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Flashcards in Membrane Structure and Function Deck (20)
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1
Q

Why are lipid bilayers highly impermeable to ions and most polar molecules?

A
  • The ability of small molecules of cross a membrane is a function of its hydrophobicity
  • Ions cannot cross membranes because of the energy cost of shedding their associated water molecules
2
Q

Membranes performing different functions contain different kinds and amounts of proteins:

A

Plasma membranes: ~50% proteins

Internal membranes of mitochondria and chloroplast: ~75% proteins

3
Q

What are some of the important cellular processes that membrane proteins are responsible for?

A
  • Pumps
  • Channels
  • Receptors
  • Enzymes
4
Q

Membrane proteins make membranes selectivity permeable. Why?

A

Membrane proteins allow transport of molecules and information across the membrane.
- Membranes vary in protein content from as little as 18% to as much as 75%

5
Q

What are integral membrane proteins?

A

Proteins that are embedded in the hydrocarbon chains of membrane lipids.
Released only when the membrane is disrupted.

6
Q

What are the factors that determine whether a small molecule will cross a membrane?

A

1) The [gradient] of the molecule across the membrane

2) The molecule’s solubility in the hydrophobic environment of the membrane

7
Q

By what process do lipophilic molecules cross the membrane?

A

Simple diffusion

8
Q

By what processes can polar molecules cross the membrane?

A
  • Passive transport
  • Facilitated transport
  • Active transport
9
Q

Passive-transport systems called ion channels

A

Ion transport rates are 1000x faster than ion pumps

10
Q

Voltage-gated channels

A

Open in response to changes in membrane potential

11
Q

Ligand-gated channels

A

open in response to the binding of small molecules (ligands) such as neurotransmitters

12
Q

What is passive transport?

A

Movement with the [gradient]

No added energy is needed

13
Q

What is facilitated diffusion?

A

Diffusion through a protein channel

14
Q

What is active transport?

A

Movement against the [gradient]

Additional energy is needed

15
Q

What are primary transporters?

A

Hydrolyze ATP and transport molecules against the [gradient]

16
Q

What are secondary transporters/cotransporters?

A

Couple transport of molecules with the [gradient] to transport of a molecule with its [gradient]

17
Q

What is a symporter?

A

Transport molecules in the same direction

18
Q

What is an antiporter?

A

Transport molecules in opposite directions

19
Q

Na+ - K+ Pump (Na+ - Ka+ ATPase)

A

The hydrolysis of ATP by the pump provides the energy needed for the transport of 3Na+ ions out of the cell and 2K+ ions into the cell, generating the gradient

20
Q

The structure of the potassium ion channel reveals the basis of specificity:

A
  • The potassium channel selectively and rapidly transports K+ across the cell membrane. Larger ions are not transported because they are too big to enter the channel
  • Smaller ions are excluded because they cannot interact with the selectivity filter. Such ions are small enough that the energy of desolvation cannot be compensated for by interactions with the selectivity filter.