Forces Across Membranes Flashcards
(91 cards)
1
Q
What can pass the cell membrane?
A
Gases - allows oxygen to enter cells and carbon dioxide to leave cells
Water
Nutrients
Waste
2
Q
What cannot pass the cell membrane?
A
Ions
3
Q
What does the cell membrane separate?
A
ECF (plasma and ISF) and ICF
4
Q
What does the capillary wall separate?
A
Plasma and ISF
5
Q
What can pass through the capillary wall?
A
Ions
6
Q
Where components have the same concentration of ions?
A
Plasma and ISF, as the capillary wall allows which separates these components is permeable to ions
7
Q
What are the concentrations of sodium, plasma proteins and potassium in plasma?
A
High Na concentration
High plasma proteins
Low K
8
Q
What are the concentrations of sodium, proteins and potassium in ISF?
A
High Na concentration
Low proteins
Low K
9
Q
What are the concentrations of sodium, proteins and potassium in ICF?
A
Low Na concentration
High proteins
High K
10
Q
What cannot pass the capillary wall?
A
Everything but plasma proteins and blood cells. This means that there are no proteins in ISF.
11
Q
Does the permeability of cell membranes vary?
A
Yes, it can increase or decrease at different times.
12
Q
Is the cell membrane dynamic?
A
Yes, it is continually being formed and maintained or dismantled and metabolised according to the needs of the cell
13
Q
What is the cell membrane composed of?
A
Bi-layer of phospholipids.
Proteins
14
Q
Describe the structure of phospholipids.
A
Phospholipids have a hydrophilic (water loving) phosphate head and a hydrophobic (water repellent) fatty acid tail.
15
Q
Describe the structure of the bi-layer of phospholipids in aqueous environments.
A
The polar, hydrophilic head is outside of the membrane where it can interact with water and that the non-polar, hydrophobic tail is situated inside, away from water.
16
Q
What is the other term we can use to describe hydrophilic?
A
Lipophobic.
17
Q
What is the other term we can use to describe hydrophobic?
A
Lipophillic
18
Q
Are cell membranes flexible?
A
Yes, because fatty acids are able to stretch. If they over stretch they can rupture, known as cell lysis.
19
Q
Are membranes insulators against movement of electrical charge?
A
Yes. This prevents the passage of electrons as they carry a negative electric charge and charged molecules, which can be important in maintaining electrical stability of the cell.
20
Q
What are membranes embedded with?
A
Proteins
Carbohydrates
21
Q
What are integral proteins?
A
Proteins that span the whole width of the membrane, which means that they are exposed to both the intracellular and extracellular sides.
22
Q
What are peripheral proteins?
A
Proteins that don’t span the whole width of the membrane and therefore exposed to only the internal side of the membrane or the external side.
23
Q
What are carbohydrates attached to in the membrane?
A
Proteins and lipids
24
Q
What are carbohydrates that are attached to proteins referred to as?
A
Glycoproteins
25
What are carbohydrates that are attached to lipids referred to as?
Glycolipids
26
What side are carbohydrates exposed to?
Extracellular side
27
What is the role of carbohydrates in the membrane?
Cell to cell communication
Self and non-self recognition by the immune system
28
What are receptor membrane proteins? What are their role? How do they carry out their role?
Receptor membrane proteins are membrane proteins that span the whole width of the membrane, which means that they are exposed to both the intracellular (ICF) and extracellular (ECF) side of the membrane.
Their role is to convert extracellular signals to an intracellular response within the cell.
Receptors are able to carry out their role due to the fact that they have a extracellular binding site that is specific to a signalling molecule (ligand). When the signalling molecule (ligand) binds to the receptor it causes the binding sites to undergo a conformational change that results in the binding site so that it fits the shape of the ligand better. Only tissues that express receptors for that particular signalling molecule can respond.
29
What are transporter membrane proteins?
They allow the movement of ions and molecules across the membrane.
30
What are the two types of transporter proteins?
Channel proteins
Carrier proteins
31
What are channel proteins?
Channel proteins create a pore through the membrane, which molecules and ions use to cross the cell membrane. They can be gated or open.
32
What are open channel proteins?
These channel proteins are open at all times, allowing their molecule to move freely across the membrane.
33
What are gated channel proteins?
Gated channel proteins are usually specific to a particular ion or molecule. They are usually closed and in order to open they require an extracellular or intracellular signal to bind to it. Gated channel proteins can either be voltage gated or ligand gated.
34
How do ligand gated channels work?
