Biological and Biochemical Foundations of Living Systems: Content Category 1A

Structure and function of proteins and their constituent amino acids
Macromolecules formed from amino acids adopt well-defined, three-dimensional structures with chemical properties that are responsible for their participation in virtually every process occurring within and between cells. The three-dimensional structure of proteins is a direct consequence of the nature of the covalently-bonded sequence of amino acids, their chemical and physical properties, and the way in which the whole assembly interacts with water.

Enzymes are proteins that interact in highly regio- and stereo-specific ways with dissolved solutes. They either facilitate the chemical transformation of these solutes, or allow for their transport innocuously. Dissolved solutes compete for protein-binding sites, and protein conformational dynamics give rise to mechanisms capable of controlling enzymatic activity.
The infinite variability of potential amino acid sequences allows for adaptable responses to pathogenic organisms and materials. The rigidity of some amino acid sequences makes them suitable for structural roles in complex living systems.

Content in this category covers a range of protein behaviors which originate from the unique chemistry of amino acids themselves. Amino acid classifications and protein structural elements are covered. Special emphasis is placed on enzyme catalysis, including mechanistic considerations, kinetics, models of enzyme-substrate interaction, and regulation.

Topic Level Key

The abbreviations found in parentheses indicate the course(s) in which undergraduate students at many colleges and universities learn about the topics and associated subtopics. The course abbreviations are:

BC = first-semester biochemistry
BIO = two-semester sequence of introductory biology
OC = two-semester sequence of organic chemistry

Please note topics that appear on multiple content lists will be treated differently. Questions will focus on the topics as they are described in the narrative for the content category.

Amino Acids (BC, OC)
  • Description
    • Absolute configuration at the α position
    • Amino acids as dipolar ions
    • Classifications
      • Acidic or basic
      • Hydrophobic or hydrophilic
  • Reactions
    • Sulfur linkage for cysteine and cystine
    • Peptide linkage: polypeptides and proteins
    • Hydrolysis
Protein Structure (BIO, BC, OC)
  • Structure
    • 1° structure of proteins
    • 2° structure of proteins
    • 3° structure of proteins; role of proline, cystine, hydrophobic bonding
    • 4° structure of proteins (BIO, BC)
  • Conformational stability
    • Denaturing and folding
    • Hydrophobic interactions
    • Solvation layer (entropy) (BC)
  • Separation techniques
    • Isoelectric point
    • Electrophoresis
Non-Enzymatic Protein Function (BIO, BC)
  • Binding (BC)
  • Immune system
  • Motors
Enzyme Structure and Function (BIO, BC)
  • Function of enzymes in catalyzing biological reactions
  • Enzyme classification by reaction type
  • Reduction of activation energy
  • Substrates and enzyme specificity
  • Active Site Model
  • Induced-fit Model
  • Mechanism of catalysis
    • Cofactors
    • Coenzymes
    • Water-soluble vitamins
  • Effects of local conditions on enzyme activity
Control of Enzyme Activity (BIO, BC)
  • Kinetics
    • General (catalysis)
    • Michaelis–Menten
    • Cooperativity
  • Feedback regulation
  • Inhibition – types
    • Competitive
    • Non-competitive
    • Mixed (BC)
    • Uncompetitive (BC)
  • Regulatory enzymes
    • Allosteric enzymes
    • Covalently-modified enzymes
    • Zymogen

To support your studies, see the following video tutorials below from the Khan Academy MCAT Collection. The videos and associated questions were created by the Khan Academy in collaboration with the AAMC and the Robert Wood Johnson Foundation.