1- Cell Membranes

Question 1

What perfect of encoded eukaryotic protein are membrane proteins?

Answer 1

30%

Question 2

What types of bonds hold together the membrane?

Answer 2

Noncovalent interactions

Question 3

What creates the kink in a phospholipid hydrophobic tail?

Answer 3

cis double bond (unsaturated).

Kinks = more loosely associated phospholipids. More difficult to pack together

Question 4

What are some of the varieties of phospholipids and what are they derived from?

Answer 4

Phosphatidyl-ethananoalanine, phosphatidyl-serine, phosphatidyl-choline, sphingo-mylin

Derived from glycerol and sphingosine

Important because some of these can be modified to recruit other proteins (like receptors)

Question 5

Why do phospholipids arrange like they do?

Answer 5

Free energy cost is minimized if hydrophobic parts are clustered together.

create sphere so no edges are showing.

Question 6

lipid micelle

Answer 6

form a ball, not a bilayer.

Question 7

Movement of phospholipids in bilayer

Answer 7

Lateral diffusion, rotation, flexion and rarely flip flop

Question 8

Describe how phospholipids are related to extracellular signals with PI-3-kinase and phospholipase C.

Answer 8

In both, extracellular signal attaches:

PI-3-Kinase (also P inositol PLs)- activates PI3K > phosphyrlates lipid > recognized by intracellular protein > relay signal.

Phospholiapse C activated > fragmetnts phospholipid (head)> used to help relay signals

Question 9

Sterols

Answer 9

Major components of membranes.

Up to one cholesterol for ever PL.

Also has hydrophilic head, rigid steroid ring, and hydrophobic tail (segment that interacts with other lipids

Question 10

Lipid Raft

Answer 10

domain to organize membrane proteins (usually for cell signaling or transport)

Question 11

Glycolipids

Answer 11

Lipids attached to sugar molecules. Sugar added in golgi.

Typically on the extracellular side of the membrane.

aobut 5% of lipids on outside part of membrane.

Can provide entry points

Made from sphingosine.

Question 12

How do glycolipids arrange in the cell membrane?

Answer 12

They self associate through bonds with sugars

Also vander waals forces between hydrocarbon tails.

Question 13

How are soluble proteins attached to membranes?

2 examples she mentioned specifically?

Answer 13

1. Protein anchored by fatty acid chain
   amide link between terminal amino group and fatty acid.
2. Protein anchored to membrane by a prenyl group
   Thioether linkage between cysteine and prenyl group
   lipid-CH2-S-CH2-protein

Slide 13 for pictures

Question 14

Beta barrel

Answer 14

Multipass transmembrane proteins

transmembrane portion is arranged in B sheets (more rigid than alpha helix)

Abundant in outer membrane of mito, chloroplasts and bacteria.

many functions: transport (ex. iron), receptor for bacterial virus, hydrolyse lipid molecules, form porin (water filled)

Question 15

Are there disulfide bonds on cytosol of transmembrane proteins?

Answer 15

No the cytosol maintains them in there reduced form.

Question 16

What are detergents used for?

Answer 16

For studying membrane components, use detergents: only agent that disrupts hydrophobic associations and destroys lipid bilayer, can solubilize transmembrane proteins

detergents also have hydrophobic tail and hydrophilic head and form into micelles

This allows us to separate components and study them independantly

Question 17

Two ways to get single chain multi-pass protein converted to two chain multi-pass protein.

Answer 17

1. use protease to clip one loop of multi pass transmembrane protein so you have two fragments.
2. two proteins synthesized and integrated into membrane. lateral mobility brings the two segments together

Question 18

Bacteriorhodopsin

Answer 18

Proton pump made up of seven a helices found in archaea and bacterial cells.

Able to be integrated into the hydrophobic core in order to transport hydrophilic molecules (H+)

Light driven proton transfer. Retinal very similar to vitamin A

Question 19

What are the ways of restricting lateral mobility of specific plasma proteins

Answer 19

1. proteins can self assemble into large aggregates
2. Proteins can be tethered by interactions with macromolecules outside or inside the cell
3. Proteins can interact with proteins on the surface of another cell. (adhesion proteins)

Question 20

Glycocalyx

Answer 20

Cell-surface carbohydrate layer

Protects cell from mechanical and chemical damage, keeps cell at a distance, preventing unwanted protein to protien interactions.

