Biology Book 2: Chapter 2: Cell Membranes

Integral Proteins

• Integral proteins are amphipathic, possessing both hydrophobic and hydrophilic regions.
• Hydrophobic portions interact with the lipid bilayer's core.
• Can be classified as single-pass or multi-pass transmembrane proteins based on the number of times they traverse the bilayer.
• Single-pass transmembrane proteins cross the membrane once, while multi-pass proteins cross multiple times.

Peripheral Proteins

• Peripheral proteins do not penetrate the lipid bilayer.
• They associate indirectly with the membrane through non-covalent interactions with other proteins or directly with the hydrophilic heads of lipids.

Lipid-Linked Membrane Proteins

• Lipid-linked proteins are anchored to the membrane by lipid attachments at either the cytosolic or extracellular surfaces.

Fluid Mosaic Model

• Represents the cell membrane as a fluid lipid bilayer embedded with proteins.
• Highlights the mobility of lipids and proteins within the membrane.

Function of the Cell Membrane

• Regulates the transport of solutes in and out of the cell, maintaining homeostasis.

Polar vs Non-Polar

• Polar molecules are hydrophilic (water-loving), while non-polar molecules are hydrophobic (water-hating).

Learning Outcomes

• Describing membrane structure and properties (fluid-mosaic model, lipid rafts).
• Explaining the chemical environment's impact on membrane protein structure.
• Understanding factors influencing water movement across membranes.
• Interpreting how ion gradients create membrane potential.
• Differentiating between passive diffusion, facilitated transport, and active transport.
• Outlining the secretory pathway and endocytosis for substance transport.

Structure-Function Relationship

• The physical and chemical properties of membranes are key to their biological functions, necessitating an exploration of their molecular components.

Types of Membrane Lipids

• Phospholipids: Include phosphatidylcholine (PC), phosphatidylserine (PS), phosphatidylethanolamine (PE), and phosphatidylinositol (PI); characterized by a hydrophilic head and hydrophobic tails.
• Glycolipids: Feature sugar residues as hydrophilic heads; can be glycerol-based or sphingosine-based.
• Cholesterol: An amphipathic sterol with a unique four-ring structure; influences membrane fluidity.

Types of Membrane Proteins

• Integral Proteins: Span the lipid bilayer, include transmembrane proteins (single-pass and multi-pass types).
• Peripheral Proteins: Interact with the membrane without spanning it; often exposed to the cytoplasmic or extracellular space.