Comprehensive Study Notes: Amines, Lipids, Carbohydrates, Amino Acids, Proteins, and Enzymes

Chapter 18: Amines

Classification of Amines

Amines are organic compounds derived from ammonia by replacement of one or more hydrogen atoms with alkyl or aryl groups. They are classified based on the number of organic substituents attached to the nitrogen atom.

• Primary (1°) amine: Nitrogen attached to one alkyl/aryl group and two hydrogens.

• Secondary (2°) amine: Nitrogen attached to two alkyl/aryl groups and one hydrogen.

• Tertiary (3°) amine: Nitrogen attached to three alkyl/aryl groups and no hydrogens.

• Quaternary ammonium ion: Nitrogen attached to four alkyl/aryl groups, carrying a positive charge.

Naming Amines

• Common names: Name the alkyl groups attached to nitrogen, followed by "amine" (e.g., ethylamine).

• IUPAC names: Use the parent alkane name, replace "-e" with "-amine" (e.g., ethanamine).

• For secondary and tertiary amines: Use "N-" to indicate substituents on nitrogen (e.g., N-methylethanamine).

Physical Properties of Amines

• Boiling points: Amines have higher boiling points than alkanes but lower than alcohols due to hydrogen bonding (primary and secondary only).

• Solubility: Lower amines are soluble in water; solubility decreases with increasing molecular weight.

Amines as Bases

• Amines act as Lewis bases due to the lone pair on nitrogen.

• They accept protons to form ammonium ions:

$\mathrm{RNH_2 + H^+ \rightarrow RNH_3^+}$

Reactions as Bases

• Amines react with acids to form water-soluble salts (ammonium salts).

• They can also participate in alkylation and acylation reactions.

Neurotransmitters

• Many neurotransmitters (e.g., dopamine, serotonin) are amines.

• They play crucial roles in nerve signal transmission.

Chapter 19: Lipids

Classification of Lipids

• Hydrolysable lipids: Can be broken down by hydrolysis (e.g., waxes, triacylglycerols, phospholipids).

• Nonhydrolyzable lipids: Cannot be hydrolyzed (e.g., steroids, fat-soluble vitamins, eicosanoids).

Fatty Acids

• Saturated fatty acids: No double bonds between carbon atoms.

• Unsaturated fatty acids: One or more double bonds present.

• Drawings typically show a long hydrocarbon chain with a terminal carboxylic acid group.

Formation and Reactions of Lipids

• Waxes: Formed by esterification of a fatty acid with a long-chain alcohol.

• Triacylglycerols: Formed by esterification of glycerol with three fatty acids.

• Hydrolysis of triacylglycerols: Produces glycerol and fatty acids (saponification yields soap).

Soap and Its Mechanism

• Soap is the sodium or potassium salt of a fatty acid.

• It works by forming micelles that trap nonpolar dirt and grease, allowing them to be washed away with water.

Phospholipids

• Composed of glycerol, two fatty acids, a phosphate group, and an amino alcohol.

• Phosphoacylglycerols: Glycerol backbone.

• Sphingosine-based phospholipids: Sphingosine backbone.

Amino Alcohols in Phospholipids

• Three common amino alcohols: choline, serine, and ethanolamine.

Cell Membrane and Transport

• Phospholipids form a bilayer, creating the cell membrane.

• Transport across the membrane can be passive (diffusion) or active (requires energy).

Steroids and Cholesterol

• Steroids have a characteristic four-ring structure.

• Cholesterol: Essential for membrane fluidity; precursor for steroid hormones.

• LDL (Low-Density Lipoprotein): "Bad" cholesterol; transports cholesterol to tissues.

• HDL (High-Density Lipoprotein): "Good" cholesterol; removes cholesterol from tissues.

Steroid Hormones and Fat-Soluble Vitamins

• Examples of steroid hormones: testosterone, estrogen, cortisol.

• Fat-soluble vitamins: A, D, E, K.

Chapter 20: Carbohydrates

Classification of Carbohydrates

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

• Disaccharides: Two monosaccharides linked (e.g., sucrose).

