2.5 Biological Membranes

Question 1

What is the general role of the cell membrane ?

Answer 1

-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.

Question 2

What is the phospholipid bilayer?

Answer 2

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).

Question 3

What type of substances can pass through the phospholipid bilayer?

Answer 3

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

Question 4

What type of substances cannot bass through the phospholipid bilayer?

Answer 4

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

Question 5

What are polar molecules?

Answer 5

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

Question 6

What are non-polar molecules?

Answer 6

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

Question 7

What is the Fluid Mosaic Model ?

Answer 7

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

Question 8

What is the structure of the fluid mosaic model ?

Answer 8

-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.

Question 9

What are Glycoproteins ?

Answer 9

They are proteins with a carbohydrate attached.

Question 10

What is the function of glycoproteins ?

Answer 10

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.

Question 11

What is an example of a glycoprotein ?

Answer 11

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

Question 12

What is a glycolipid ?

Answer 12

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

Question 13

What is the function of a glycolipid ?

Answer 13

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

Question 14

Why are glycolipids important ?

Answer 14

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

Question 14

What is cholesterol ?

Answer 14

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

Question 14

What is the function of cholesterol ?

Answer 14

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

Question 15

What does semi-permeable membrane mean ?

Answer 15

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

Question 16

What is the role of the membrane at the surface ?

Answer 16

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

Question 17

What is the role of membrane within the mitochondria ?

Answer 17

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

Question 18

What is role of thylakoid membrane in chloroplasts ?

Answer 18

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

Question 19

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

Answer 19

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

Question 20

What are Intrinsic Proteins ?

Answer 20

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

Question 21

What is a carrier protein ?

Answer 21

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

Question 22

What do carrier proteins act as ?

Answer 22

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

Question 23

Extrinsic Proteins

Answer 23

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

Question 24

What is membrane integrity vital for ?

Answer 24

Vital for membrane permeability.

Question 25

4 factors that affect membrane permeability

Answer 25

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

Question 26

Phospholipid molecules are constantly what ?

Answer 26

They are constantly moving.

Question 27

What does increased temperature and kinetic energy of phospholipids mean?

Answer 27

More fluidity.

Question 28

What does increased fluidity mean ?

Answer 28

Less membrane integrity.

Question 29

If there is excessive temperature what happens to the membrane ?

Answer 29

The membrane disintegrates.

Question 30

What happens to the tertiary layer during excessive temperatures ?

Answer 30

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

Question 31

What is the role of cholesterol ?

Answer 31

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

Question 32

Why are unsaturated fatty acid tails helpful in low temperatures ?

Answer 32

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.

Question 33

Why are saturated fatty acid tails helpful in higher temperatures ?

Answer 33

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

Question 34

What does viscous mean ?

Answer 34

less fluidity

Question 35

What is the function of an organic solvent ?

Answer 35

Organic solvents dissolve membranes, which disrupts the cell.

Question 36

Ethanol as an organic solvent

Answer 36

Ethanol is used in antiseptics as it kills bacteria.

Question 37

Is ethanol polar ?

Answer 37

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.

Question 38

Strong alcohol’s are what ?

Answer 38

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

Question 39

What effect does weak alcohol’s have on membranes ?

Answer 39

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

Question 40

How does alcohol and organic solvents affect membranes ?

Answer 40

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

Question 41

What is diffusion ?

Answer 41

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.

Question 42

What is a concentration gradient ?

Answer 42

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

Question 43

What is simple diffusion ?

Answer 43

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

Question 44

What substances can diffuse via simple diffusion ?

Answer 44

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.

Question 45

How does water diffuse ?

Answer 45

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

Question 46

In the alveoli, how does diffusion occur ?

Answer 46

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.

Question 47

In cells, how does diffusion occur ?

Answer 47

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

Question 48

What is facilitated diffusion ?

Answer 48

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

Question 49

How do channel proteins work ?

Answer 49

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.

Question 50

What are the 4 factors that affect rate of diffusion ?

Answer 50

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

Question 51

What is active transport ?

Answer 51

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

Question 52

Does active transport require energy ?

Answer 52

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.

Question 53

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

Answer 53

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.

Question 54

What is the process of active transport ?

Answer 54

-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.

Question 55

What is cytosis ?

Answer 55

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

Question 56

Why is cytosis possible ?

Answer 56

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

Question 57

What is exocytosis ?

Answer 57

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

Question 58

What is endocytosis ?

Answer 58

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

Question 59

What is phagocytosis ?

Answer 59

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

Question 60

What is pinocytosis ?

Answer 60

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

Question 61

What is osmosis ?

Answer 61

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.

Question 62

What is water potential ?

Answer 62

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

Question 63

What is the highest water potential ?

Answer 63

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

Question 64

What is the suffix tonic ?

Answer 64

Amount of solutes in a solution.

Question 65

What is isotonic ?

Answer 65

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

Question 66

Prefix hyper ?

Answer 66

High, excess, over.

Question 67

Prefix hypo ?

Answer 67

Low, under, beneath.

Question 68

Does a hypertonic solution contain less or more solutes ?

Answer 68

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

Question 69

Does a hypotonic solution contain more of less solutes ?

Answer 69

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

Question 70

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

Answer 70

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

Question 71

What happens to plant cells in a hypertonic solution ?

Answer 71

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.

Question 72

What is plasmolysis ?

Answer 72

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

Question 73

What happens to an animal cell in a hypotonic solution ?

Answer 73

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

Question 74

What is haemolysis ?

Answer 74

When red blood cell bursts due to cytolysis.

Question 75

What happens to a plant cell in a hypotonic solution ?

Answer 75

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.