Organic Molecules, Functional Groups, and Carbohydrates: Structure and Properties

Organic Molecules and Functional Groups

Introduction to Biological Macromolecules

Biological macromolecules are large, complex molecules essential for life, constructed from smaller subunits called monomers. The formation and breakdown of these macromolecules involve specific chemical reactions, primarily condensation (dehydration synthesis) and hydrolysis.

• Polymer: A large molecule made by covalent bonding of many smaller molecules (monomers).

• Monomer: A small molecule that can join with other similar molecules to form a polymer.

• Condensation (Dehydration Synthesis): A reaction where two monomers are joined by a covalent bond, releasing a molecule of water.

• Hydrolysis: A reaction where a polymer is broken down into monomers by the addition of water, catalyzed by enzymes.

Key Equations:

• Condensation: $\text{Monomer} + \text{Monomer} \rightarrow \text{Polymer} + \text{Water}$

• Hydrolysis: $\text{Polymer} + \text{Water} \rightarrow \text{Monomer} + \text{Monomer}$

Example: The formation of a peptide bond between two amino acids is a condensation reaction, while the breakdown of starch into glucose monomers is a hydrolysis reaction.

Properties of Condensation and Hydrolysis Reactions

• Mass Change: The product of a condensation reaction weighs less than the sum of the monomer reactants because a water molecule is removed for each bond formed.

• Enzymatic Role: Enzymes catalyze both condensation (polymerase) and hydrolysis (hydrolase) reactions.

• Stoichiometry: To completely hydrolyze a polymer that is 10 monomers long, 9 molecules of water are required (one less than the number of monomers).

Properties of Water and Hydrogen Bonding

Hydrogen Bonding in Water

Hydrogen bonds are weak interactions between the partially positive hydrogen atom of one water molecule and the partially negative oxygen atom of another. These bonds give water its unique properties, which are essential for life.

Property	Explanation	Significance to Living Things
Thermal Properties: High Specific Heat & Heat of Vaporization	H-bonds limit the motion of water molecules and absorb heat energy.	Bodies of water absorb heat, stabilizing environments.
Cohesive Properties	H-bonds create a network between water molecules, making them stick together.	Water can move up plant stems (capillary action), surface tension.
Adhesive Properties	Water adheres to other polar molecules, creating a network.	Water acts as a lubricant and helps move substances in plants.
Solvent Properties	Polarity allows water to dissolve ionic and polar substances.	Water dissolves ions and polar molecules, supporting biochemical reactions.

Functional Groups in Biological Molecules

Overview of Functional Groups

Functional groups are specific groups of atoms within molecules that have characteristic properties and chemical reactivity. They determine the behavior of organic molecules in biological systems.

• Charged (at physiological pH): Phosphate, Amino, Carboxyl

• Polar (uncharged): Sulfhydryl, Carbonyl, Hydroxyl

• Non-polar: Methyl

Example Table: Functional Groups

Functional Group	Structure	Example	Properties
Sulfhydryl (–SH)	–SH	Cysteine	Forms disulfide bonds in proteins
Phosphate (–PO4)	–OPO32–	Organic phosphate	Imparts negative charge, energy transfer
Methyl (–CH3)	–CH3	5-Methylcytosine	Non-polar, affects gene expression

Behavior in Solution: Charged and polar groups are hydrophilic (water-loving), while non-polar groups are hydrophobic (water-repelling).

Example: The amino group (–NH2) can accept a proton to become –NH3+ at physiological pH, making it positively charged.

Recognizing Functional Groups in Biomolecules

• Be able to identify and label functional groups in molecular structures.

• Circle and note polar or charged regions in biomolecules.

• Predict the types of bonds and interactions (e.g., hydrogen bonds, ionic bonds) that functional groups can form.

Carbohydrates: Structure and Isomerism

Monosaccharides and Their Features

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, typically with the formula (CH2O)n. Simple sugars (monosaccharides) are the building blocks of complex carbohydrates (polysaccharides).

• Defining Features of Monosaccharides:

  1. Number of carbon atoms (e.g., trioses, pentoses, hexoses)

  2. Location of functional groups (e.g., aldehyde or ketone)

  3. Orientation of functional groups around a carbon atom (isomerism)

Classification Table: Monosaccharides

Type	Example	Formula	Functional Group
Aldose (Aldehyde sugar)	Glucose	C6H12O6	Aldehyde
Ketose (Ketone sugar)	Fructose	C6H12O6	Ketone

Isomerism: Glucose and fructose are structural isomers; they have the same molecular formula but different arrangements of atoms and functional groups.

Example: The ring forms of glucose and fructose differ in the position of the carbonyl group and the orientation of hydroxyl groups.

Summary Table: Hexose Isomers

Hexose	Structure	Notes
Glucose	Six-membered ring	Main energy source in cells
Galactose	Six-membered ring	Differs from glucose at one carbon
Fructose	Five-membered ring	Ketose sugar, found in fruit

Additional info: Recognizing the chemical structure of monomers and functional groups is essential for predicting the properties and reactivity of biological molecules in aqueous solutions.