In sickle-cell anemia, a point mutation in the mRNA for hemoglobin results in the replacement of glutamate with valine in the resulting hemoglobin molecule. Why does the replacement of one amino acid cause such a drastic change in biological function?

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All right. Hello everyone. So this question says that a mutation in the enzyme lactase results in the substitution of alanine with thine at a crucial active site leading to a significant decrease in the rate of lactose digestion. Explain why the single amino acid substitution causes such a drastic change in the function of lactase. So, first and foremost, right, what's happening here? Well, proteins or enzymes which are proteins, if you recall are made up of amino acids. And so here we have alanine in the original protein having been replaced with three anine. And so for a question like this, it's often important to understand the properties of these amino acids. So, alanine is a relatively small amino acid, that's nonpolar, right? Because its side chain is a hydrocarbon, it's a hydrocarbon chain spine. On the other hand, is larger than alanine and it's actually polar because its side chain has a hydroxy group. So now what could this change or what could this change do to the efficacy of the protein of the enzyme lactase? Now, because enzymes are proteins. It's very important to recall the importance of I wrote this backwards. But as I was saying before, it's very important to understand the importance of structure of proteins such as enzymes and how that affects their function or their ability to function. Enzymes are incredibly sensitive to changes in their structure. And this is especially true if that change is in the active site of the enzyme where the reaction in question is being catalyzed. Now, lactase, if you recall is an enzyme that breaks down lactose for further digestion. And so by changing the amino acid alanine to three anine in the active site of this enzyme again, where the reaction takes place. What's essentially happening is that the the local environment of the active site is different, right? The structure is different and the chemical environment is different because thine being a polar amino acid interacts differently with the environment compared to alanine, a nonpolar amino acid. And that change, right, that change in polarity in particular has now affected the interactions that have to take place between the enzyme and lactose. So essentially, right, this change from alanine to three anine has changed the structure of the active site. And if you're changing the structure of the active site, the function of that enzyme is now going to be significantly reduced or even compromised. And so now lactase is no longer able to break down lactose as efficiently as it normally would, which leads us to our final answer. Our final answer reads as follows, thine has a larger side chain and introduces a polar hydroxyl group which disrupts the active side's ability to bind lactose and there you have it. So, with that being said, thank you so very much for watching. And I hope you found this helpful.

In sickle-cell anemia, a point mutation in the mRNA for hemoglobin results in the replacement of glutamate with valine in the resulting hemoglobin molecule. Why does the replacement of one amino acid cause such a drastic change in biological function?

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Key Concepts

Point Mutation

Protein Structure and Function

Biological Impact of Hemoglobin Changes