MCAT Chemistry and Biochemistry Guide
Essential chemistry concepts for the MCAT Chemical and Physical Foundations section. Covers general chemistry, organic chemistry, and biochemistry with a focus on biological applications.
Learning Objectives
- ✓Master high-yield chemistry topics for MCAT
- ✓Understand chemistry in biological contexts
- ✓Develop passage-based problem-solving skills
- ✓Connect general, organic, and biochemistry concepts
1. Atomic and Molecular Structure
The MCAT emphasizes understanding over memorization. Know electron configurations, periodic trends, and how atomic structure explains chemical behavior. Focus on how electronic structure determines reactivity and properties of biologically relevant molecules.
Key Points
- •Electronegativity differences determine bond type and polarity
- •Transition metals often have multiple oxidation states
- •Noble gas configurations are especially stable
- •Effective nuclear charge explains many periodic trends
2. Bonding and Intermolecular Forces
Critical for understanding protein structure and membrane dynamics. Hydrogen bonds are essential in DNA base pairing, protein secondary structure, and water properties. Hydrophobic interactions drive protein folding and membrane formation.
Key Points
- •Hydrogen bonds are strong dipole-dipole interactions (N-H, O-H, F-H)
- •Hydrophobic effect: non-polar groups cluster to minimize contact with water
- •Ion-dipole forces explain solvation of ionic compounds
- •Van der Waals forces stabilize non-polar regions of proteins
3. Thermodynamics and Kinetics
Know the difference between thermodynamics (will it happen?) and kinetics (how fast?). Many biological processes are kinetically controlled. Enzymes accelerate reactions by lowering activation energy without changing delta G.
Key Points
- •Enzymes are biological catalysts that lower Ea
- •delta G determines spontaneity, not rate
- •Coupling unfavorable reactions with ATP hydrolysis
- •Le Chatelier's principle applies to metabolic pathways
4. Acids, Bases, and Buffers
Blood pH is maintained at 7.4 by the bicarbonate buffer system. Amino acids have multiple pKa values due to multiple ionizable groups. Understanding titration curves helps predict charge states at different pH values.
Key Points
- •Blood buffer: CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-
- •Amino acid charge depends on pH vs pKa of each group
- •At pI (isoelectric point), net charge is zero
- •Henderson-Hasselbalch applies to all buffer systems
5. Electrochemistry
Relevant for understanding electron transport chain and redox reactions in metabolism. Reduction potentials indicate electron flow direction. NAD+/NADH and FAD/FADH2 are key electron carriers in cellular respiration.
Key Points
- •Electrons flow from lower to higher reduction potential
- •NAD+ is reduced to NADH (gains electrons)
- •Proton gradient drives ATP synthesis
- •Standard reduction potentials are additive
6. Organic Chemistry Fundamentals
Focus on functional groups and reaction mechanisms relevant to biochemistry. SN1/SN2 mechanisms explain enzyme active site chemistry. Understand carbonyl chemistry for amino acid and carbohydrate reactions.
Key Points
- •Carboxylic acids, amines, and alcohols are the key functional groups
- •Nucleophilic addition to carbonyls forms hemiacetals/hemiketals
- •Amide bonds link amino acids (peptide bonds)
- •Ester hydrolysis is key in lipid metabolism
7. Amino Acids and Proteins
Know all 20 amino acids, their properties, and their one-letter codes. Understand protein structure levels and how non-covalent interactions stabilize each level. Enzyme kinetics and inhibition are heavily tested.
Key Points
- •Primary: sequence, Secondary: alpha helix/beta sheet, Tertiary: 3D fold, Quaternary: multiple subunits
- •Disulfide bonds form between cysteine residues
- •Michaelis-Menten: V = Vmax[S]/(Km + [S])
- •Competitive inhibitors increase apparent Km, non-competitive decrease Vmax
8. Carbohydrates and Lipids
Understand monosaccharide structure, glycosidic bonds, and carbohydrate metabolism. Know lipid types (triglycerides, phospholipids, steroids) and their roles in energy storage and membrane structure.
Key Points
- •Glucose exists in alpha and beta anomeric forms
- •Glycosidic bonds link sugars in di- and polysaccharides
- •Fatty acids: saturated = no double bonds, unsaturated = double bonds
- •Phospholipids are amphipathic - form bilayers
High-Yield Facts
- ★The Chemical and Physical Foundations section is 59 questions in 95 minutes
- ★Approximately 25% is biochemistry, 30% general chemistry, 25% organic chemistry, 20% physics
- ★Most questions are passage-based - practice reading scientific passages quickly
- ★The MCAT rewards understanding mechanisms over memorizing facts
- ★Know how to estimate calculations without a calculator
Practice Questions
1. At pH 2, what is the predominant form of glycine (pKa1 = 2.3, pKa2 = 9.6)?
2. How does a competitive inhibitor affect a Lineweaver-Burk plot?
3. Why do unsaturated fatty acids have lower melting points than saturated fatty acids?
FAQs
Common questions about this topic
Most students spend 3-6 months preparing, with 300-500 hours total. Chemistry and biochemistry should comprise about 30-40% of your study time if those are weaker areas.
Strongly recommended. Biochemistry is heavily tested and understanding it makes both the chemistry and biology sections easier. Many concepts overlap between sections.