The coat protein of tomato bushy stunt virus consists of 180...

The coat protein of tomato bushy stunt virus consists of 180 chemically identical subunits, each of which is composed of -386 amino acid residues. The probability that a wrong amino acid residue will be biosynthetically incorporated in a polypeptide chain is 1 part in 3000 per residue. (a) Calculate the average number of coat protein subunits that would have to be synthesized to produce a perfect viral coat. (b) What would this number be if the viral coat were a single polypeptide chain with the same number of residues that it actually has?

The coat protein of tomato bushy stunt virus consists of 180 chemically identical subunits, each of which is composed of -386 amino acid residues. The probability that a wrong amino acid residue will be biosynthetically incorporated in a polypeptide chain is 1 part in 3000 per residue.
(a) Calculate the average number of coat protein subunits that would have to be synthesized to produce a perfect viral coat.
(b) What would this number be if the viral coat were a single polypeptide chain with the same number of residues that it actually has?

Key Concepts

Biosynthetic Error Rate and Fidelity

This concept deals with the probability that each individual amino acid residue is correctly incorporated during protein synthesis. In processes like ribosomal translation, even a low error rate per residue, when multiplied across the length of a protein, greatly reduces the chances of obtaining a completely error?free sequence. It highlights the importance of the accuracy of each step in biosynthesis for the overall fidelity of protein production.

Multiplicative Probability of Independent Events

When synthesizing a protein, the incorporation of each residue is an independent event. To calculate the probability of obtaining a perfect protein chain, you multiply the probability of each residue being correct for every position in the sequence. This principle explains why the overall probability of a flawless long polypeptide chain can be extremely small, as even small error rates have compounded effects over many residues.

Expected Value in a Geometric Distribution

This concept is used to determine the average number of trials required to achieve a first success in a series of independent events with a fixed failure probability. In the context of protein synthesis, if each synthesis attempt has a low probability of being error?free, the expected number of attempts needed to obtain one perfect protein is given by the inverse of the success probability. This approach is fundamental in probability theory for predicting the number of trials before the first success occurrence.

Transcript

00:01 So here we have some true false statements, and we have to assess them.

00:05 The first statement is that proteins are diverse because each of them is made from a unique mixture of amino acids in a random order.

00:14 Of course, proteins, they are not random.

00:16 So false because the sequence is not random.

00:22 The sequence determines the function and the order is important.

00:28 So it is important to protein function.

00:38 And so we have 20 amino acids and both the amino acids the protein contains and the order is important, but mostly the order.

00:48 So, and both the amino acids contains and their order are vital to diversity.

01:01 Let's look at b.

01:01 Lipid bilayers are macromolecules mostly made up of phospholipid subunits.

01:08 So it's true that the bilayer is mostly phospholipid, but it is not a polymer.

01:18 This is not a macromoleculecure.

01:20 The phospholipids are not bound to each other covalently.

01:23 So false, the phospholipids are not covalently bound, so they are not a macromoleculecule.

01:33 They interact, but non -convailably.

01:38 C, nucleic acids have sugar groups.

01:40 Okay, this is true...

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