QP 2.4 Biological Membranes

What do membranes surround?

The cell and most organelles

What are membranes made up of

Lipid bilayer among other components

Why is a carbohydrate coat important

It is important for recognition

Phospholipid structure

Glycerol backbone (polar (electric))

Polar head group

Long nonpolar tail (fatty acid → long hydrocarbon chain and a carboxylic acid (-COOH))

Amphipathic (polar and nonpolar ends)

Unsaturated vs saturated fatty acid

Unsaturated fatty acids have at least one double bond between carbons while saturated fatty acids have no double bonds

Unsaturated fatty acid effect on plasma membrane

Unsaturated fatty acids make the plasma membrane more fluid because they require more space (their bent shape) and therefore the phospholipids can’t be as tightly packed together

Why does water have surface tension?

Because water molecules on the surface are partially evaporated and have more energy

True or false: phospholipids lower surface tension

True

The polar head of a phospholipid lowers the energy of the water molecules on the surface

5 ways lipid bilayers are dynamic

Rotation of individual molecules

Lateral diffusion (get new neighbors)

Stretch

flip flop to other side (not energetically favorable)

Lipids only added to the intracellular side (enzymes help with flipping them)

Fluid mosaic model

Lipids and proteins are not found in the same ratio on either side of the membrane, the membrane is asymmetrical

Cholesterol effect on membrane

It makes the membrane stiffer because it shoves itself in-between phospholipids and makes the space more packed.

Peripheral proteins

Attached to only 1 surface of the membrane

Integral proteins

They are on both surfaces of the membrane and span across the bilayer

They have transmembrane domains (typically nonpolar amino acids)

Liposome

Small hollow sphere of lipid bilayer

Used in some drug delivery

What are proteins in the membrane in charge of (5)

Transport

Recognition

Signal response

Attachment

Movement/force production

Hydrophobic tails are _____ loving

fat loving (lipophilic)

Scramblase

An enzyme that randomly flips lipids

Flippase

An enzyme that flips certain lipids to maintain asymmetric composition

Lipid raft

Domains that contain different portions of lipids and proteins than the rest of the membrane