Membrane-structure-and-function

Membrane Structure and Function

• Cell membranes enclose and protect cells, regulating substances entering and leaving.
• Membranes are semi-permeable, maintaining internal and external composition differences. Mechanisms like transporters, channels, and endocytosis/exocytosis control this.
• Membranes are primarily a lipid bilayer, constructed from phospholipids.
• Phospholipid heads are hydrophilic and face the aqueous environment, while the tails are hydrophobic and face inwards.
• Cholesterol is embedded within the bilayer and influences membrane fluidity.
• Membrane proteins are either integral (firmly embedded) or peripheral (loosely attached). These proteins facilitate transport, signaling, and other functions.

Membrane Fluidity

• Unsaturated hydrocarbon tails have kinks, which increases fluidity. Saturated tails are straight, which decreases fluidity.
• Cholesterol intercalates amongst phospholipids to regulate fluidity

Membrane Proteins

• Membrane proteins often act as channels or transporters for specific molecules
• Involved in signal transduction
• Crucial for bi-directional transport

Types of Transport

• Simple diffusion: molecules move from high to low concentration without protein assistance
• Facilitated diffusion: molecules move down their concentration gradient, often through protein channels
• Active transport: molecules move against their concentration gradient, requiring energy (ATP).

Types of Endocytosis

• Phagocytosis ("cell eating"): cell engulfs large particles or cells via pseudopods
• Pinocytosis ("cell drinking"): cell takes in small droplets of extracellular fluid
• Receptor-mediated endocytosis: specific receptors bind to target molecules, bringing them into the cell in vesicles

Membrane Disorders

• Mutations affecting membrane proteins can cause various diseases, impacting transport and other critical functions.
• Examples include achondroplasia, familial hypercholesterolemia, cystic fibrosis, long QT syndrome, Wilson disease, and I-cell disease. These are caused by various mutations of genes involved in cell membrane structures/function. Genetic defects can lead to various diseases.