Biomolecules: Functional Groups and Size

Study Notes

Biomolecules contain a variety of functional groups, including alcohols, amines, aldehydes, ketones, and carboxylic acids.
Many biomolecules are polyfunctional, containing two or more types of functional groups.

Biomolecules can be classified into two categories: small molecules (Mr ≈ 100 to 500) and macromolecules (Mr > 500).

Weak interactions play a critical role in macromolecular structure integrity.
Types of weak interactions:
- Hydrogen bonds (ΔG ≈ -8 to -30 kJ/mol)
- Ionic bonds (ΔG ≈ -20 to -30 kJ/mol)
- Van der Waals force (ΔG ≈ -3 to -4 kJ/mol)
- Hydrophobic interactions

Proteins:
- Long polymers of amino acids
- Constitute the largest fraction (besides water) of cells
- Serve as enzymes, structural elements, signal receptors, or transporters
Nucleic acids (DNA and RNA):
- Polymers of nucleotides
- Store and transmit genetic information
- Some RNA molecules have structural and catalytic roles
Polysaccharides:
- Polymers of simple sugars such as glucose
- Have three major functions: energy-rich fuel stores, rigid structural components of cell walls, and extracellular recognition elements
Lipids:
- Water-insoluble hydrocarbon derivatives
- Structural components of membranes, energy-rich fuel stores, pigments, and intracellular signals
- Individual lipid molecules are much smaller (Mr 750 to 1,500) and are not classified as macromolecules

Molecules with the same chemical structures/bonds but different stereochemistry are called stereoisomers.
Types of stereoisomers:
- Conformational isomers (rotamers)
- Configurational isomers

Configuration is conferred by the presence of either:
- Double bonds (Geometric isomers or cis-trans isomers)
- Chiral centers (Optical isomers)
Geometric isomers or cis-trans isomers:
- Differ in the arrangement of their substituent groups with respect to the non-rotating double bond
Chiral centers:
- A carbon atom with four different substituent is called asymmetric
- One chiral carbon = two stereoisomers; two or more (n) chiral carbons = 2n stereoisomers
Enantiomers:
- Pairs of stereoisomers that are mirror images of each other
- Rotate the plane of plane-polarized light in opposite directions
Diastereomers:
- Pairs of stereoisomers that are not mirror images of each other
Racemic mixture:
- An equimolar solution of two enantiomers that shows no optical rotation

Water is an integral part of life
Prokaryotic and eukaryotic cells:
- Prokaryotes: lack a true nucleus and other membrane-bound organelles
- Eukaryotes: have a true nucleus and other membrane-bound organelles
Major elements in living organisms:
- Hydrogen
- Oxygen
- Nitrogen
- Carbon
Trace elements:
- Essential to life, usually because they are essential to the function of specific proteins, including many enzymes
- Represent a minuscule fraction of the weight of the human body

The chemistry of living organisms is organized around carbon (>50% of the dry weight of cells)
Carbon's bonding versatility was a major factor in the selection of carbon compounds for the molecular machinery of cells during the origin and evolution of living organisms
Covalently linked carbon atoms in biomolecules can form linear chains, branched chains, and cyclic structures