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Biology > 2.5 Biological Membranes > Flashcards

2.5 Biological Membranes Flashcards

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1
Q

What is the general role of the cell membrane ?

A

-Separates cell contents from outside the cell.
-Separates cell components from cytoplasm
-Important in cell recognition and signalling.
-Holds components of metabolic pathways in place.
-Regulates transport of materials in and out of the cell.

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2
Q

What is the phospholipid bilayer?

A

Made up of 2 layers of phosphate heads that face the aqueous solution. The heads are connected to hydrophobic tails that face inwards(fatty acid tails).

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3
Q

What type of substances can pass through the phospholipid bilayer?

A

Gases, small polar molecules and hydrophobic molecules can pass across the bilayer as they are fat soluble.

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4
Q

What type of substances cannot bass through the phospholipid bilayer?

A

Large polar molecules, ions and fat insoluble molecules require a membrane proteins to move across the bilayer.

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5
Q

What are polar molecules?

A

Partially charged molecules that are fat insoluble and hydrophilic so can get across first layer of bilayer.

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6
Q

What are non-polar molecules?

A

Uncharged(neutral) molecules that are soluble in fats and are hydrophobic so can pass easily through middle layer of bilayer.

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7
Q

What is the Fluid Mosaic Model ?

A

States that membranes are composed of layer with various protein molecules floating around within it.

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8
Q

What is the structure of the fluid mosaic model ?

A

-Lipid bilayer has lipid molecules with the hydrophilic heads contact to the watery exterior.
-Hydrophilic phosphate heads form hydrogen bonds with water molecules. Hydrophobic tail regions are in centre of the membrane, away from the water.

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9
Q

What are Glycoproteins ?

A

They are proteins with a carbohydrate attached.

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10
Q

What is the function of glycoproteins ?

A

They play a role in cell adhesion and as cell receptors for signalling.
They are receptor binding, that either triggers a direct response or a cascade of events in a cell.

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11
Q

What is an example of a glycoprotein ?

A

Receptors for insulin and glucagon are glycoproteins. Both affect the uptake and storage of glucose by cells.

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12
Q

What is a glycolipid ?

A

They are a lipid with a carbohydrate attached to it by a glycosidic bond (covalent).

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13
Q

What is the function of a glycolipid ?

A

Maintain stability of cell membrane and to facilitate cellular recognition (antigens).

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14
Q

Why are glycolipids important ?

A

Important to immune response and in connections that allow cells to connect to one another to form tissues.

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14
Q

What is cholesterol ?

A

Cholesterol is a type of lipid that has a hydrophobic end and hydrophilic end.

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14
Q

What is the function of cholesterol ?

A

Regulates fluidity and stability of the membrane. Also helps membrane resist temperature changes.

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15
Q

What does semi-permeable membrane mean ?

A

Allows small molecules, like water and certain molecules to pass through but does not allow passage of large solute molecules.

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16
Q

What is the role of the membrane at the surface ?

A

-Separates cell components.
-Cell recognition and signalling via receptors
-Regulates transport of materials.
-Site of chemical reactions.

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17
Q

What is the role of membrane within the mitochondria ?

A

Folded inner membrane of mitochondria, called cristae, gives large surface area for aerobic respiration.

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18
Q

What is role of thylakoid membrane in chloroplasts ?

A

Thylakoid membranes in chloroplasts, which is part of inner membrane containing chlorophyll, where light dependent reaction occurs.

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19
Q

What is the role of enzymes in plasma membranes of epithelial cells ?

A

Digestive enzymes on plasma membranes of epithelial cell of a small intestine catalyse some final stage of breakdown of certain types of sugars.

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20
Q

What are Intrinsic Proteins ?

A

Transmembrane
Some are channel proteins that act as passageways to allow ions with electrical charges to pass through.

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21
Q

What is a carrier protein ?

A

Can change shape (conformational change) to allow specific molecules across bilayer.

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22
Q

What do carrier proteins act as ?

A

When carrier protein are attached to glycoproteins, they act as enzymes, antigens and receptor sites for chemicals such as hormones.

