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The underlying structure > Membranes and membrane transport > Flashcards

Membranes and membrane transport Flashcards

1
Q

What are the properties of the plasma membrane?

A

1- Forms the outer boundary of the cell 2- It’s selectively permeable 3- Controls the entrance of nutrients and exit of waste products. 4- Mantain the difference in concentration between the inside and the outside of the cell. 5- Particippiate in the joining of cells to form tissues and organs. 6- Allow cells to interact in different ways with the same extracellular fluid.

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2
Q

What are the three main components of the plasma membrane that form the fluid mosaic models?

A

-Phospholipid bilayer -Proteins -Carbohydrates

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3
Q

Describe phospholipids:

A

They have a phosphate group that links a substituent group to a glycerlo unit (this form the hydrophilic and polar head) and two fatty acids chains (that form the hydrophobic and nonpolar tails).

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4
Q

What happens to phospholipids in acqueous environment?

A

They thend to form a lipid bilayer.

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5
Q

What is a lipid bilyaer?

A

Is a double layer of lipid molecules with an hydrophobic inner core.

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6
Q

Describe the structure of the lipid bilayer

A

It has a trilaminar structure with the hydrophobic tails buried in teh centre of the bilayer away from water and the hydrophilic heads lined up on both sides in contact with water.

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7
Q

State the properties of the lipid bilayer:

A

1- Is fluid because phospholipids are not held togeterh by covalent bonds. 2- Cholesterlo contributes to both the fluidity and the stability of the membrane. 3- The phospholipids are constantly moving 4- The phospholipid bilayer is impermeable to charged molecules and water soluble molecules.

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8
Q

State the functions of the lipid bilayer:

A

1- It forms the basic sctructure of the plasma membrane 2- Its hydrophobic interior serves as a barrier between the inside and the outside of the cell. 3-It’s responsable for the fluidity of the membrane.

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9
Q

What are the two kinds of membrane proteins?

A

1- Integral membrane proteins 2- Peripheral membrane proteins.

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10
Q

Describe integral membrane proteins:

A

They are noncovalently embedded in the phospholipid bilayer by their hydrophobic regions.

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11
Q

What are transmembrane proteins?

A

They are integral proteins that extend through the entire thickness of the lipid bilayer one or several times.

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12
Q

Describe peripheral membrane proteins:

A

Polar molecules that don’t penetrate the membrane, instead they adhere tightly to the cytoplasmic or extracellular surface.

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13
Q

State the seven functions of membrane proteins:

A

1) Ligand Binding Receptor 2) Cell Adhesion Molecules (CAM) 3) Channels 4) Carriers and pumps 5) Membrane-bound enzymes 6) They participate to intracellular signaling 7) Docking marker acceptor

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14
Q

Describe Ligand Binding Receptor

A

Sites that recognize and bind with specific extracellular chemical messengers.

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15
Q

Describe cell adhesion molecules (CAM)

A

They can either protrude from the outer membrane surface and form hooks and loops or span the plasma membrane where they serve as structural link between the outer membrane surface and its extracellular sorroundings.

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16
Q

Why are CAMs important?

A

Because they hepl regulating cell shape, growth and differentiation and allow the cell to adapt to its immediate sorroundings.

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17
Q

What are channels?

A

Water filed pathways that serve as conduits that allow water molecules and ions to flow passively through the lipid bilayer.

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18
Q

What are carriers?

A

They can either facilitate the trnasport of a specific molecules or couple transport of a molecule with the transport of a solute

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19
Q

What is the function of membrane-bound enzymes?

A

They control specific chemical reactions.

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20
Q

What are docking marker acceptors?

A

They are located on the inner membrane surface and allow the docking of vesicles for exocytosis

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21
Q

What are the two different kinds of membrane carbohydrates?

A

Glycoproteins and glycolipids and they form the glycocalix.

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22
Q

What are the two functions of membrane carbohydrates?

A

1) They act as self identity markers that enable cells to identify and interact with one another. 2) They have a role in tissue growth and prevent cells to trespass across the boundary of neighbouring tissues.

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23
Q

What are the three different forms of cell adhesion?

A

-CAMs -Extracellular Matrix -Specialized cell junctions.

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24
Q

What are the three different type of cell junctions?

A

1) Tight junctions 2) Gap Junctions 3) Desmosomes.

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25
Q

Describe tight junctions:

A

Adjacent cells bind firmly with one another at points of direct contact to seal of the passageway betweent cells.

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26
Q

Describe desmosomes:

A

Adhering jucntions that anchor cells together.

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27
Q

What are the two units that constitute a desmosome:

A

A pair of plaques and a strong filament containing cadherin that extend across the space between the two cells attaching the plaques at both sides.

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28
Q

Describe gap junctions:

A

Comunicating junctrions that allow the movement of charge molecules between two adjacent cells.

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29
Q

What does selectively permeable means?

A

That the plasma membrane permits some particles to pass through while excluding other particles.

30
Q

What are the two properties that influence whether a particle can permeate the membrane?

A

1) Solubility of that particles to lipids. 2) Size of the molecule.

31
Q

What are the two things necessary for movement across the membrane?

