Short answer questions: 21. Protein A has a binding site...

Short answer questions: 21. Protein A has a binding site for ligand L with a Kd of 10-6 M. Protein B has a binding site for ligand L with a Kd of 10-9 M. (a). Which protein has a higher affinity for ligand L? Explain your reasoning. (b). At what concentration of ligand L is proteins A half-saturated? At what concentration of L is protein B half-saturated. y = [L] / ([L] + Kd) 22. A protein binds to a ligand L with a Ka =5 ?M-1. What is the concentration of the ligand when Y is (a) 0.35, (b) 0.65, (c) 0.90? Show your calculations.

Transcript

00:01 Hello everyone, for this question we have to answer various parts starting with a where we have to name the protein having higher affinity for ligand l given.

00:10 So, first of all the affinity of protein for ligand it is inversely proportional to kd that is the dissociation constant.

00:40 So, thus the protein a which has the kd equal to 10 raised to the power minus 6 molar will be having greater affinity for ligand as compared to protein b having kd is equal to 10 raised to the power minus 9 molar.

01:09 For b we have to provide the concentration of ligand l at which both proteins will be half saturated.

01:20 So, when protein a is half saturated in this case y will be equal to 0 .5.

01:34 Now, as we know that y is equal to concentration of l divided by concentration of l plus 10 raised to the power minus 6.

01:44 So, 0 .5 equals to l divided by concentration of l plus 10 raised to the power minus 6 we get 5 into 10 raised to the power minus 7 equals to 0 .5 l and then concentration of l will be equal to 10 raised to the power minus 6 molar.

02:13 Similarly, for protein b when y is equal to 0 .5 this will be equal to concentration of l divided by the concentration of l plus 10 raised to the power minus 9.

02:31 So, this will be equal to 0 .5 multiplied by concentration of l plus 5 into 10 raised to the power minus 8 is equal to concentration of l this equals 5 into 10 raised to the power minus 10 is equal to 0 .5 concentration of l.

02:56 So, we get the concentration of l in this case equal to 10 raised to the power minus 9 molar.

03:05 For the next question that is 22 given we have to find the value of or the concentration of ligand when various values of y are given.

03:14 So, when y equal to 0 .35 in this case the above equation has been rearranged as concentration of l is equal to minus yk divided by y minus 1...

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