Topic№12: -Amino acids. Peptide.Proteins.
Basicquestions:
1. Amino acids. Conception.Classification, nomenclature.
2. Biologicalsignificance (unsaturated -amino acids)
3. Stereoisomerism of - amino acids
4. Synthesis of amino acids in living organism:
a) transamination reaction
в) reductionaminationof- keto acids
5. Chemical properties of amino acids.
a) acid-base properties
b) Chirality in Amino Acids
c) Desamination reaction;
d) Formation of ester,halogenanhydrates, decarboxylation (Acetylation, Reduction, Reaction with Nitrous acid, Reaction involving both the carboxyl & the amino group)
E)Synthesis of α - amino acids
6. Conceptaboutpeptidesandproteins, its general characteristic. Biological role of peptides and proteins.
7. Level of organization of peptides and proteins (primary, secondary, tertiary structure of proteins)
8. Types of precipitation of proteins.
9. Concept about complex proteins.
1) Amino acids. Conception.Classification, nomenclature.
Amino acids are biologically important organic compounds made from amine (-NH2) and carboxylic acid (-COOH) functional groups, along with a side-chain specific to each amino acid. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen.
Classification:
Structure:
Nomenclature:
The carboxyl carbon of an amino acid is numbered as C-1 and the α-carbon is C-2
In Latin numbers
Central chiral carbon is α
Carbon next to it is β and so on
Carboxylic carbon is not numbered in this system.
2) Biologicalsignificance (unsaturated -amino acids)
Amino acids, in human metabolism, have three main usages:
As building blocks for our own protein synthesis. Animals, including humans, are essentially parasites and have a lazy synthetic metabolism. Accordingly, we possess synthetic pathways for only 10 out of the 20 standard amino acids. The residual 10 amino acids have to be obtained from the diet and are called the essential amino acids.
As a source of energy. Depending on the composition of the diet, this role may be very significant. Carbohydrates occur nearly exclusively in plant-derived foodstuffs. Therefore, on a meat-only diet, amino acids become the major source of glucose.
As building blocks for other things such as nucleotides and heme.
Hundreds of types of non-protein amino acids have been found in nature and they have multiple functions in living organisms. Microorganisms and plants can produce uncommon amino acids. In microbes, examples include 2-aminoisobutyric acid and lanthionine, which is a sulfide-bridged alanine dimer. Both these amino acids are both found in peptidiclantibiotics such as alamethicin. While in plants, 1-Aminocyclopropane-1-carboxylic acid is a small disubstituted cyclic amino acid that is a key intermediate in the production of the plant hormone ethylene. In humans, non-protein amino acids also have biologically-important roles. Glycine, gamma-aminobutyric acid and glutamate are neurotransmitters and many amino acids are used to synthesize other molecules, for example: * Tryptophan is a precursor of the neurotransmitter serotonin * Glycine is a precursor of porphyrins such as heme * Arginine is a precursor of nitric oxide * Carnitine is used in lipid transport within a cell, * Ornithine and S-adenosylmethionine are precursors of polyamines, * Homocysteine is an intermediate in S-adenosylmethionine recycling Also present are hydroxyproline, hydroxylysine, and sarcosine. The thyroid hormones are also alpha-amino acids. Nutritional importance: Of the 20 standard proteinogenic amino acids, 10 are called essential amino acids because the human body cannot synthesize them from other compounds through chemical reactions, and they therefore must be obtained from food. Cysteine, tyrosine, hystedine and arginine are considered as semi-essential amino acids in children, because the metabolic pathways that synthesize these amino acids are not fully developed.