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Physiology, Pharmacology and Neuroscience > Lecture 2 > Flashcards

Lecture 2 Flashcards

1
Q

What is facilitated diffusion? What does it enable? Give an example.

A

Transmembrane transport mediated by proteins. It enables movement of membrane impermeable solutes across membranes (e.g. ions, large molecules).

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2
Q

What is facilitated diffusion used for?

A

Regulation of solute flow across the membrane.

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3
Q

What are the main differences between facilitated diffusion and simple diffusion? (2)

A

Both are passive but facilitated diffusion can be saturated whereas simple diffusion depends linearly on solute concentration.
Also, facilitated diffusion is more temperature dependent than simple diffusion.

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4
Q

What is the water permeability (um/s) of:
Artificial lipid bilayer
Cell membranes

A

Artificial lipid bilayer = <1 to 100

Cell membranes = 0 to 600

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5
Q

Where in the body has low water permeability?

A

Ascending loop of henle (especially the thick limb)

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6
Q

Where in the body has high water permeability?

A

Red blood cells, renal proximal-tubule cells

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7
Q

What does water permeability depend on?

A

Lipid composition:
High fluidity phospholipids are more permeable to water.
Sterol content (e.g cholesterol) decreases fluidity and water permeability.

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8
Q

What are aquaporins and where are they found?

A

Water pores. They are widespread throughout the body.

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9
Q

What is the common structure of an aquaporin?

A

It is a transmembrane protein that consists of four subunits which makes it a tetrameric protein. Each subunit has 6 alpha-helical transmembrane regions.

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10
Q

What is the transport rate of Aquaporins?

A

Fast - up to 10^9 molecules/sec

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11
Q

What is the diameter of a pore compared to the diameter of a water molecule?

A

Pore diameter = around 2.8 Angstrom

Water molecule diameter = around 2.75 Angstrom

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12
Q

Name a specialised type of aquaporin.

A

Aquaglyceroporin.

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13
Q

What can modulate the permeability of an aquaporin?

What else can also affect water transport rate?

A

pH

The number of channels.

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14
Q

What is the function of Ion channels and where are these found?

A

Ion channels allow ions to cross the membrane and these are found in all cell types and are highly diverse (more than 300 have been cloned)

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15
Q

What ions do Ion channels specify in?

A

Ion channels can be highly selective (e.g. sodium channel) or more general (e.g. non-selective cation channels)

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16
Q

What determines where the ions enter/exit the ion channel?

A

Direction of movement is determined by the electrochemical gradient.

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17
Q

Do ion channels remain open? If not, what does this enable.

A

Ion channels are gated and have two states - open and closed. This enables control of ion movements.

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18
Q

What are ion channels gated by?

A

Membrane voltage, extracellular messengers, intracellular messengers and mechanical stress.

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19
Q

What are the differences/similarities between ion channels and solute carriers.

A

Both allow facilitated diffusion (passive transport), but ion channels have a central pore and solute carriers undergo conformational change.

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20
Q

Give an example of a solute carrier and explain how it works.

A

Glucose transporter.
Glucose binds to transporter, the protein undergoes a conformational change and glucose is released on the opposing side.

21
Q

What drives passive transport? Why is this important?

A

Concentration gradient.
This is important because cells have to be able to transport solutes against concentration gradient to maintain gradients, this requires energy.

22
Q

What are the two forms of active transport?

A

Primary active transport and Secondary active transport.

23
Q 
How much of the following are in the extracellular fluid?
Sodium
Potassium
Chlorine
Calcium
A 
Sodium = 135-147
Potassium = 3.5-5
Chlorine = 95-105
Calcium = 1.1-1.4
24
Q 
How much of the following are in the intracellular fluid?
Sodium
Potassium
Chlorine
Calcium
A 
Sodium = 10-15
Potassium = 120-150
Chlorine = 20-30
Calcium = around 10^-7
25
Q

How does primary active transport work?

A

It uses hydrolysis of ATP to generate energy for transport (ATP-dependent transporters [pumps])

26
Q

Name the two categories of primary active transporters.

A

ATPase ion transporters and ATP-binding cassette (ABC) transporters.

27
Q

What are the subtypes of ATPase ion transporters?

A

P-type, V-type and F-type.

