Basic knowledge for midterm 1

Question 1

What are the characteristics of the lipid bilayer?

Answer 1

1- Basic structure common to all cells and almost all eukaryotic organelles.
2 - composed mainly of phospholipids and other amphiphilic molecules.
3 - Will form and seal spontaneously
4 - barrier to diffusion of charged molecules, most polar molecules, macromolecules
5 - assymetric: cytosolic (PI) vs. lumenal (extracellular surfaces)
6 - animal cells maintain a negative membrane potential
7 - membrane proteins regulate transport and maintain potential (among other activities)

Question 2

Where is PI found?

Answer 2

Found in cytosolic layer of membrane.

Question 3

How is PI phosphorylated?

Answer 3

Inositol ring is phosphorylated by PI kinases to form PIPS.

Question 4

PI cleavage is accomplished by what?

Answer 4

PI phospholipases.

Question 5

Lipids are what type of molecules, in regards to polarity?

Answer 5

Bi-polar

Question 6

Planar phospholipids are energetically ________ and thus switch to a different more energetically _______ state. What is it?

Answer 6

1. favourable

2. Cell shape to remove edges (i.e. exposure of water to hydrophobic ends)

Question 7

Glycolipids and glycoproteins are always on the?

Answer 7

Lumenal/extracellular side.

Question 8

Charged lipids such as PI are found in what layer?

Answer 8

cytosolic

Question 9

Transmembrane domains can be detected by what? and what is it?

Answer 9

Hydropathy index, gives value of hydrophobicity of amino acids in a sequence of a known protein. More positive is more hydrophobic.

Question 10

What are the characteristics of integral membrane proteins?

Answer 10

1 - can be transmembrane (i.e. single or multipass) and thus have polar ends and hydrophobic transmembrane domains.
2 - can be covalently linked to membrane lipids
3 - solubilized by membrane disrupting detergents (SDS)

Question 11

GPI anchor is found?

Answer 11

lumenal side

Question 12

transmembrane domains have what types of motifs?

Answer 12

Alpha helices (can H-bond with backbone) or B-barrel

Question 13

What are the characteristics of peripheral membrane proteins?

Answer 13

1. Non-covalently linked to integral membrane proteins.

2. Solubilized by weak detergents (Triton), high or low pH/salt

Question 14

Describe lac permease.

Answer 14

LacY is the gene that encodes it.
LacY required for transport of lactose into the cell.
Later found that it is a lactose/H+ symporter
Composed of 12 predicted transmembrane alpha helices.

Question 15

Cell membranes can bring in specific molecules that cannot otherwise cross-lipid bilayers using what?

Answer 15

transporters

Question 16

Ion channels and transporters are important in what?

Answer 16

1 - Transport of molecules across the lipid bilayer
2 - maintenance of osmolarity
3- establishment of ion and electrochemical gradients

Question 17

Animal cells have a ________ membrane potential.

Answer 17

negative

Question 18

What is the electrochemical gradient for a given ion?

Answer 18

ion gradient + membrane electrical potential (basically charge + concentration)

Question 19

In a typical resting cell, Na is ___ from its equilibrium potential and K+ is ____ to its equilibrium potential.

Answer 19

far

close

Question 20

Chloride channels allow chloride to ____ the cell.

Answer 20

Exit, partially offsetting the negative membrane potential