The average mass of the 20 common amino acids is about 125 daltons each. Suppose

Question

The average mass of the 20 common amino acids is about 125 daltons each. Suppose an E. coli protein called your favorite protein (YFP) is 75 kilodaltons. a. What is the length in nucleotides of the portion of the E. coli mRNA (i.e. the coding region) that is translated to make YFP? b.The E. coli mRNA that makes YFP contains a 5’-UTR and a 3’-UTR. What is the function of the 5’-UTR and the 3’-UTR? c.How many GTP molecules are required to translate 50 copies of YFP? d.How many ATP molecules are required to translate 100 copies of YFP?

Explanation / Answer

Answer:

(a) The number of amino acids can be calculated as follows: (Note: the average mass of the amino acids have been used directly for calculation. In general, we also need to consider the water eliminated during peptide bond formation. That has not been considered)

Average mass of amino acid = 125, Molecular mass of YFP = 75 kDa = 75,000 Da

Number of amino acids = 75,000 / 125 = 600

So, length of the mRNA = 600 x 3 = 1800 nucleotides

(b) The 5' untranslated region (5' UTR) is the region of the mRNA transcript that is located between the cap site and the initiation codon. The 5’ UTR is known to influence mRNA translation efficiency. In eukaryotic cells, initiation factors first interact with the 5' cap structure and prepare the mRNA by unwinding its secondary structure.

The 3' UTR is defined as the mRNA sequences following the termination codon. The 3' UTR is thought to play a potential role in mRNA stability.

(c) 1 molecule of GTP is required for initiation, and 1198 molecules of GTP are needed to form 599 peptide bonds.

So, for 1 copy, 1199 molecules of GTP are required

For 50 copies, 59950 GTP are required.

(d) 600 molecules of ATP are converted into AMP + 1200 Pi to activate the 600 amino acids, which is equivalent to 1200 molecules of ATP.

For 100 copies of YFP, number of ATP required is = 1200 x 100 = 120000

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