28
Q

Give an example of a P-type ATPase ion transporter and explain how it works.

A

Examples are sodium/potassium-ATPase, hydrogen/potassium-ATPase and hydrogen/calcium-ATPase.

ATP hydrolysis leads to phosphorylation causing conformational change.

29
Q

Give an example of a V-type ATPase ion transporter and explain what it does.

A

An example is vaculolar-type hydrogen-ATPase.

These are highly complex (up to 14 subunits) and contribute to the set-up of pH gradients.

30
Q

Give an example of a F-type ATPase ion transporter and explain what it does.

A

An example is F-ATPase or ATP synthase (mitochondria).

These use the proton gradient for ATP synthesis.

31
Q

What is the sodium/potassium-ATPase pump and what does it do?

A

It is a complex transmembrane protein with 4 main domains.

This is a transport mechanism that maintains the sodium/potassium gradient.

32
Q

What are the four main domains of the sodium/potassium-ATPase pump?

A

N - nucleotide (ATP) binding domain
P - phosphorylation domain
A - actuator domain (involved in conformational changes)
M - transmembrane domain.

33
Q

Give some examples of molecules that use ABC transporters.

A

Chlorine, cholesterol, bile acids, drugs, iron, organic anions.

34
Q

What are the common features on ABC transporters?

A 
ATP-binding cassette (ABC)
Usually homodimer (2 identical subunits)
Each subunit consists of - a transmembrane domain and a nucleotide binding domain.
35
Q

What is the ABC transporters mode of action?

A

Open dimer has a high ligand affinity.
This means that the ligand binding increases ATP affinity and ATP-binding.
This leads to a conformational change and this reduces ligand affinity and the ligand is released.
ATP hydrolysis and release and it returns to open configuration.

36
Q

What are the two types of co-transport?

A

Symporters, where both solutes are transported in the same direction.
Antiporters, where solutes are transported in opposite directions.

37
Q

Explain co-transport and secondary active transport.

A

Movement of solute A down its electrochemical gradient can be used to drive co-transport of solute B against its electrochemical gradient. This is not directly coupled to ATP hydrolysis.

38
Q 
What is the transport rate of the following (molecules/s)?
Water channel (pore [gated])
Ion channel (gated)
Solute carrier (cycle)
ATP-dependent (cycle)
A 
Water channel (pore [gated]) = up to 10^9 
Ion channel (gated) = 10^6 to 10^8
Solute carrier (cycle) = 10^2 to 10^4
ATP-dependent (cycle) = 10^2 to 10^4
39
Q

What types of vesicular transport is there in Endocytosis?

A

Pinocytosis and Phagocytosis.

40
Q

What does Pinocytosis transport and where does it happen?

A

It’s non-specific and transports small molecules and water.

It is prominent in endothelial cells.

41
Q

What does Phagocytosis transport and where is it important?

A

It transports large particles such as bacteria and cell debris. It is important in macrophages and neutrophils but is relatively non-specific.

42
Q

What does receptor-mediated endocytosis involve/require?

A

It involves membrane-bound receptors and that makes it more specific that pino/phagocytosis. It also requires various proteins, such as Adaptin, Clathrin and Dynamin (GTPase).

43
Q

What types of vesicular transport is there in Exocytosis?

A

Constitutive and Regulated.

44
Q

What happens during Exocytosis?

A

Molecules are packaged into vesicles and fusion with the membrane releases content.

45
Q

What happens during constitutive exocytosis?

A

Immunoglobulin secretion and collagen secretion.

46
Q

What happens during regulated exocytosis?

A

Hormones, neurotransmitters and digestive enzymes are released.

47
Q

What is Transcytosis, what is it used for?

Give an example.

A

Endocytosis followed by exocytosis for transport of material across epithelia.
E.g. - IgA (Immunoglobulin A) secretion across lung epithelia.

48
Q

What are the steps of IgA (Immunoglobulin A) secretion across lung epithelia?

A

1 - Binding of IgA to receptor on basolateral face of epithelial cell.
2 - Endocytosis
3 - Transport to apical face of epithelial cell
4 - Release of IgA dimer at apical face of epithelial cell.

Physiology, Pharmacology and Neuroscience (3 decks)

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