Membrane Transport + Potential

Question 1

What do cells use electrochemical gradients for? (4 points)

Answer 1

• Transport
• ATP Production (mitochondria, bacteria, chloroplasts)
• Cell Signalling (action potential)
• Other functions (e.g. opening and closing stroma)

Question 2

What type of transport diffusion is the slowest out of simple, channel mediated, and transporter mediated?

Answer 2

• Transporter mediated is slowest
• simple diffusion and channel mediated are faster because molecules can just go right through without a conformational change

Question 3

What is the example of passive transport that brings glucose in the cell?

Answer 3

GLUT Trasnporters

Question 4

Difference between GLUT1 and GLUT2?

Answer 4

-GLUT 1 is expressed mainly in red blood cells and other tissues
-GLUT 2 is expressed in the liver and gut epithelium
Mutations in these GLUT transporters can lead to disease (neuro diseases that associated with epilepsy)

Question 5

3 different forms of energy that powers conformational change? (Active transport)

Answer 5

• coupled transport (help of another solute)
• ATP-driven pump (uses ATP hydrolysis)
• light-driven pump

Question 6

What type of transport can coupled transport be?

Answer 6

-antiporters or uniporters 9secondary active transport)
antiporters–> transports two molecules across the membrane in DIFFERENT directions
symporters–> transports two molecules across the membrane in the SAME direction

Question 7

What is an example of coupled transport?

Answer 7

Na+ - glucose cotransporter (type of symporter)

Question 8

What are the 3 classes of ATP driven pumps?

Answer 8

• P Type
• ABC
• V Type

Question 9

What drives the conformational change of P-type pumps

Answer 9

• During the pumping stage, P-type pumps are phosphorylated by ATP which drives the conformational change to move solutes against its concentration gradient
• specifically, the conformational change is by the amino acids shift in position, which is shifted by the phosphorylation and dephosphorylation of asparic acid

Question 10

Some of the roles of P-Type pumps inside the cell?

Answer 10

• Maintain calcium levels in the cytoplasm/cytosol - keep them low
  
  • Some of them pump calcium in the ER and the plasma membrane
• Create Na+/K+ gradients (eg in plants and fungi)
• Transport of important trace metal ions such as iron, magnesium, cobalt, copper, manganese, and zinc copper
• Many are drug targets for drug development
• They are responsible for primary transport

Question 11

Typical P-Pump Structure?

Answer 11

10 transmembrane α helices connected to three

cytosolic domains

Question 12

What are the 3 cytosolic domains of a P-Type Pump?

Answer 12

• Nucleotide binding domain: uses atp to move solute across the membrane
• Phosphorylated aspartic acid: this domain is phosphorylated. The phosphate is from ATP
• Activator domain:

Question 13

What is the structure of the ABC Transporter and what do they transport?

Answer 13

• ABC transporters contain two highly conserved ATPase, domains or ATP-binding cassettes on the cytoplasmic side and two hydrophobic domains
• Transport of sterols, lipids, sugars, vitamins, nucleotides, peptides, amino acids, etc

Question 14

difference between bacteria ABC pump and eukaryotic ABC pump

Answer 14

Some ABC transporters export solutes and take in solutes. In eukaryotes, the transporter mainly only exports solutes out of the cell

Question 15

What are 3 types of membrane transport flip flops

Answer 15

• Flippase (P-Type ATPase)
  - flips phospholipid from outer to inner membrane layer
• Floppase (ABC flippase)
  - flops phospholipids from inner to outer membrane layer or out of membrane
• Scramblases
  - move in both directions (do not require ATP)

Question 16

What are the types of channels associated with PASSIVE transport?

Answer 16

• Water Channels (aquaporins)

- Ion channels (Voltage, ligand and mechanically)

Question 17

What channel proteins are selective?

Answer 17

While some channel proteins can be non-selective, the majority of them are selective. Selective channel proteins include aquaporins, and most ion channels (sodium, potassium, calcium, chloride)

Question 18

What is the structure of water channels?

Answer 18

One half of the channel (left side) is hydrophobic and the other side that are the carbonyl bonds

Question 19

What are the 3 properties of ion channels?

Answer 19

• Selectivity
• Gating–> They can open and close in confirmation
• desensitization/inactivation–> Many gated channels can be stimulated to open for a certain amount of time and it just closes up again

Question 20

What is the selectivity filter on Ion channels?

Answer 20

Selectivity filter is the point in which the channel becomes very narrow, only allowing only 1 and sometimes a specific ion through
- This controls which ions can pass through the channel

Question 21

How does an Ion channel open and close?

Answer 21

• This happens through the movement of inner helices

Question 22

What is associated with the voltage-gated ion channels?

Answer 22

• neurons, membrane potential

Question 23

What is membrane potential?

Answer 23

-The membrane potential is created by the Na+/K+ pump (10%) and the activity of K+ leak channels (90%)

Question 24

What is resting membrane potential?

Answer 24

-cells are at rest; there are equal charges on both sides of the membrane which means voltage or membrane potential is 0

Question 25

What are the 3 conformational states of voltage-gated Na+ Ions

Answer 25

-Closed, Open and inactivated

Question 26

What happens as soon as membrane potential shifts enough near the Na+ Channels?

Answer 26

As soon as the membrane potential shifts enough near the channel, Sodium ions will flow through and as they move into the axon, the membrane is depolarized and voltage increases. When It becomes depolarized, it opens up the neighbouring sodium channel

Question 27

How is action potential triggered?

Answer 27

An action potential is triggered by a depolarization of the plasma membrane that is, by a shift in the membrane potential to a less negative value inside.

• action potential is depolarized (goes up) when sodium channel opens up and sodium rushes in the cell.
• it then gets depolarized (down) when potassium leak channels open up and K+ leaks out of the cell

Question 28

how does membrane potential restore to its initial negative value

Answer 28

the Na+ channels automatically inactivate and voltage-gated K+
channels open

Question 29

What is hyperpolarization?

Answer 29

-when channels don’t close right at resting potential and a lot of potassium leaks out. This goes below resting potential