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Biology > 5.1-5.5 Plasma membranes > Flashcards

5.1-5.5 Plasma membranes Flashcards

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1
Q

What does the cell surface membrane do?

A

It separates the cell from its external environment.
Regulate transport of substances

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2
Q

What is another name for cell surface membrane?

A

Plasma membrane

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3
Q

What is the structure of a membrane called?

A

Phospholipid bilayer

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4
Q

How would you describe the structure of a phospholipid bilayer?

A

Hydrophilic phosphate heads form both the outer and inner surface of a membrane. Hydrophobic core inside the membrane

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5
Q

What is the fluid mosaic model?

A

A model proposed by Singer and Nicolson in 1972 which they built upon an earlier lipid-bilayer model in which proteins occupy various positions in the membrane. Phospholipids are free to move within the layer relative to each other, flexible membrane.

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6
Q

What are the two types of membrane proteins?

A

Intrinsic (integral) and extrinsic (peripheral)

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7
Q

Describe intrinsic proteins.

A

Transmembrane proteins that are embedded through both layers of a membrane. They have amino acids with hydrophobic R-groups on their external surfaces, which interact with the hydrophobic core of the membrane, keeping them in place.

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8
Q

Name 2 proteins that are intrinsic proteins

A

Channel and carrier

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9
Q

What are channel proteins?

A

They provide a hydrophilic channel that allows the passive movement of polar molecules and ions down a concentration gradient through membranes.

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10
Q

What are carrier proteins?

A

They help with passive transport (down a concentration gradient) and active transport (against a concentration gradient) . This involves the shape of the protein changing.

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11
Q

What are glycoproteins

A

They are intrinsic proteins that are embedded in the cell-surface membrane with attached carbohydrate chains.
They play a role in cell adhesion and as receptors for chemical signals.

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12
Q

How do receptors work in glycoproteins?

A

When the chemical binds to the receptor, it makes a response from the cell which causes a direct response or set off a cascade of events (cell communication/signalling)

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13
Q

What are glycolipids?

A

They are lipids with attached carbohydrate chains. These molecules are called cell markers or antigens and can be recognised by the cells of the immune system.

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14
Q

What are extrinsic proteins?

A

Proteins that are only present on one side of the bilayer, normally have hydrophilic R-groups on their outer surfaces and interact with the polar heads of the phospholipids or with intrinsic proteins.

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15
Q

Describe the meaning of fluid mosaic model.

A

Fluid: phospholipid bilayer in which individual phospholipids can move = membrane has flexible shape.
Mosaic: extrinsic and intrinsic proteins of different sizes and shapes are embedded

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16
Q

Explain the role of cholesterol

A

Steroid molecule in some plasma membranes; connects phospholipids and reduces fluidity to make bilayer more stable

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17
Q

Explain the function of extrinsic proteins

A

Binding sites/ receptors e.g. for hormones and drugs
Antigens
Bind cells together
Involved in cell signalling

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18
Q

Explain the function of intrinsic proteins

A

Electron carriers (respiration/photosynthesis)
Channel proteins (facilitated diffusion)
Carrier proteins (facilitated diffusion/active transport)

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19
Q

What is the function of membranes

A

Provide internal transport system
Selectively permeable to regulate passage of molecules into / out of organelles
Provide reaction surface
Isolate organelles from cytoplasm for specific metabolic reactions.

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20
Q

What are the three factors that affect membrane permeability

A

Temperature, pH, use of a solvent

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21
Q

How does temperature affect membrane permeability

A

High temperature denatures membrane proteins/phospholipids molecules have more kinetic energy and move further apart

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22
Q

How does pH affect membrane permeability

A

Changes tertiary structure of membrane proteins

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23
Q

How does the use of a solvent affect membrane permeability

A

It may dissolve the membrane

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24
Q

How could colorimetry be used to investigate membrane permeability

A
  1. Use plant tissue with soluble pigment in the vacuole. Tonoplast and cell-surface membrane disrupted so there is an increase of permeability and pigment diffuses into solution.
  2. Select colorimetry filter with complementary colour.
  3. Use distilled water to set colorimeter to 0. Measure absorbance/% transmission value of solution.
  4. High absorbance/ low transmission =more pigment in solution
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25
Q

What is osmosis

A

Water diffuses across semi-permeable membranes from an area of higher water potential to an area of lower water potential until a dynamic equilibrium is established.

