Amino and carboxylic acid functional groups can both be found in organic compounds known as amino acids. Although there are more than 500 amino acids in nature, the alpha-amino acids, which make up proteins, are by far the most significant. The genetic code of every living thing contains just 22 alpha glucosamine.

1. Amino Acids
June 11, 2023admin
Amino and carboxylic acid functional groups can both be found in organic
compounds known as amino acids. Although there are more than 500 amino
acids in nature, the alpha-amino acids, which make up proteins, are by far the
most significant. The genetic code of every living thing contains just 22 alpha
glucosamine.
Alpha, beta, gamma, and delta glucosamine can be categorized according to
where the main structural functional groups are located; other classifications
are based on polarity, ionization, and the type of side chain group (aliphatic,
acyclic, aromatic, containing hydroxyl or Sulphur, etc.). glucosamine residues
are the second-largest component of human muscles and other tissues,
behind water, in the form of proteins. Aside from serving as protein
residues,glucosamine also take involvement in the transfer of
neurotransmitters and biosynthesis. They are believed to have been crucial in
permitting the origin of life on Earth. The Joint Commission on Biochemical
Nomenclature of the IUPAC and IUBMB officially names amino acids using
the fake “neutral” structure seen in the figure. For instance, alanine is known
scientifically as 2-aminopropanoic acid, which is derived from the formula
CH3CH(NH2)COOH. Following is how the Commission defended this
strategy:

2. The systematic names and formulae are for hypothetical forms with
unprotonated amino groups and undissociated carboxyl groups. This
approach is helpful in avoiding a number of nomenclatural issues, but it
should not be interpreted as meaning that these structures account for a
sizable portion of amino acid molecules.
History
In the early 1800s, the first few glucosamine were identified. The first
glucosamine was found in 1806, when French scientists Louis-Nicolas
Vauquelinite and Pierre Jean Sobriquet extracted a substance from
asparagus that they later termed asparagine. Cystine was found in 18, while
cysteine, its monomer, wasn’t found until 1884. Leucine and glycine were
found in 1820 . William Cumming Rose, who also identified the necessary
glucosamine and defined the minimal daily needs of all amino acids for
healthy growth, made the final discovery of the 20 common amino acids in
1935: threonine.
Wirtz acknowledged the unity of the chemical category in 1865, although he
did not give it a specific name. The phrase “glucosamine” was first used in the
English language in 1898, but the German name, Amino sure, was first used
earlier. After enzymatic digestion or acid hydrolysis, glucosamine have been
identified to come from proteins. Emil Fischer and Franz Hofmeister
separately postulated in 1902 that proteins are made up of a large number of
glucosamines, and that these interactions between one amino acid’s amino
group and another’s carboxyl group result in a linear structure that Fischer
dubbed “peptides.”
General structure of glucosamine

3. R denotes a side chain unique to each amino acid in the structure at the top of
the page. The -carbon is the carbon atom adjacent to the carboxyl group. The
word “amino acid” describes amino acids that have an amino group directly
connected to the -carbon. These include the secondary amines proline and
hydroxyproline. They were previously frequently referred to as amino acids,
which is incorrect because they lack the imine grouping HN=C.
Isomerism amino acids
Amino acids often exist in their zwitterionic natural forms, having the
molecular formula NH + 3.
The functional groups (NH + 2 in the case of proline) and (CO 2 in the case of
glycine) are joined to the same C atom, making them -amino acids. Natural
amino acids are the only ones to have the L configuration and are exclusively
present in proteins during translation in the ribosome, with the exception of
achiral glycine. Since D-glyceraldehyde is dextrorotatory and L-
glyceraldehyde is levorotatory, the L and D convention for amino acid
configuration refers to the optical activity of the isomer of glyceraldehyde
rather than the optical activity of the amino acid itself.
The (S) and (R) designators can be used as an alternate convention to
describe the absolute configuration. Almost all (S) amino acids, with the
exception of cysteine (R) and glycine (non-chiral), are found in proteins. The
side chain of cysteine is located geometrically in the same place as the side
chains of the other amino acids, but the R/S terminology is reversed due to
sulfur’s higher atomic number than the carboxyl oxygen, which gives the side
chain a higher priority by the Cahn-Ingold-Prelog sequence rules. This is in
contrast to most other side chains, which have lower priority compared to the
carboxyl group due to their atom composition. Rarely, proteins include D-
amino acid residues, which are created as a post-translational modification
from l-amino acids.
Side chains of amino acids
When the amino nitrogen atom is joined to the -carbon, the
carbon atom next to the carboxylate group, amino acids are
referred to as -. Although there are many methods to categories
amino acids, they are frequently categorized according to the
polarity of their side chains, as shown in the figure:

