila holds great promise in this respect, as the phenotypic effects of many Drosophila genes are well known, so the data already exist for inferring the mode of action of human disease genes that have homologs in the Drosophila genome but the greatest success has been with yeast. Several human disease genes have homologs in the S. Cerevisiae genome.