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26
Q

What is water potential

A

Pressure created by water molecules measured in kPa

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27
Q

What is cholesterol

A

Is a lipid with a hydrophilic end and a hydrophobic end (like a phospholipid) and regulates the fluidity of membranes

28
Q

What is compartmentalisation

A

Formation of separate membrane-bound areas in a cell.

29
Q

State 1 difference between intrinsic and extrinsic proteins with examples

A

Intrinsic protein - embedded in both sides of the bilayer (channel and carrier proteins)
Extrinsic protein - embedded in one side of the bilayer (glycoprotein/ enzyme)

30
Q

Why do lipid soluble molecules have an instant and widespread effect of the body?

A

Lipid soluble molecules can pass through membranes by simple diffusion so diffuses quickly through the whole body

31
Q

What are the advantages of folded membranes?

A

Process occur within membranes, folding gives increased surface area so more enzymes and an increased rate of reactions so an increased rate of ATP production

32
Q

How does temperature affect membrane structure?

A

When temp increases, the phospholipids gain more kinetic energy and will move more which makes the membrane more fluid and begins to lose its structure. This increases the permeability of the membrane, make it easier for particles to pass through it. Carrier and channel proteins will become denatured at higher temperatures.

33
Q

How do solvents affect membrane structure?

A

Organic solvents are mainly less polar than water, which will dissolve membranes, disrupting cells (this is why alcohol is used in antiseptic wipes.
When the membrane is disrupted it becomes more fluid and more permeable.

34
Q

What is the practical to investigate the factors affecting membrane structure and permeability.`

A

Beetroot cells.

35
Q

Why are beetroot cells used for the practical of factors affecting membrane structure and permeability?

A

Beetroot cells contain betalain, a red pigment that gives them their distinctive colour, because of this they are useful for investigating the effects of temperature and organic solvents on membrane permeability. When beetroot cells membranes are disrupted the red pigment is released and the surrounding solution is coloured, the amount of pigment released into a solution is related to the disruption of the cell membranes.

36
Q

What is the method of the beetroot practical?

A

Five small pieces of beetroot cut at equal size using a cork borker. The beetroot pieces were thoroughly washed in running water, they were placed in 100ml of distilled water in a water bath. The temperature of the water bath was increeased in 10 degrees intervals. Samples of the water containing the beetroot were taken five minutes after each temperature was reached. The absorbance of each sample was measured using a colorimeter with a blue filter. The experiment was done 3 times, each time with fresh beetroot pieces and a mean calculated for each temperature.

37
Q

Why is the beetroot washed with water?

A

To remove all surface pigment released from damaged cells

38
Q

Why are the samples of water containing the beetroot were taken fave minutes after each temperature was reached?

A

To allow the mixture to equilibrate

39
Q

Why was the experiment repeated 3 times?

A

Repeats for reliability

40
Q

Why were the absorbance of the samples measured using a colorimeter with a blue filter

A

Because the pigment is red.

41
Q

Why would the absorbance would change as the amount of pigment increases?

A

More pigment molecules absorb more light, light transmitted decreases.

42
Q

What is passive transport?

A

Uses energy from the natural motion of particles (down the concentration gradient)

43
Q

What is diffusion?

A

Is the net, or overall, movement of particles (atoms, molecules or ions) from a region of higher concentration to a region of lower concentration and it is passive and will continue until there is a concentration equilibrium between the two areas.

44
Q

Why does diffusion happen?

A

Because the particles in a gas or liquid have kinetic energy.

