`alpha` - amino acids are high melting crystalline solids because of the zwitterion structure. They are moderately soluble in water. In acidic medium, `alpha` - amino acids exist as cations (I) and thus migrate towards cathode under the influence of an electric field. On the other hand, in alkaline medium, `alpha` - amino acids exist as anions (III) and thus migrate towards anode under the influence of an electric field. However, at some intermediate value of `p^(H)`, the concentration of the cationic form (I) and anionic form (III) will become equal and consequently the `alpha` - amino acid will exist primarily as the neutral dipolar ion (II). At this `p^(H)`, there would be no net migration of the amino acid in an electric field. This `p^(H)` at which there is no net migration of the amino acid under the influence of an applied electric field is called isoelectric point (pI). Each amino acid has a characteristic isoelectric point. The pH of an amino acid that does not have an ionisable side chain such as alanine isd average of `pK_(a)` values of the carboxyl group and the protonated amino group.
`H_(3)overset(+)(N)-overset("R")overset("|")("C")H-COOH overset(" "OH^(-)" ")underset(" "H^(+)" ")hArr H_(3)overset(+)(N)-underset("Zwitterion (II)")(overset("R")overset("|")("C")H)-COO^(-)overset(" "OH^(-)" ")underset(" "H^(+)" ")hArr underset((III))(overset(+)(N)-overset("R")overset("|")("C")H)-COO^(-)`
Further, the `alpha` - carbon of all the amino acids (except glycine) is chiral (asymmetric) and hence amino acids can exist in teo stereoisomeric forms i.e., D and L. However, all the nautrally occurring amino acids belong to the L - series.
`underset("L(-)Glyceraldehyde")(HO-overset("CHO ")overset("| ")underset(" "CH_(2)OH)underset("| ")("C ")-H)" " underset("L-Amino acid")(H_(2)N-overset("COOH")overset("| ")underset("R ")underset("| ")("C ")-H)`
N - terminus of the peptide structure is on the

Options

A. left hand side
B. right hand side
C. both sides
D. random way

Explanation

To solve the problem regarding the properties of alpha-amino acids, we will break down the information provided step by step.

### Step 1: Understanding the Structure of Alpha-Amino Acids
Alpha-amino acids are characterized by having both an amino group (-NH2) and a carboxyl group (-COOH) attached to the same carbon atom, known as the alpha carbon. This structure allows them to exist in different ionic forms depending on the pH of the solution.

**Hint:** Remember that the alpha carbon is the central carbon to which both the amino and carboxyl groups are attached.

### Step 2: Zwitterion Formation
In neutral or slightly acidic conditions, alpha-amino acids exist predominantly as zwitterions. A zwitterion is a dipolar ion that has both a positive and a negative charge but is overall neutral. This occurs when the amino group is protonated (-NH3+) and the carboxyl group is deprotonated (-COO-).

**Hint:** Zwitterions are crucial for understanding the solubility and migration of amino acids in electric fields.

### Step 3: Migration in Electric Fields
In acidic conditions, the amino acid exists primarily as a cation (positively charged) and will migrate towards the cathode (negative electrode). Conversely, in alkaline conditions, the amino acid exists as an anion (negatively charged) and migrates towards the anode (positive electrode).

**Hint:** The charge of the amino acid determines its direction of movement in an electric field.

### Step 4: Isoelectric Point (pI)
At a specific pH known as the isoelectric point (pI), the concentrations of the cationic and anionic forms of the amino acid are equal. At this point, the amino acid exists mainly as a zwitterion, leading to no net migration in an electric field.

**Hint:** The pI is unique for each amino acid and can be calculated as the average of the pKa values of the carboxyl and amino groups for amino acids without ionizable side chains.

### Step 5: Chirality of Amino Acids
All alpha-amino acids (except glycine) are chiral, meaning they can exist in two stereoisomeric forms: D (dextrorotatory) and L (levorotatory). Naturally occurring amino acids are predominantly in the L configuration.

**Hint:** The chirality of amino acids is important in biological systems, as enzymes and receptors are often specific to one stereoisomer.

### Step 6: N-terminus of Peptide Structure
In a peptide chain, the N-terminus refers to the end of the peptide that has a free amino group (-NH2). This is the starting point of the peptide sequence.

**Hint:** The N-terminus is always at the left side when writing the structure of a peptide.

### Conclusion
The properties and behavior of alpha-amino acids are influenced by their zwitterionic nature, their migration in electric fields based on pH, their chirality, and the structure of peptides. Understanding these concepts is crucial for studying proteins and their functions in biological systems.