Membrane Proteins and Membrane Structure

Review of Biological Membranes

• Main Components: Lipids and Proteins
• Lipid Structure:
  • Membranes are bilayers
  • Lipids are amphipathic with hydrophilic and hydrophobic components
  • Hydrophobic part: Fatty acid chains (two chains per lipid molecule)
  • Triacylglycerols: Storage lipids with three fatty acid chains

Lipid Variants

• Glycolipids: Lipids with sugar bindings
• Phospholipids: Have a phosphate group, sometimes with additional polar groups (e.g., choline)

Protein Components in Membranes

• Types of Proteins:
  • Integral Proteins: Embedded within the lipid bilayer, can be in one or both layers
  • Peripheral Proteins: Form temporary bonds with membranes, not embedded

Protein Structure

Importance of Proteins

• Proteins perform essential cellular functions
• Seven functions include:
  • Enzymes, Structural Support, Transport, Motor functions, Storage, Receptors, Transcriptional Regulation

Basic Structure of Proteins

• Made of amino acids
• Amino acids have a carboxyl group, amino group, and a central carbon
• Exist in ionized form in cells, allowing for peptide bond formation

Amino Acids

• Optical Isomers: L and D forms; cells use L amino acids
• Types:
  • Charged (positive/negative)
  • Uncharged but polar
  • Nonpolar (hydrophobic)

Protein Folding

• Non-covalent Bonds: Electrostatic attractions, Van der Waals interactions, Hydrogen bonds
• Common folding patterns: Alpha helices and Beta sheets
  • Alpha Helices: Formed by NH and CO bonds, create cylindrical structures
  • Beta Sheets: Parallel or antiparallel arrangements creating stable sheets

Influences on Folding

• Hydrophobic forces and hydrogen bonds dictate folding
• Chaperone proteins assist in proper folding

Levels of Protein Structure

• Primary: Amino acid sequence
• Secondary: Alpha helices and beta sheets
• Tertiary: 3D conformation
• Quaternary: Association with other polypeptides or proteins

Misfolding and Disease

• Misfolded proteins can lead to diseases like Alzheimer's
• Proper folding is crucial for function

Protein Function and Interaction

Functional Domains

• Proteins have structured and unstructured regions
• Functional domains perform specific tasks

Protein Complexes

• Proteins can function alone or in complexes (e.g., hemoglobin)
• Symmetrical Proteins: Identical subunits (e.g., dimers, tetramers)
• Asymmetrical Bindings: Different isoforms or proteins

Structural Variants

• Fibrous Proteins: Structural proteins like collagen, providing strength and elasticity
• Globular Proteins: Enzymes or functional proteins

Protein Models and Analysis

• Models: Backbone, Ribbon, Wire, Space Filling
• Structural determination techniques: NMR, X-ray crystallography, Cryo-electron microscopy

Additional Notes

• Proteins are dynamic and change conformation based on cellular environment
• Lab information and schedule: Online resources and activities available