Amino Acids OMAR A. ALOMAIR Biochemistry 1 References Biochemistry (Lippincott's Illustrated Reviews Series), 6E

Amino Acid Structure More than 300 amino acids have been discover In mammals, 20 amino acids make up every protein Each amino acid contains a carboxyl group Each amino acid contains a primary amino group except for proline which has a secondary amino group A side chain (R) is present in every amino acid and is connected to the α carbon

Amino Acid Structure

The human body function at a physiological pH of 7.4 At this physiological pH, both the carboxyl group and the amino group dissociate The carboxyl group dissociate to give the a negatively charged carboxylate ion (– COO–) While the amino part is protonated to form a positively charged amine (– NH3+) The role of any amino acid is decided according to the nature of the side chain (R)

Amino Acid Structure

Amino Acid Classification Each amino acid is classified according to the chemical properties of the side chain The classification is according to the distribution of the electron in the R group As a result, the 20 amino acids are divided into non-polar polar and amino acids Polar amino acid is further classified at physiological pH to 1- No charge polar amino acids 2- Positively charged amino acids 3- Negatively charged amino acids

Non-Polar Amino Acids Non-Polar amino acids has the same number of amino and carboxyl groups They has hydrophobic characteristic They have no charge on the side chain They have low water solubility The create the core of most globular proteins

Non-Polar Amino Acids

Polar Amino Acids Uncharged Polar amino acids that dose not have the same number of amino and carboxyl groups They have no charge on the side chain They are mostly involved in forming hydrogen bonds in globular protein The sulfhydryl(thiol) group (–SH) of cysteine is important in creating disulfide bond in extra cellular protein, e.g. Albumin Phosphate group, which is involved in important physiological activity binds to the hydroxyl group of serine and thyronine

Polar Amino Acids Uncharged

Polar Amino Acids Positively Charged Polar amino acids that does not have the same number of amino and carboxyl groups They have a positive charge on the side chain They are basic in nature Histidine play an important role as a buffer moiety in many protein This due to its unique ability to be deprotonated or protonated when its incorporated into a protein depending on the protein environment

Polar Amino Acids Positively Charged

Polar Amino Acids Negatively Charged Polar amino acids that does not have the same number of amino and carboxyl groups They have a negative charge on the side chain They are acidic in nature They are also called dicarboxylic mono-amino acids Glutamic acid and aspartic acid are essential as a fuel intermediate in glycolysis and gluconeogenesis

Polar Amino Acids Negatively Charged

Amino Acids Sources The main source of amino acids is diet Meat provide all the 20 amino acids involved in protein synthesis Since meat contain all the 20 amino acids it is called “complete protein” Some plant act as a source for most of the aforementioned amino acid but not all of them Examples of “incomplete protein” include legumes, seeds and vegetable

Amino Acids Sources The main source of amino acids is diet Meat and egg white provide all the 20 amino acids involved in protein synthesis Since meat and egg white contain all the 20 amino acids it is called “complete protein” Some plant act as a source for most of the aforementioned amino acid but not all of them Examples of “incomplete protein” include legumes, seeds and vegetable

Amino Acids Essential and Non-Essential Another classification amino acids is according to the ability of the body to produce them Essential amino acids are the ones the normal adult body can not synthesis and need an external sources to supplement Non-Essential amino acids include all the amino acids that the healthy adult human synthesis de-novo Conditional-Non-Essential amino acids are the amino acids that only children, elderly and people with diseases such as phenylketonuria need to have in their diet

Amino Acids Essential and Non-Essential Source:

Amino Acids Digestion and Absorption Hydrochloric acid, released from parietal cells, activate the zymogen pepsinogen to form pepsin enzyme Pepsin enzyme unfold and break down protein to form short peptides It is released form the chief cells lining the stomach Another proteolytic enzyme is trypsin which is produced in pancreases and released in the duodenum The result of the breakdown is single amino acids and short peptides which can readily be absorbed

Amino Acids Digestion and Absorption

Amino Acids Non-Protein function Molecules Precursors Numerous Amino acids act as starting block of not only protein but also other molecules These molecules involve neurotransmitter, porphyrins and nucleotide Example of this is the neurotransmitter serotonin which is synthesized from tryptophan Another Example is the function of glycine as heme porphyrin precursor

Amino Acids Non-Protein function Molecules Precursors

Numerous Amino acids act as starting block of not only protein but also other molecules These molecules involve neurotransmitter, porphyrins and nucleotide Example of this is the neurotransmitter serotonin which is synthesized from tryptophan Another Example is the function of glycine as heme porphyrin precursor

Amino Acids Non-Protein function Urea Cycle The urea cycle is one the early biochemical process discovered It takes place mainly in the liver The main function of the urea cycle is to convert the toxic ammonia (NH3) to the much less toxic urea molecule (CH4N2O) Arginine plays an essential role in the cycle as an intermediate to remove excess nitrogen Argininemia is a disease associated with high level of arginine and ammonia

Amino Acids Non-Protein function Urea Cycle

Amino Acids Non-Protein function Nucleotide biosynthesis The main molecule that form both DNA and mRNA Each nucleotide consist of Phosphate connected to sugar, the sugar it self is bond to nitrogen base A number of amino acid is salvaged to provide structural component to the nitrogen base through the process of nucleotide biosynthesis Source:

Amino Acids Non-Protein function Nucleotide biosynthesis Source: