6.2.2: Reactions of amino acids

Question 1

What are amino acids?

Answer 1

• A class of compounds with two functional groups:
• A carboxylic acid -COOH
• and an amine group -NH2
• When both functional groups are attached to the same carbon atom, the compound is called an alpha-amino acid.

Question 2

What is thee general formula for an amino acid?

Answer 2

RCH(NH2)COOH

Question 3

what are proteins?

Answer 3

-Polymer chains made up of amino acid monomers bonded together.

Question 4

How many amino acids are there in human biochemistry?

Answer 4

20 alpha-amino acids

Question 5

What is an amphoteric?

Answer 5

Being able to act as both an acid and a base.

Question 6

Why are amino acids amphoteric?

Answer 6

• The carboxylic acid functional group can act as a weak acid that will partially ionise in water.
• The nitrogen atom an the amine group has a lone pair of electrons that can act as a base.
• The carboxylic acid group can react with bases and their amine group can react with acids.

Question 7

How can amino acids form zwiterions?

Answer 7

• Their two functional groups exchange a proton and make an internal salt.
• The carboxylic acid donates a proton to the amino group.

Question 8

What is the overall charge of a zwitterion?

Answer 8

-As the two charges cancel each other out, the resultant molecule has no overall charge.

Question 9

What is the isoelectric point?

Answer 9

-When there is no net electrical charge due to each zwitterion having an internal balance of charge.

Question 10

By altering the pH, you can alter the amino acid structure so that only one of its functional groups is charged.
What happens at a low pH?

Answer 10

• There are a lot of H+
• The amino acid acts as a base and accepts a proton from the acid.
• The carboxylic acid functional group becomes -COOH
• Only the amine group is charged
• A positive ion is formed in acidic solutions.

Question 11

By altering the pH, you can alter the amino acid structure so that only one of its functional groups is charged.
What happens at a high pH?

Answer 11

-The amino acid acts as an acid and donates a proton to the hydroxide ion.
-The amine group becomes -NH2
-Only the carboxylic acid group is charged.
-A negative ion is formed in alkaline solution.
(water also produced)

Question 12

The carboxylic acid functional group is a weak acid which partially ionises in solution, this functional group will undergo all of the common reactions of an organic acid with:

Answer 12

• Metal oxides
• Alkalis
• Carbonates
• Alcohol

Question 13

What happens when an amino acid (the -COOH functional group) reacts with a metal oxide?

Answer 13

• Metal oxides are bases, so a neutralisation reaction occurs.
• The hydrogen atom on the carboxylic acid group is exchanged for a metal ion to produce a metal salt.
• Water is also produced in he reaction.

Question 14

What happens when an amino acid (the -COOH functional group) reacts with an alkali?

Answer 14

• alkalis are soluble bases, so a neutralisation reaction occurs.
• This reaction produces a salt and water.

Question 15

What happens when an amino acid (the -COOH functional group) reacts with a carbonate?

Answer 15

• this neutralisation reaction produces a salt, water and carbon dioxide gas.
• As a gas is evolved, effervescence is observed.

Question 16

What happens when an amino acid (the -COOH functional group) reacts with an alcohol?

Answer 16

-This reaction produces an ester and releases a molecule of water.

Question 17

Why can the amine functional group act as a base and what happens when an acid is added to an amino acid?

Answer 17

• Because of the lone pair of electrons on the nitrogen atom.
• when an acid is added to an amino acid, the amine group accepts a proton. The result is a ammonium salt.