Ligand gated channels open as a result of a specific ligand binding to the channel protein’s receptor site, this binding causes the channel protein to change conformation which allows the specific molecules to pass through. This means that they are multitasking membrane proteins, as they act as both a receptor and a transporter. When the ligand unbinds from the receptor site, due to a loss of affinity, the channel protein will revert to its original conformation, where it was closed, and no molecules could pass through.
35
What are ligands usually in the form of when they bind to ligand gated channels?
Ligands are usually in the form of a neurotransmitter or a hormone.
36
How do voltage gated channels work?
Voltage gated channels open as a result of a change of voltage/ion concentration across the membrane. This voltage/ion concentration increase is as a result of a ligand channel opening, which transports an ion across the membrane. If a significant number of ions cross the membrane, in other words the voltage difference increases by a significant amount, then a voltage gate will open. The opening of one voltage gated channel results in the neighbouring channels to open, which means more molecules cross the membrane and that the voltage/ion concentration across the membrane continues to increase. This continues into depolarisation is reached, which results in the ligand gated channel that caused the depolarisation of the membrane closing, decreasing the voltage difference across the membrane. This in turn causes the voltage gated channels to close too and the membrane resulting to a stable state.
37
What is the direction of diffusion across gated channel proteins dependent on?
Concentration gradient
| Electrical gradient, in the case of charged particles
38
What is the electrochemical gradient?
The net effect of the electrical gradient and the concentration gradient can create an electrochemical gradient which ultimately drives the direction of passive moment.
The concentration and electrical gradient forces can sometimes co-operate which means that they both indicate the same direction. However, sometimes they oppose one another, which means one suggests one direction and the other suggests the opposite direction. In this case the greater gradient decides the direction.
39
What is the electrochemical equilibrium?
When the chemical and electrical gradient is equal
40
Describe the structure of carrier proteins? How do they work?
These proteins do not create a continuous pore but instead is only open/exposed to one side at a time.
When a molecule binds to the exposed binding site of the carrier protein, then the protein will change conformation and flip so that the binding site is now exposed to the other side. This change in conformation will result in the molecule’s affinity for the carrier protein decreasing, allowing it to be released.
41
What are enzymes?
Enzymes are also membrane proteins and catalyse chemical reactions on the cell membrane. Enzymes can only be exposed to one side of the membrane at a time.
42
What are internal enzymes?
Internal enzymes are those associated with converting signals carried from receptors into intracellular responses. This means that internal enzymes will have a receptor linked to them
43
What are structural proteins?What are their roles?
Structural proteins are also membrane proteins, which are always peripheral.
Structural proteins are involved in anchoring the cell membrane to the intracellular skeleton as well as the extracellular matrix (collagen). Their role is to ensure normal function of the cell and give the cell membrane support.
44
What is the protein content in cell membranes?
Membranes involved in energy transaction have the highest protein content.
Plasma membranes have the second highest protein content
Myelin has the lowest protein content. This membrane serves as an insulator around nerve fibres
45
What are the five methods used to transport molecules between compartments?
1. Endocytosis & Exocytosis
2. Diffusion
3. Mediated Transport
4. Osmosis
5. Filtration - only active method of transport
46
What molecules do endocytosis and exocytosis transport across the membrane?
Macromolecules
47
What does endocytosis involve?
There is invagination of the membrane (which is where membrane folds back on itself) to form a vesicle. This vesicle is then filled with extracellular fluid. The plasma membrane folds back on itself until the ends of the membrane meet. This traps the fluid inside the vesicle. The vesicle is then pinched off from the membrane as the ends of the membrane fuse together. This vesicle eventually disintegrates on the cytoplasmic (inside) surface of the membrane, releasing its contents which then migrate within the cell to their destination.
48
What does exocytosis involve?
Vesicles containing molecules are transported from within the cell to the cell membrane and attaches itself onto it. Fusion of the vesicle membrane with the cell membrane releases the vesicle contents outside the cell into the ECF.
49
What is diffusion?
A process where molecules spread from regions of high concentration to regions of low concentration
50
Do all molecules move from a high concentration to a low concentration in diffusion?
No, a small number of molecules bounce back through the membrane.
51
What properties of molecules are required to all them to diffuse through the lipid bilayer?
Small
Hydrophobic/Lipophillic
Uncharged
52
How do small, uncharged hydrophobic/lipophilic molecules diffuse through the lipid bilayer?
Rapidly
53
How do small, uncharged, hydrophilic/lipophobic molecules diffuse through the lipid bilayer?
Relatively quick.
54
How do large, uncharged hydrophilic/lipophobic molecules diffuse through the lipid bilayer?
More slowly
55
How do large, charged particles diffuse through the lipid bilayer?
