Question

At isoelectric point, a protein has
A. No net charge
B. Negative charge
C. Positive charge
D. Both B and C

Answer 1

Proteins are complex macromolecules that are required by the body to carry out vital functions such as provide structure and regulate body tissues and organs. They are derived from food sources such as milk, eggs, cheese, fish, nuts, tofu, beans, legumes, seeds, lean meat, and poultry.

Step by step answer: Proteins are macromolecules synthesized by amino acids. Amino acids are monomers that combine to form protein molecules. Amino acids carry charges and are either acidic, basic, or non-polar in nature. They are either negative, positive, neutral, or polar in nature. A combination of charged amino acids forms the proteins. Therefore, if more basic amino acids combine to form a protein, then the protein is positively charged and if the protein is made up of a combination of more acidic amino acids, then it carries a negative charge.
Proteins have a very diverse range of functions. For example, they may serve a purpose in storage,
transport, protection, and may either function as toxins or enzymes. They are present in different
shapes and could either be a fibrous protein or a globular protein. Haemoglobin is an example of a
globular protein, whereas collagen is an example of a fibrous protein. Collagen is present in human
skin and provides it with strength and elasticity. When at a certain pH a molecule is electrically neutral or does not carry any net electrical charge, then that pH is called the isoelectric point.
A molecules net charge depends on the pH of its surroundings and can either be positive or negative
based on the gain or loss of protons. The solubility of a molecule is also determined or affected by
the isoelectric point at a given pH.
Proteins comprise of both acidic and basic functional groups and carry a charge because of the amino acids forming them. Therefore, proteins carry a net positive charge below their isoelectric point at a given pH and carry a net negative charge above their isoelectric point at a given pH. So naturally, proteins carry no net charge at their isoelectric point.
Therefore, the correct answer is option A, i.e., No net charge

Note: The two techniques of separation of proteins by their net charges include gel electrophoresis and isoelectric focusing. The separation is carried out in a polyacrylamide gel. Gel electrophoresis separates proteins by the use of constant pH, whereas isoelectric focusing uses
pH gradient to carry out the separation of proteins.