Chapter 7 Membrane Structure and Function

What are the three determinants of membrane fluidity?

1. Temperature, 2. Cholesterol, and 3. Unsaturated/Saturated

phospholipid bilayer

A double layer of phospholipids that makes up plasma and organelle membranes, composed of hydrophilic heads and a hydrophobic tail.

selective permeability

A property of a plasma membrane that allows some substances to cross more easily than others.

Cholesterol within the animal cell membrane

Cholesterol reduces membrane fluidity at moderate temperatures by reducing phospholipid movement, but at low temperatures it hinders solidification by disrupting the regular packing of phospholipids.

Experiment: Larry Frye and Micheal Edidin, at Johns Hopkins University, labeled the plasma membrane proteins of a mouse cell and a human cell with two different markers and fused the cells. Using a microscope, they observed the markers of the hybrid cell. What was the conclusion?

Conclusion: The mixing of the mouse and the human membrane proteins indicates that at least some membrane proteins move sideways within the plane of the plasma membrane.

Why is cholesterol called a "fluidity buffer"?

It is called a "fluidity buffer" because it resists changes in membrane fluidity that can be caused by changes in temperature.

How does the saturation of hydrocarbon tails affect the fluidity of a membrane?

Low Temperature: hydrocarbon tails stack together neatly (less fluidity) and High Temperature: hydrocarbon tails do NOT stack together neatly more space (higher fluidity)

How does cholesterol affect membrane fluidity?

Low Temperature: increases the distance between the phospholipids by inserting itself (high fluidity) and High Temperature: more cholesterol pulls the phospholipids together (less fluidity)

How does temperature affect cell membrane fluidity?

Low Temperature: phospholipids huddle together (less fluidity) High Temperature: phospholipids have more distance in between each other (high fluidity)

peripheral proteins

The proteins of a membrane that are not embedded in the lipid bilayer; they are appendages loosely bound to the surface of the membrane.

What is the evolution of differences in membrane lipid composition? Why?

There has been evolution of differences in membrane lipid composition to maintain the appropriate membrane fluidity under specific environmental conditions.

Fishes that live in extreme cold have membranes with a high proportion of (unsaturated/saturated) hydrocarbon tails, enabling their membranes to remain fluid.

Unsaturated - because unsaturated tails do NOT stack together neatly causing higher amounts of fluidity needed to maintain the appropriate membrane fluidity under extreme cold

A phospholipid is an _______________ molecule meaning it has both hydrophillic ("water-loving") region and a hydrophobic ("water-fearing") region.

ampithatic

ampithatic molecule

meaning it has both hydrophillic ("water-loving") region and a hydrophobic ("water-fearing") region

fluid mosaic model

model that describes the arrangement and movement of the molecules that make up a cell membrane

Glycoproteins

most are covalently bonded to proteins

integral proteins

penetrate the hydrophobic interior of the lipid bilayer and located inside the cell membrane

Glycolipids

some are covalently bonded to lipids forming molecules

What are some functions of membrane proteins?

transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, attachment to the cytoskeleton and extracellular matrix