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MCM test 2 > 1- Cell Membranes > Flashcards

1- Cell Membranes Flashcards

1
Q

What perfect of encoded eukaryotic protein are membrane proteins?

A

30%

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2
Q

What types of bonds hold together the membrane?

A

Noncovalent interactions

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3
Q

What creates the kink in a phospholipid hydrophobic tail?

A

cis double bond (unsaturated).

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

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4
Q

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

A

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)

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5
Q

Why do phospholipids arrange like they do?

A

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

create sphere so no edges are showing.

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6
Q

lipid micelle

A

form a ball, not a bilayer.

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7
Q

Movement of phospholipids in bilayer

A

Lateral diffusion, rotation, flexion and rarely flip flop

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8
Q

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

A

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

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9
Q

Sterols

A

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

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10
Q

Lipid Raft

A

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

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11
Q

Glycolipids

A

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.

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12
Q

How do glycolipids arrange in the cell membrane?

A

They self associate through bonds with sugars

Also vander waals forces between hydrocarbon tails.

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13
Q

How are soluble proteins attached to membranes?

2 examples she mentioned specifically?

A
  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

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14
Q

Beta barrel

A

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)

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15
Q

Are there disulfide bonds on cytosol of transmembrane proteins?

A

No the cytosol maintains them in there reduced form.

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16
Q

What are detergents used for?

A

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

17
Q

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

A
  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
18
Q

Bacteriorhodopsin

A

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

19
Q

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

A
  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)
20
Q

Glycocalyx

A

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.

21
Q

Relative permeability of the membrane

A

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

22
Q

Two general classes of transport proteins

A
  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
23
Q

What are the two different general class of transport?

A
  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.

24
Q

Ionophores

A

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.

25
Q

Carrier protein passive transport

A

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.

26
Q

Uniport
Synport
Antiport

A

Uniport- One molecule transported at a time

Synport- two molecules moving the same direction

Antiport- Two molecules moving opposite directions

27
Q

3 varieties of Active transport

A

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.

28
Q

Three types of ATP-driven pumps in cell membranes

A
  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
29
Q

Na+/K+ pump overview

A

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

30
Q

Na+/K+ pump steps

A
  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.
31
Q

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

A

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.

32
Q

ABC transporter

A

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

33
Q

Ion channel types

A
  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.

34
Q

What causes an action potential?

A

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

35
Q

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

A
  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.

MCM test 2 (15 decks)

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