obsidianvault/biology/Cell Structure and Function/Plasma Membrane.md

Cell Structure and Function

Summary

• Phospholipids are amphipathic (both hydrophobic and hydrophilic): hydrophilic phosphate heads point towards water hydrophobic fatty acid tails point away.
• Embedded proteins have hydrophilic regions facing the cytosol or extracellular fluid. Also have hydrophobic regions that contact the fatty acid tails in membrane interior.
• Cholesterol (in vertebrate animals) acts as a fluidity buffer, preventing the membrane from getting too loose or stiff in head or cold.
• Fluid mosaic model describes a membrane with phospholipids, proteins, cholesterol, glyco(proteins/lipids) can move around the surface.
• Fatty acid affects fluidity, unsaturated with kinks increases it, while saturated makes the phospholipids pack tightly together.
• Glycoprotein and glycolipid sit on the outside and help with cell recognition.

Plasma membrane defines the edge of every cell, it's not a wall and is flexible.

Components of the Plasma Membrane

Phospholipids are main structural framework as a bilayer. Hydrophobic fatty acid tails point away from aqueous environment, hydrophilic phosphate heads point towards.

Steroids (cholesterol in vertebrates) restrain phospholipid movement at high temps and prevents them from packing tightly at low temps.

Gylco(proteins/lipids) are carbohydrates, attached to proteins and lipids, helps cells recognize each other.

Fluid Mosaic Model

Describes the plasma membrane as structural framework of phospholipids embedded with proteins, steroids(cholesterol) and glyco(steroids/lipids). Describes them as being able to move freely.

Fluid nature, phospholipids can move laterally like they're in a sea of lipids. Allows components to shift and form regions for different jobs.

Variety of molecules creates a mosaic appearance, thus the name.

Factors Affecting Membrane Fluidity

• Temp
• Fatty acid composition (look below)
• Cholesterol content (look above)

How Structure Connects to Function

Hydrophobic interior blocks polar molecules while allowing small non-polar molecules pass more freely. Basis for selective permeability.

Embedded proteins allow for specific interactions. Receptor proteins bind to signaling molecules, transport proteins move them.