[FMS] CBS - membrane transport

Question 1

what 4 characteristics must molecules have to freely cross the membrane by simple diffusion

Answer 1

Small
Uncharged
Hydrophobic
Non-polar

Question 2

what molecules require specialist proteins to allow them to cross the membrane

Answer 2

charged polar molecules

Question 3

give 5 examples of what hydrophobic molecules can pass through the membrane via simple diffusion

Answer 3

O2
N2
CO2
BENZENE
SHORT CHAIN FATTY ACIDS

Question 4

give 3 examples of small uncharged polar molecules that can pass through the membrane via simple diffusion

Answer 4

H2O
UREA
GLYCEROL

Question 5

what large, uncharged polar molecules can pass through the membrane

Answer 5

glucose
sucrose

Question 6

what are the 5 transport mechanisms

Answer 6

1. simple passive transport/diffusion
2. facilitated diffusion
3. gated ion channels
4. primary active transport
5. secondary active transport

Question 7

what is passive transport

Answer 7

down concentration gradient

Question 8

in passive transport what does the diffusion rate depend on?

Answer 8

diffusion rate depends on Partition Coefficient Solute

Question 9

what does a high Partition Coefficient mean? what kind of molecule has a high Partition Coefficient?

Answer 9

Solutes that are more hydrophobic have a higher Partition Coefficient and
equilibrate more quickly

Question 10

what is facilitated diffusion/carrier-mediated diffusion

Answer 10

down concentration gradient

Question 11

what does facilitated diffusion/carrier-mediated diffusion need? give 3 examples

Answer 11

membrane protein required (ion channel) like:

• aquaporin: water channel
• GLUT glucose transporters
• Cl-/HCO3- channel in erythrocytes

Question 12

the transporter affinity for a solute is given by the?

Answer 12

Km

**LOWER Km ** = **HIGHER affinity **

Question 13

where is GLUT1 transporter found?

Answer 13

high in erythrocytes, low in
skeletal muscle

Question 14

where is GLUT2 transporter found?

Answer 14

Liver, pancreatic ßcells

Question 15

where is GLUT3 transporter found?

Answer 15

Neurones

Question 16

where is GLUT4 transporter found?

Answer 16

Muscle, Adipocytes

Question 17

what is the function of GLUT1

Answer 17

Low Km (high affinity).

Mediates glucose uptake in many tissues.

Question 18

what is the function of GLUT2

Answer 18

High Km (low affinity)

Transports glucose into
hepatocytes and pancreatic ß-cells when blood is high to regulate blood glucose levels.

Question 19

does GLUT3 have a high or low Km

Answer 19

Low Km (high affinity)

Question 20

high insulin levels indicate a high level of which GLUT transporter? 1,2,3,or 4

Answer 20

GLUT 4

Question 21

what do gated ion channels do?

Answer 21

• allows facilitated diffusion selective for different ions
• exemplar ions: K+, Na+, Ca2+

Question 22

2 types of gated ion channels

Answer 22

ligand-gated
e.g. acetylcholine and acetylcholine-gated Na+/K+ channel (acetylcholine receptor) on postsynaptic membranes

voltage-gated
e.g. Na+ and K+ channels in axons involved in nerve transduction in axons

Question 23

what is active transport?

Answer 23

Solutes move against a concentration gradient

Question 24

what 2 things does active transport require

Answer 24

membrane protein

energy via the hydrolysis of ATP

Question 24

give an example of primary active transport

Answer 24

Na+/K+ pump

Question 24

what is primary active transport?

Answer 24

needs energy from ATP hydrolysis

Question 24

Describe the NA+/K+ pump, what goes in and what goes out

Answer 24

2K+ IN 3NA+ OUT

Question 25

what does the Na+ /K+ pump consist of?

Answer 25

tetramer (α2β2)

Question 26

what is a co-transport system?

Answer 26

Pre-established gradient that's used to drive transport of solute across membrane gainst a gradient

Question 27

what is used to establish the primary gradient in co-transport systems?

