Chapter 6, Problem 43A

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 43A

Correct answer :

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

Explanation of Solution

Explanation/justification for the correct answer :

Option (A) peptide bonds. 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 between the amino group (-NH₂) of an amino acid and the carboxyl group (-COOH) of another. So, the correct answer is option (A).

Explanation for incorrect answer :

Option (B) hydrogen bonds. The force of attraction between the electronegative atom and hydrogen molecules is known as hydrogen bond. Water has a bent shape and the electrons are not shared equally between hydrogen and oxygen, therefore hydrogen bonds form among the molecules. The amino acids are joined together by several covalent bonds called peptide bonds to form proteins. So, this is an incorrect option.

Option (C) van der Waals forces. The attractive forces between the positive and negative regions of molecules that hold them together is known as van der Waals forces. The amino acids are joined together by several covalent bonds called peptide bonds to form proteins. So, this is an incorrect answer.

Option (D) ionic bonds. Chemical bonds are of two types- covalent and ionic bonds. Covalent bond is formed by sharing of electrons. An ionic bond results from electrical attraction between two oppositely charged atoms or group of atoms. The amino acids are joined together by several covalent bonds called peptide bonds to form proteins. Hence, this is an incorrect answer.