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Peptide Bonds, Amino Acids and Chemical Structures

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I need some help with biochemical questions:
1. How do you calculate the pH of a solution of lysine if the side chain amino group is 3/4 dissociated?
2. What is the isoelectric point of His?
3. For L-Ile, describe with drawings why it is 2S,3S?
4. What are the 6 atoms that are coplanar due to the resticted rotation about the peptide bond?
5. How many different tetrapeptide sequences are possible of the number of different amino acid types is 20?
6. Draw the chemical structures for tripeptides G-F-F and for F-F-G..are they the same?

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Solution:
1. The Henderson-Hasselbalch equation states that:

pH = pKa + log [A-]/[HA]

The pKa of the side chain amino group is 10.53. You can look this number up in a table of pKa values for the amino acids. Since 3/4 is dissociated, i.e. the form --NH2, then 1/4 must be protonated, i.e. the form --NH3+.

pH = 10.53 + log (3/4)/(1/4)
pH = 10.53 + log 3
pH = 10.53 + 0.48
pH = 11.01

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2. You can look this up in a table attached below. The pI of histidine is 7.59.

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3. See attached graphic. I've included a graphic that shows all of the four possible stereoisomers of isoleucine with each one labelled as to what it is. The first one is 2S,3S. Remember the rule. If you place the lowest priority atom in the back, ...

Solution Summary

This solution contains answers to the aforementioned biochemistry questions with clear explanations and attached diagrams for better understanding. All formulas and workings are shown.

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The general stucure of enzyme protiens, and

how the stucture of enzymes allows them to fulfill their biological role.

I am to include the following terms into the above account:-
Amino-Acids
Primary Stucture
Peptide bonds
Weak Bonds
Higher-order Stucture
Globular protien
Specificity
Energy barrier
Active site
Enzyme-substrate complex
Catalyst

I know all the terms are their and can be easily looked up, I am having trouble trying to put things in order and keep within the word limit. Can anyone please help me with this

Thank you

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