45
Q

What slows down particles overall movements?

A

Particles move at high speeds and are constantly colliding therefore diffusion at long distances it will slow the particles down more than short distances.

46
Q

What are the factors that affect the rate of diffusion?

A

Temperature, concentration difference

47
Q

How does temperature affect diffusion?

A

The higher the temperature the higher the rate of diffusion. This because the particles have more kinetic energy and move at higher speeds.

48
Q

How does concentration difference affect diffusion?

A

The greater the difference in concentration between 2 regions the faster the rate of diffusion, because the overall movement from the higher concentration to lower concentration will be larger.

49
Q

How can rate of diffusion be calculated?

A

Distance travelled/time (not affected by changes in surface area) or volume/time (varies depending on surface area)

50
Q

Describe diffusion across membranes.

A

Involves particles passing through the phospholipid bilayer, it can only happen if the membrane is permeable to the particles-non-polar molecules such as oxygen diffuse through freely down a concentration gradient.

51
Q

Describe partially permeable.

A

The hydrophobic interior of the membrane repels substances with a positive or negative charge (ions), so they cannot easily pass through. Polar molecules, such as water, with partial positve and negative charges, can diffuese through membranes, but only at a very slow rate.

52
Q

What affects the rate of molecules and ions diffusing across membranes?

A

Surface area - the larger the area of an exchange surface is the higher the rate of diffusion.
Thickness of membrane - the thinner the exchange surface, the higher the rate of diffusion.

53
Q

What is facilitated diffusion?

A

Diffusion through protein channels from which polar molecules and ions pass through, the movement of molecules is down a concentration gradient and does not require external energy.

54
Q

What do you call membranes with protein channels?

A

Selectively permeable as most protein channels are specific to one molecule or ion.

55
Q

Can carrier proteins be involved with facilitated diffusion?

A

Yes, they change shape when a specific molecule binds.

56
Q

What factors affect the rate of facilitated diffusion?

A

Temperature, concentration gradient, membrane surface area and thickness and by the number of channel proteins present.

57
Q

What is active transport?

A

The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration, it requires energy and carrier proteins

58
Q

Why is energy needed in active transport?

A

The particles are moved up a concentration gradient, in the opposite direction to diffusion, metabolic energy is supplied by ATP>

59
Q

Describe the process of active transport.

A
  1. The molecule or ion to be transported binds to receptors in the channel of the carrier proteins on the outside of the cell.
  2. On the inside of the cell ATP binds to the carrier protein and is hydrolysed into ADP and phosphate.
  3. Binding of the phosphate molecule to the carrier protein causes the protein to change shape - opening up to the inside of the cell.
  4. The molecule or ion is released to the inside of the cell.
  5. The phosphate molecule is released from the carrier protein and recombines with ADP to form ATP.
  6. The carrier protein returns to its original shape.
60
Q

What is bulk transport?

A

Another form of active transport. Large molecules such as enzymes, hormones, and whole cells like bacteria are too large to move through channel or carrier proteins, so they are moved into and out of cell by bulk transport.

61
Q

What is endocytosis?

A

Bulk transport of material into cells.Q

62
Q

What are the two types of endocytosis?

A

Phagocytosis - for solids
Pinocytosis - for liquids

63
Q

Describe how endocytosis works

A

The cell-surface membrane first invaginates (bends inwards) when it comes into contact with the material to be transported. The membrane enfolds the materials until eventually the membrane fuses, forming a vesicle. The vesicle pinches off and moves into the cytoplasm to transfer the material for further processing within the cell. For example, vesicles containing bacteria are moved towards lysosomes, where the bacteria are digested by enzymes.

64
Q

What is exocytosis?

A

Transport of material outside of the cell.

65
Q

Describe exocytosis.

A

Vesicles, usually formed by the golgi apparatus, move towards and fuse with the cell - surface membrane. The contents of the vesicle are then released outside of the cell.

Biology (28 decks)

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