Chapter 6, Problem 42A

Summary Introduction

Introduction :

Carbon atoms join to form carbon molecules. Similarly, most cells have small carbon compounds that act as the building blocks for large molecules. Smaller organic molecules join together to form macromolecules or polymers. Polymers are formed by repeating units of nearly identical or identical compounds known as monomers joined by a series of covalent bonds. The biological macromolecules are divided into four major classes - carbohydrates, proteins, lipids and nucleic acids.

Answer to Problem 42A

Correct answer :

The correct answer is option (B) carbon and oxygen.

Explanation of Solution

Explanation/justification for the correct answer :

Option (B) carbon and oxygen. Proteins are the building blocks of life. They are made of small carbon compounds called amino acids. Amino acids are composed of carbon, nitrogen, oxygen, hydrogen and sometimes sulfur. All amino acids have the same general structure with a central carbon surrounded by four groups. The amino acids are joined together by several covalent bonds called peptide bonds to form proteins. A peptide bond is formed by the amino group (-NH₂) of an amino acid and the carboxyl group (-COOH) of another. So, the correct answer is option (B).

Explanation for incorrect answer :

Option (A) nitrogen and sulfur. Amino acids are composed of carbon, nitrogen, oxygen, hydrogen and sometimes sulfur. All amino acids have the same general structure with a central carbon surrounded by four groups. The amino acids are joined together by several covalent bonds called peptide bonds to form proteins. A peptide bond is formed by the amino group (-NH₂) of an amino acid and the carboxyl group (-COOH) of another. So, this is an incorrect option.

Option (C) hydrogen and phosphorus. All amino acids have the same general structure with a central carbon atom surrounded by four groups. Amino acids are composed of carbon, nitrogen, oxygen, hydrogen and sometimes sulfur. A peptide bond is formed by the amino group of an amino acid and the carboxyl group of another. The remaining two bonds are formed with hydrogen and a variable group (-R). So, this is an incorrect answer.

Option (D) sulfur and oxygen. All amino acids have the same general structure with a central carbon atom surrounded by four groups. A peptide bond is formed between the amino group of an amino acid and the carboxyl group of another. The remaining two bonds are formed with hydrogen and a variable group (-R). Hence, this is an incorrect answer.