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BIOL 186 > Membranes > Flashcards

Membranes Flashcards

1
Q

How are lipids arranged?

A

They arrange into bilayers of phospholipids, glycolipids and cholesterol.

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2
Q

What are the two types of proteins associated with membranes?

A

Integral (between the layers) and peripheral (attached to one side)

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3
Q

Do proteins in membranes affect function? How?

A

Yes, the position and type of protein affects the function.

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4
Q

Membranes maintain fluidity even as temperatures drop. How?

A

They remain fluid due to saturated and unsaturated hydrocarbon tails that affect packing - unsaturated fats have double bonds that prevents efficient packing of molecules that leads to them being fluid at room temperature.

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5
Q

What is the fluid mosaic model?

A

The fluid mosaic model represents how proteins are organized in a mosaic that moves constantly in the fluid lipid bilayer.

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6
Q

Can proteins and lipids move?

A

Yes, they can move laterally and spin and can even flip layers (very rarely)

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7
Q

What does amphipathic mean?

A

Amphipathic describes the nature of having both hydrophilic and hydrophobic regions.

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8
Q

What holds membranes together?

A

The hydrophilic and hydrophobic regions, which are weaker than covalent bonds.

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9
Q

What are lipid rafts?

A

Lipid rafts are organized areas of proteins and lipids in the membrane that form slightly thicker. They move around the membrane, constantly dissolving and reforming.

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10
Q

Describe the ‘sidedness’ of membranes.

A

There is the cytosolic and non-cytosolic side which is always maintained - different functions occur depending on what side.

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11
Q

What are the 6 different functions of membrane proteins?

A
  1. transport, 2. enzymes, 3. signal transduction, 4. cell-cell recognition, 5. intercellular joining, 6. attachment to the cytoskeleton and ECM.
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12
Q

Describe the process of signal transduction.

A

Receptors bind signaling molecules on the extracellular side of the cell, which activate the receptors and relays information to the inside of the cell, usually making a signal transduction pathway.

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13
Q

Why do glycoproteins act as identification signals?

A

So they can be recognized by proteins on other cells as a form of short-term cell-cell interation.

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14
Q

What is an example of short term cell-cell interaction?

A

Glycoproteins as identification signals

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15
Q

What is an example of long term cell-cell interaction?

A

Intercellular joining

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16
Q

What is intercellular joining and why is it important?

A

Proteins in adjacent cells hook together, forming gap and tight junctions. It is important in multicellular organisms to maintain cell polarity and integrity.

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17
Q

What is one way multicellular organisms maintain cell polarity and integrity?

A

Through intercellular joining which forms gap and tight junctions to pass ions, molecules and particles etc.

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18
Q

How is the location of certain membrane proteins stabalized?

A

Membrane proteins attach to the cytoskeleton and ECM with the use of fibronectin.

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19
Q

What is selective permability?

A

It is the exchange of certain molecules across membranes, but only some molecules are allowed to cross.

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20
Q

What is the permeability through the lipid bilayer of hydrophobic molecules (O2, CO2) and why?

A

Since hydrophobic molecules are very small, they can easily diffuse across the membrane.

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21
Q

What is the permeability through the lipid bilayer of small polar molecules (sugar, water) and why?

A

They diffuse, but slowly because of their polarity.

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22
Q

What is the permeability through the lipid bilayer of charged molecules (Na+, K+, Ca2+, Cl-) and why?

A

Charged molecules are small but cannot diffuse through lipids because of their charges.

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23
Q

What is the permeability through the lipid bilayer of macromolecules?

A

Because macromolecules are big, they cannot easily squeeze through.

24
Q

What are transport helpers?

A

They are membrane proteins that help with the transport of particles through the lipid bilayer.

