Transport across cell membrane

Question 1

Describe the fluid-mosaic model of the cell membrane

Answer 1

• Fluid: Individual phospholipids in the phospholipid bilayer can move = flexible shape
• Mosaic: Embedded with proteins + glycoproteins + glycolipids

Question 2

Describe the phospholipid bilayer

Answer 2

• Phospholipids form as 2 layers
• Hydrophilic heads = attracted to water = facing outside
• Hydrophobic tails = repelled by water = facing inside
• 1 layer faces extracellular 1 layer faces intracellular

Question 3

What are some components of a cell membrane?

Answer 3

• Cholesterol
• Proteins
• Glycoproteins/Glycolipids
• Channel proteins
• Carrier proteins

Question 4

Function of cholesterol

Answer 4

• Restricts movement of molecules = makes membrane more rigid
• Membranes less fluid in high temperatures so water and dissolved ions don’t leak in/out of the cell = dehydration/bursting

Question 5

Function of proteins

Answer 5

• Mechanical support
• Attached to carbohydrates

Question 6

Function of glycolipids/glycoproteins

Answer 6

• Cell signaling
• Cell recognization as receptors

Question 7

Function of channel proteins

Answer 7

Tubes fill with water = water-soluble diffuse through

Question 8

Function of carrier proteins

Answer 8

Larger molecules bind to protein = shape changes to transport to other side of membrane

Question 9

Why is the phospholipid bilayer a partially permeable membrane?

Answer 9

CAN PASS THROUGH:
- Lipid soluble = hormones
- Small molecules = H2O + CO2 +O2
CANNOT PASS THROUGH:
- Water soluble molecules = ions
- Large molecules = glucose + aminos

Question 10

Describe simple diffusion

Answer 10

• Net movement of molecules from area of high concentration to area of low concentration until equilibrium is reached
• Due to KE so don’t need ATP
• Molecules must be lipid soluble + small

Question 11

Describe facilitated diffusion

Answer 11

• Net movement of molecules from area of high concentration to low concentration via channel/carrier proteins
• Due to KE so don’t need ATP
• Channel proteins: Tube fills with water and selective water-soluble ions diffuse through
• Carrier proteins: Larger complementary molecule binds = shape change = molecule released on other side

Question 12

Describe osmosis

Answer 12

Movement of water from an area of high water potential to an area of low water potential across partially permeable membrane

Question 13

What is water potential?

Answer 13

• Pressure created by water molecules
• Measured in kPa
• Pure water has water potential of 0
• The more solute dissolved = more negative

Question 14

What happens to a cell in isotonic solution?

Answer 14

No net gain as it is already at equilibrium = same WP inside/outside

Question 15

What happens to a cell in hypotonic solution?

Answer 15

-Water will move into cell
- Animal cell will burst without cell wall
- Plant cell will become turgid

Question 16

What happens to a cell in hypertonic solution?

Answer 16

• Water will move out of cell
• Animal/plant cell will both shrivel

Question 17

Describe active transport

Answer 17

• Movement of molecules from an area of lower concentration to an area of higher concentration = against concentration gradient
• Using ATP and carrier proteins
• Specific molecules can bind to receptor site on carrier protein
• ATP binds to inside of protein membrane = hydrolyzed into ADP + Pi = change in shape of protein = opens on the inside of membrane and releases molecule
• Pi released = protein goes back to original shape