Which one of the following characteristics is not common among carbohydrates, lipids, and proteins?
Correct answer: D. The molecules are held together by ionic bondings
- A. They are composed of a carbon backbone with functional group attached
- B. They all play a role in cell signaling and communication
- C. Their polymers are broken apart by hydrolysis
- D. The molecules are held together by ionic bondings
Explanation
The molecules of all carbohydrates, lipids and proteins are held together by covalent bonds and not ionic bonds. The main bonds within these biological macromolecules are:Carbohydrates: Monosaccharide units are linked by glycosidic bonds, which are covalent bonds.Proteins: Amino acids are linked by peptide bonds (a type of amide bond), which are also covalent bonds. While ionic bonds can form between the charged side chains (R groups) of amino acids and are important for stabilizing the specific three-dimensional (tertiary and quaternary) structure of a protein, they are secondary interactions, and the main structural link between amino acids is the covalent peptide bond.Lipids: In the most common lipids like triglycerides, fatty acids are linked to a glycerol backbone by ester bonds, which are covalent bonds. The hydrocarbon chains themselves are composed of nonpolar covalent bonds.
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The chapter covers water's polarity and biological roles, carbohydrates, lipids, proteins and nucleic acids, including their monomers, bonds, structures and functions. It also distinguishes RNA from DNA and explains conjugated molecules such as glycoproteins, glycolipids and nucleoproteins, which combine organic molecules with a non-protein component.
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