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MD2001 Week 7 > Molecular Movement Across Cell Membranes > Flashcards

Molecular Movement Across Cell Membranes Flashcards

1
Q

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

A

Passive and active

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2
Q

What are used to transport water across the cell membrane?

A

Aquaporins

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3
Q

What is the structure of aquaporins?

A

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

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4
Q

How many pores does an aquaporin have?

A

4

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5
Q

How many different aquaporins are there?

A

13

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6
Q

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

A

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

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7
Q

Describe the mechanism of recruiting AQP2

A

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

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8
Q

How can channels be selective?

A

Through pore diameter or charge/chemical property

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9
Q

How does facilitated diffusion work?

A

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

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10
Q

What is rate of diffusion limited by in facilitated diffusion?

A

Vmax of carrier protein

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11
Q

What are the two ion channels?

A

Voltage and chemical

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12
Q

Explain the process of the sodium channel

A

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

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13
Q

How are different channels selective?

A

Through their amino acid structure

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14
Q

Describe the structure of the potassium channel?

A

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

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15
Q

What is facilitated diffusion?

A

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

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16
Q

Why would you need active transport?

A

To move molecules up their concentration gradients

17
Q

Example of substances requiring active transport

A

Na

K

Ca

Fe

H

Cl

Iodide

Urates

Some sugars

Most amino acids

18
Q

What are the two types of active transport?

A

Primary active transport

Secondary active transport

19
Q

Describe primary active transport?

A

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

20
Q

Describe secondary active transport

A

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

21
Q

Example of primary active transport

A

Na/KATPase

22
Q

What is the structure of sodium potassium pump?

A

Globular protein with 2 subunits

23
Q

What are the three features of the sodium potassium pump?

A

Three sodium binding sites on internal side

Two potassium binding sites on external side

Internal side near sodium binding sites has ATPase acitivity

24
Q

Describe the sodium potassium pump

A

3 Na bind to inside

ATP binds

3Na are released

2 K binds

ADP leaves

2 K released inwards

25
Q

What are the functions of the sodium potassium pump?

A

Controlling cell volume

Creates an electrical potential across the membrane

Responsible for secondary active transport

26
Q

Where are Ca ATPase transporters found?

A

Cell membrane and sarcoplasmic reticulum in muscle fibres

Undergoes active transport

27
Q

Where are H ATPase transporters found?

A

Parietal cells if gastric glands and intercalated cells of renal tubules

28
Q

Example of secondary active transport

A

Sodium symporter

29
Q

Describe the sodium symporter

A

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

30
Q

What molecules use the Na symporter?

A

Bicarbonate

Glucose

Amino acid

31
Q

What are sodium antiporters?

A

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

32
Q

What molecules use the Na antiporters?

A

Calcium

Hydrogen ions

Chlorine and hydrogen for sodium and bicarbonate

MD2001 Week 7 (10 decks)

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