Membrane-structure-and-function

Study Notes

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.

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

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).

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

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.