Concept 7.1: Cellular membranes are fluid mosaics of lipids and proteins

Flashcards from Concept 7.1 of Pearson's Campbell Biology, Twelfth Edition.

Passive transport

The transport of small molecules from areas of high to low concentration that does not require energy

• May require transport proteins in a cell membrane

Active transport

The transport of small molecules from areas of low to high concentration that does require energy and a transport protein

Bulk transport

The transport of large molecules as a form of active transport that utilizes exo- or endocytosis

Membrane

Cellular substance comprised of phospholipids and proteins with some carbohydrates

• Hydrophobilc phospholipid tails remain on the inside of the bilayer

• Hydrophilic heads remain on the outside of the bilayer toward the cytosol and extracellular fluid

Amphiphile

A molecule that contains hydrophobic and hydrophilic regions, such as phospholipids

Fluid mosaic model

A model of the membrane as a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids

• Proteins typically form groups that carry out common functions

• Most lipids and some proteins can move sideways within the membrane

Membrane solidification

Occurs as temperatures cool around a membrane depending on the types of lipids present

• More unsaturated fatty acids have higher fluidity than saturated fatty acids

• Lowers membrane function through higher packing of molecules — but too fluid membranes do not support protein function

• Addressed by some animal behaviors such as hibernation or migration

Cholesterol

Membrane component in animal cells that can affect membrane fluidity

• Warmer temperatures lead to restriained movement

• Cooler temperatures prevent tight packing

Lipid composition

Depends on the environmental conditions of an organism

• Extremely cold environments are more conducive to higher unsaturated fats in the membrane

• Seasonal changes can occur such as in winter wheat’s increased levels to prevent solidification

Membrane proteins

Proteins held in place via the cytoskeleton or materials outside the cell that function in:

• Transport

• Enzymatic activity

• Signal transduction

• Cell-cell recognition

• Intercellular joining

• Attachment to the cytoskeleton and extracellular matrix

HIV

A disease that enters immune cells by binding to a cell-surface protein and co-receptor

• Individuals without the receptor are immune, so drugs are in development to mask the receptor and block entrance in nonimmune individuals

Cell identification

Performed through the binding of molecules on the surface of the membrane; these molecules include glycolipids and glycoproteins for identification markers