B2.1 Membrane Proteins & their functions

Question 1

What are the definitions of hydrophobic and hydrophilic?

Answer 1

Hydrophobic = does not mix with water. Hydrophilic = does mix with water.

Question 2

How does insulin affect specific cell types?

Answer 2

Insulin will only interact with cells which have a surface receptor for insulin.

Question 3

What is the structure of a lipid bilayer?

Answer 3

Sheet-like bilayers formed by amphipathic lipids in water.

Question 4

What is selective permeability in the context of lipid bilayers?

Answer 4

The ability of the lipid bilayer to regulate the movement of substances.

Question 5

What is the role of aquaporins?

Answer 5

Transporting water across cell membranes.

Question 6

What are the two main types of membrane proteins?

Answer 6

• Integral proteins
• Peripheral proteins

Question 7

What is the fluid mosaic model?

Answer 7

A model describing the structure of membranes with integral and perpheral proteins embedded in a fluid lipid bilayer.

Question 8

Describe the permeability of membranes.

Answer 8

Dependent on the size and hydrophobic nature of molecules.

Question 9

What is simple diffusion?

Answer 9

The movement of small molecules like oxygen and carbon dioxide directly through the lipid bilayer.

Question 10

What are integral proteins?

Answer 10

Transmembrane proteins that are embedded through both layers of the membrane.

Question 11

What are peripheral proteins?

Answer 11

Proteins that do not span the membrane and are located on its surface.

Question 12

What is osmosis?

Answer 12

The movement of water from a region of higher water potential to lower potential

Question 13

What is facilitated diffusion?

Answer 13

The process allowing polar or large molecules to pass through membranes via channel or carrier proteins.

Question 14

What is the difference between active transport and passive transport?

Answer 14

Active transport requires energy to move substances against their concentration gradient.
* ATP
* against concentration gradient
* transport proteins

Question 15

What is endocytosis?

Answer 15

The process where the cell membrane engulfs material to form a vesicle.

Question 16

What is exocytosis?

Answer 16

The process where vesicles fuse with the cell membrane to release contents outside the cell.

Question 17

What are gated ion channels?

Answer 17

Channels that open or close in response to stimuli, allowing specific ions to pass.

Question 18

What are cell-adhesion molecules (CAMs)?

Answer 18

Glycoproteins that mediate the binding of cells to each other.

1) Continuous transport
2) structural support

Question 19

What are the two types of active transport?

Answer 19

• Direct active transport
• Indirect active transport (cotransport)

Question 20

What factors affect membrane fluidity?

Answer 20

• Fatty acid composition
• Presence of cholesterol

Question 21

What are the three types of cell junctions found in animals?

Answer 21

• Adhesive junctions -> structure (epithelial)
• Tight junctions -> seal for contnuous transport
• Gap junctions -> movement of molecules

Question 22

What are the main components of biological membranes?

Answer 22

• Lipids
• Proteins
• Small amounts of cholesterol

Question 23

What is an example of direct active transport?

Answer 23

Sodium–potassium pumps

Question 24

What is an example of indirect active transport?

Answer 24

Sodium-dependent glucose cotransporters

Question 25

Voltage gated ion channels

Answer 25

**Nerve signalling** 1. stimulus causes temporary reversal in pot. diff. = action potential 2. voltage-gated sodium channel opens = defuse = depolarisation (less -) 3. VGSC opens = diffuse = repolarisation (more -) 4. Treshold value = gate closes 5. channel inactivation = particle blcosk opening = prveents reopening

Question 26

Role of cholesterol in membrane

Answer 26

* stuffens & reduces lateral movement = less fluidity * at high temp = stabilises * at low temp = prevents fatty acid chains form coming close (cant become solid)

Question 27

Use of active transport

Answer 27

* uptake of glucose & AA in small intestine * excretion of H+ & urea * absorption of mineral ions by plant roots

Question 28

Ligand gates channels - Nicotonic Acetyl choline receptor

Answer 28

* binding creates conformational change => channel opens * sodium diffuses down conc grad. = depolarisation = enzyme cholinestrase breaks down acetylcholine => channel close Nictoine can activate this

Question 29

Difference between direct vs indirect sodium potassium pump

Answer 29

Direct = in cell membrane & generates energy + 3Na & 2K bidnign sites Indirect = two way solute transport

Question 30

Indirect sodium potassium pump

Answer 30

1. Na+ bind to bidning site on oiter surface 2. simultaneously glucose molecule binds on cotransporter 3. conformational change => transports both inside

Question 31

Direct sodium potassium pump

Answer 31

1. Pump opens to inside = Na+ binds 2. Bond triggers ATP hydrolysis =>attaches => conformational change to outside facing 3. pump releases Na+ to exterior 4. 2 x K+ bind & phosphate latter detaches 5. conformational change back to original form

Question 32

cholesterol function (2)

Answer 32

* membrane fluidity * membrane permeability

Question 33

factors affecting diffusion

Answer 33

* temperature * concentration gradient * composition of molecule * surface area * distance of diffusion pathway

Question 34

function of membrane proteins

Answer 34

* cell recgnition = glycoproteins * transport = carrier/transport proteins * receptors / binding site for neurotransmitter * immobilise enzymes * cell adhesion

Question 35

sodium dependnet glucose cotransporter

Answer 35

* absorption of glucose into small intestine * reabsorption of glucose in nephron

Question 36

Indirect active transport

Answer 36

Transport of two solutes where one goes down its concnetration gradient to be able to move the other against its concnetration gradient