Lesson 6A: Proteins

Question 1

Proteins

Answer 1

These are organic compounds that contain N,C, H, and O.

Proteins are responsible for most of the chemical functions that
take place in the cells of the body.

Question 2

Amino Acids

Answer 2

Proteins are polymers of Amino Acids

An amino acids contain an amine
functional group at one end and a
carboxylic acid functional group at
the other end

Amino acids bond together in long
chains to form proteins

There are 20 naturally occurring
amino acids

Question 3

Properties of Amino Acids

Answer 3

Amino acids have the ability to act as both an acid and a base due to the carboxyl
group at one and the amino group at the other.

The central carbon in naturally occurring amino acids is called the α-carbon or the
2-carbon. Therefore these are called α-amino acids or 2-amino acids.

Most amino acids are “neutral” as they contain one acid group and one alkaline
group.

Some amino acids contain side chains (R groups) that contain –NH2 groups which
makes them basic amino acids; while others contain –COOH in their side chains
which makes them acidic amino acids.

Question 4

Twenty
Naturally
Occurring
Amino Acids

Answer 4

Amino acids are colourless, crystalline solids with relatively high
melting points for organic compounds and are generally soluble in
water but not other organic solvents.

With 2-amino acids, when R ≠ H, the 2-carbon atom is asymmetric
and gives rise to optical isomerism.

In the crystalline state and in aqueous solution, amino acids exist as
zwitterions and are amphoteric in nature. This explains the high
melting points.

Question 5

Amino Acids as Buffers

Answer 5

The amphoteric nature of amino
acids makes it possible for them to
act as buffers in aqueous solution.

When a strong acid (H+) is added
the zwitterion accepts the proton
thereby minimizing the effect of the
acid added.

When a strong base is added (OH-)
the zwitterion donates a an H+ to
neutralize the base to form water.

Question 6

The Formation of Proteins

Answer 6

Amino acids undergo condensation
reactions to form substituted amides
in the presence of enzymes.

Example:

Glycine and alanine can combine to
form two possible dipeptides.
A dipeptide is a substituted amide
made up of two amino acids joined by a
peptide bond or peptide linkage.

Water is formed in this enzyme
controlled reaction.

If a compound contains many peptide
bonds it is considered a polypeptide,
and after some folding, a protein.