Membrane Transport (1)

Question 1

What does the plasma membrane do?

Answer 1

Controls a cells intracellular environment by creating a barrier between inter- and extra- cellular space

Question 2

What is the role of membrane transport proteins?

Answer 2

Molecular movements between the cell and extracellular space and between cellular components

Question 3

What are the main types of biological membranes that contain transport proteins?

Answer 3

Plasma (cytoplasmic) membrane, nuclear membrane, and intracellular membranes

Question 4

What are the major lipid components of the plasma membrane?

Answer 4

Phospholipids, including sphingolipids (~49%)
Cholesterol (~49%)
Glycolipids (~2%)

Question 5

What is the composition of phospholipids and glycolipids?

Answer 5

2 long non-polar hydrophobic chains
Hydrophilic head group

Question 6

What can phospholipids contain in their phosphorylated head group?

Answer 6

Glycerol (phosphoglyceride)
Sphingosine (e.g. sphingomyelin)

Question 7

What is an example of a sterol?

Answer 7

Cholesterol

Question 8

What lipids are associated with the predominantly outer membrane?

Answer 8

Phosphatidycholine
Sphingomylein

Question 9

What lipids are associated with the exclusively outer membrane?

Answer 9

Glycolipids

Question 10

What lipids are associated with the predominantly inner membrane?

Answer 10

Phosphatidylethanolamine
Phosphatidylserine

Question 11

What lipid is associated with the exclusively inner membrane?

Answer 11

Phosphatidylinositol

Question 12

What lipid is found in both the outer and inner membrane?

Answer 12

Cholesterol

Question 13

At high temperatures, does cholesterol reduce or maintain the fluidity of the lipid bilayer?

Answer 13

Reduces

Question 14

At low temperatures, does cholesterol reduce or maintain fluidity of the lipid bilayer?

Answer 14

Maintains

Question 15

When the membrane is permeable, what direction do solutes move in?

Answer 15

It is bi-directional

Question 16

What does a bi-directional movement cause?

Answer 16

A net movement from high to low concentration

Question 17

If movement of solutes into the cell is equal to movement out, is there a net charge?

Answer 17

No - creates equilibrium

Question 18

Define influx

Answer 18

Net movement into a cell

Question 19

Define efflux

Answer 19

Net movement out of a cell

Question 20

What is passive diffusion?

Answer 20

A non-selective net movement of molecules from a high to a low concentration (to equilibrium)

Question 21

What is the name for solutes that can’t cross water’s semi-permeable membrane?

Answer 21

They are ‘osmotically active’

Question 22

What are factors that affect the rate of passive diffusion (in physiological systems)?

Answer 22

Steepness of concentration gradient (Dm)
Surface area

Question 23

What are ion channels?

Answer 23

Selective membrane proteins that allow ions to move across the membrane down their electrochemical gradient.

Question 24

What are the 3 types of gated ion channels?

Answer 24

Ligand gated
Voltage gated
Mechano gated

Question 25

How do you prevent smaller Na+ accessing K+ channels?

Answer 25

Solution uses the fact that ions exist in a hydrated form in aqueous solution

Question 26

What are the factors that affect passive diffusion through channels?

Answer 26

Steepness of the concentration gradient (Dm) Number of channel proteins Permeability/affinity

Question 27

What is the function of aquaporins?

Answer 27

They facilitate the rapid movement of water across membranes while preventing ion leakage

Question 28

What are the 3 classes of carrier proteins?

Answer 28

Uniport - single solute Symport - 2 different solutes together Antiport - 2 solutes transported in opposite directions together

Question 29

What is transporter mediated diffusion?

Answer 29

Selective diffusion of a solute using transport/carrier protein

Question 30

What is Vmax referring to in carrier protein kinetics?

Answer 30

A measure of total transport proteins - where all transport proteins are 'occupied'

Question 31

What is Km referring to in carrier protein kinetics?

Answer 31

[solute] at which 1/2 binding sites are occupied - a measure of the affinity of solute for carrier protein

Question 32

What does Glucose Transporter (GLUT4) have a specificity for?

Answer 32

D-glucose Galactose Arabinose

Question 33

What is GLUT4 upregulated by?

Answer 33

Insulin

Question 34

How does insulin regulate GLUT4?

Answer 34

Insulin increases the number of GLUT4 transporters in the membrane, enhancing glucose uptake

Question 35

Where is GLUT3 found?

Answer 35

Predominantly in brain neurons but foound widely in other tissues

Question 36

What is primary active transport?

Answer 36

Movement of a substance from low concentration/electric potential to higher, requires ATP and can be uniporters/antiporters

Question 37

What are P-type ATPases? Include examples

Answer 37

Phosphate of ATP binds to a particular aspartate to form an intermediate Examples: Na+K+-ATpase, H+K+-ATPase, Ca2+-ATPase

Question 38

What are V-type ATPases? Include function

Answer 38

H+ pumps in membranes of intracellular vacuoles which acidify the lumens Important for accumulating neurotransmitters into secretory vesicles by H+ antiports

Question 39

What are F-type ATPases (F0F1)?

Answer 39

Electron transport system derived H+ gradient transported back to mitochondrial matrix through ATP synthase

Question 40

What can ATP-binding cassette (ABC) transporters mutations result in?

Answer 40

Cystic Fibrosis Transmembrane Regulator (CFTR)

Question 41

What is the Na+/K+ ATPase pump?

Answer 41

A P-type ATPase that exchanges 3 Na+ out and 2 K+ into the cell, maintaining electrochemical gradients

Question 42

What are the three main functions of the Na+/K+ ATPase pump?

Answer 42

1. Maintaining resting membrane potential 2. Regulating cell volume 3. Enabling secondary active transport

Question 43

What is secondary active transport?

Answer 43

Coupling the down-gradient movement of solute (mainly Na+) to the up-gradient movement of another

Question 44

What are the two types of secondary active transport?

Answer 44

Symport Antiport