Ch 3 lecture proteins

Proteins, Carbohydrates, and Lipids

Overview

This study guide summarizes the chemical structures and biological functions of the three major classes of macromolecules found in living organisms: proteins, carbohydrates, and lipids. Understanding these molecules is fundamental to General Biology, as they form the basis of cellular structure and function.

What Kinds of Molecules Characterize Living Things?

Major Biological Macromolecules

• Proteins: Provide structure and catalyze biochemical reactions.

• Carbohydrates: Supply energy and offer structural support.

• Lipids: Form cell membranes and store energy.

• Nucleic Acids (DNA/RNA): Store and transmit genetic information.

Most macromolecules are polymers composed of smaller units called monomers. For example, proteins are polymers of amino acids, carbohydrates are polymers of monosaccharides, and nucleic acids are polymers of nucleotides.

Definition of Macromolecules

• Macromolecules: Large polymers made up of smaller monomers, typically with molecular weights greater than 1,000.

• They form the backbone of living organisms and are essential to biological functions.

Functional Groups and Molecular Function

The function of a biological molecule depends on the presence of specific functional groups. These are clusters of atoms that impart distinct chemical properties and determine molecular behavior.

• Hydroxyl Group (-OH): Increases hydrophilicity (water solubility).

• Carboxyl Group (-COOH): Confers acidic properties.

• Amino Group (-NH2): Imparts basic properties, essential for proteins.

• Phosphate Group (-PO4): Involved in energy transfer, key to nucleic acids.

Many macromolecules contain multiple functional groups, enabling complex chemical functions.

Some Functional Groups Important to Living Systems

Functional Groups: Properties and Examples

Functional Group	Class of Compounds and Example	Properties
Hydroxyl (-OH)	Alcohols (e.g., Ethanol)	Polar due to the electronegativity of oxygen. Forms hydrogen bonds with water, increasing solubility of organic molecules. Enables molecules to link via condensation reactions (removal of water).
Carbonyl (C=O)	Aldehydes (e.g., Acetaldehyde), Ketones (e.g., Acetone)	Very reactive; important in building molecules. Plays a role in energy-releasing reactions in metabolic processes. Key in carbohydrates and metabolism.
Carboxyl (-COOH)	Carboxylic acids (e.g., Acetic acid)	Acidic; can ionize in living tissues to form carboxylate ion (-COO-). Participates in condensation reactions, forming larger molecules. Important in energy-releasing reactions and metabolism of carbohydrates and fatty acids.
Amino (-NH2)	Amines (e.g., Methylamine)	Basic; can accept a proton (H+), forming positively charged ammonium ion. Participates in condensation reactions, such as peptide bond formation during protein synthesis.

Additional info:

• Functional groups are critical for the reactivity and interaction of biomolecules. For example, the phosphate group is essential for ATP (adenosine triphosphate) function in energy transfer, and the sulfhydryl group (-SH) in cysteine allows the formation of disulfide bridges in proteins.