Functional Groups and Biological Macromolecules: Study Guide for General Biology

Functional Groups in Biological Molecules

Overview of Functional Groups

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. Understanding functional groups is essential for studying the structure and function of biological macromolecules.

• Hydroxyl Group (-OH): Found in alcohols and carbohydrates; increases solubility in water due to hydrogen bonding.

• Methyl Group (-CH3): Non-polar; found in lipids and some amino acids; affects molecule hydrophobicity.

• Carbonyl Group (C=O): Found in aldehydes and ketones; increases reactivity and polarity.

• Carboxyl Group (-COOH): Found in amino acids and fatty acids; acts as an acid by donating H+.

• Amino Group (-NH2): Found in amino acids; acts as a base by accepting H+.

• Sulfhydryl Group (-SH): Found in cysteine; forms disulfide bonds important for protein structure.

Example: The structure of amino acids includes both amino and carboxyl groups, which allow them to link together via peptide bonds.

Macromolecules: Structure and Function

Carbohydrates

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen. They serve as energy sources and structural components in cells.

• Monosaccharides: Simple sugars like glucose and fructose.

• Disaccharides: Formed by joining two monosaccharides via a dehydration reaction (removal of water).

• Polysaccharides: Long chains of monosaccharides; examples include starch, glycogen, and cellulose.

Equation for Dehydration Synthesis:

$\text{Monosaccharide}_1 + \text{Monosaccharide}_2 \rightarrow \text{Disaccharide} + H_2O$

Example: Sucrose is formed from glucose and fructose via dehydration synthesis.

Lipids

Lipids are hydrophobic molecules that include fats, oils, and steroids. They are important for energy storage, membrane structure, and signaling.

• Saturated Fatty Acids: No double bonds; straight chains; solid at room temperature.

• Unsaturated Fatty Acids: One or more double bonds; bent chains; liquid at room temperature.

Type	Structure	Properties
Saturated	All single C-C bonds	Solid, less healthy
Unsaturated (cis)	Cis double bond	Liquid, healthier
Unsaturated (trans)	Trans double bond	Solid, less healthy

Example: Olive oil contains mostly cis-unsaturated fatty acids, while butter contains saturated fatty acids.

Proteins

Proteins are polymers of amino acids. Their structure and function are determined by the sequence and properties of their amino acids.

• Amino Acid Structure: Central carbon, amino group, carboxyl group, hydrogen, and R group (side chain).

• R Groups: Can be polar, non-polar, acidic, or basic; determine protein folding and function.

• Peptide Bond Formation: Occurs via dehydration synthesis between amino and carboxyl groups.

Amino Acid	R Group	Polarity
Tyrosine	CH2-C6H4OH	Polar
Cysteine	CH2-SH	Polar
Alanine	CH3	Non-polar

Example: Disulfide bonds between cysteine residues stabilize protein structure.

Nucleic Acids

Nucleic acids, such as DNA and RNA, store and transmit genetic information. They are polymers of nucleotides.

• Nucleotide Structure: Phosphate group, pentose sugar, nitrogenous base.

• Phosphodiester Bonds: Link nucleotides together to form the backbone of DNA/RNA.

• Base Pairing: Adenine pairs with thymine (DNA) or uracil (RNA); cytosine pairs with guanine.

Equation for DNA/RNA Polymerization:

$\text{Nucleotide}_n + \text{Nucleotide}_{n+1} \rightarrow \text{Polynucleotide} + H_2O$

Example: ATP (adenosine triphosphate) is a nucleotide used for cellular energy.

Summary Table: Functional Groups and Their Properties

Functional Group	Structure	Properties	Example
Hydroxyl	-OH	Polar, forms hydrogen bonds	Alcohols, sugars
Methyl	-CH3	Non-polar, hydrophobic	Lipids
Carboxyl	-COOH	Acidic, donates H+	Amino acids, fatty acids
Amino	-NH2	Basic, accepts H+	Amino acids
Sulfhydryl	-SH	Forms disulfide bonds	Cysteine
Phosphate	-PO4	Negative charge, energy transfer	ATP, nucleic acids

Additional info:

• Images and diagrams in the file illustrate the chemical structures of functional groups, macromolecules, and their monomers.

• Some diagrams show the difference between saturated and unsaturated fatty acids, and the structure of nucleotides and polynucleotides.

• Context inferred: The notes are designed for practice and review of key concepts in Chapters 4-5 of a General Biology textbook, focusing on the chemistry of life and macromolecules.