4. Charged side chains amino acids
At a pH of 7, five amino acids have a charge. To enable proteins to dissolve in
water, these side chains frequently occur at their surfaces. Side chains with
opposing charges then establish crucial electrostatic connections known as
salt bridges, which keep structures within a single protein or between
interacting proteins stable. In order to selectively attach metal into their
structures, many proteins interact with it through charged side chains like
aspartate, glutamate, and histidine. Aspartate (Asp, D) and glutamate (Glue,
E) are the two amino acids with negative charges when the pH is neutral. In
most cases, the anionic carboxylate groups act as Bronsted bases. The
aspartic protease pepsin found in the stomachs of mammals may feature
catalytic aspartate or glutamate residues that function as Bronsted acids in
very low pH settings.
The side chains of three amino acids—arginine (Argo, R), lysine (Lys, K), and
histidine (His, H)—are cations at neutral ph. At pH 7, arginine and lysine,
which each include charged guanidine groups and charged alkyl amino
groups, are entirely protonated. At neutral pH, only around 10% of the
imidazole group of histidine is protonated, according to its pike value of 6.0.
Histidine frequently takes part in catalytic proton transfers in enzyme
processes because it is readily available in both its basic and conjugate acid
forms.

5. Polar uncharged side chains
Serine (Ser, S), threonine (Thru, T), asparagine (Assn, N), and glutamine
(Glenn, Q) are polar, uncharged amino acids that easily form hydrogen bonds
with water and other amino acids. Normal circumstances prevent them from
ionizing, with the catalytic serine in serine proteases being a notable
exception. This is not typical of serine residues in general and is an illustration
of extreme disruption. In addition to the L (2S) chiral center at the -carbon that
is shared by all amino acids with the exception of achiral glycine, threonine
also possesses a 3R chiral center at the -carbon. The complete
stereochemical formula for threonine is (2S,3R).
Hydrophobic side chains
The mechanisms that fold proteins into their useful three-dimensional
structures are mostly driven by nonpolar amino acid interactions. With the
exception of tyrosine (Tyr, Y), none of the side chains of these amino acids
are easily ionized and do not, therefore, have pikes. At high pH, the tyrosine
hydroxyl can deprotonate to generate the negatively charged phenolate.
Tyrosine might be classified as a polar, uncharged amino acid because of
this, although its extremely low water solubility more closely resembles that of
hydrophobic amino acids.
Special case side chains
The charged, polar, and hydrophobic categories do not adequately
characterize a number of side chains. Due to its tiny size and the fact that its
solubility is mostly governed by the amino and carboxylate groups, glycine
(Glee, G) may be regarded as a polar amino acid. Glycine, however, has a
special flexibility among amino acids with significant implications for protein
folding since it lacks any side chains. Although cysteine (Cays, C) frequently
forms covalent interactions with other cysteines in protein structures known as
disulphide bonds, it can also readily create hydrogen bonds, which would
classify it as a polar amino acid. These bonds are crucial for the development
of antibodies and have an impact on the stability and folding of proteins.
Although proline (Pro, P), which has an alkyl side chain and may be regarded
as hydrophobic, becomes extremely rigid when integrated into proteins
because the side chain connects back onto the alpha amino group. This has a
unique effect on protein structure among amino acids, much like glycine. Rare
amino acid selenocysteine (Sec, U) is integrated into proteins via the
ribosome rather than being directly encoded by DNA. Selenocysteine
participates in a number of distinctive enzymatic processes and has a lower

