Chapter 3: The Molecules of Cells – Study Notes

Chapter 3: The Molecules of Cells

Introduction to Organic Compounds

Organic compounds are molecules primarily composed of carbon atoms bonded with hydrogen, oxygen, nitrogen, and other elements. These compounds form the basis of life and are distinguished by their unique chemical properties.

• Organic Compound: A molecule containing carbon and hydrogen, often forming the backbone of biological macromolecules.

• Example: Ethyl alcohol (ethanol) is an organic compound due to its carbon-hydrogen structure.

Properties of Carbon

Carbon atoms can form four covalent bonds, allowing for a diversity of stable structures, including chains and rings. This versatility is essential for the complexity of biological molecules.

• Tetrahedral Structure: Carbon's ability to bond with up to four other atoms enables the formation of large, complex molecules.

• Isomers: Molecules with the same molecular formula but different structures (e.g., glucose and fructose).

Functional Groups in Organic Molecules

Functional groups are specific groups of atoms within molecules that determine the chemical properties and reactions of those molecules.

Structure	Hydroxyl	Carbonyl	Carboxyl	Amino	Phosphate	Methyl
Formula	-OH	-C=O	-COOH	-NH2	-OPO32-	-CH3

• Hydroxyl Group: Found in alcohols; makes molecules polar and hydrophilic.

• Carboxyl Group: Acts as an acid; found in amino acids and fatty acids.

• Amino Group: Acts as a base; found in amino acids.

• Phosphate Group: Important in energy transfer (e.g., ATP).

• Methyl Group: Nonpolar; affects gene expression.

Dehydration and Hydrolysis Reactions

Macromolecules are formed and broken down by dehydration synthesis and hydrolysis reactions.

• Dehydration Synthesis: Joins monomers by removing a water molecule.

• Hydrolysis: Breaks polymers into monomers by adding water.

Equation:

• Dehydration: $\text{Monomer}_1 + \text{Monomer}_2 \rightarrow \text{Polymer} + H_2O$

• Hydrolysis: $\text{Polymer} + H_2O \rightarrow \text{Monomer}_1 + \text{Monomer}_2$

Carbohydrates

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, typically with a ratio of 1:2:1. They serve as energy sources and structural components.

• Monosaccharides: Simple sugars (e.g., glucose, fructose).

• Disaccharides: Two monosaccharides joined by dehydration synthesis (e.g., sucrose).

• Polysaccharides: Long chains of monosaccharides (e.g., starch, cellulose, glycogen).

Description	Ketone	Aldehyde
Location of carbonyl group	Within carbon chain	At end of carbon chain
Example	Fructose	Glucose

Polysaccharides and Their Functions

Name	Monomer or Polymer	Function
Starch	Polymer of glucose	Energy storage in plants
Glycogen	Polymer of glucose	Energy storage in animals
Cellulose	Polymer of glucose	Structural support in plant cell walls

Lipids

Lipids are hydrophobic molecules, including fats, phospholipids, and steroids. They are important for energy storage, membrane structure, and signaling.

• Saturated Fat: No double bonds; solid at room temperature.

• Unsaturated Fat: One or more double bonds; liquid at room temperature.

• Phospholipids: Major component of cell membranes; amphipathic nature.

Proteins

Proteins are polymers of amino acids and perform a wide range of functions, including catalysis, transport, and structural support.

• Primary Structure: Sequence of amino acids.

• Secondary Structure: Alpha helices and beta sheets formed by hydrogen bonding.

• Tertiary Structure: Overall 3D shape due to interactions among R groups.

• Quaternary Structure: Association of multiple polypeptide chains.

Description	Primary	Secondary	Tertiary	Quaternary
Structure	Sequence of amino acids	Alpha helix, beta sheet	3D folding	Multiple polypeptides

Nucleic Acids

Nucleic acids (DNA and RNA) store and transmit genetic information. DNA is the hereditary material, while RNA is involved in protein synthesis.

• DNA: Double-stranded, contains deoxyribose, bases A, T, C, G.

• RNA: Single-stranded, contains ribose, bases A, U, C, G.

Venn Diagram Comparison:

• DNA: Double helix, thymine, deoxyribose.

• RNA: Single strand, uracil, ribose.

• Both: Nucleotides, genetic information, phosphate backbone.

Transcription and Translation

Transcription is the process of synthesizing RNA from DNA, while translation is the synthesis of proteins from RNA.

• Transcription: DNA → RNA

• Translation: RNA → Protein

Connecting Concepts

Understanding the structure and function of biological molecules is essential for grasping how cells operate and how life is sustained at the molecular level.

• Application: Knowledge of macromolecules is used in food science, medicine, and biotechnology.