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23
Q

Extrinsic Proteins

A

Present in one side of the bilayer.
Serve in transport of molecules and as receptors.

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24
Q

What is membrane integrity vital for ?

A

Vital for membrane permeability.

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25
Q

4 factors that affect membrane permeability

A

Temperature, proportion of cholesterol, proportion of saturated/unsaturated fats and presence of solvents.

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26
Q

Phospholipid molecules are constantly what ?

A

They are constantly moving.

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27
Q

What does increased temperature and kinetic energy of phospholipids mean?

A

More fluidity.

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28
Q

What does increased fluidity mean ?

A

Less membrane integrity.

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29
Q

If there is excessive temperature what happens to the membrane ?

A

The membrane disintegrates.

30
Q

What happens to the tertiary layer during excessive temperatures ?

A

The tertiary layer shape changes permanently and the protein becomes denatured due to hydrogen bonds and ionic bonds breaking.

31
Q

What is the role of cholesterol ?

A

Reduces membrane fluidity at membrane temperatures but at low temperatures, it hinders solidification.

32
Q

Why are unsaturated fatty acid tails helpful in low temperatures ?

A

Unsaturated tails have kinks in the tail because of the double covalent bonds. This is useful because the kinks allow the membrane to remain permeable.

33
Q

Why are saturated fatty acid tails helpful in higher temperatures ?

A

Saturated tails have no kinks in tail as they are only single covalent bonds. This keeps membrane structure.

34
Q

What does viscous mean ?

A

less fluidity

35
Q

What is the function of an organic solvent ?

A

Organic solvents dissolve membranes, which disrupts the cell.

36
Q

Ethanol as an organic solvent

A

Ethanol is used in antiseptics as it kills bacteria.

37
Q

Is ethanol polar ?

A

Ethanol is a non-polar molecule. This allows it to diffuse across the lipid bilayer and through channel proteins, disrupting membrane structure. This increases permeability.

38
Q

Strong alcohol’s are what ?

A

Strong alcohols are toxic so dissolve membranes and are very damaging.

39
Q

What effect does weak alcohol’s have on membranes ?

A

Less concentrated alcohol solutions don’t dissolve membranes, but are still damaging.

40
Q

How does alcohol and organic solvents affect membranes ?

A

Alcohol disrupts neuronal membranes and nerve impulses. This leads to lack of coordination and slower reaction time (drunkness).

41
Q

What is diffusion ?

A

Net movement of particles from a high concentration to a low concentration due to random movement of particles. Liquids and gases have more kinetic energy so move randomly.

42
Q

What is a concentration gradient ?

A

Difference in concentration of molecules across two sides, one side is more concentrated than the other. Diffuse down concentration gradient until equilibrium is reached.

43
Q

What is simple diffusion ?

A

Unassisted membrane pass through down the concentration gradient. It is a passive process and does not require energy.

44
Q

What substances can diffuse via simple diffusion ?

A

No proteins are involved. Some water molecules will diffuse. Despite being large, lipid molecules can diffuse across the membrane as they are lipid soluble, so dissolve in lipid bilayer.

45
Q

How does water diffuse ?

A

Water can diffuse across hydrophobic layer using aquaporin channels. This is a form of facilitated diffusion.

46
Q

In the alveoli, how does diffusion occur ?

A

Oxygen diffuses into the blood from an area of high concentration to low concentration. As oxygen is pumped away, the concentration of oxygen becomes lower than in the alveolus, so concentration gradient is maintained.

47
Q

In cells, how does diffusion occur ?

A

Oxygen diffuses into cytoplasm and then into mitochondria for respiration, constantly lowering oxygen concentration in cell. This maintains concentration gradient.

48
Q

What is facilitated diffusion ?

A

Aided diffusion by protein channels and carriers. Diffuse down the concentration gradient and does not require energy.

49
Q

How do channel proteins work ?

A

Transmembrane proteins (carrier) bind with specific molecules, opening proteins so molecules can cross membrane. They have a specific shape, normally carrying 1 specific shaped molecules.

