Week 2A Cell Membranes

What is the basic structure of all cellular membranes?

They consist of a double layer of lipid molecules containing embedded proteins.

What are the major lipid molecules found in cell membranes?

The major membrane lipids are phospholipids.

How are the nonpolar fatty acid chains of phospholipids organized in a plasma membrane?

They are located in the middle of the bilayer, away from the aqueous environment.

Why are the polar regions of phospholipids oriented toward the membrane surfaces?

This is due to their attraction to the polar water molecules in the extracellular fluid and cytosol.

The head of a phospholipid has a charged, _____ region.

hydrophilic

The two long fatty acid tails of a phospholipid have a _____ region.

hydrophobic

A molecule that contains both hydrophobic and hydrophilic regions, like a phospholipid, is described as _____?

amphipathic

What are the two major classes of membrane proteins?

Integral membrane proteins and peripheral membrane proteins.

Which class of membrane proteins cannot be extracted without disrupting the lipid bilayer?

Integral membrane proteins.

Integral membrane proteins are described as _____ because they have both hydrophilic and hydrophobic regions.

amphipathic

Most integral proteins that span the entire membrane are referred to as what?

Transmembrane proteins.

Which class of membrane proteins is not amphipathic?

Peripheral membrane proteins.

Where are peripheral membrane proteins located?

They are located at the membrane surface, bound to the polar regions of the integral membrane proteins

What do peripheral membrane proteins typically bind to?

They bind to the polar regions of integral membrane proteins.

What is the function of cholesterol within the cell membrane?

It contributes to the fluidity and stability of the membrane.

What is the primary function of glycoproteins and glycolipids in the cell membrane?

They act as self-recognition molecules.

What does the Fluid-Mosaic Model of the plasma membrane describe?

It describes the membrane as a mix of proteins that move freely amongst the lipid bilayer.

What is a 'lipid raft' in the context of the cell membrane?

It is a membrane area with decreased fluidity that is anchored to cytoplasmic proteins.

A type of membrane junction characterized by dense plaques and cadherins that holds cells firmly together.

desmosome

In desmosomes, what are the anchoring points for cadherin proteins called?

Dense plaques.

What specific proteins interact to hold cells together in a desmosome?

Cadherins.

In a desmosome, the plasma membranes of adjacent cells are separated by about _____ nanometers.

20

A membrane junction where extracellular surfaces of adjacent plasma membranes join, leaving no space and forming a barrier to material movement.

What is a tight junction?

What is the main function of tight junctions?

They form barriers that limit the movement of material between cells.

How much extracellular space remains between cells at a tight junction?

No extracellular space remains between them.

The _____ pathway across an epithelium is blocked by tight junctions.

extracellular

A membrane junction composed of protein channels that directly link the cytosols of adjacent cells.

What is a gap junction?

The proteins that form the channels in gap junctions are known as _____?

connexins

What do the channels of gap junctions link together?

They link the cytosols of adjacent cells to small molecules and ions

The small diameter of gap junction channels (about 1.5 nm) limits passage to what types of substances? (they let these ones in but not large proteins)

Small molecules and ions, such as Na+ and K+

functions of plasma membranes (4)

L - linking adjacent cells using membrane junctions

A - anchoring cells to ECM

D - detecting chemical messengers arriving at the surface

S - signalling transduction and communication