Amino Acids: Theory and Calculations

Question 1

At what point is the pH of an amino acid solution equal to the pK of one of its functional groups?

Answer 1

when half of that functional group has been deprotonated

ex: glycine’s carboxyl pK = 2.3 so…

With 20 ml of 0.1 N glycine solution, addition of 10 ml 0.1 NaOH will cause deprotonation of half the carboxyls and thus give the solution a pH of 2.3

Question 2

How does an ⍺-ketoacid’s structure differ from the amino acid it is derived from?

Answer 2

The H and amino groups of the alpha carbon are replaced by a double-bonded oxygen.

Thus they have a ketone on the alpha carbon…

Question 3

What are the non-polar amino acids?

Answer 3

aliphatic - Met, Gly, Ala, Val, Leu, Ile, Pro,

aromatic - Phe, Trp

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Question 4

Which amino acids are polar?

Answer 4

aliphatic - Ser, Thr, Cys, Gln, Asn

aromatic - Tyr

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Question 5

What amino acids have aliphatic side chains?

Answer 5

this is most easily remembered by just knowing the aromatic side chain amino acids and knowing that ALL others are aliphatic

Question 6

What amino acids have aromatic side chains?

Answer 6

Phe, Trp, Tyr, His

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Question 7

How does one indicate the number of carbons in an amino acid?

Answer 7

The number of carbons plus the letter C in parentheses

EX: Ala (3C), Gly (2C)

Question 8

What is transamination?

Answer 8

Transamination (AKA aminotransfer)

• an exchange between two molecules (an amino acid and a keto acid) of the amino group -NH₂ and the keto group =O

Question 9

What are the branched chain amino acids?

How can their structures be remembered?

Answer 9

Valine, Leucine and Isoleucine

• Valine is the simplest and contains a “V” of methyls branching off a carbon
• Leucine is just valine with an extra carbon
• Isoleucine is just leucine with its branching from the first carbon instead

Question 10

How can buffers be formed from fully protonated amino acid solutions?

Answer 10

By **partially neutralizing **the solution with NaOH so that the acidic and conjugate base forms of the amino acid exist in equal amounts.

EX: 10 ml of a 1 M fully protonated AA solution can be made into a buffer with the addition of 5 ml 1M NaOH

Question 11

What is a peptide bond?

Answer 11

a bond formed between two amino acids

• between the alpha amino and alpha carboxyl groups
• occurs via condensation (AKA dehydration)