**Question:** Different sequence of amino acid having similar structure of proteins is an example of

A. Homologous proteins
B. Allo-proteins
C. Paralogous proteins
D. Analogous proteins

**Correct Answer:** C. Paralogous proteins

**Core Concept:**
Paralogs are proteins that share a common ancestor and have arisen due to gene duplication events. They are similar in structure and function but may have subtle differences in their amino acid sequences. These differences can be attributed to random mutations during replication or further changes after duplication. On the other hand, homologs are proteins with a common ancestor and similar functions but may have significant differences in their amino acid sequences. Analogous proteins share similar functions but have different structures, while allo-proteins refer to proteins with similar structures but different functions.

**Why the Correct Answer is Right:**
Paralogous proteins share a common origin but have evolved through random mutations, resulting in minor differences in their amino acid sequences. These differences in sequence can affect the protein's structure, stability, and function. Although they may have various functions, the overall structure and function of paralogs are more similar compared to other protein groups with different structures or functions.

**Why Each Wrong Option is Incorrect:**

A. Homologous proteins: While homologous proteins share a common ancestor and similar functions, their amino acid sequences can be significantly different due to time-dependent mutations. This makes paralogs a more suitable answer for proteins with similar structures.

B. Allo-proteins: These proteins have similar structures but distinct functions. The correct answer for proteins with similar functions but different structures is paralogs.

D. Analogous proteins: Analogous proteins share similar functions but have different structures. Paralogs are a better match for proteins with similar structures but different functions due to their shared ancestry and minor differences in sequences.

**Clinical Pearl:**
Understanding protein families like paralogs is crucial for understanding genetic variations, molecular evolution, and disease associations. For example, mutations in paralogous genes can lead to various diseases, as seen in the case of sickle cell anemia, where mutations in the HBB gene encoding for beta-globin protein lead to abnormal hemoglobin structure and function.

**Example:**
Sickle cell anemia is an autosomal recessive genetic disorder caused by mutations in the HBB gene, which encodes beta-globin protein. The disease results from the presence of abnormal hemoglobin molecules with altered structure and function due to amino acid substitutions in the beta-globin chain. In sickle cell anemia, the mutation occurs in one of the beta-globin chains, leading to the formation of abnormal hemoglobin (hemoglobin S) with altered properties. This results in the sickle-shaped red blood cells and their impaired function, leading to the characteristic features of sickle cell anemia.