7 Membrane - Lecture

Question 1

What are 7 functions of membranes in the cell?

Answer 1

Create unique chemical compartments in eukaryotes
Organize biochemical reactions – acting as a scaffold
Provide a selectively permeable barrier
Establish concentration gradients
Sense and transduce extracellular signals
Mediate cell-cell communication
Essential role in energy conversion, or transduction

Question 2

What was used to find the structure of the plasma membrane?

Answer 2

technique: plasma membrane stained (with heavy metal osmium) so it could be examined by TEM (transmission electron microscopy).

Question 3

Describe plasma membrane?
thickness?
function?

Answer 3

Very thin structure: (5-10 nm thick)
Separates the inside of the cell from the outside of the cell.
Selectively permeable.
Contains transmembrane proteins that mediate this selective permeability

Question 4

Cell membranes are composed primarily of a ___ composed of ____

Answer 4

phospholipid bilayer amphipathic lipids

Question 5

The ___ of the lipid dictates the properties that it will have in an aqueous environment.

Answer 5

structure

Question 6

What is the basic structure of a phospholipid?

Answer 6

It has a hydrophilic head that contains a polar group, phosphate and glycerol. It has 2 hydrophobic tails made up of fatty acids. It is an amphipathic molecule.

Question 7

Lipid bilayer sheets “self-assemble” –_____ close to form spheres. spontaneously or not spont?

Why a spherical shape?

Answer 7

spontaneously

A spherical shape minimizes the energetically unfavorable interactions between water and the hydrophobic fatty acid tails

Question 8

What is a phosphatidic acid?

Fatty acyl chains (R) are ____ – saturated or unsaturated

Answer 8

the simplest phospholipid with no extra polar head group

hydrophobic

Question 9

Membrane fluidity is affected by its ____ composition

Answer 9

lipid

Question 10

Transition temperature (Tm) ??

Any factor that increases the transition temperature makes a material

Answer 10

or “melting point” – temperature at which a membrane transitions from a solid to become a liquid or when it (“melts”)

“more solid,” or “less fluid”

Question 11

Do saturated bonds inc or dec transition temp? So it makes it more ___

Shorter fatty acid chains show a ___ transition temp and ___ membrane fluidity

more unsaturated, ____ fluid, & more saturated, ___ fluid

Answer 11

inc more solid/less fluid
less double bonds = less fluid

reduced inc

more, less

Question 12

Cholesterol makes membranes ____ fluid

How?

Answer 12

less

Interferes with flexibility of the unsaturated fatty acid chains to make the membrane more stable (less fluid)

Question 13

Common Functions of Membrane Proteins (4):

Answer 13

Cellular receptors- mechanical, chemical, biochemical
Transporters- Ion channels, large molecule, drug resistance proteins
Adhesion and recognition- Role in structure and immunity
Localization based on Function

Question 14

3 Classes of Membrane Proteins?

Answer 14

Integral proteins (transmembrane proteins)
peripheral proteins
lipid-anchored proteins

Question 15

Integral membrane proteins?

Answer 15

(inside) span lipid bilayer
make up 20-30% of all proteins in cell
transmembrane domain have hydrophobic character
can move laterally within membrane, not always fixed

Question 16

Lipid-linked Proteins

Answer 16

-located outside lipid bilayer
Can be anchored on either side of the membrane but each protein with this linkage is found on one side or the other (covalently linked to lipid)

Question 17

Peripheral membrane proteins

Answer 17

• located outside lipid bilayer

- Non-covalently attached either to the polar headgroup of a lipid or to an integral membrane protein

Question 18

Connexin – Hydrophobicity plots predict:

Transmembrane struct?

Answer 18

transmembrane helicies from determined sequences
graph: hydropathy v. aa #
hydrophobic if hydropathy above 0 and hydrophilic if below 0 ( + delta G means hydrophobic)

4 hydrophobic regions that correspond to 4 alpha-helical regions

Question 19

Proteins arranged in beta sheets (barrels) are found in:

Answer 19

outer membranes of bacteria, mitochondria, choloroplasts

Question 20

Amphipathic helices of multipass transmembrane proteins can interact to form an ___ domain through the bilayer

Answer 20

polar

Question 21

How are membrane proteins studied?

Answer 21

Gel Electrophoresis
ImmunoStaining
Mass-Spectroscopy

Question 22

Common Detergents (amphipathic) Used in Membrane Biochemistry:

Answer 22

SDS -ionic & charged

Triton X-100 -nonionic & uncharged (doesn’t affect protein’s tertiary structure)

Question 23

Can peripheral membrane proteins be extracted from the membrane without destroying the physical integrity of the membrane?

Answer 23

YES

Question 24

What solubilizes membrane proteins?

Answer 24

anionic detergents

Question 25

SDS-polyacrylamide gel electrophoresis (PAGE):

Answer 25

SDS disrupts non-covalent bonds in the proteins, denaturing them, so the molecules to lose their conformation. Also, anions of SDS bind to the peptide chain at a ratio of one SDS anion for every two amino acid residue to give a negative charge on the protein proportional to the mass of that protein (about 1.4 g SLS/g protein).

Question 26

Where would the larger and smaller proteins be located on the gel of a PAGE experiment?

Answer 26

larger would be on top near the cathode (negative charged side) and smaller would be at bottom towards anode (+ charged side)

Question 27

What kind of detergent can solubilize membrane components and remove integral membrane proteins?

Answer 27

nonionic detergents

Question 28

How can proteins movement within membranes be studied?

Answer 28

Studying Membrane Lipid Mobility with FRAP

Fluorecscent Recovevery After Photobleaching

Question 29

Shape of:
saturated fatty acid?
cis-unsaturated fatty acid

Answer 29

straight, flexible rod

crooks in chain at sites of double bond