Organic Macromolecules: Carbohydrates and Proteins

Organic Macromolecules

Introduction

Organic macromolecules are large, complex molecules essential for life. The four major classes are carbohydrates, proteins, lipids, and nucleic acids. These molecules perform a wide range of functions in cells, including energy storage, structural support, catalysis, and information storage.

Carbohydrates

Structure and Function

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, typically with the formula $C_n(H_2O)_n$. They serve as a primary source of energy and as structural components in cells.

• Monomer: Monosaccharides (simple sugars, e.g., glucose)

• Dimer: Disaccharides (two monosaccharides joined, e.g., sucrose, lactose, maltose)

• Polymer: Polysaccharides (long chains of monosaccharides, e.g., starch, glycogen, cellulose)

General formula for glucose: $C_6H_{12}O_6$

Carbohydrates are used in cellular respiration to produce ATP, the energy currency of the cell.

Disaccharides

• Sucrose: Glucose + Fructose

• Lactose: Glucose + Galactose

• Maltose: Glucose + Glucose

Disaccharides are formed by dehydration synthesis, where a water molecule is removed to join two monosaccharides.

Polysaccharides

Polysaccharides are polymers made of many monosaccharide units. They have different functions depending on their structure.

Polysaccharide	Function	Where Found
Starch	Energy storage	Plants
Glycogen	Energy storage	Animals (liver, muscle)
Cellulose	Structural support	Plant cell walls

Additional info: Cellulose is not digestible by most animals, but some (e.g., cows) have symbiotic microbes that help break it down.

Proteins

Structure and Function

Proteins are polymers made of amino acid monomers. They are the most versatile macromolecules, serving as enzymes, structural components, transporters, and more.

• Monomer: Amino acid

• Polymer: Polypeptide (chain of amino acids)

Each amino acid has a central (α) carbon, an amino group ($-NH_2$), a carboxyl group ($-COOH$), a hydrogen atom, and a variable R group (side chain).

Types of Proteins and Their Functions

Type	Function	Example
Enzymatic	Catalyze chemical reactions	Digestive enzymes
Defensive	Protect against disease	Antibodies
Storage	Store amino acids	Ovalbumin (egg white)
Transport	Transport substances	Hemoglobin (oxygen transport)
Hormonal	Coordinate activities	Insulin
Receptor	Respond to chemical signals	Receptors in nerve cells
Contractile/Motor	Movement	Actin, myosin (muscle)
Structural	Support	Collagen (connective tissue)

Amino Acids

• Alanine (Ala)

• Cysteine (Cys)

• Tyrosine (Tyr)

There are 20 different amino acids, each with a unique side chain (R group) that determines its properties.

Protein Structure

Proteins have four levels of structure:

1. Primary structure: Sequence of amino acids

2. Secondary structure: Local folding (α-helix, β-pleated sheet)

3. Tertiary structure: Overall 3D shape of a polypeptide

4. Quaternary structure: Association of multiple polypeptides

Proper folding is essential for protein function. Misfolded proteins can lead to diseases.

Example: Hemoglobin

• Function: Oxygen transport in blood

• Structure: Quaternary (four polypeptide subunits)

• Application: Sickle cell anemia is caused by a mutation that alters hemoglobin structure, reducing its oxygen-carrying capacity.

Additional info: Enzymes are proteins that speed up chemical reactions by lowering activation energy. The sequence and structure of amino acids determine the specificity and function of each protein.