6. redox potential than the related cysteine. Another amino acid, pyrrolidine
(Pyle, O), is not encoded in DNA but is instead produced by ribosomes into
protein. It is present in archaeal species and participates in a number of
methyltransferases’ catalytic activity.
β- and γ-amino acids
NH + 3 CXYCXYCO 2 amino acids, such as -alanine, a component of
carnosine and a few other peptides, are known as -amino acids. NH + 3
CXYCXYCXYCXYCO 2 is the structure of -amino acids, and so on, where X
and Y are two substituents (of which one is often H).
Zwitterions amino acids
Amino acids exist as zwitterions, or dipolar ions, in aqueous solution at pH
levels near to neutrality.
NH + 3 CHR CO 2 makes up the main structure, as do CO 2 in charged
states. The so-called “neutral forms” NH2, CHR, and CO2H are not present in
any appreciable quantity at physiological ph. Although the two charges in the
zwitterion structure sum to zero, it is inaccurate to refer to a species as
“uncharged” when its net charge is zero. The carboxylate group becomes
protonated in severely acidic circumstances (pH below 3), and the structure
changes to an ammonoid carboxylic acid, NH + 3 CHRCO2H. However, it
does not notably apply to enzymes like pepsin that are active in acidic
environments like the human stomach and lysosomes.
Although there are several definitions of acids and bases used in chemistry,
only Bronsted’s definition is applicable to chemistry in aqueous solution: A
base is a species that can take a proton, whereas an acid is a species that
can donate a proton to another species. The groupings in the graphic above
are identified using this criterion. The main Bronsted bases in proteins are the
carboxylate side chains of aspartate and glutamate residues. Similar to
cysteine, lysine, and tyrosine, these amino acids frequently serve as Branstad
acids. In these circumstances, histidine can function as both a Bronsted acid
and a base.
Isoelectric point of amino acids
The zwitterion predominates for amino acids with uncharged side chains at pH
levels in the middle of the two pike ranges, although it coexists in equilibrium
with trace quantities of net negative and net positive ions. The balance
between the trace amounts of net negative and net positive ions occurs at the

7. halfway point between the two pike values, resulting in a zero average net
charge for all forms that are present. The isoelectric point (phi) of this pH is
equal to 1 / 2 (pKa1 + pKa2).
The side chain’s pike plays a role for amino acids with charged side chains.
Therefore, the terminal amino group for aspartate or glutamate with negative
side chains is almost fully in the charged form NH + 3. but this positive charge
has to be countered by the negatively charged state that has only one C-
terminal carboxylate group. Between the two carboxylate pike values,
something happens in the middle: In the equation phi = 1 / 2 (pKa1 + pike(R)),
pike(R) denotes the side chain pike.
Other amino acids with ionizable side chains must also be taken into account,
such as glutamate (which functions similarly to aspartate), as well as amino
acids with positive side chains including cysteine, histidine, lysine, tyrosine,
and arginine. Amino acids exhibit zero mobility in electrophoresis at their
isoelectric point, while peptides and proteins are more frequently used than
single amino acids to take advantage of this feature. Zwitterions have a
minimal solubility at their isoelectric point, and by changing the pH to the
necessary isoelectric point, certain amino acids (especially those with
nonpolar side chains) may be precipitated out of water and separated.
Physicochemical properties
The 20 canonical amino acids can be divided into groups based on how they
behave. Charge, hydrophilicity or hydrophobicity, size, and functional groups
are significant variables. Protein structure and protein-protein interactions are
influenced by these characteristics. Leu, Ile, Val, Phi, and Tarp are
hydrophobic residues that are frequently buried in the center of water-soluble
proteins, whereas hydrophilic side chains are exposed to the aqueous solvent.
An individual monomer found in the polymeric chain of a polysaccharide,
protein, or nucleic acid is referred to as a residue in biochemistry. The outer
rings of exposed hydrophobic amino acids on the integral membrane proteins
usually serve as anchors for the proteins in the lipid bilayer. A patch of
hydrophobic amino acids on the surface of several peripheral membrane
proteins causes them to adhere to the membrane.
Certain amino acids have unique qualities. Other cysteine residues and
cysteine can bind covalently through disulfide bonds. Glycine is more flexible
than other amino acids, and proline creates a cycle to the polypeptide
backbone. Unlike the other amino acids, which are highly reactive, complex,
or hydrophobic, such as cysteine, phenylalanine, tryptophan, methionine,