• Polysaccharides: Many monosaccharides linked (e.g., starch, cellulose).

Glucose Structure

• Glucose is a six-carbon (hexose) aldose sugar.

Fischer and Haworth Projections

• Fischer projection: Two-dimensional representation showing stereochemistry.

• Haworth structure: Cyclic form of sugars, commonly used for pyranoses and furanoses.

Anomers vs. Enantiomers

• Anomers: Isomers differing at the anomeric carbon (α and β forms).

• Enantiomers: Non-superimposable mirror images.

Hemiacetal Formation

• Monosaccharides cyclize via intramolecular reaction between carbonyl and hydroxyl groups, forming a hemiacetal.

Reactions of Monosaccharides

• Oxidation: Aldoses can be oxidized to aldonic acids; ketoses oxidize less readily.

• Reaction with alcohols: Forms acetals (glycosidic bonds).

• Glycosidic bond formation: Links monosaccharides to form di- and polysaccharides.

Hydrolysis of Di- and Polysaccharides

• Breaks glycosidic bonds, yielding monosaccharides.

Formation of Phosphate Esters

• Phosphate groups can be added to sugars, important in metabolism (e.g., glucose-6-phosphate).

Chapter 21: Amino Acids, Proteins, and Enzymes

Amino Acids: Structure and Classification

• There are 20 standard amino acids, classified by side chain properties:

  • Nonpolar, neutral

  • Polar, neutral

  • Acidic

  • Basic

Ionization States at Different pH

• At acidic pH: Both amino and carboxyl groups are protonated.

• At basic pH: Both groups are deprotonated.

• At neutral pH: Zwitterion form (NH3+ and COO-).

Isoelectric Point (pI)

• The pH at which the amino acid has no net charge.

• Calculated as the average of the pKa values for the ionizable groups.

$\mathrm{pI = \frac{pK_a1 + pK_a2}{2}}$

Chirality in Amino Acids

• All amino acids except glycine are chiral (have a stereocenter at the α-carbon).

Protein Structure Levels

• Primary: Sequence of amino acids.

• Secondary: Local folding (α-helix, β-sheet) stabilized by hydrogen bonds.

• Tertiary: 3D folding due to side chain interactions (hydrophobic, hydrophilic, hydrogen bonds, salt bridges, disulfide bonds).

• Quaternary: Association of multiple polypeptide chains.

Naming and Drawing Peptides

• Name from N-terminus to C-terminus.

• Draw peptide bonds between amino acids; identify amino acids in sequence.

Fibrous vs. Globular Proteins

• Fibrous: Structural, elongated (e.g., collagen).

• Globular: Spherical, functional (e.g., enzymes, hemoglobin).

Peptide Bond Formation and Hydrolysis

• Amidation: Formation of peptide bond (condensation reaction).

• Amide hydrolysis: Breaking peptide bond (requires acid/base or enzyme).

$\mathrm{Amino\ acid_1 + Amino\ acid_2 \rightarrow Dipeptide + H_2O}$

Protein Denaturation

• Loss of secondary, tertiary, or quaternary structure (not primary) due to heat, pH, or chemicals.

Enzymes: Structure and Function

• Enzymes are biological catalysts; they lower activation energy.

• Form enzyme-substrate complex; specificity determined by active site.

• Follow the induced fit model (enzyme changes shape to fit substrate).

• Enzyme activity affected by pH, temperature, and inhibitors.

Classes of Enzymes

• Oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases.

How Enzymes Catalyze Reactions

• Stabilize transition state, bring substrates together, provide acidic/basic groups, or strain substrate bonds.

Table: Classification of Amino Acids (Example)

Category	Examples
Nonpolar, neutral	Glycine, Alanine, Valine, Leucine, Isoleucine, Methionine, Proline, Phenylalanine, Tryptophan
Polar, neutral	Serine, Threonine, Cysteine, Tyrosine, Asparagine, Glutamine
Acidic	Aspartic acid, Glutamic acid
Basic	Lysine, Arginine, Histidine

Additional info: The above notes expand on the provided outline with definitions, examples, and key reactions to ensure a self-contained study guide for exam preparation.