MCAT Biochem: Non-Enzymatic Protein Functions and Protein Analysis

Non-Enzymatic Protein Functions

Examples: Collagen, elastin, keratin, actin, tubulin.
Collagen: Trihelical fiber, strength & flexibility, found in connective tissues.
Elastin: Stretch and recoil, restores tissue shape.
Keratins: Intermediate filaments in epithelial cells, mechanical integrity, regulatory proteins; main component of hair and nails.
Actin: Makes up microfilaments and thin filaments in myofibrils, abundant in eukaryotic cells, has polarity for unidirectional motor protein movement.
Tubulin: Makes up microtubules, important for structure, chromosome separation in mitosis/meiosis, intracellular transport; has polarity with negative end near nucleus.

Functions: Muscle contraction, cellular movement, enzymatic activity (acting as ATPases).
Myosin: Interacts with actin, responsible for the power stroke in sarcomere contraction, involved in cellular transport.
Kinesins: Associated with microtubules, align chromosomes during metaphase, depolymerize microtubules during anaphase, transport vesicles towards positive end.
Dyneins: Associated with microtubules, involved in sliding movement of cilia and flagella, transport vesicles towards negative end.

Functions: Transport or sequester molecules, binding for stability.
Examples: Hemoglobin (oxygen transport), calcium-binding proteins, DNA-binding proteins.
Affinity curves vary based on environmental conditions.

Types: Cadherins, integrins, selectins.
Cadherins: Calcium-dependent adhesion, hold similar cell types together.
Integrins: Membrane-spanning (alpha and beta chains), bind to extracellular matrix, involved in cell signaling and functions like cell division and apoptosis.
Selectins: Bind to carbohydrate molecules, weak interactions, expressed on white blood cells and endothelial cells, role in inflammation and white blood cell migration.
Medical Applications: Targeting CAMs can prevent metastasis in cancer, stop clotting during heart attacks.

Functions: Neutralize targets (toxins, bacteria) and recruit other immune cells.
Structure: Y-shaped, with two heavy and two light chains, held together by disulfide links and non-covalent interactions. Has antigen-binding regions and constant region for Recruitment.
Outcomes of antibody binding: Neutralization, opsonization (marking for destruction), agglutination (forming large protein complexes for digestion).

Process: Cells receive and act on signals, involving proteins like ligands, transporters, receptors, and second messengers.
Types:
- Ion Channels: Ungated, voltage-gated, ligand-gated pathways for ions.
- Enzyme-Linked Receptors: Membrane-spanning, ligand-binding, catalytic domains. Initiate second messenger cascades (e.g., receptor tyrosine kinases).
- G Protein-Coupled Receptors (GPCRs): Involved in signal transduction, have seven membrane-spanning alpha helices, use G proteins (Gs, Gi, Gq) to transmit signals.

Electrophoresis: Separation by charge and size under an electric field.
- Native PAGE: Analyzes proteins in their native states.
- SDS-PAGE: Separates proteins based on mass using detergent SDS.
- Isoelectric Focusing: Separates proteins based on isoelectric point (pI).
Chromatography: Separation based on physical and chemical properties.
- Column Chromatography: Uses silica/alumina beads; separates by size and polarity.
- Ion Exchange Chromatography: Beads with charged substances attract/bind oppositely charged compounds.
- Size Exclusion Chromatography: Beads with tiny pores separate proteins by size; larger molecules elute first.

X-ray Crystallography: Measures electron density, used to determine protein structures (most common method).
Nuclear Magnetic Resonance (NMR) Spectroscopy: Also used to determine protein structures.