**Question:** True about structure of protein is

A. Proteins are composed of amino acids
B. Proteins are made of nucleotides
C. Proteins are synthesized in the mitochondria
D. Proteins are linear molecules made of nucleotides

**Core Concept:**
Proteins are essential biomolecules in living organisms, composed of amino acids. They serve various functions, such as enzymes, hormones, antibodies, and structural components (e.g., collagen, keratin). Proteins are linear polymers formed by the covalent bonding of amino acids. Each amino acid has a carboxyl group (-COOH) and an amino group (-NH2), which can form peptide bonds with other amino acids.

**Why the Correct Answer is Right:**
Proteins are correctly described as linear molecules formed by the covalent bonding of amino acids. The amino acid structure consists of a carboxyl group (-COOH) and an amino group (-NH2), which react with each other to form peptide bonds. This covalent bonding results in the formation of a polypeptide chain, which is the basic structural unit of proteins.

**Why Each Wrong Option is Incorrect:**

A. Proteins are not composed of nucleotides; nucleic acids (DNA and RNA) contain nucleotides that make up the genetic information, not proteins.

B. Proteins are not made of nucleotides; nucleotides are the building blocks of nucleic acids, not proteins. Proteins are formed from amino acids.

C. Proteins are synthesized in the mitochondria; proteins are actually synthesized in the ribosomes, which are cellular organelles found in the cytoplasm and nucleus. The mitochondria are involved in converting amino acids into energy through processes like oxidative phosphorylation.

D. Proteins are linear molecules made of nucleotides; as mentioned earlier, proteins are made of amino acids, not nucleotides.

**Clinical Pearl:**
Understanding the structure of proteins is crucial for grasping their diverse functions in the body. Proteins are essential for various biological processes like enzymatic reactions, cell signaling, and transport of nutrients and waste products. Knowledge of protein structure aids in recognizing potential errors in protein synthesis, such as in genetic disorders like cystic fibrosis or sickle cell anemia.