A

1) Pathway 2) Driving forces

32
Q

What are driving forces?

A

Even if a particle can permeate the membrane or pass trhough a channel some force is needed to move it across the membrane.

33
Q

What are the two types of driving forces?

A

Active and passive driving forces.

34
Q

What are passive driving forces?

A

Forces that do not require cells to spend energy to produce movement.

35
Q

What are the two types of passive forces?

A

-Diffusion down a concentration gradient -Diffusion down an electrical gradient

36
Q

Describe simple diffusion:

A

Molecules within a particular species tend to evenly distributed over time.

37
Q

What happens if the membrane is permeable to a molecule

A

Molecules move down their concentration gradient (from high concentration to low concentration).

38
Q

What happens if the membrane is impermeable to a molecule

A

No diffusion takes place across the membrane even if a concentration gradient exists.

39
Q

What are the 5 parameters that affect Flick’s Law of Diffusion?

A

1) The magnitued of the concentration gradient 2) The surface of area across which diffusion takes place 3) The lipid solubility of the substance. 4) Molecular weight of the substance 5) Distance through which diffusion must take place (thickness of the membrane).

40
Q

Describe diffusion down an electrical gradient:

A

A difference in charge across two adjacent areas promotes the movements of ions toward the area with opposite charge.

41
Q

What is the electrochemical gradient?

A

Is the net effect of simultanoeus chemical and electrical gradient on the movement of ions across the membrane.

42
Q

What is osmosis?

A

The net diffusion of water down its concentration gradient through a selectively permeable molecule.

43
Q

What are aquaporins?

A

Specific channels for water located on the plasma membrane

44
Q

What is osmolarity?

A

The concentration of osmotically active particles present in a solution.

45
Q

What’s tonicity?

A

The effect that a solution has on the cell volume.

46
Q

What are the three different types of tonic condition?

A

-Isotonic -Hypotonic -Hypertonic

47
Q

Describe isotonic condition:

A

The osmolarity of the inside is equal to the osmolarity of the outside so there’s no net movement of water and no change in volume of the cell.

48
Q

Describe hypotonic condition:

A

The osmolarity of the inside is greater than the osmolarity of the outside therefore water diffuse into the cell and the cell swell.

49
Q

Describe hypertonic condition:

A

The osmolarity of the inside is lower than the osmolarity of the outside therefore water diffuse out of the cell causing the cell to shrink.

50
Q

Describe active driving forces:

A

Require cell to expend energy in the form of ATP to transport substances across the membrane.

51
Q

What are the two kinds of active driving forces?

A

-Carrier mediated transports -Vesicular transport

52
Q

Describe carrier mediated transports:

A

A carrier protein spans the thickness of the plasma membrane and undergoes specific conformational change that allow the transport of substances.

53
Q

State three aspects that affect the efficiency of these transport:

A

1) Specificty 2) Saturation 3) Competition

54
Q

Describe specificty of carrier mediated transports:

A

Each carrier is specialise to transport specific substances.

55
Q

Describe saturation of carrier mediated transports:

A

A limited number of carrier binding sites are availabel within a particular plasma membrane for a specific substance. This limit is know as the transport maximum.

56
Q

Describe compotetition of carrier mediated transports:

A

Several closelsy related compounds may compoter for the same carriers and the presence of both diminishes the rate of transfer of either.

57
Q

What are the two forms of carrier-mediated transport:

A

1) Facilitated diffusion. 2) Active transport.

58
Q

Describe facilitated diffusion:

A

It doesn’t require energy and use a carrier to facilitate the transfer of a substance down its concentration gradient.

59
Q

Describe active transport

A

It requires energy to transfer molecules against the concentration gradient.

60
Q

What are the two forms of active transport?

A

-Primary active transport -Secondary active transport

61
Q

Describe primary active transport:

A

Energy is directly required to move a substance against its concentrationg gradient.

62
Q

Describe Na+-K+ pump roles:

A

-It helps estabilish the Na+ and K+ concentration gradient across the plasma membrane. -It regulates the cell volume by controlling the concentration of solutes inside the cell. -The energy used to drive the pump indircetly serves as energy for secondary active transports.

63
Q

Describe secondary active transport:

A

Energy is required but not used directly to produce movement against concentration gradient. The transfer of a solute across the membrane is coupled with the transfer of the ion that supplies the driving force.

64
Q

What are the two distinct forms of secondary active transport?

A

Symport and Antiport.

65
Q

Describe symport:

A

Solute and Na+ move in the same direction.

66
Q

Describe antiport:

A

Solute and Na+ move in opposite directions.

67
Q

Describe vesicular transport:

A

Requires energy for vesicle formation and movement outside the cell.

68
Q

What are the two forms of vesicular transport?

A

1) Exocytosis 2) Endocytosis

69
Q

Describe endocytosis:

A

The plasma membrane pinch-off forming a membrane-enclosed vesicle so that the engulfed material is trapped within the cell.

70
Q

Describe exocytosis:

A

Membrane enclosed vesicles formed within the cells fuse with the plasma membrane releasing its content to the exterior.

The underlying structure (13 decks)

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