Membranes and Lipid Proteins

Question 1

Functions of the cell membranes

Answer 1

• Define cell boundary and serve as permeability barriers
• Represent sites of specific functions
• Regulate the transport of solutes
• Detect and transmit electrical and chemical signals
• Mediate cell to cell communication

Question 2

Describe the fluid-mosaic model

Answer 2

membrane is a two-dimensional sea of mobile lipid in which proteins diffuse or float

Question 3

Purpose of phospholipid reorganisation

Answer 3

allow for merging and release of neurotransmitter in synaptic cleft

Question 4

Role of cholesterol in the lipid bilayer

Answer 4

helps with stability, changes fluidity of membrane

Question 5

Diffusion of ions through plasma membrane

Answer 5

via integral proteins -> plasma membrane will not let through any large or charged molecules

Question 6

Define lipids

Answer 6

fat-soluble substances, phospholipids and cholesterol

Question 7

Structure of phospholipids

Answer 7

• share a glycerol backbone and two hydroxyl groups -> esterified to fatty acid (acyl) groups
• phosphate group attached to two carbons, which attach to nitrogen atom and oxygen atom
• head = polar = hydrophilic
• fatty acid chain tails = non-polar = hydrophobic

Question 8

Formation of monolayer

Answer 8

low concentrations of phospholipids in water

Question 9

Formation of micelles

Answer 9

higher concentration of phospholipids, but not high enough to form a bilayer

Question 10

How is the width of the bilayer determined

Answer 10

length of fatty-acid side chains

Question 11

Nature of head groups determines…

Answer 11

how densely packed adjacent phospholipid molecules are in each layer of membrane

Question 12

How can phospholipids be dissolved with detergents

Answer 12

they are also amphipathic and interact through tails

Question 13

Rate of phospholipid diffusion at high temperatures

Answer 13

rapid (sol state)

Question 14

Rate of phospholipid diffusion at low temperatures

Answer 14

slowly (gel state)

Question 15

Define transition temperature

Answer 15

temperature between conversion from sol state to gel state -> reducing length of fatty acid chains redicts transition temperature

Question 16

How do modest concentrations of cholesterol influence fluidity

Answer 16

decreases fluidity by holding phospholipids together

Question 17

How do high concentrations of cholesterol influence fluidity

Answer 17

increases fluidity

Question 18

Where are integral proteins

Answer 18

embedded in cell membrane (channels and pores)

Question 19

Where are peripheral proteins

Answer 19

embedded on exterior of membrane

Question 20

What are glycoproteins

Answer 20

carbohydrates attached to proteins

Question 21

What is a glycolipid

Answer 21

carbohydrate attached to a phospholipid

Question 22

Structure of cholesterol

Answer 22

hydroxyl group and four fused rings

Question 23

Layers of cell membrane

Answer 23

plasma membrane, internal membranes, intracellular vesicles

Question 24

Membrane lipids

Answer 24

• “barrier properties”
• phospholipids
• steroids
• neutral fats
• glycolipid

Question 25

Formation of lipid bilayer

Answer 25

- spontaneous in aqueous solution - stabilised by tail-tail and head-head interactions - makes exocytosis and endocytosis possible

Question 26

How are transmembrane proteins arranged in membrane

Answer 26

asymmetrically, orientation is established during biosynthesis

Question 27

Single spanning proteins

Answer 27

- e.g. receptor tyrannise kinase - anchoring, receptor-transducer function

Question 28

Multiple spanning proteins

Answer 28

- e.g. pores of ion channels - may form aqueous pore in membrane

Question 29

Structure of cys-loop receptors (ligand-gated ion channels)

Answer 29

- extracellular N-terminus - composed of five protein subunits which form a pentameric arrangement around a central pore - four hydrophobic transmembrane domains - extracellular C-terminus

Question 30

How can you find what regions of proteins are hydrophilic/hydrophobic

Answer 30

conducting hydrography analysis

Question 31

Protein regions of high charge density

Answer 31

are relatively hydrophilic

Question 32

Protein regions of low charge density

Answer 32

are relatively hydrophobic

Question 33

Evidence for structure of fluid-mosaic model

Answer 33

- lipid area (unimolecular film) = 2 x membrane area - X-ray and neutron diffraction - transmission electron microscopy - freeze-etching (reveals embedded proteins in fracture faces)

Question 34

Evidence for dynamics of fluid-mosaic model

Answer 34

- Electron-Spin-Resonance (ESR) Spectroscopy - Phase-Transition - Protein-tagging to observe protein movement

Question 35

ESR Spectroscopy

Answer 35

- one of most efficient - applies spin-probe to head, allowing to track movement of phospholipids

Question 36

FRAP (Fluorescence recovery after photobleaching)

Answer 36

- fluorescent antibody attaches to epitope that has been commonly expressed - antibody binds to tag - see movement of proteins

Question 37

Mechanisms by which substances cross membrane

Answer 37

- diffusion (lipophilic) - osmosis (net water (solvent) flow) - transport (facilitative or active solute movement)