Membrane Structure 1.3

Question 1

Essential Idea (Membrane Structure 1.3)

Answer 1

• The structure of biological membrane makes them fluid and dynamic
• Fluidity allows for endocytosis and exocytosis without the membrane bursting
• Membrane is important for maintaining internal cell conditions

Question 2

Size / Composition of the Membrane

Answer 2

5-10nm thick with three layers, 45% lipid, 45% protein, 10% carbohydrates

Question 3

Triglycerides

Answer 3

Type of lipid made up of one glycerol and three fatty acid molecules

Question 4

Phospholipid Bilayer

Answer 4

• Form bilayers due to the amphiphilic properties
• Made of one glycerol, two fatty acid tails (saturated and unsaturated), and a phosphate-linked head group

Question 5

Phosphate Head

Answer 5

hydrophilic, attracted to water

Question 6

Fatty Acid Tails

Answer 6

Hydrophobic and non polar, afraid of water

Question 7

Amphipathic molecule

Answer 7

Molecule with both hydrophilic and hydrophobic parts

Question 8

Membrane Proteins

Answer 8

• Classified as integral (in) or peripheral (on top) depending of position
• Integral are amphipathic and embedded
• Peripheral are polar (hydrophilic) and are attached outside the membrane

Question 9

Membrane Protein Types (5)

Answer 9

• Channel
• Carriers
• Recognition
• Receptors
• Enzymes

Question 10

Channel Membrane Protein

Answer 10

• Pore / channel that allows passive transport of substance in and out without the requirement of energy
• Allows hydrophilic particles across by facilitated diffusion

Question 11

Carrier Membrane Protein

Answer 11

• Aka protein pumps, bind to substances on one side of the membrane then change shape to transport to other side, uses energy (active)

Question 12

Active vs Passive Transport

Answer 12

Passive doesn’t require energy for movement will active does

Question 13

Recognition Membrane Protein

Answer 13

Helps the cell differentiate between self and non self cells, important in triggering immune response

Question 14

Receptor Membrane Protein

Answer 14

Span the whole membrane to relay information on the inside or outside of the cell

Question 15

Enzyme Membrane Protein

Answer 15

Enhances the rate of reaction that happens at membrane level

Question 16

Glycolipids

Answer 16

Are phospholipid and a carbohydrate attached together and are important in maintaining the structure and differentiating cells (self and non self)

Question 17

Cholesterol

Answer 17

• Steroid only found in animal membrane and it is vital for maintaining structure, fluidity and permeability
• Body makes own cholesterol
• Steroid is made up of non polar part comprising of four hydrocarbon rings, a hydrocarbon tail and a polar hydroxyl group
• Inserted in the membrane by interacting with the phospholipids
• Restricts the movement of phospholipids and other molecules by reducing the fluidity, however are low temperature prevents solidification
• Reduces membrane permeability

Question 18

Permeability

Answer 18

Means certain molecules can pass through while others cannot

Question 19

3 Different Membrane Models & Date

Answer 19

• Gorter-Grendel, 1924
• Davson-Danielli, 1935
• Singer-Nicolson, 1972

Question 20

Gorter-Grendel Model

Answer 20

• Founders of the bilayer model
• Extracted and examined phospholipids from red blood cells
• Determined the total lipid surface to total cell membrane area was a 2:1 ratio, which suggested there were two layers
• Evidence from electron microscopy

Question 21

Davson-Danielli Model

Answer 21

• Suggested there was a layer of protein on either side of the membrane

Question 22

Singer-Nicolson Model

Answer 22

• Irregular rough surface in the phospholipid bilayer revealed proteins were embedded
• Allows for maximum exposure of water resulting in stable structure
• Discovered through freeze-etched electron micrograph images