Macromolecules

Biological Macromolecules

The Molecules of Life

• Macromolecules are critical nutrients necessary for life that provide raw materials for the body to use.

Macromolecules

• Definition: Macromolecules are built from different combinations of smaller organic molecules called monomers.

• Monomers: The building blocks (bricks) of macromolecules.

• Examples: Include carbohydrates, lipids, proteins, and nucleic acids.

Types of Macromolecules

• Four Major Groups:

  1. Carbohydrates

  2. Lipids

  3. Proteins

  4. Nucleic Acids

Structure of Macromolecules: Polymers

• Polymers: Most macromolecules are polymers composed of repeated chains of monomers bonded covalently.

• Lipids: Are the exception (do not typically form polymers).

• Reactions:

  • Condensation (Dehydration Synthesis): Joins monomers, producing a water molecule.

  • Hydrolysis: Breaks apart polymers into monomers, requiring the input of water.

Forming a Polymer: Dehydration Synthesis

• Example: Linking two glucose molecules to form the disaccharide maltose.

  • The dehydration reaction forms water (H2O).

  • Hydrogen from one monomer's hydroxyl group combines with the hydroxyl group of another monomer.

  • This process forms a covalent bond and repeats forming a chain of monomers.

Breaking Down a Polymer: Hydrolysis

• Example: Maltose is broken down into two glucose monomers with the addition of a water molecule.

  • This process is the reverse of dehydration and can be sped up by enzymes.

  • Energy is released when bonds are broken.

  • Specific enzymes break down each type of macromolecule (e.g., nucleic acids, proteins, carbohydrates, lipids).

Carbohydrates

• Composition: Built from individual sugars (monosaccharides) with 3-7 carbons each, containing carbon, hydrogen, and oxygen.

• Forms:

  • Monosaccharides (single sugars)

  • Disaccharides (bonded in pairs)

  • Polysaccharides (long chains of 3+ sugars)

• Main Types:

  • Starch: Energy storage in plants.

  • Chitin: Structural component in fungi and arthropods.

  • Cellulose: Structural component in plant cell walls.

  • Glycogen: Energy storage in animals (muscles/liver).

Carbohydrates Functions

• Energy Source: Provide quick energy for cellular functions.

• Energy Storage:

  • Starch: Storage in plants.

  • Glycogen: Short-term storage in animals.

• Structural: Materials for cell walls.

  • Cellulose: Found in plant cell walls.

  • Chitin: Exoskeleton of arthropods and cell walls of fungi.

Lipids

• Definition: Serve as long-term energy storage; non-polar, hydrophobic, and insoluble in water.

• Types of Lipids:

  • Fats

  • Phospholipids (in cell membranes)

  • Waxes

  • Steroids

• Triglycerides: Composed of a glycerol head and three fatty acid tails (chains of carbon and hydrogen).

Lipids Functions

• Energy Source: Provide long-term energy storage for cells.

• Structural: Form cellular membranes via phospholipids and cholesterol.

• Water Barrier: Hydrophobic nature prevents water loss.

• Messenger Molecules: Includes hormones, such as steroids, for cell signaling.

Lipid Structure: Glycerol and Fatty Acids

• Glycerol: A three-carbon chain with three hydroxyl groups.

• Fatty Acids: Chains of carbons and hydrogens with a carboxyl group (COOH) at the end.

  • Saturated Fatty Acids: No carbon-carbon double bonds.

  • Unsaturated Fatty Acids: One or more carbon-carbon double bonds, causing bending in structure.

Lipid Structure: Triglycerides

• Example: Made from one glycerol and three fatty acid chains, with the removal of three water molecules during synthesis.

Phospholipids

• Similar to triglycerides but have only 2 fatty acid molecules.

• The third hydroxyl group of glycerol is replaced with a phosphate/choline group.

Phospholipid Bilayers

• Structure: Formed by hydrophilic heads facing outward and hydrophobic tails facing inward, creating a bilayer essential for cell membranes.

Proteins

• Definition: The most structurally diverse macromolecules, composed of amino acids (peptides).

• Amino acids are bonded by peptide bonds, forming long chains called polypeptides.

• Each amino acid contains:

  • Amino group

  • Carboxyl group

  • Hydrogen atom

  • R group (side chain), which can vary.

Functions of Proteins

• Structural: Form the framework for blood cells, body tissues, and muscles.

• Transport: Hemoglobin carries oxygen in blood, and membrane proteins transport ions across cell membranes.

• Chemical Signals: Hormones and neurotransmitters facilitate communication.

• Movement: Proteins aid muscle contraction (e.g., actin and myosin).

• Immune Response: Proteins (e.g., antibodies) provide mechanisms for fighting infections.

• Enzymes: Act as catalysts to speed up chemical reactions (e.g., amylase).

Amino Acids

• Building blocks (monomers) of proteins; 20 different amino acids exist.

• Composed of carbon, hydrogen, oxygen, and nitrogen, with the variability coming from the R group that differs between amino acids.

A Guide to the Twenty Common Amino Acids

• Essential Amino Acids: Must be obtained from diet, while non-essential can be synthesized by the body.

• Characteristics: Include aliphatic, aromatic, acidic, basic, hydroxylic, sulfur-containing, amidic amino acids.

Peptide Bonds

• Definition: Formed between the carboxyl group of one amino acid and the amine group of another via dehydration reaction.

Nucleic Acids

• Monomers: Nucleotides composed of:

  1. 5-carbon sugar

  2. Phosphate group

  3. Nitrogenous base

• Nitrogenous Bases: Include cytosine, adenine, guanine, and thymine (with uracil in RNA).

• Polymers: DNA and RNA; linked by phosphodiester bonds.

Functions of Nucleic Acids

• Genetic Code: DNA contains genetic instructions; RNA is involved in protein synthesis.

• Energy Transfer: ATP (adenosine triphosphate) is used in cellular energy transfer.

ATP (Adenosine Triphosphate)

• Formed similarly to an RNA nucleotide but contains three phosphate groups instead of one.

Summary of Macromolecules