Molecular Movement Across Cell Membranes

Question 1

What are the two ways to transport molecules across the cell membrane?

Answer 1

Passive and active

Question 2

What are used to transport water across the cell membrane?

Answer 2

Aquaporins

Question 3

What is the structure of aquaporins?

Answer 3

6 transmembrane alpha-helices with a tri-amino motif of asparagine-proline-alanine

Question 4

How many pores does an aquaporin have?

Answer 4

4

Question 5

How many different aquaporins are there?

Answer 5

13

Question 6

How does ADH (arginine vasopressin) increase water absorption in the kidneys?

Answer 6

By increasing the up-regulation of AQP2 channels in the epithelial cells of the late distal tubules, collecting ducts and collecting tubules

Question 7

Describe the mechanism of recruiting AQP2

Answer 7

ADH binds to the G protein receptor, this then activated cAMP within the cell

This then activated protein kinase which phosphorylates the AQP2 recruiting them to the cell membrane

Question 8

How can channels be selective?

Answer 8

Through pore diameter or charge/chemical property

Question 9

How does facilitated diffusion work?

Answer 9

Transported molecule binds causing a conformational change allowing it to be released into the cell

Question 10

What is rate of diffusion limited by in facilitated diffusion?

Answer 10

Vmax of carrier protein

Question 11

What are the two ion channels?

Answer 11

Voltage and chemical

Question 12

Explain the process of the sodium channel

Answer 12

Sodium channels are lined with negatively charged amino acids that pull the sodium through the channel

Question 13

How are different channels selective?

Answer 13

Through their amino acid structure

Question 14

Describe the structure of the potassium channel?

Answer 14

Carbonyl oxygens strip water molecules from the potassium molecule so it can pass through the channel

Question 15

What is facilitated diffusion?

Answer 15

Molecules moving down their concentration gradients with the help from another molecule, usually integral proteins

Question 16

Why would you need active transport?

Answer 16

To move molecules up their concentration gradients

Question 17

Example of substances requiring active transport

Answer 17

Na

K

Ca

Fe

H

Cl

Iodide

Urates

Some sugars

Most amino acids

Question 18

What are the two types of active transport?

Answer 18

Primary active transport

Secondary active transport

Question 19

Describe primary active transport?

Answer 19

Molecules are “pumped” against an electrochemical gradient at the expense of energy (ATP)

Question 20

Describe secondary active transport

Answer 20

Transport is driven by the energy stored in the electrochemical gradient of another molecule that was already pumped into/out of the cell using active transport

Question 21

Example of primary active transport

Answer 21

Na/KATPase

Question 22

What is the structure of sodium potassium pump?

Answer 22

Globular protein with 2 subunits

Question 23

What are the three features of the sodium potassium pump?

Answer 23

Three sodium binding sites on internal side

Two potassium binding sites on external side

Internal side near sodium binding sites has ATPase acitivity

Question 24

Describe the sodium potassium pump

Answer 24

3 Na bind to inside

ATP binds

3Na are released

2 K binds

ADP leaves

2 K released inwards

Question 25

What are the functions of the sodium potassium pump?

Answer 25

Controlling cell volume Creates an electrical potential across the membrane Responsible for secondary active transport

Question 26

Where are Ca ATPase transporters found?

Answer 26

Cell membrane and sarcoplasmic reticulum in muscle fibres Undergoes active transport

Question 27

Where are H ATPase transporters found?

Answer 27

Parietal cells if gastric glands and intercalated cells of renal tubules

Question 28

Example of secondary active transport

Answer 28

Sodium symporter

Question 29

Describe the sodium symporter

Answer 29

Due to the electrochemical gradient created by the Na/KATPase, sodium and a second molecule bind to the symporter and both are transported into the cell

Question 30

What molecules use the Na symporter?

Answer 30

Bicarbonate Glucose Amino acid

Question 31

What are sodium antiporters?

Answer 31

When sodium comes into the cell through the concentration gradient, another molecule leaves

Question 32

What molecules use the Na antiporters?

Answer 32

Calcium Hydrogen ions Chlorine and hydrogen for sodium and bicarbonate