Membrane proteins

Question 1

Types of membrane proteins

Answer 1

Transmembrane (integral membrane) protein
Cytoplasmic (lipid-anchored) proteins
Accessory membrane proteins

Question 2

Structure of Transmembrane protein

Answer 2

Alpha helices which contain amino acids with hydrophobic side chains (which would form a hydrophobic surface +interact with lipid bilayer)

Question 3

GPCRs

Answer 3

• Integral membrane proteins
• 7 transmembrane alpha helices
• Helices are connected by loops in extracellular/cytosolic parts

Question 4

What connects helices 5 + 6?

Answer 4

Cytosolic loop 3 - which interacts with G-proteins

Question 5

Examples of GPCR

Answer 5

M3 muscarinic, H2 histamine, CCK2 receptor

Question 6

How many GPCRs does the human genome encode?

Answer 6

More than 800

Question 7

What do GPCRs represent?

Answer 7

The largest class of molecular drug targets

Question 8

Function of GPCR

Answer 8

Drug targets
Olfactory receptors (450 - 500 GPCRs) to detect odour

Question 9

What do GPCRs bind to and what happens?

Answer 9

Bind to ligand in cell exterior + induce conformational change (in cytoplasmic face of receptor) to enable binding to G protein

Question 10

Causes inactive GPCR

Answer 10

Antagonist

Question 11

Causes active GPCR

Answer 11

Agonist

Question 12

Lipid - anchored proteins

Answer 12

Cytoplasmic proteins attach to plasma membrane by lipid anchor

Question 13

3 types of lipid modifications

Answer 13

N-myristoylation
S-palmitoylation
S-prenylation

Question 14

N-myristoylation

Answer 14

Linked using Amide bond
C14 myristic fatty acid binds to N-terminus
Irreversible
Galpha protein

Question 15

S-prenylation

Answer 15

Thioether bond to link lipid to cysteine
Near C-terminus
Irreversible
Gy protein

Question 16

S-palmitoylation

Answer 16

Thioester bond links lipid to cysteine side chains
Near N-terminus
Reversible
Galpha protein

Question 17

Types of Ion channel

Answer 17

Voltage-gated

Ligand-gated

Question 18

What controls voltage-gated?

Answer 18

Changes in membrane

Question 19

What activates Ligand-gated?

Answer 19

Binding of a ligand

Question 20

Speed of Ion channels

Answer 20

Fast - 10^7 - 10^8 ions per second

Question 21

Types of solute transporter

Answer 21

Uniporter
Antiporter
Symporter

Question 22

Uniporter

Answer 22

Transport single type of solute by passive transport

Question 23

What direction do uniporters move solute?

Answer 23

Down electrochemical gradient

Question 24

Speed of Uniporters

Answer 24

Slow - 10^2 - 10^4 molecules

Question 25

Antiporter

Answer 25

Movement of 2 solutes in the opposite directions | Need active transport

Question 26

Symporter

Answer 26

Movement of 2 solutes in the same direction | Involved in uptake of glucose by epithelial cells in intestine

Question 27

Human disease affected by SLC6A2

Answer 27

Thyroid hormone transporter, Psychomotor retardation

Question 28

Human disease affecting SLC12A1 + SLC12A3

Answer 28

Bartter syndrome, Gitelman syndrome, Kidney disorder

Question 29

Human disease affecting SLC12A6

Answer 29

Andermann syndrome, Motor + sensory neuropathy

Question 30

Types of ATP-dependent transport

Answer 30

ATP-dependent ion pumps ABC transporters Both transport against gradient

Question 31

What provides energy for ATP-dependent transport?

Answer 31

ATP hydrolysis

Question 32

Speed of ATP-dependent transport

Answer 32

Slow - 10^0 - 10^3

Question 33

Examples that use ATP Transporters

Answer 33

Cystic fibrosis - Mutation in CFTR gene encoding chloride transport Sitosterolaemia - Mutations in the ABCG5 or ABCG8 genes (sterol + cholesterol transport) Drug resistance/drug interactions - MDR1

Question 34

2 ways in classifying membrane proteins

Answer 34

Architectural - transmembrane, lipid-anchored, accessory | Functional - receptors (signalling), transmembrane transport, attachment (migration)

Question 35

What can't cross lipid bilayer

Answer 35

Water

Question 36

Example of antiporter

Answer 36

Basolateral membrane uses HCO3- to facilitate Cl- ions