Module 2: Foundations In Biology - Biological Membranes 🟢

Question 1

Describe the fluid-mosaic model of membranes

Answer 1

• the membranes are described as fluid-mosaic
  -Fluid: phospholipid bilayer in which individual phospholipids can move = membrane has flexible shape.
  Mosaic: extrinsic & intrinsic proteins of different sizes and shapes are embedded. Mixture of phospholipids,glycoproteins and glycolipids

Question 2

Role of cholesterol and glycolipids In membranes

Answer 2

Cholesterol: steroid molecule in some plasma membranes; connects phospholipids & reduces fluidity to make bilayer more stable.
Glycolipids: cell signalling & cell recognition.

Question 3

Simple diffusion

Answer 3

• the net movement of molecules from a higher concentration to a lower concentration until equilibrium is reached
• molecules move due to the kinetic energy they posses
• this does not require ATP
• molecules must be small and lipid soluble to diffuse across membrane

Question 4

Facilitated diffusion

Answer 4

• this is a passive process ( doesn’t not require ATP)
• carrier proteins and protein channels are used to transport ions and polar molecules across the membrane

Question 5

Osmosis

Answer 5

The movement of water from an area of high water potential to an area of low water potential across a partially permeable membrane

Question 6

Isotonic solution

Answer 6

• the water potential is the same in the solution as it is in the cell within the solution
• no net movement will occur

Question 7

Hypertonic solution

Answer 7

• the water potential of the solution is more negative than the cell
• water moves out of the cell by osmosis

Question 8

Hypotonic solution

Answer 8

• the water potential of the solution is more positive than the cell
• water will move into the cell by osmosis

Question 9

Active transport

Answer 9

• the movement of molecules and ions from an area of lower concentration to an area of higher concentration (against the concentration gradient) using ATP and carrier proteins
• the carrier proteins act as pumps and are very selective in binding to substances to be transported

Question 10

Endocytosis

Answer 10

• a type of active transport
• the cell surface membrane bends inwards to form a vesicle
• the vesicle pinched off and moves within the cytoplasm
• this process requires ATP
• it can be classed as phagocytosis when the molecules is a solid or pinocytosis when the molecule is lipid

Question 11

Exocytosis

Answer 11

• vesicle move towards the cell-surface membrane, Fuse with the membrane and the contents of the vesicle is released outside of the cell
• ATP is required

Question 12

Explain the function of extrinsic proteins in membranes

Answer 12

• binding sites/ receptors e,g, for hormones and drugs
• Antigens (glycoproteins)
• bind cells together
• involved in cell signalling

Question 13

Explain the functions of intrinsic proteins in membranes

Answer 13

• electron carriers (respiration/photosynthesis)
• channel proteins (facilitated diffusion)
• carrier proteins (facilitated diffusion/ active transport)

Question 14

3 factors that affect membrane permeability

Answer 14

• Temperature: high temperature denatures membrane proteins / phospholipid molecules have more kinetic energy & move further apart.
• pH: changes tertiary structure of membrane proteins.
• Use of a solvent: may dissolve membrane.

Question 15

Water potential

Answer 15

pressure created by water molecules measured in kPa

Question 16

5 factors that affect the rate of diffusion

Answer 16

• temperature
• diffusion distance
• surface area
• size of molecule
• difference in concentration (how steep the concentration gradient is)

Question 17

Describe how channel and carrier proteins work

Answer 17

Channel: hydrophilic channels bind to specific ions = one side of the protein closes and the other opens
Carrier: binds to complementary molecule = conformational change releases molecule on other side of membrane; in facilitated diffusion, passive process; in active transport , requires energy from ATP hydrolysis