Comprehensive Study Guide: Carbohydrates, Lipids, Amino Acids & Proteins, Enzymes & Vitamins, Nucleic Acids, and Metabolism

Chapter 15: Carbohydrates

Definition and Classification of Carbohydrates

• Carbohydrates are organic molecules containing carbon, hydrogen, and oxygen, typically with the formula Cn(H2O)n.

• They are classified as aldehydes or ketones with multiple hydroxyl groups.

• Monosaccharides are the simplest carbohydrates and cannot be hydrolyzed into smaller units.

Classification of Monosaccharides

• Monosaccharides are classified based on the number of carbon atoms and the presence of an aldehyde (aldose) or ketone (ketose) group.

• Examples include triose (3C), tetrose (4C), pentose (5C), and hexose (6C).

• Common examples: D-Glucose (aldohexose), D-Fructose (ketohexose), D-Ribose (aldopentose).

Chirality and Stereochemistry

• A chiral carbon is a carbon atom bonded to four different groups.

• Enantiomers are stereoisomers that are non-superimposable mirror images; diastereomers are stereoisomers that are not mirror images.

• Fischer projections are used to represent monosaccharides; the -OH on the highest numbered chiral carbon determines D (right) or L (left) configuration.

Fischer and Haworth Projections

• Be able to draw and interpret Fischer projections of D-Glucose, D-Galactose, D-Fructose, and D-Ribose.

• Convert Fischer projections to Haworth (cyclic) structures, and identify the anomeric carbon (carbon 1 in aldoses, carbon 2 in ketoses).

• Recognize α-anomer (OH on anomeric carbon below the plane) and β-anomer (OH above the plane).

Redox Reactions and Reducing Sugars

• Reducing sugars can reduce mild oxidizing agents (e.g., Benedict's reagent turns brick red if reducing sugar is present).

• All monosaccharides are reducing sugars; some disaccharides (e.g., maltose, lactose) are reducing, while sucrose is not.

• Reduction of monosaccharides forms alditols (sugar alcohols).

Polysaccharides and Linkages

• Monosaccharides are linked by glycosidic bonds to form disaccharides and polysaccharides.

• Examples: Cellulose (β-1,4 linkages), Starch (amylose: α-1,4; amylopectin: α-1,4 and α-1,6), Glycogen (similar to amylopectin).

Chapter 16: Lipids

Definition and Types of Lipids

• Lipids are biomolecules that are insoluble in water but soluble in nonpolar solvents.

• They include fatty acids, triacylglycerols, phospholipids, sphingolipids, glycolipids, and steroids.

Fatty Acids and Triacylglycerols

• Fatty acids are long-chain carboxylic acids; can be saturated (no double bonds) or unsaturated (one or more double bonds).

• Melting point increases with chain length and decreases with unsaturation.

• Triacylglycerols (triglycerides) are esters of glycerol with three fatty acids; main energy storage form in animals.

Phospholipids and Sphingolipids

• Phospholipids contain a phosphate group and are major components of cell membranes.

• Sphingolipids contain a sphingosine backbone; important in nerve cell membranes.

Steroids and Lipoproteins

• Steroids have a characteristic four-ring structure; cholesterol is the most common steroid in animals.

• Lipoproteins transport lipids in the blood; LDL ("bad" cholesterol) and HDL ("good" cholesterol) differ in density and function.

Lipid Reactions

• Lipids can undergo hydrolysis (breakdown by water), hydrogenation (addition of H2), and saponification (formation of soap from fats and base).

Chapter 19: Amino Acids and Proteins

Structure and Properties of Amino Acids

• Amino acids are the building blocks of proteins; contain an amino group, carboxyl group, hydrogen, and unique side chain (R group) attached to the α-carbon.

• At physiological pH, amino acids exist as zwitterions (both positive and negative charges).

• The isoelectric point (pI) is the pH at which the amino acid has no net charge.

Peptide Bonds and Protein Structure

• Peptide bonds link amino acids via a condensation reaction (loss of water).

• Protein structure levels: primary (amino acid sequence), secondary (α-helix, β-sheet), tertiary (3D folding), quaternary (multiple polypeptide chains).

Protein Function and Denaturation

• Proteins serve structural, enzymatic, transport, storage, and regulatory roles.

• Denaturation disrupts secondary, tertiary, and quaternary structure (not primary); caused by heat, pH changes, chemicals, or agitation.

• Hydrolysis of proteins breaks peptide bonds, yielding amino acids.

Chapter 20: Enzymes and Vitamins

Enzyme Structure and Function

• Enzymes are biological catalysts that speed up chemical reactions by lowering activation energy without being consumed.

• Enzyme activity is affected by temperature, pH, substrate concentration, and inhibitors.

• Enzyme-catalyzed reactions follow three steps: substrate binds to enzyme (ES complex), conversion to product, and release of product.

Enzyme Classification and Regulation

• Enzymes are classified into six major types based on the reactions they catalyze (e.g., oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases).

• Regulation includes allosteric control, feedback inhibition, and covalent modification.

• Inhibitors can be competitive (bind active site) or noncompetitive (bind elsewhere).

Vitamins

• Vitamins are organic molecules required in small amounts for enzyme function; many act as coenzymes.

Chapter 21: Nucleic Acids

Structure and Function of Nucleic Acids

• Nucleic acids (DNA and RNA) store and transmit genetic information.

• DNA contains deoxyribose sugar; RNA contains ribose sugar.

• Nucleotides are composed of a phosphate group, a five-carbon sugar, and a nitrogenous base (A, T/U, G, C).

DNA Replication and RNA Transcription

• DNA replication is semi-conservative; each new DNA molecule contains one old and one new strand.

• Transcription is the synthesis of RNA from a DNA template; translation is the synthesis of protein from mRNA.

Genetic Code and Mutations

• The genetic code is a set of three-nucleotide codons that specify amino acids.

• Mutations are changes in DNA sequence; can be silent, missense, or nonsense.

Chapters 22-24: Metabolism

Overview of Metabolism

• Metabolism is the sum of all chemical reactions in a cell; divided into catabolism (breakdown, releases energy) and anabolism (synthesis, requires energy).

• Three stages: digestion, production of acetyl-CoA, and oxidation in the citric acid cycle and electron transport chain.

ATP and Energy Production

• ATP (adenosine triphosphate) is the main energy currency of the cell.

• Energy is released by hydrolysis of ATP:

$\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i + \text{energy}$

• Major metabolic pathways: glycolysis (glucose breakdown), citric acid cycle (oxidation of acetyl-CoA), oxidative phosphorylation (ATP synthesis).

• Electron carriers: NAD+, FAD, and CoA are essential for energy transfer.

Carbohydrate, Lipid, and Protein Metabolism

• Glycolysis: conversion of glucose to pyruvate, produces ATP and NADH.

• Citric acid cycle: oxidizes acetyl-CoA to CO2, produces NADH and FADH2.

• Electron transport chain: uses NADH and FADH2 to generate ATP.

• Fatty acid oxidation (β-oxidation) and amino acid catabolism also feed into the citric acid cycle.

Regulation and Integration of Metabolism

• Metabolic pathways are regulated by enzyme activity, energy needs, and hormonal signals (e.g., insulin, glucagon).

• Energy yield: carbohydrates and proteins provide ~4 kcal/g, fats provide ~9 kcal/g.