8. valine, leucine, and isoleucine, glycine and proline are substantially more
prevalent in low complexity regions of both eukaryotic and prokaryotic
proteins. Numerous proteins go through a variety of posttranslational
modifications, in which extra chemical groups are sometimes attached to the
side chains of amino acid residues to produce lipoproteins, which are
hydrophobic, or glycoproteins, which are hydrophilic, enabling the protein to
momentarily bind to a membrane. For instance, a signaling protein may
adhere to a cell and then separate from it.
Occurrence and functions in biochemistry
Since they help make proteins, amino acids with the amine group linked to the
(alpha-) carbon atom adjacent to the carboxyl group are of particular
relevance to living things. They are referred to as 2-, alpha-, or -amino acids
(most commonly having the general formula H2NCHRCOOH,[c] where R is an
organic substituent known as a “side chain”); frequently, the word “amino acid”
is used to explicitly refer to them. They contain the 22 proteinogenic amino
acids (also known as “protein-building”), which are combined to produce
peptide chains (also known as “polypeptides”), which are the fundamental
units of a wide variety of proteins. All of these are L-stereoisomers, or “left-
handed” enantiomers, with the exception of a few D-amino acids, or “right-
handed” enantiomers, which can be found in certain antibiotics, bacterial
envelopes, and D-serine, a neuromodulator.
Numerous glucosamine, both proteinogenic and non-proteinogenic, have
biological use. For instance, the principal excitatory and inhibitory
neurotransmitters in the human brain are glutamate (standard glutamic acid)
and gamma-aminobutyric acid (nonstandard gamma-amino acid, or GABA).
Proline is converted into hydroxyproline, which is a crucial part of the collagen
found in connective tissue. Red blood cell-useable porphyrins are
biosynthesized from glycine. Using carnitine helps move lipids. Because the
human body is unable to synthesize nine proteinogenic glucosamine from
other substances, they must be consumed through diet. These glucosamine
are referred to as “essential” for humans. For particular ages or medical
circumstances, others can be deemed conditionally necessary. Species-to-
species variations in essential glucosamine are also possible. Amino acids are
vital in biological processes because of their biological relevance.
Proteinogenic amino acids
Proteins are built from amino acids. They combine through condensation
processes to create either shorter polymer chains termed peptides or proteins,
or longer chains known as polypeptides. These chains are linear and

9. unbranched because each amino acid residue is joined to two neighboring
amino acids.The process of creating proteins in nature that are encoded by
DNA/RNA is known as translation, and it entails a ribozyme called a ribosome
adding amino acids one at a time to a building protein chain. An mRNA
template, which is an RNA copy of one of the organism’s genes, is used to
read the genetic code and determine the sequence in which the amino acids
are added.
Proteinogenic or natural glucosamine are the 22 amino acids that are naturally
integrated into polypeptides. Twenty of them are encoded by the whole
genetic code. Selenocysteine and pyrrolidine, the remaining 2, are integrated
into proteins using certain synthetic methods. When an SECIS element is
present in the mRNA being translated, the UGA codon inserts selenocysteine
rather than a stop codon.Some methanogenic archaea employ pyrrolidine in
the enzymes they use to generate methane. It is represented by the codon
UAG, which in other species is often a stop codon. Immediately after this UAG
codon, a PYLIS downstream sequence follows.
Glee, Ala, Asp, Val, Ser, Pro, Glut, Leu, and Thru may be related, according
to several independent evolutionary analyses.
Reference

10.  https://medlineplus.gov/ency/article/002222.htm#:~:text=Amino%20acid
s%20are%20molecules%20that,the%20building%20blocks%20of%20lif
e.
 https://en.wikipedia.org/wiki/Amino_acid
 https://my.clevelandclinic.org/health/articles/22243-amino-acids