50
Q

What are the 4 factors that affect rate of diffusion ?

A

-Temperature= more KE
-Diffusion distance= takes longer
-Surface area= more space to cross membrane
-Concentration gradient=increase gradient, increases rate of diffusion.

51
Q

What is active transport ?

A

Movement of particles from a low concentration to a high concentration against the concentration gradient. Opposite to diffusion.

52
Q

Does active transport require energy ?

A

Yes, active transport requires energy from ATP. This is because cells need a large supply of ATP for this but kinetic energy of the cell isn’t enough.

53
Q

What does active transport require for movement of particles across the membrane ?

A

Active transport requires carrier proteins that have a specific shape to transport substances with the matching shape. Carrier proteins undergo a conformational change to allow molecules to pas through.

54
Q

What is the process of active transport ?

A

-Ions enter carrier proteins and bind to outside.
-ATP binds to inside of carrier proteins.
-ATP is hydrolysed (reacts with water) and produced ADP and phosphate which binds to carrier protein.
-Causes conformational shape of carrier protein.
-Allows ions to enter the cell.

55
Q

What is cytosis ?

A

Large molecules that cannot be transported by active transport have to enter via bulk transport (cytosis).

56
Q

Why is cytosis possible ?

A

Possible due to fluid nature of the membrane, which requires energy and involves breaking open bilayer and reforming it.

57
Q

What is exocytosis ?

A

When vesicles fuse to plasma membrane then reforms and releases the contents. The membrane reforms once the isolated, solid substances have left the cell.

58
Q

What is endocytosis ?

A

Membrane invaginated around substances allowing them to enter the cell. Membrane reforms due to fluid nature of the membrane.

59
Q

What is phagocytosis ?

A

(Cell eating) Vesicle traps solids to be taken into the cell.

60
Q

What is pinocytosis ?

A

(Cell drinking) Vesicle traps liquid to be taken into cell.

61
Q

What is osmosis ?

A

Movement of water molecules across a partially permeable membrane from a region of high water potential to an area of low water potential, with the water potential gradient.

62
Q

What is water potential ?

A

How much water the solution contains in relation to other substances and how much pressure it exerts.
(Pa/KPa)

63
Q

What is the highest water potential ?

A

0kPa (pure/distilled water) If there is any dissolved substances in the water, this decreases the water potential.

64
Q

What is the suffix tonic ?

A

Amount of solutes in a solution.

65
Q

What is isotonic ?

A

Isotonic has same amount of solutes and therefore water potential as a cell suspended in the solution. No net movement of water.

66
Q

Prefix hyper ?

A

High, excess, over.

67
Q

Prefix hypo ?

A

Low, under, beneath.

68
Q

Does a hypertonic solution contain less or more solutes ?

A

Contains more solutes and therefore has a lower water potential than a cell suspended in the solution.

69
Q

Does a hypotonic solution contain more of less solutes ?

A

Contains less solutes and therefore has a higher water potential than a cell suspend in the solution.

70
Q

What happens to animal cells in a hypotonic solution (crenation) ?

A

Osmotic water potential gradient is established. Water moves down the water potential gradient and out of the cell by osmosis. This causes crenation (shrinkage).

71
Q

What happens to plant cells in a hypertonic solution ?

A

Net movement of water across a partially permeable membrane from a plant cell to a hypertonic solution. Cell membrane shrinks and pulls away from the cell wall and has become plasmolysed.

72
Q

What is plasmolysis ?

A

When cell membrane pull away from cell wall in plant cells.

73
Q

What happens to an animal cell in a hypotonic solution ?

A

Water diffuses into animal cell down water potential gradient causing cell to swell and burst when membrane breaks down.

74
Q

What is haemolysis ?

A

When red blood cell bursts due to cytolysis.

75
Q

What happens to a plant cell in a hypotonic solution ?

A

Water diffuses into a plant cell causing it to swell, increasing turgor pressure. This continues until cellulose cell wall resists any further swelling. The cell is turgid.

Biology (16 decks)

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