Impermeable
56
What are aquaporins?
A specific family of channel proteins that allow water to move through the membrane. They are constantly open.
57
Why do transporter proteins not transport glucose through the cell membrane?
Glucose is too large
58
Describe the structure of channel proteins?
They are composed of several subunits. These subunits can function as binding sites for ligands, if the protein is ligand gated.
59
What is facilitated diffusion?
Passive diffusion that requires a protein.
60
Is carrier-mediated transport through carrier-proteins a passive or active process?
If electrochemical gradient favours the direction of movement, movement occurs by diffusion and no energy is required. However, If the electrochemical gradient opposes the movement, then energy (ATP) if required to move the molecule against the gradient.
61
What are protein pumps?
Transport proteins that carry out active transport.
62
What is osmosis?
The net movement of water from regions of high water concentration to regions of low water concentration.
63
What is the difference between water and other solutes?
The difference between water and other solutes is that water can move freely between cells and the ECF.
64
Is osmosis always passive?
Yes, no movements are ever active
65
How is water concentration related to the concentration of solute?
Inversely. For example, the more solute particles there are in the solution, the more they will displace water molecules and lower the concentration of water.
66
What will happen if we have a membrane that is permeable to both solute and water, and two compartments with different concentrations of solute?
Due to diffusion and osmosis, there will be equal concentrations and equal volumes of water and solute on either side of the membrane
67
What will happen if we have a membrane that is permeable to only water, and two compartments with different concentrations of solute?
You will end up with equal concentration on either side of the membrane but different volumes. This is because water will move from the lower concentrated compartment into the higher concentrated compartment.
Or osmotic pressure will be applied, which is the pressure that must be applied to oppose osmosis.
68
Does diffusion and osmosis always occur together?
No.
Where we have diffusion, we also have osmosis (water and solute move in opposite directions).
Where we have osmosis, we may or may not have diffusion
69
What is osmolarity?
Osmolarity measures the concentration of solutions in units of osmoles.
It describes the total number of particles.
70
What are osmoles?
Osmoles describes the number of particles per litre of solution.
71
What are the unites of osmoles?
osmol/l but we actually use mOsmol/l because biological solutions are so weak.
72
What is the osmolarity of 1mM solution of glucose?
1 mOsmol/L
73
What is the osmolarity of 1mM solution of NaCl?
2 mOsmol/L
74
What is the osmolarity of plasma and cells?
285 (300) mOsmol/L
75
What is cell volume dependent on?
Non-penetrating particles/tonicity. This is because if a solute cannot cross the membrane, any change in its concentration produced an osmotic flux, causing a net movement of water in one direction or the other, which changes the cell volume.
76
What are the non-penetrating molecules in ECF?
Na
| Cl
77
What are the non-penetrating molecules in ICF?
K
78
What determines osmolarity?
Non-penetrating and penetrating particles.
79
What is an isosmotic solution?
A solution that has the same total number of solute particles as normal ECF, which is 300.
80
What is a hypo-osmotic solution?
A solution with fewer total solute particles as normal ECF
81
What is a hyper-osmotic solution?
A solution with greater number of total solute particles as normal ECF.
82
What is tonicity?
The number of non-penetrating particles in solution.
83
What determines tonicity?
Non-penetrating particles
84
What is an isotonic solution?
A solution that has the same number of non-penetrating solute particles as normal ECF.
85
What is a hypo-tonic solution?
A solution with fewer non-penetrating solute particles as normal ECF
86
What is a hyper-tonic solution?
A solution with greater non-penetrating solute particles as normal ECF.
87
What is the tonicity of plasma and cell?
285 mosmol/L.
This is because most of the 285 mOsmol/L in osmolarity is due to Na and Cl, which are non-penetrating particles in ECF.
88
What do cell in hypotonic solution do? Why?
They swell, because there are fewer nonpenetrating molecules which means that more water can move into the cell. This can lead to haemolysis.
89
What do cell in hypertonic solution do? Why?
They shrink, because there are more nonpenetrating molecules which means that less water can move into the cell.
90
What happens to RBC's in water? Why?
They swell and burst, because water moves in by osmosis due to the presence of non-penetrating ions in the ICF of the cell.
91
What happens to RBC's in hyperosmotic aqueous urea solution? Why?
They swell and burst, because urea is a penetrating particle and will move into the cell until there are is an equal number of urea particles inside and out. Due to the fact that there are non-penetrating particles in addition to urea in the RBC, the water concentration remains greater outside than inside and enters by osmosis. We can also think of the idea that water needs to move in to balance the concentration of non-penetrating particles.
