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
Amino Acid Structure
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
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:https://amit1b.files.wordpress.com
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
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:https://www.wikiwand.com/en/Nucleotide
Amino Acids Non-Protein function
Nucleotide biosynthesis
Source:https://www.wikiwand.com/en/Nucleotide