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BIO353 > Chapter 12 - Transport Across Cell Membranes > Flashcards

Chapter 12 - Transport Across Cell Membranes Flashcards

1
Q

Diffusion

A

The tendency of molecules to move from areas where they are in higher concentration to areas where their concentration is lower until reaching equilibrium or minimum free energy.

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2
Q

At equilibrium, molecules are still in constant motion, but no ___.

A

Net Flow

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3
Q

The cellular membrane is a ___ structure.

A

Dynamic.

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4
Q

(T/F) Amphipathic lipids and proteins are constantly moving laterally.

A

True.

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5
Q

The dynamic structure of the cellular membrane creates opportunities for what?

A

For other compatible molecules to join or pass through.

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6
Q

Membrane Potential

A

Voltage difference across the membrane generated by the differential distribution of ions.

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7
Q

The diffusion of non-charged solutes is determined by what?

A

Its concentration gradient.

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8
Q

The diffusion of ions and other charged solutes is determined by what two ideas?

A

Concentration gradient and membrane potential.

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9
Q

Electrochemical Gradient

A

The net drive force of the concentration gradient and membrane potential.

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10
Q

Electrochemical gradient determines what?

A

The direction of solute flow in passive transport.

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11
Q

Passive Transport

A

This transport requires no energy input.

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12
Q

What are examples of passive transport (diffusion)?

A

1) Simple diffusion
2) Facilitated diffusion
3) Osmosis

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13
Q

Active Transport

A

This transport requires energy input.

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14
Q

What are the two types of active transport?

A

Primary active transport and secondary active transport.

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15
Q

Primary Active Transport

A

Requires ATP directly

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16
Q

Secondary Active Transport

A

Requires ATP indirectly

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17
Q

Vesicular Transport

A

Movement of material between organelles in the eukaryotic cell via membrane-enclosed vesicles.

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18
Q

What are the three types of vesicular transport?

A

1) Endocytosis
2) Exocytosis
3) Transcytosis

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19
Q

Endocytosis

A

Process by which cells take in material through an invagination of the plasma membrane, which surrounds the ingested material in a membrane-enclosed vesicle.

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20
Q

Exocytosis

A

Process by which most molecules are secreted from a eukaryotic cell. These molecules are packaged in membrane-enclosed vesicles that fuse with the plasma membrane, releasing their contents to the outside.

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21
Q

Transcytosis

A

A type of transcellular transport in which various macromolecules are transported across the interior of a cell. Macromolecules are captured in vesicles on one side of the cell, drawn across the cell, and ejected on the other side.

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22
Q

What is simple diffusion limited to?

A

1) small nonpolar molecules

2) small uncharged polar molecules

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23
Q

Which way do solutes moves?

A

Down the concentration gradient.

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24
Q

____ have identical permeability values in either an artificial ___ system or a ___.

A

Nonpolar molecules, lipid bilayer, biological membrane.

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25
Q

___ and ___ molecules like water, the permeability of these molecules in a biological membrane is increased by ___ or more orders of magnitude.

A

Ionic, polar, one

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26
Q

Why is the permability of ionic and polar molecules increased?

A

They are assisted by membrane transport proteins.

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27
Q

What are the two types of membrane transport proteins?

A

Transporters and channels

28
Q

Transporter Proteins

A

Change conformation and highly specific.

29
Q

Channel Proteins

A

Form tiny hydrophilic pores for diffusion.

30
Q

Carrier proteins cycle between how many conformations?

A

Three

31
Q

What are the conformations of carrier proteins?

A

1) Outward open
2) Inward open
3) Occluded state

32
Q

(T/F) With carrier proteins there is never an open channel all the way through the membrane?

A

True

33
Q

The transport rate mediated by carriers is ___ than in the absence of them, but ___ than with channels.

A

faster, slower

34
Q

A carrier transports how many solute molecules per conformational cycle?

A

One, for a few.

35
Q

A channel transport how many solute molecules per conformational cycle?

A

Many thousands of ions.

36
Q

Are carrier proteins specific?

A

Yes

37
Q

Carrier proteins often transfer only ___ type of molecule.

A

One

38
Q

What determines the specificity of the carrier?

A

Binding of the solute to the carrier binding site.

39
Q

Carrier-mediated transport can either be ___ or ___.

A

1) Passive transport (facilitated diffusion like in uniports) OR Primary active transport (pumps)
2) Secondary active transport (like in symporters and antiporters that require stored energy).

