LEHNINGER PRINCIPLES OF BIOCHEMISTRY 8TH EDITION
2026 STUDY GUIDE | COMPLETE CHAPTER-BY-CHAPTER
LEARNING MANUAL || UPDATED VERSION
Chapter 1 — Biochemistry & the Unity of Life
1. Q: What is the basic chemical composition of all living organisms?
A: Carbon, hydrogen, oxygen, nitrogen — arranged into macromolecules like proteins,
nucleic acids, carbohydrates, and lipids.
2. Q: Why is carbon so central to biochemistry?
A: Because it can form four stable covalent bonds, allowing the formation of complex,
diverse biological molecules.
3. Q: What distinguishes a macromolecule from a small molecule in biochemistry?
A: Macromolecules are large polymers (like proteins, nucleic acids) built from repeating
monomer subunits; small molecules are the monomers or metabolites.
4. Q: What is a polymerization reaction in biological systems?
A: A reaction that links monomer units (e.g. amino acids, nucleotides) into a polymer
(e.g. proteins, DNA) via covalent bonds.
5. Q: What role do noncovalent interactions play in biological structures?
A: They stabilize three-dimensional structures of macromolecules and mediate
molecular recognition (e.g. enzyme–substrate, protein–DNA).
6. Q: What is the significance of molecular complementarity in biochemistry?
A: It enables specific interactions between molecules (e.g. enzyme–substrate binding,
receptor–ligand binding) based on shape and charge complementarity.
7. Q: What is a metabolic pathway?
A: A series of enzyme-catalyzed chemical reactions in a cell, where the product of one
reaction becomes the substrate for the next.
8. Q: What is homeostasis in the context of biochemistry?
A: The maintenance of stable internal environment (pH, temperature, concentrations)
that allows proper biochemical function.
Chapter 2 — Water, pH, and Buffers
, 9. Q: Why is water considered the “matrix of life”?
A: Because it serves as the solvent for biochemical reactions and influences molecular
structure and reactivity via hydrogen bonding.
10. Q: What gives water its high cohesion and surface tension?
A: Hydrogen bonds between water molecules.
11. Q: What is the approximate pH of the interior of most human cells?
A: Around 7.0–7.4.
12. Q: Define an acid and a base according to the Brønsted–Lowry definition.
A: An acid donates a proton (H⁺), a base accepts a proton.
13. Q: What is a buffer?
A: A solution that resists changes in pH when small amounts of acid or base are added,
usually consisting of a weak acid and its conjugate base (or vice versa).
14. Q: Why are buffers important in biological systems?
A: They help maintain stable pH in cells and bodily fluids, essential for enzyme activity
and structural integrity of biomolecules.
15. Q: What is the Henderson–Hasselbalch equation?
A: pH = pKa + log([A⁻]/[HA]) — relates pH, pKa, and the ratio of conjugate base ([A⁻]) to
acid ([HA]).
16. Q: If you have an acid with pKa = 6.5 and you want a buffer at pH 7.5, should you have
more A⁻ or HA?
A: More A⁻ (conjugate base), because the pH is higher than the pKa.
Chapter 3 — Amino Acids, Peptides & Proteins
17. Q: How many standard amino acids are used in proteins?
A: 20 standard amino acids.
18. Q: What are the two ends of an amino acid?
A: The amino (–NH₃⁺) end (N-terminus) and the carboxyl (–COO⁻) end (C-terminus).
19. Q: What type of bond links amino acids in a polypeptide chain?
A: A peptide bond (amide bond).
, 20. Q: What defines the primary structure of a protein?
A: The linear sequence of amino acids in the polypeptide chain.
21. Q: What are side-chain (R group) properties that influence protein folding?
A: Hydrophobic/hydrophilic nature, charge (acidic/basic), ability to form hydrogen
bonds, size and shape.
22. Q: Why are cysteine residues important in proteins?
A: Because their thiol (–SH) groups can form disulfide bonds, stabilizing protein
structure.
23. Q: What is the physiological pH ~7.4 significance for amino acids with ionizable side
chains?
A: Side chains may be charged (acidic or basic), affecting protein folding and
interactions.
24. Q: What does it mean for a protein to be “amphipathic”?
A: It has both hydrophobic and hydrophilic regions — part interacts with water, part
avoids water.
