Page 31 - 86 human physiology part-2

Chapter 13

B. Polypeptide a group of amino acids bonded together 1000 or more.

The body requires amino acids to produce new body protein (protein retention) and to replace
damaged proteins (maintenance) that are lost in the urine.

Proteins are relatively large molecules made of amino acids joined together in chains by peptide
bonds. Amino acids are the basic structural building units of proteins. They form short polymer chains
called peptides or longer poly-peptides which in turn formstructures called proteins. The process of
protein synthesis is controlled by an mRNA template. In this process tRNA transfers amino acids to the
mRNA to form protein chains.

There are twenty standard amino acids used by cells in making proteins. Vertebrates, including
humans, are able to synthesize 11 of these amino acids from other molecules. The remaining nine
amino acids cannot be synthesized by our cells, and are termed "'essential amino acids'". These
essential amino acids must be obtained from foods.

The 9 Essential Amino Acids have the following names: Histidine, Isoleucine, Leucine, Lysine,
Methionine, Phenylalanine, Threonine, Tryptophan, Valine

You can remember these with this saying “Hey It's Like Lovely Material; Please Touch The
Velvet”.

The 11 Non-essential Amino Acids are as follows:

Alanine, Arginine, Aspartic acid, Cysteine, Cystine, Glutamic acid, Glutamine, Glycine, Proline,
Serine, Tryosine

How about this memory device, "Almost Always Aunt Cindy Can Get Great Gum Popping Sounds
Together"

The 20 Amino Acids and What They Do!

Amino Acid Abbrev. Remarks
Very abundant, very versatile. More stiff than glycine, but small enough to
pose only small steric limits for the protein conformation. It behaves fairly
Alanine A Ala
neutrally, can be located in both hydrophilic regions on the protein outside
and the hydrophobic areas inside.
The sulfur atom binds readily to heavy metal ions. Under oxidizing
conditions, two cysteines can join together in a disulfide bond to form the
amino acid cystine. When cystines are part of a protein, insulin for example,
this stabilises tertiary structure and makes the protein more resistant to
Cysteine C Cys denaturation; disulphide bridges are therefore common in proteins that have
to function in harsh environments including digestive enzymes (e.g., pepsin
and chymotrypsin) and structural proteins (e.g., keratin). Disulphides are
also found in peptides too small to hold a stable shape on their own (eg.
insulin).

246 | Human Physiology