Lecture 5: Principles of active an passive membrane transport Flashcards Preview

BIOC 341 > Lecture 5: Principles of active an passive membrane transport > Flashcards

Flashcards in Lecture 5: Principles of active an passive membrane transport Deck (33):
1

Downside to compartmentalization of the cell

While membranes provide the requisite barrier function to allow separation of constituents, proteins and other molecules must traverse this barrier

2

Relative Permeability of a synthetic bilayer 

A image thumb
3

Which ions are highly concentrated in the cytosol?

K+

4

Which ions are highly concentrated outside the cell?

Na+, Mg2+, Ca2+, Cl-

5

What are the two types of membrane transport proteins?

  • Transport proteins (Transporters)
  • Channel proteins (Channels)

6

Transporters

  • Permeases, carriers, or pumps
  • Active or passive transport 

A image thumb
7

Channels

Always passive transport 

A image thumb
8

Passive transport or facilitated diffusion

  • Movement of a solute down a concentration or electrochemical gradient
  • All channel proteins and many carrier proteins use this method of transport 

9

Active transport

  • Use Transporters (pumps) to move solutes up a concentration of electrochemical gradient
  • Coupled to an energy source 

10

What's the difference between a concentration gradient and an electrochemical gradient?

An electrochemical gradient factors in membrane potential, not just concentrations

11

What are three types of active transport pumps?

A image thumb
12

Name two types of coupled transporters

  • antiport-coupled solutes move in opposing directions
  • symport- coupled solutes move to same side

 

  • uniport- not coupled, solute moves in one direction

13

Sodium driven glucose uptake is an example of ___

an ion-driven symporter

A image thumb
14

SGLT is an___

Na-glucose co-transporter in epithelial cells of the proximal tubule of the kidney. SGLT inhibitors are new drug for diabetes.

15

Neurotransmitter Transporters

• Built from inverted repeats 

• LeuT- a bacterial leucine tranporter 

– First transporter of this class to be characterized structurally 

• DAT-Dopamine Transporter 

• SERT-Serotonin transporter 

• NET-Norepinephrine Transporter 

16

What are the three types of ATP-driven pumps?

P-type, V-type, and ABC transporters

A image thumb
17

P-Type pumps

– Phosphorylate themselves during their reaction cycle

18

F-type (V-type) pumps 

– ATP synthetase-uses proton gradient to make ATP 

– V-type-use ATP to pump protons 

19

ABC transporters (ATP Binding Cassette) 

– Pump small molecules rather than ions 

– Largest family of membrane transport proteins

20

What type of pump is the sarcoplasmic reticulum calcium pump?

 A P-type pump 

• Moves calcium from the cytoplasm back into the SR following muscle contraction 

21

Na+-K+-ATPase 

• Plasma membrane protein that exchanges sodium (3-going out) for potassium (2- coming in)

• ATP driven antiporter

• Electrogenic 

• P-type ATPase 

• Responsible for generation the large Na+ gradient across the plasma membrane 

22

Describe the Na-K pumping cycle

A image thumb
23

What's the difference between ABC transporters in bacterial cells vs eukaryotic cells

Bacteria-solute pumped into cytosol

Eukaryotic-solute pumped out of cells

24

Channel proteins 

• Form hydrophilic pores across membranes 

• Most plasma membrane channels in animal transport inorganic ions, hence they are called “ion channels”

25

Ion Channels

• Ion selectivity – Highly selective and narrow pores

• Gated – Not continuously open, rather open in response to specific stimuli

• Much faster than carrier proteins – ~108 ions/sec vs. ~1000

• Cannot be coupled to an energy source and must rely on electrochemical gradients 

26

Types of gated ion channels

  • Voltage-gated
  • mechanically gated
  • ligand-gated

27

Voltage-gated ion channels

open in response to a change in voltage across the membrane

28

Mechanically-gated ion channels

open/close in response to mechanical stress

29

Ligand-gated ion channels

open/close in response to a ligand binding

30

Membrane potential

  • A membrane voltage generated by small differences in electrical charges across a membrane 
  • Most all cells have a membrane potential with negative charge inside the cell
  • Neurons (nerve cell) in particular utilize membrane potential to communicate information 

31

Generating a membrane potential

• The electrogenic Na+-K+-ATPase has a minor role in membrane potential

• In animals, the K+-leak channel is the ion channel primarily responsible for generating a membrane potential 

– A plasma membrane ion channel selective for potassium (conducts K+ 10,000 better than Na+) 

32

K+ Channel Selectivity Filter

The amino acids lining the pore of the K+ channel are arranged in such a way the energetically favorable interactions with a K+ ion devoid of if its hydration shell will “fit”. 

33

How do mechanosensitive filters work?

Pressure from the membrane, like with swelling from osmosis, can trigger the gate to open or close.