40
Q

What must carrier proteins do in order to move the solute through the membrane?

A

Undergo a shape (conformation) change.

41
Q

Carrier proteins can move either ___ or ___ specific molecules at a time.

A

One, two

42
Q

Active Transport

A

Pumps that transport solute against its electrochemical gradient (“uphill” transport)

43
Q

ATP driven pumps

A

Use energy from ATP hydrolysis directly. Also known as primary active transport.

44
Q

Coupled Pumps

A

Linked in the uphill transport of one solute to the downhill transport of another. Also known as secondary active transport.

45
Q

Where does the energy from coupled pumps come from?

A

The electrochemical potential gradient of the second solute - indirectly from ATP.

46
Q

Light-driven Pumps

A

Use energy from sunlight to drive uphill transport.

47
Q

What is the steps of an ATP-driven pump (Na+/K+)?

A

1) The pump binds 3 Na+ inside the cell
2) The pump catalyzed ATP hydrolysis and the pump is phosphorylated
3) The phosphorylation causes a conformational change that expels the 3 Na+ to the outside.
4) 2 K+ accepted from the outside.
5) Dephosphorylation triggers a conformation change - 2 K+ expelled to the inside, restores the initial conformation and the pump allowing a new pumping cycle to begin.

48
Q

Na+/K+ pump establishes a electrochemical gradient that can be used for what?

A

Secondary active transport or ATP biosynthesis.

49
Q

What is the steps of a coupled pump (glucose/Na+)?

A

1) Two conformation: “outward open” and “inward open” via occluded state.
2) Occluded state can only be reached when both glucose and Na+ or neither is bound.
3) The binding of the two solutes is cooperative - binding of one enhances the binding of the other.
4) Both molecules must bind for coupled transport to occur.
5) The steep electrochemical gradient of Na+ established by the Na+/K+ pump drives Na+ to move into the cell down its gradient and into the processes “dragging” glucose into the cell with it.

50
Q

Channel Proteins

A

Trans-membrane proteins that function as selective pores through which ions and sometimes non-ionic molecules can diffuse across the membrane.

51
Q

For channel proteins, is transport through the channels active or passive?

A

Passive

52
Q

Are channel proteins selective?

A

Yes, only certain ions can pass through.

53
Q

What two characteristics determine if a molecule can pass through a channel protein?

A

The size of the pore and the electric charge of the amino acid residue that line the pore determine its transport specificity.

54
Q

What are some external signals that would cause a channel protein to open or close?

A

Membrane potential, ligands, hormones, light, and phosphorylation.

55
Q

Osmosis

A

(Passive) Diffusion of water through membranes.

56
Q

Water can pass through the membrane ___ via simple diffusion.

A

Slowly

57
Q

Water is also transported by the ___ via facilitated diffusion.

A

Channel Protein (aquaporin)

58
Q

(T/F) Aquaporin has a selectivity filter.

A

True.

59
Q

Water transport is always ___ - from high water concentration to low water concentration.

A

Passive.

60
Q

Can a Na+ ion pass through a K+ channel?

A

No, Na+ ion is to small to pass through a K+ channel.

61
Q

What is specificity governed by for ion channels?

A

Diameter, shape, and the distribution of the charged and polar amino acids that line it.

62
Q

Homotetrameric protein

A

a protein complex made up of four identical subunits which are associated but not covalently bound. A heterotetramer is a 4-subunit complex where one or more subunits differ.

63
Q

Does a homotetrameric protein have a selectivity filter?

A

Yes, at its most narrow part.

64
Q

What is does the selectivity on a homotetrameric protein do?

A

1) Forces the shedding of water molecules surrounding the ion.
2) Forces ions into contact with the channel wall.
3) The interactions of the ion and the amino acid side chains of the wall will decide - only the ions with appropriate size and charge (most favorable free energy) are allowed to pass through in single file.

65
Q

In which direction does passive transport flow?

A

Down the electrochemical gradient.

66
Q

What are examples of facilitated diffusion?

A

Carrier or channel proteins.

67
Q

What are 5 functions of membranes?

A

1) Define boundaries and serves as permeability barriers.
2) Sites of specific functions.
3) Regulate the transport of solutes.
4) Detect and transmit electrical/chemical signals.
5) Mediate cell-cell communication and tissue formation.

BIO353 (8 decks)

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