[size=24]presented to Dr Hamed Abd Elbary[/size]
The
Chemistry of Amino AcidsIntroduction
Essential
amino acids
Why
learn this? Amino acids play central roles both as building blocks of proteins and as
intermediates in metabolism. The 20 amino acids that are found within proteins
convey a vast array of chemical versatility. The
precise amino acid content, and the sequence of those amino acids, of a
specific protein, is determined by the sequence of the bases in the gene that
encodes that protein. The chemical properties of the amino acids of proteins
determine the biological activity of the protein. Proteins not only catalyze
all (or most) of the reactions in living cells, they control virtually all
cellular process. In addition, proteins contain within their amino acid
sequences the necessary information to determine how that protein will fold
into a three dimensional structure, and the stability of the resulting
structure. The field of protein folding and stability has been a critically
important area of research for years, and remains today one of the great
unsolved mysteries. It is, however, being actively investigated, and progress
is being made every day.
As we learn about amino acids, it is important to keep in mind that one of
the more important reasons to understand amino acid structure and properties is
to be able to understand protein structure and properties. We will see that the
vastly complex characteristics of even a small, relatively simple, protein are
a composite of the properties of the amino acids which comprise the protein.
Top
Essential amino acidsHumans can produce 10 of the 20 amino acids. The others must be supplied in the
food. Failure to obtain enough of even 1 of the 10 essential amino acids, those
that we cannot make, results in degradation of the body's proteins—muscle and
so forth—to obtain the one amino acid that is needed. Unlike fat and starch,
the human body does not store excess amino acids for later use—the amino acids
must be in the food every day.
The 10 amino acids that we can produce are alanine, asparagine, aspartic
acid, cysteine, glutamic acid, glutamine, glycine, proline, serine and
tyrosine. Tyrosine is produced from phenylalanine, so if the diet is deficient
in phenylalanine, tyrosine will be required as well. The essential amino acids
are arginine (required for the young, but not for adults), histidine,
isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan,
and valine. These amino acids are required in the diet. Plants, of course, must
be able to make all the amino acids. Humans, on the other hand, do not have all
the the enzymes required for the biosynthesis of all of the amino acids.
Why learn these
structures and properties?It is critical that all students of the life sciences know well the structure
and chemistry of the amino acids and other building blocks of biological
molecules. Otherwise, it is impossible to think or talk sensibly about proteins
and enzymes, or the nucleic acids
يا رب يا جماعة الموضوع يفيدكم وادعولى.