Macromolecules: Carbohydrates and Proteins – Structure and Function

Macromolecules

Introduction to Macromolecules

Macromolecules are large, complex molecules essential for life, composed of smaller units called monomers. The four major classes of macromolecules are carbohydrates, proteins, lipids, and nucleic acids. This section focuses on carbohydrates and proteins, their monomers, structure, and biological functions.

• Monomers: Small, repeating units that join to form polymers.

• Polymers: Chains of monomers linked by covalent bonds.

• Elements in Macromolecules: Commonly carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur.

• Function: Macromolecules serve as energy sources, structural materials, and facilitate biological processes.

Carbohydrates

Overview of Carbohydrates

Carbohydrates are macromolecules whose primary function is to provide energy and structural support. They are composed of carbon, hydrogen, and oxygen, typically in a 1:2:1 ratio.

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

• Polymer: Polysaccharides (e.g., starch, glycogen, cellulose)

• General Formula: $C_nH_{2n}O_n$

Monosaccharides

Monosaccharides are the simplest carbohydrates and serve as building blocks for more complex sugars.

• Examples: Glucose (C6H12O6), Fructose, Galactose

• Function: Immediate energy source for cells

Disaccharides

Disaccharides consist of two monosaccharides joined by a glycosidic linkage (covalent bond).

• Examples: Sucrose (glucose + fructose), Lactose (glucose + galactose), Maltose (glucose + glucose)

• Glycosidic Linkage: The bond formed between two monosaccharides by dehydration synthesis.

• Lactose Intolerance: Individuals lacking the enzyme lactase cannot break down lactose into monosaccharides.

Polysaccharides

Polysaccharides are long chains of monosaccharides linked together, serving as energy storage or structural materials.

• Starch: Energy storage in plants

• Glycogen: Energy storage in animal cells

• Cellulose: Structural component of plant cell walls

Comparison of Starch and Cellulose

Property	Starch	Cellulose
Function	Energy storage	Structural support
Location	Plants	Plants
Structure	Alpha glucose monomers, branched or unbranched	Beta glucose monomers, straight chains
Digestibility	Digestible by humans	Indigestible by humans

• Structural Differences: Starch has alpha-1,4 and sometimes alpha-1,6 glycosidic bonds; cellulose has beta-1,4 glycosidic bonds.

• Energy Storage: Both starch and glycogen store energy, but in different organisms.

Proteins

Overview of Proteins

Proteins are macromolecules composed of amino acids. They perform a wide range of functions, including catalysis (enzymes), structural support, transport, and regulation.

• Monomer: Amino acid

• Polymer: Polypeptide (protein)

• Elements: Carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur

Amino Acids

Amino acids are organic molecules with a central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a variable R group (side chain).

• General Structure: $\text{H}_2\text{N}-\text{CHR}-\text{COOH}$

• Number of Amino Acids: 20 different types

• Properties: Determined by the R group; can be hydrophobic, hydrophilic, acidic, or basic

Classification of Amino Acids

Type	Example	Property
Nonpolar (hydrophobic)	Leucine	Repels water
Polar (hydrophilic)	Serine	Attracts water
Acidic	Aspartic acid	Negative charge
Basic	Lysine	Positive charge

Polypeptides and Protein Structure

Proteins are formed by linking amino acids through peptide bonds, resulting in polypeptide chains. The structure of proteins is hierarchical and determines their function.

• Primary Structure: Sequence of amino acids in a polypeptide

• Secondary Structure: Local folding into alpha helices and beta sheets, stabilized by hydrogen bonds

• Tertiary Structure: Overall three-dimensional shape, stabilized by interactions between R groups (hydrophobic interactions, ionic bonds, disulfide bridges)

• Quaternary Structure: Association of multiple polypeptide chains

Factors Affecting Protein Structure

• Denaturation: Loss of protein structure due to changes in temperature, pH, or chemical exposure, resulting in loss of function

• Mutations: Changes in amino acid sequence can alter protein folding and function

Examples and Applications

• Enzymes: Proteins that catalyze biochemical reactions (e.g., lactase breaks down lactose)

• Structural Proteins: Collagen in connective tissue, keratin in hair

• Transport Proteins: Hemoglobin transports oxygen in blood

Additional info: The notes infer the importance of protein folding and the impact of mutations on protein function, which are critical concepts in molecular biology and genetics.