Made up of: oligosaccharides side chains of glycolipids and integral membrane glycoproteins, and polysaccharides chains of integral membrane proteaglycans.

Question 21

Relative permeability of the membrane

Answer 21

Hydrophobic (O2, CO2, N2, benzenes)= easily
small uncharged polar (H2O, urea, glycerol,)= ehh
large uncharged pola (glucose, sucrose)= not great
ions= do not diffuse

Question 22

Two general classes of transport proteins

Answer 22

1. Carrier protein- alternate between two different confirmations. Bind on one side and released on the other.
2. Channel proteins- water pore through which certain molecules can diffuse

Question 23

What are the two different general class of transport?

Answer 23

1. Passive transport - follows concentration gradient
   simple, channel-mediated, carrier mediated
2. Need energy to go against conc. gradient.

If solute has a charge you also need to account for the membrane potential.

Question 24

Ionophores

Answer 24

Chemical species that binds reversibly to and transports IONS.

2 kinds: carrier (whole protein moves sides of membranes) and channel forms

Some are synthesized by microbes to import ions into their cells.

Question 25

Carrier protein passive transport

Answer 25

Two different confirmations, transition occurs RANDOMLY Driven by solute concentration, more solutes will bind on the higher concentrated side. When a molecule binds it will change confirmation and release it to the other side of the cell.

Question 26

Uniport Synport Antiport

Answer 26

Uniport- One molecule transported at a time Synport- two molecules moving the same direction Antiport- Two molecules moving opposite directions

Question 27

3 varieties of Active transport

Answer 27

ATP driven- couples uphill transport to hydrolysis Coupled carrier- two molecules pass through. one is going up conc gradient coupled with one going down conc. gradient Light driven pump- couple uphill transport with energy input from light. All are against electrochemical gradient. which is why you need energy.

Question 28

Three types of ATP-driven pumps in cell membranes

Answer 28

1. P type pump: phosphorylates itself, setting up and maintaining gradients of ions (Na+, K+, H+, Ca2+) 2. F type pump= turbine like protein/ATP synthases 3. ABC transporter- pump small molecules across membranes

Question 29

Na+/K+ pump overview

Answer 29

P-type pump Transports Na+ OUT OF and K+ INTO the cell against their electrochem gradients 3 Na+/2K+ per ATP Oubain (inhibitor) competes for K+ binding site on outside of cell membrane

Question 30

Na+/K+ pump steps

Answer 30

1. Bind intracellular Na+ (3) 2. Phosphorylation by ATP on cytosolic side. 3. Conformational change releases Na+ on outside of cell. 4. K+ binds on extract side. Subsequent dephospho rylation 5. pump returns to original conformation 6. K+ is transferred inside the cell.

Question 31

How does Na+/K+ pump help to balance osmolarity of the cell?

Answer 31

Cells have lot of solutes/(-) molecules in cell and accompanying cations. This creates osmotic gradient that pulls H2O into cell. Na+ and Cl- are typically outside of cell. Pump helps keep balance by moving Na+ outside of cell when it moves in. Cl- is kept out by membrane potential.

Question 32

ABC transporter

Answer 32

Use ATP for binding and hydrolysis to transport small molecules across the bilayer. Pumps out (can be in) nutrients and hydrophobic drugs out Uses 2 ATP

Question 33

Ion channel types

Answer 33

1. voltage gated- open in response to membrane potential (depolarization) 2. ligand-gated (extracellular) 3. Ligand-gated (intracellular ligand) 4. Mechanically gated Ion channels allow for inorganic ions to diffuse rapidly down their electrochemical gradients across bilayer. Ion selective and fluctuate between open and closed states. Needs stimulus.

Question 34

What causes an action potential?

Answer 34

Activating neurotransmitter depolarizes cell a little. Na+ channels open, depolarize cell rapidly until it shuts.

Question 35

What are the two mechanisms to stop depolarization during action potential?

Answer 35

1. Na+ channels inactivate/close. channels recycle through the 3 confirmations-- which is why action potentials travels away from site of initial depolarization. 2. Voltage gaited K+ channels open-- eject potassium from cell and allows for balance of charge.