Biological Membranes and Lipids

Question 1

What are membranes?

Answer 1

Membranes enclose every living cell and define its boundaries

Question 2

What is the composition of membranes?

Answer 2

Two layers of phospholipids connected by hydrophobic tails

Question 3

What are phospholipids and what is their defining structure?

Answer 3

Class of lipid whose molecules have a hydrophilic head containing a phosphate group and two hydrophobic tails derived from fatty acids

Joined by an alcohol residue eg glycerol molecule

Question 4

What are the major classes of lipids?

Answer 4

1. Fatty acids
2. Triglycerols (fats and oils that occur in plants and animals)
3. Glycerphospholipids
4. Sphingolipids / Glycolipids
5. Cholesterol or Steroids

Question 5

What are fatty acids?

Answer 5

Hydrocarbon chains

Can be saturated (stearic) and unsaturated (linoleic or alpha-linolenic)

Question 6

What are the differences between saturated and unsaturated fatty acids?

Answer 6

Saturated fatty acids are highly flexible with a wide range of conformation

Unsaturated fatty acids have double bonds and a rigid 30 degree bend in the hydrocarbon chain

Question 7

What is a triglycerol?

Answer 7

A glycerol molecule with three fatty acids

Question 8

What is the difference between a micelle and a lipid bilayer?

Answer 8

Micelles are donut-like rings formed by single tailed lipids

A lipid bilayer is formed by glycerphospholipds and sphingolipids with two hydrocarbon chains (heads out, tails in)

Question 9

How is the fluidity of the lipid bilayer influenced by saturated and unsaturated fatty acids?

Answer 9

Increase in unsaturated fatty acids increases fluidity

Increase in saturated fatty acids increases viscosity (can be packed tighter without the 30 degree bend)

Cholesterol reduces fluidity at moderate temperatures

Question 10

What are the major functions of membrane proteins?

Answer 10

Transport
Signal transduction
Enzymatic activity
Cell-to Cell recognition proteins
Intercellular joining
Anchorage of cells to ECM

Question 10

What are membrane carbohydrates and what function do they play in the plasma membrane?

Answer 10

Third major component of plasma membranes, found on the exterior of surface cells

Bound to proteins or lipids (glycoproteins / glycolipids)

Function = cell-to-cell recognition, cell surface antigencity, and receptors for various microbe infections / invasions

Question 11

What kind of permeability do membranes have?

Answer 11

Selective permeability (intake of nutrients, output of waste products)
Depends on type of molecules

Hydrophobic molecules = easy to cross
Hydrophillic molecules = difficult to cross, aided by transport proteins

Question 12

What are channel proteins?

Answer 12

Transport proteins
Form hydrophillic pores in membranes, transporting molecules down the concentration gradient

EXAMPLE: water via aquaporins or ions via ion channels

Question 13

What are carrier proteins?

Answer 13

Transport proteins
Move substances across the membrane both down and against the concentration gradient

EXAMPLE: glucose through glucose transporters

Question 14

What is diffusion?

Answer 14

Method of passive tranport following the concentration gradient
No energy required

The process by which molecules spread out evenly across a given space to attain equilibrium

Question 15

Describe the features of passive transport (H2O)

Answer 15

Movement across a membrane is called osmosis
Affected by solute concentration

Isotonic = same inside and outside the cell, no movement required
Hypertonic = More concentrated outside the cell (shirveled)
Hypotonic = More concentrated insde the cell (lysed)

Question 16

What is active transport?

Answer 16

Movement against the concentration gradient that requires energy (ATP)

Can only occur via carrier proteins

Question 17

What are active bulk transport processes?

Answer 17

Exocytosis = Secretion via vesticles
Endocytosis = Intake via vesticles

Question 18

What is membrane potential and electrical potential?

Answer 18

A potential gradient that forces ions to passively move in one direction

Positive = Outside cell
Negative = Inside cell
Favours cation (positively charged ion) entry

Electrical potential = difference in charged ions across a membrane

Active transport maintains membrane potential