Answer 27

ATP hydrolysis

Question 28

2 types of cotransport systems

Answer 28

Symport Antiport

Question 29

what is symport

Answer 29

transport of two solutes in the **same direction** **S**ymport = **S**ame

Question 30

what is antiport

Answer 30

transport of two solutes in opposite direction Antiport = Anti = Opposite

Question 31

what is uniport?

Answer 31

transport of ONE (uni) solutes in ONE direction

Question 32

what kind of cotransport system is SGLUT?

Answer 32

symport

Question 33

What's an example of an antiport cotransport system?

Answer 33

Na+/Ca2+

Question 34

what process is used to drive ca2+ export from cells in Na+/Ca2+ cotransporter

Answer 34

ATP hydrolysis

Question 35

Describe the NA+/Ca+ cotransporter, what goes in and what goes out

Answer 35

NA+ IN CA2+ OUT

Question 36

what does digitoxin do?

Answer 36

- inhibit Na+/K+ pump by **blocking dephosphorylation step** - [Na+] inside heart muscle increases - Na+ gradient lost - export of Ca2+ via **antiport does not happen** - [Ca2+] inside heart muscle increases and contraction increases - tachycardia

Question 37

what does oubain do?

Answer 37

- inhibit Na+/K+ pump by **blocking binding of K+** - [Na+] inside heart muscle increases - Na+ gradient lost - export of Ca2+ via **antiport does not happen** - [Ca2+] inside heart muscle increases and contraction increases - tachycardia

Question 38

What causes Cystic Fibrosis?

Answer 38

- reduced chloride transport - production of thick mucus - no movement of chloride ions means movement of water is not regulated

Question 39

what is CFTR

Answer 39

transmembrane protein Chloride ions move by facilitated diffusion down concentration gradient – out of cell ATP-gated ion channel ABC (ATP-binding cassette) transporter family Cytoplasmic regulatory domain is phosphorylated by cyclic AMP dependent protein kinase (PKA) PKA activates and opens channel

Question 40

what does chloera toxin stimulate

Answer 40

Cholera toxin **stimulates increase in cAMP** level that **activates CFTR and secretion of chloride ions** **Na+ and water follow into lumen of via osmosis** and the paracellular route

Question 41

what does Vibrio cholerae cause

Answer 41

electrolyte and fluid secretion

Question 42

how to treat chloera

Answer 42

**Oral rehydration** therapy includes **high glucose concentration** which drives Na+ (and consequently Cl- and H2O) uptake into cells via **SGLUT**

Question 43

which GLUT transporter facilitates the transport of glucose into beta cells

Answer 43

GLUT2

Question 44

how is insulin secreted by beta cells, outline the events

Answer 44

1. glucose transported into beta cells through facilitated diffusion by **GLUT2** 2. metabolized glucose increases ATP level 3. increases level of ATP/ADP ratio induces closure of cell-surface ATP-sensitive K+ (K-ATP) channels, leading to cell membrane depolarization 4. Voltage-gated Ca2+ channels are opened, intracellular [Ca2+] increases 5. Increase in [Ca2+] triggers the exocytosis of insulin stored in vesicles

Question 45

do keats quiz on membrane transport

Answer 45

https://keats.kcl.ac.uk/mod/quiz/view.php?id=6701135

Question 46

what is the Ion gradient of [Na+] and [K+] across plasma membrane (in cells vs blood plasma)

Answer 46

Question 47

Membranes are ____ permeable barriers that block passage of almost all ___ molecules

Answer 47

Selectively, hydrophillic

Question 48

summarise 1 example of primary active transport, and 2 examples of secondary active transport

Answer 48

Question 49

whats the difference between primary and secondary active transport

Answer 49

PRIMARY = uses energy from ATP hydrolysis SECONDARY = uses energy stored in concentration gradient of ions

Question 50

where does: diffusion facilitated diffusion primary active transport and secondary active transport get its **energy** from to drive the process

Answer 50

diffusion = kinetic energy of molecules facilitated diffusion = kinetic energy of molecules + the assistance of transport proteins, primary active transport = ATP hydrolysis secondary active transport = energy stored in electrochemical gradients established by primary active transport or other cellular processes.