A definitive diagnosis of LHON caused by the mutation in the mitochondrial NADH

Question

A definitive diagnosis of LHON caused by the mutation in the mitochondrial NADH Dehydrogenase subunit 4 (ND4) gene is possible by analysis of the patients DNA, first using PCR to amplify the ND4 gene, second cutting the PCR product (a.k.a., amplicon) with the restriction enzyme Accl, and third, identification of restriction fragment length polymorphisms (RFLP) after agarose gel electrophoresis and staining of the restriction fragments with ethidium bromide. The data are shown in Figure 1. The restriction enzyme Accl recognizes the 6 bp sequence, CTNNAC where N means any nucleotide is possible. LHON patients have the CTNNAC seqeuence in the ND4 gene. Unfortunately, your lab technician forgot to label the lanes. The protein encoded by the ND4 gene has an apparent molecular mass of 52 kD and is composed of 459 amino acids. What is the expected size of the ND4 amplicon? 2. FIGURE 2 3 2 kb 1 kb 0.1 kb A 24000 bp B) 3000 bp 1300 bp D 600 bp E 200 bp

Explanation / Answer

Given the ND4 protein is 459 amino acid long. We know that 1 amino acid is coded by three nucleotides. So the total gene length will be 459*3 = 1377.

If we look at the gel picture in the lane two there is the DNA fragment which is running between 2kb and 1 kb marker which makes us conclude that the length of the gene is around 1400 base pair.

Since the nearest option is option 3 which is 1300

So the answer is option C- 1300bp

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