Chapter 4 — Protein Structure & Function
25. Q: What are the levels of protein structure?
A: Primary, secondary, tertiary, and quaternary structures.
26. Q: What are common types of secondary structure in proteins?
A: α-helix and β-sheet.
27. Q: What stabilizes α-helices and β-sheets?
A: Hydrogen bonds between backbone carbonyl oxygens and amide hydrogens.
28. Q: What is tertiary structure of a protein?
A: The three-dimensional folding of a single polypeptide chain, stabilized by side-chain
interactions (hydrophobic interactions, hydrogen bonds, ionic bonds, disulfide bonds).
29. Q: What is quaternary structure?
A: The assembly of two or more polypeptide chains (subunits) into a functional protein
complex.
, 30. Q: Why is the “hydrophobic effect” important for protein folding?
A: Hydrophobic side chains cluster inside the protein to avoid water, driving folding and
stability.
31. Q: What is a domain in a protein?
A: A distinct functional or structural unit within a protein, often capable of folding
independently.
32. Q: What is the role of post-translational modifications (PTMs) in proteins?
A: PTMs (e.g. phosphorylation, glycosylation) regulate protein activity, localization,
stability, or interactions.
Chapter 5 — Enzymes
33. Q: What is an enzyme?
A: A biological catalyst — a protein (or RNA) that accelerates a chemical reaction without
being consumed.
34. Q: How do enzymes accelerate reactions?
A: By lowering the activation energy, stabilizing the transition state, and orienting
substrates properly.
35. Q: What is the active site of an enzyme?
A: The region where substrate binds and catalysis occurs.
36. Q: What is the difference between competitive and non-competitive inhibition?
A: Competitive inhibitors bind the active site (compete with substrate), while
non-competitive inhibitors bind elsewhere and reduce enzyme activity regardless of
substrate concentration.
37. Q: What is Km in enzyme kinetics?
A: The Michaelis constant — the substrate concentration at which the reaction rate is
half of Vmax.
38. Q: What does a low Km value indicate about an enzyme’s affinity for its substrate?
A: High affinity (the enzyme achieves half-maximal activity at low substrate
concentration).
39. Q: What is Vmax?
A: The maximum reaction rate achieved by an enzyme when fully saturated with
substrate.
2026 STUDY GUIDE | COMPLETE CHAPTER-BY-CHAPTER
LEARNING MANUAL || UPDATED VERSION
Chapter 1 — Biochemistry & the Unity of Life
1. Q: What is the basic chemical composition of all living organisms?
A: Carbon, hydrogen, oxygen, nitrogen — arranged into macromolecules like proteins,
nucleic acids, carbohydrates, and lipids.
2. Q: Why is carbon so central to biochemistry?
A: Because it can form four stable covalent bonds, allowing the formation of complex,
diverse biological molecules.
3. Q: What distinguishes a macromolecule from a small molecule in biochemistry?
A: Macromolecules are large polymers (like proteins, nucleic acids) built from repeating
monomer subunits; small molecules are the monomers or metabolites.
4. Q: What is a polymerization reaction in biological systems?
A: A reaction that links monomer units (e.g. amino acids, nucleotides) into a polymer
(e.g. proteins, DNA) via covalent bonds.
5. Q: What role do noncovalent interactions play in biological structures?
A: They stabilize three-dimensional structures of macromolecules and mediate
molecular recognition (e.g. enzyme–substrate, protein–DNA).
6. Q: What is the significance of molecular complementarity in biochemistry?
A: It enables specific interactions between molecules (e.g. enzyme–substrate binding,
receptor–ligand binding) based on shape and charge complementarity.
7. Q: What is a metabolic pathway?
A: A series of enzyme-catalyzed chemical reactions in a cell, where the product of one
reaction becomes the substrate for the next.
8. Q: What is homeostasis in the context of biochemistry?
A: The maintenance of stable internal environment (pH, temperature, concentrations)
that allows proper biochemical function.
Chapter 2 — Water, pH, and Buffers
, 9. Q: Why is water considered the “matrix of life”?
A: Because it serves as the solvent for biochemical reactions and influences molecular
structure and reactivity via hydrogen bonding.
10. Q: What gives water its high cohesion and surface tension?
A: Hydrogen bonds between water molecules.
11. Q: What is the approximate pH of the interior of most human cells?
A: Around 7.0–7.4.