25
What form of transport helpers are channel proteins and what do they do?
Channels use passive transport to help move small polar molecules and charged molecules across the lipid bilayer.
26
What type of transport helpers are aquaporins?
They are channel proteins.
27
What form of transport helpers are carrier proteins and what do they do?
Carrier proteins use passive and active transport. Conformational change shuttles molecules across the membrane, usually specific for substrate.
28
How are macromolecules transported through the lipid bilayer?
Since they are so large, they are transported by specific processes known as endo and exocytosis.
29
What is passive transport?
Transport of molecules that requires no energy or force.
30
What is diffusion and what form of transport does it move?
Diffusion is the movement of particles down a concentration gradient that spread out into available space randomly that occurs with no force or energy so it is a form of passive transport.
31
What does it mean to move 'down' a concentration gradient?
It means to move from a high concentration of a solute to a low concentration of a solute.
32
What is osmosis?
Osmosis is the diffusion of molecules through a semi-permeable membrane from regions of low concentration of solute to areas of higher concentration of solute.
33
What is tonicity?
Tonicity is the capability of a solution to modify the volume of a cell by changing its H2O content, and occurs differently in cells with and without cell walls.
34
What is a hypertonic solution?
A hypertonic solution has a higher concentration of non-permeable solutes.
35
What is a hypotonic solution?
A hypotonic solution has a lower concentration of non-permeable solutes.
36
What happens when a cell without a cell wall is placed in a hypotonic solution?
A hypotonic solution has a lower concentration of non-permeable solutes, meaning that is has a higher concentration of H2O. This causes excess H2O to ENTER the cell and the cell becomes lysed and bursts.
37
What happens when a cell without a cell wall is placed in a hypertonic solution?
A hypertonic solution has a higher concentration of non-permeable solutes, meaning it has a higher concentration of H2O. This causes excess H2O to LEAVE the cell and the cell becomes shrivelled and dry.
38
What happens when a cell without a cell wall is placed in a isotonic solution?
It means it has the same concentration of solute inside and outside the cell so there is an equal amount of H2O exiting and entering the cell and the cell is normal.
39
What happens when a cell with a cell wall is placed in a hypotonic solution?
A hypotonic solution has a lower concentration of non-permeable solutes, meaning that is has a higher concentration of H2O. This causes excess H2O to ENTER the cell and the cell becomes turgid and stable.
40
What happens when a cell with a cell wall is placed in a hypertonic solution?
A hypertonic solution has a higher concentration of non-permeable solutes, meaning it has a higher concentration of H2O. This causes excess H2O to LEAVE the cell and the cell becomes plasmolyzed and dry.
41
What happens when a cell with a cell wall is placed in a isotonic solution?
It means it has the same concentration of solute inside and outside the cell so there is an equal amount of H2O exiting and entering the cell and the cell becomes flaccid.
42
What is facilitated diffusion?
It is diffusion via channel and carrier proteins that speeds up the transport process but does not alter the direction of transport from high to low concentration of solute so it is a form of very selective passive transport.
43
What is active transport and why is it important?
It allows the transport of solutes against the concentration gradient using ATP and allows cells to maintain solute concentrations that differ from the concentrations in their environment.
44
Describe the electrogenic pump
When there is a low concentration of Na+ in the cytosol, ATP is used to pump Na+ outside the cell where there is a high concentration of Na+ (active transport --> against gradient.) When there is a low concentration of K+ outside the cell, K+ is binded using dephosphorylation that brings K+ inside the cytosol.
45
Describe the proton pump.
The proton pump transports protons (H+) outside of the cell (up gradient) using ATP.
46
Describe the H+/Sucrose cotransporter
The cotransporter pumps H+ and sucrose into the cell, H+ is moving down its concentration gradient and sucrose is moving up its concentration gradient. It can do this with the gradient from the proton pump.
47
How are the proton pump and the H+/sucrose cotransporter related?
The proton pump moves protons up the concentration gradient outside the cell, and the H+/sucrose cotransporter is what brings the protons back in down the concentration gradient with sucrose (up).
48
Describe the process of the electrogenic pump (6 steps)
1. In the cytosol, Na+ binds, 2. Phosphorylation occurs by ATP, 3. Conformational change occurs, inside of the cell has a low affinity for Na+ so it is released outside the cell, 4. K+ binds in the extracellular fluid, 5. dephosphorylation occurs, 6. Conformational change occurs, OG shape is restored and K+ is released into the cytosol so Na+ can bind again.
49
What are the two types of bulk transport?
Exocytosis and endocytosis
50
What is exocytosis and its function?
Exocytosis is the secretion of large molecules (proteins, polysaccharides) to the extracellular side via vesicles. It is used to secrete molecules and deliver material to the plasma membrane, cell wall and ECM.
51
Why does the size of the plasma membrane stay equal during exocytosis?
Because of the equilibrium between exocytosis and endocytosis.
52
How does exocytosis contribute to the formation of the cell wall?
In plants, exocytosis secretes carbohydrates through the plasma membrane, forming the cell wall
53
What is endocytosis and its three types?
Endocytosis is the uptake of large molecules and particles via phagocytosis, pinocytosis, and receptor-mediated endocytosis.
54
What is pinocytosis?
Pinocytosis is cell-drinking, the cell takes up non-specific cell particles from the surroundings (random).
55
What is receptor-mediated endocytosis?
It is a form of endocytosis with which bulk quantities of specific particles bind to a receptor to increase the uptake of specific molecules.

BIOL 186 (17 decks)

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