Unit 1: Biochemistry - Comprehensive Study Notes

1.3 Introduction to Macromolecules

  • Dehydration Synthesis (Condensation): join monomers by covalent bonds; removal of H from one monomer and OH from another; results in loss of a water molecule; forms a covalent bond and polymerizes monomers

  • Polymerization is the joining of many monomers into polymers

  • Hydrolysis: cleave covalent bonds by adding water; water splits a polymer into monomers

  • In biological reactions, enzymes catalyze specific hydrolysis or dehydration steps

1.3 Macromolecule Formation & Hydrolysis (Figure-based prompts)

  • Example: formation of a peptide bond between amino acids via dehydration synthesis

  • In peptide bond formation, a water molecule is released (H from one amino acid and OH from another)

  • The resulting bond is a covalent peptide bond

1.3 Biomolecules Overview

  • Monomers and Polymers by category:

    • Carbohydrates: Monosaccharides

P

** Monosaccharides

  • Lipids: Fatty acids + glycerol

  • Proteins: Amino acids

  • Nucleic Acids: Nucleotides

  • All biomolecules have functional roles (energy, storage, structure, catalysis, information storage, etc.)

1.4 Carbohydrates

  • Functions: energy source; structural support

  • Monomer: Monosaccharide; Polymer: Polysaccharide

  • Bonds: Glycosidic bonds; CH2O ratio 1:2:1

  • Important examples: glycogen, starch (energy storage); cellulose (structure in plants); chitin (fungi/exoskeletons); peptidoglycan (bacteria)

  • Monosaccharide isomers: glucose, galactose, fructose share formula C6H12O6 but differ structurally

  • Disaccharides: two monosaccharides joined by glycosidic bond via dehydration synthesis

  • Oligosaccharides: 3–10 monosaccharides; found in glycoproteins/glycolipids; important for cell recognition; often not digested by stomach acid; fermented in the gut to short-chain fatty acids

  • Polysaccharides: starch, glycogen, cellulose; starch/glycogen are energy storage; cellulose is structural; other polysaccharides include chitin and peptidoglycan

  • Digestive differences: humans digest starch with amylase; cellulose requires cellulase (not produced by humans)

  • Key AP-style Qs emphasize that structure and branching affect properties and digestibility

1.4 Carbohydrates – Monosaccharides & Disaccharides

  • Glucose formula: C6H12O6; glucose, fructose, galactose are isomers

  • Disaccharides formed by dehydration synthesis (glycosidic bonds)

  • Oligosaccharides: 3–10 units; often linked to proteins/lipids (glycoproteins/glycolipids) for cell recognition

  • Cellulose vs. starch: different glycosidic linkages (α−1,4\alpha -1,4 in starch; β−1,4\beta -1,4 in cellulose) explain digestibility differences

1.4 Cellulose & Starch

  • Humans can digest starch (amylose; α−1,4\alpha -1,4 linkages) but not cellulose (β−1,4\beta -1,4 linkages) due to enzyme specificity (amylase vs cellulase)

  • Cellulose passes as dietary fiber; important for colon health

  • RCQ prompts discuss how polymer structure influences digestibility

1.4 Carbohydrates – Polysaccharides

  • Polysaccharides serve as energy storage (starch in plants; glycogen in animals) and structural support (cellulose in plants; chitin in some fungi and in exoskeletons)

  • Other structural polysaccharide: peptidoglycan in bacterial cell walls

  • Important note: substantial variety in structure but general purpose across categories

1.4 Quick AP-style Questions on Carbohydrates

  • Statements about structure: monosaccharides vs. polysaccharides; linkage types; hydrogen bonding; and disaccharide structure

1.4 Carbohydrates: Glucose & Isomers

  • Glucose, fructose, galactose all C6H12O6 but with different structural formulas

  • Isomerism →\rightarrow different properties despite same formula

1.5 Lipids

  • Lipids are composed mainly of fatty acids (long hydrocarbon chains) with elements C, H, O

  • Generally nonpolar and hydrophobic

  • Bond formation: ester bond forms when a fatty acid bonds with glycerol or another alcohol, releasing H2O

  • Major classes: fats/oils (triglycerides), phospholipids, steroids, waxes, vitamins (lipophilic examples: A, D, E, K)

1.5 Lipid Structure – Fatty Acids

  • Fatty acids: long hydrocarbon chain ending in –COOH (carboxyl group)

  • Hydrocarbon tails are nonpolar; carboxyl group is polar/acidic

1.5 Saturated vs. Unsaturated Lipids

  • Saturated fatty acids: only single bonds between carbons; typically solid at room temperature

  • Unsaturated fatty acids: include one or more double bonds causing kinks; typically liquid at room temperature

  • More double bonds →\rightarrow more unsaturated →\rightarrow more liquid at room temperature

1.5 Lipids – AP-style Question (Solid at room temperature)

  • Linoleic acid (with double bonds) vs. Palmitic acid (saturated, no double bonds)

  • Correct reasoning: absence of double bonds in palmitic allows closer packing and solid at room temperature; double bonds in linoleic introduce kinks preventing tight packing

1.5 Lipids – Functions

  • Fats: energy storage and insulation

  • Steroids (e.g., cholesterol): hormones; modulate membrane fluidity

  • Phospholipids: form lipid bilayers; amphipathic (polar heads, nonpolar tails)

  • Waxes: protective barriers; dehydration prevention

1.5 Lipids – Phospholipids (Structure & Membranes)

  • Glycerol + two fatty acids + phosphate group

  • Amphipathic: polar head (glycerol + phosphate) and nonpolar tails

  • Phospholipid bilayer forms cell membranes; outer and internal membranes of organelles

  • The phosphate group provides a negative charge, contributing to membrane properties

1.5 Lipids – Membrane Stability & Saturation in Thermophiles (AP-style)

  • Predictions: more saturated fatty acids increase membrane stability at high temperatures due to tighter packing; less fluidity is beneficial for stability in heat

1.5 Lipids – Steroids & Vitamins

  • Steroids: four fused carbon rings; regulate growth, development, metabolism, homeostasis

  • Cholesterol: modulates membrane fluidity; provides structural stability

  • Vitamins: lipid-soluble vitamins (A, D, E, K) functioning as coenzyme precursors; fat-soluble

  • Water-soluble vitamins (B and C) differ in solubility and storage

1.5 Lipids – Waxes & Soaps

  • Waxes formed by dehydration synthesis between fatty acids and alcohols

  • Soap: amphipathic molecules with hydrophobic tails and hydrophilic heads; they emulsify oils/dirt; disrupt lipid membranes of microbes