Problem 49 - Objective Biology for NEET

Question

In the primary structure of protein (a) Left end represents \(\rightarrow\) 1st amino acid (C-terminal amino acid) (b) Right end represents \(\rightarrow\) Last amino acid (N terminal amino acid) (c) Left end represents \(\rightarrow\) lst amino acid (N-terminal amino acid) (d) Right end represents \(\rightarrow\) 1st amino acid (C-terminal amino acid)

Step-by-Step Solution

Answer

The correct answers are (c) and (d). The left end of the primary protein structure represents the first amino acid, which is the N-terminal amino acid (c). The right end represents the first amino acid or the C-terminal amino acid (d).

Step 1: Understand Protein Structures

Proteins are made up of amino acids that join together to form a long chain. This chain is known as the primary structure of a protein. For a protein, the N-terminus is the end of the protein where the amino group (-NH2) is not involved in a peptide bond and is free. The C-terminus, on the other hand, is the end of the protein where the carboxyl group (-COOH) is not involved in a peptide bond and is free.

Step 2: Identify the N-terminal and C-terminal amino acids

When synthesizing a protein, the first amino acid (the one with the free amino group) is the N-terminal amino acid. The last amino acid (the one with the free carboxyl group) is the C-terminal amino acid. Therefore, the left end usually represents the first amino acid (the N-terminal) and the right end represents the last amino acid (the C-terminal).

Key Concepts

N-terminal amino acid

In protein chemistry, the N-terminal amino acid holds a significant role. It is the first amino acid in a peptide chain and defines the start of the protein. The term "N-terminal" refers to the free amine group \((-NH_2)\) at this end, which is not bound to any other amino acid by a peptide bond.
When a protein is synthesized in cells, it begins with the N-terminal amino acid linking to the subsequent amino acid through a process called peptide bonding.
An important thing to note is that the N-terminal amino acid has specific biochemical properties that can influence the protein's function and stability.

• Each amino acid has a unique side chain or R group, which interacts with the protein chain causing a specific folding pattern essential to the protein's function.
• The N-terminal can sometimes be modified after protein synthesis, impacting its activity further.

Understanding the N-terminal amino acid is crucial, as it signifies the starting point of protein synthesis and impacts many functional properties of the protein.

C-terminal amino acid

The C-terminal amino acid marks the end of the peptide chain in proteins, characterized by the presence of a free carboxyl group \((-COOH)\).
This carboxyl end is the stopping point for protein synthesis, as it does not form a peptide bond with another amino acid.
During expertise in protein functions, it is essential to recognize that the C-terminal amino acid can significantly affect the protein's properties and interactions.

• The C-terminal often plays a role in protein targeting and processing functions, determining where a protein might be localized within a cell.
• Just like the N-terminal, the C-terminal can undergo post-translational modifications that may alter a protein's activity or stability.

In summary, the C-terminal amino acid signifies an essential structural component and terminal point of a polypeptide chain in protein synthesis.

Protein Synthesis

Protein synthesis is a pivotal biological process where cells build proteins from amino acids. This process occurs in two main stages: transcription and translation.
First, during transcription, the DNA's instructions are transcribed into messenger RNA (mRNA) in the nucleus. Then, during translation, this mRNA is used to synthesize proteins in the ribosomes.
Understanding protein synthesis includes grasping how proteins are built from their starting block of N-terminal amino acids to their ending C-terminal amino acids.
The synthesis follows a linear sequence from the N-terminal at the start to the C-terminal as the conclusion of the structure.

• Each amino acid added to the chain forms a peptide bond with the previous amino acid, under the guidance of transfer RNA (tRNA).
• This continuous addition of amino acids proceeds until a stop codon is reached, signifying the end of protein translation.
• The sequence and structure of the resulting protein determine its function within the living organism.

Protein synthesis is a critical mechanism for life, ensuring proteins are correctly assembled for various cellular functions and repair.