12. Q: Define an acid and a base according to the Brønsted–Lowry definition.
A: An acid donates a proton (H⁺), a base accepts a proton.
13. Q: What is a buffer?
A: A solution that resists changes in pH when small amounts of acid or base are added,
usually consisting of a weak acid and its conjugate base (or vice versa).
14. Q: Why are buffers important in biological systems?
A: They help maintain stable pH in cells and bodily fluids, essential for enzyme activity
and structural integrity of biomolecules.
15. Q: What is the Henderson–Hasselbalch equation?
A: pH = pKa + log([A⁻]/[HA]) — relates pH, pKa, and the ratio of conjugate base ([A⁻]) to
acid ([HA]).
16. Q: If you have an acid with pKa = 6.5 and you want a buffer at pH 7.5, should you have
more A⁻ or HA?
A: More A⁻ (conjugate base), because the pH is higher than the pKa.
Chapter 3 — Amino Acids, Peptides & Proteins
17. Q: How many standard amino acids are used in proteins?
A: 20 standard amino acids.
18. Q: What are the two ends of an amino acid?
A: The amino (–NH₃⁺) end (N-terminus) and the carboxyl (–COO⁻) end (C-terminus).
19. Q: What type of bond links amino acids in a polypeptide chain?
A: A peptide bond (amide bond).
, 20. Q: What defines the primary structure of a protein?
A: The linear sequence of amino acids in the polypeptide chain.
21. Q: What are side-chain (R group) properties that influence protein folding?
A: Hydrophobic/hydrophilic nature, charge (acidic/basic), ability to form hydrogen
bonds, size and shape.
22. Q: Why are cysteine residues important in proteins?
A: Because their thiol (–SH) groups can form disulfide bonds, stabilizing protein
structure.
23. Q: What is the physiological pH ~7.4 significance for amino acids with ionizable side
chains?
A: Side chains may be charged (acidic or basic), affecting protein folding and
interactions.
24. Q: What does it mean for a protein to be “amphipathic”?
A: It has both hydrophobic and hydrophilic regions — part interacts with water, part
avoids water.
Chapter 4 — Protein Structure & Function
25. Q: What are the levels of protein structure?
A: Primary, secondary, tertiary, and quaternary structures.
26. Q: What are common types of secondary structure in proteins?
A: α-helix and β-sheet.
27. Q: What stabilizes α-helices and β-sheets?
A: Hydrogen bonds between backbone carbonyl oxygens and amide hydrogens.
28. Q: What is tertiary structure of a protein?
A: The three-dimensional folding of a single polypeptide chain, stabilized by side-chain
interactions (hydrophobic interactions, hydrogen bonds, ionic bonds, disulfide bonds).
29. Q: What is quaternary structure?
A: The assembly of two or more polypeptide chains (subunits) into a functional protein
complex.
, 30. Q: Why is the “hydrophobic effect” important for protein folding?
A: Hydrophobic side chains cluster inside the protein to avoid water, driving folding and
stability.
31. Q: What is a domain in a protein?
A: A distinct functional or structural unit within a protein, often capable of folding
independently.
32. Q: What is the role of post-translational modifications (PTMs) in proteins?
A: PTMs (e.g. phosphorylation, glycosylation) regulate protein activity, localization,
stability, or interactions.
Chapter 5 — Enzymes
33. Q: What is an enzyme?
A: A biological catalyst — a protein (or RNA) that accelerates a chemical reaction without
being consumed.
34. Q: How do enzymes accelerate reactions?
A: By lowering the activation energy, stabilizing the transition state, and orienting
substrates properly.
35. Q: What is the active site of an enzyme?
A: The region where substrate binds and catalysis occurs.
36. Q: What is the difference between competitive and non-competitive inhibition?
A: Competitive inhibitors bind the active site (compete with substrate), while
non-competitive inhibitors bind elsewhere and reduce enzyme activity regardless of
substrate concentration.
37. Q: What is Km in enzyme kinetics?
A: The Michaelis constant — the substrate concentration at which the reaction rate is
half of Vmax.
38. Q: What does a low Km value indicate about an enzyme’s affinity for its substrate?
A: High affinity (the enzyme achieves half-maximal activity at low substrate
concentration).
39. Q: What is Vmax?
A: The maximum reaction rate achieved by an enzyme when fully saturated with
substrate.
