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Science for Medicine > Forces Acting Across the Membrane > Flashcards

Forces Acting Across the Membrane Flashcards

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Biology 101 flashcards
1
Q

What is the function of the cell membrane?

A

Acts as a selective barrier of entry/exit to the cell.

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2
Q

What does the cell membrane allow?

A

Differential distribution of ions and molecules in relevant body tissues.

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3
Q

What is the structure of a cell membrane?

A

Phospholipid bilayer.

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4
Q

Describe phospholipids.

A

Phospholipids are molecules composed of a phosphate head (ionic) which are hydrophilic and fatty acid chains which are hydrophobic.

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5
Q

What word describes the dual nature of phospholipids?

A

Amphipathic.

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6
Q

What can cross the cell membrane?

A

Small molecules.

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7
Q

Why can cell membrane permeability vary?

A

Essential for some physiological functions.

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8
Q

Why are cell membranes flexible?

A

Fatty acid chain structures in the phospholipid bilayer.

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9
Q

Why are cell membranes good insulators?

A

Can provide a balanced electrical charge which prevents passage of electrons thus maintaining electrical stability.

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10
Q

What are membrane proteins?

A

Proteins within the cell membrane- can be integral or peripheral and are often necessary for function.

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11
Q

What are membrane proteins often associated with?

A

Carbohydrates.

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12
Q

What are membrane carbohydrates?

A

Membrane carbohydrates are small amounts linked to proteins/lipids such as glycoproteins and glycolipids. They are always peripheral (extracellular) and have key role in immune system.

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13
Q

What are the 4 main functions of membrane proteins?

A

Receptors
Transporters
Enzymes
Maintaining cellular structure

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14
Q

What do cell membrane receptors do?

A

They are integral to cell function and allow the conversion of extracellular signals into intracellular responses.

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15
Q

What do cell membrane transporter proteins do?

A

Allow the transport of ions and charged molecules.

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16
Q

What are the 2 types of CM receptor protein?

A

Transport proteins

Carrier proteins

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17
Q

What do transport proteins do?

A

Create a pore through the membrane through which ions and molecules can flow through- can be open (water) or gated (ions).

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18
Q

What do carrier proteins do?

A

Do not create a continuous pore but open to ICF/ECF although not at the same time. Typically transport larger molecules (eg. Glucose)

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19
Q

What do cell membrane enzymes do?

A

Catalyse membrane reactions. Can be internal or external.

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20
Q

What do cell membrane structural proteins do?

A

These are peripheral proteins which are associated with the cell membrane but not incorporated into it. They can anchor the cell membrane both to the intracellular skeleton and to the extracellular matrix (collagen).

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21
Q

What are forces which produce ion movement driven by?

A

Concentration gradients.

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22
Q

How are electrochemical gradients created?

A

Because the ions that create concentration gradients are charged, there is a difference in the charge across the membrane. This creates an electrical gradient. The net effect of an electrical and chemical gradient creates an electrochemical gradient which drives passive movement.

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23
Q

What does movement against an electrochemical gradient require?

A

Active transport.

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24
Q

What are the 5 mechanisms of movement between compartments?

A
  1. Endocytosis / exocytosis
  2. Diffusion
  3. Mediated transport
  4. Osmosis
  5. Filtration (capillary walls)
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25
Q

What are endocytosis/exocytosis?

A

Mechanisms for the movement of macromolecules without disrupting them.

26
Q

What is endocytosis?

A

Endocytosis is the invagination of the membrane to form a vesicle which disintegrates onto the cytoplasmic surface of the membrane; releasing the macromolecular contents which then migrate.

27
Q

What is exocytosis?

A

The opposite of endocytosis.

28
Q

What is diffusion?

A

Diffusion is the movement of molecules from an area of high concentration to an area of low concentration- the gas/substance in solution will expand to fill the whole system.

29
Q

When does net movement finish in diffusion?

A

When an equilibrium is achieved.

30
Q

What must molecules be to pass through the cell membrane?

A

Small
Lipophilic (lipid-loving /hydrophobic)
Uncharged

31
Q

How can ions pass through the cell membrane?

A

Transmembrane proteins- channel or carrier.

32
Q

What do channel transmembrane proteins allow the entry of?

A

Mineral ions.

33
Q

How do channel transmembrane proteins act?

A

Typically gated- rely on stimulus to allow entry.

34
Q

What types of gated channel transmembrane proteins are there?

A

Ligand-gated

Voltage-gated

35
Q

What do chemical/electrical stimuli cause in gated channel proteins?

A

Conformational change in the configuration of the channel proteins allowing them to open/close as required.

36
Q

When is electrochemical equilibrium reached?

A

When the electrical and chemical gradients are in balance

37
Q

What is the movement using carrier transmembrane proteins called?

A

Facilitated diffusion.

38
Q

Why are carrier proteins an example of facilitated diffusion?

A

They require energy to go against the electrochemical gradient.

39
Q

How do carrier-mediated transporter systems work?

A

Carrier-mediated transport proteins have binding sites for solutes such as glucose. When they bind the solute, the carrier undergoes a change in shape which exposes the binding site on the other side of the membrane. The solute moves away and the carrier returns to its original configuration.

40
Q

What is an example of a carrier-mediated transporter?

A

NaKATPase pump.

41
Q

What is osmosis?

A

Osmosis is the net movement of water molecules from an area of high water concentration to an area of low water concentration.

42
Q

What is osmotic equilibrium disrupted by?

A

Ions.

43
Q

What is osmolarity?

A

Osmolarity is a measurement of the concentration of a solution, describing the number of particles per litre of solution.

44
Q

What is osmolarity measured in?

A

Osmoles.

45
Q

What is the normal osmolarity of human plasma?

A

285mOsmoles/L

46
Q

What does osmolarity fail to show?

A

The permeability across the membrane.

47
Q

If a solute cannot cross the membrane, what will a change in its concentration produce?

A

Osmotic flux- net movement of water which changes the volume.

48
Q

What is the volume of a cell dependent on?

A

The number of non-penetrating solutes on the extracellular side of the membrane.

49
Q

What are the non-penetrating solutes in the ECF?

A

Na+ and Cl-

50
Q

What are the non-penetrating solutes in the ICF?

A

K+

51
Q

What is tonicity?

A

Tonicity is used to describe the number of non-penetrating particles in a volume.

52
Q

Why is tonicity important in practice?

A

It determines volume.

53
Q

What does iso-osmotic mean?

A

Same total number of particles as in the extracellular fluid (plasma).

54
Q

What does hypo-osmotic mean?

A

Less particles than in the extracellular fluid (plasma).

55
Q

What does hyper-osmotic mean?

A

More particles than in the extracellular fluid (plasma).

56
Q

What does isotonic mean?

A

Same number of non-penetrating particles as in the extracellular fluid (plasma).

57
Q

What does hypotonic mean?

A

Less non-penetrating particles than ECF (plasma).

58
Q

What does hypertonic mean?

A

More non-penetrating particles than ECF (plasma).

59
Q

What happens to cells in hypotonic solution?

A

Swelling

60
Q

What happens to cells in hypertonic solution?

A

Shrink

61
Q

When should tonicity and osmolarity be considered in clinical practice?

A

Administration of intravenous fluids.

62
Q

What is the bursting of cells called?

A

Intravascular haemolysis.

Science for Medicine (19 decks)

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