fluid mosaic model

Question 1

what does the cell surface membrane consist of

Answer 1

• bilayer of phospholipids
• proteins
• carbohydrate chains (attached to protein/ phospholipid, in contact with external environment)

Question 2

details about phospholipid

Answer 2

• two fatty acid chains bonded to 2 of the 3 carbons in glycerol molecule
• phosphate group attached to last carbon
• fatty acid chains are hydrophobic
• phosphate group is polar, it is hydrophillic

Question 3

how do phospholipids arrange themselves

Answer 3

• cytosol and external environment are both aqueous.
• hydrophillic head in contact with aqueous environment (external facing)
• hydrophobic tails shielded from aqueous environment. (internal facing)

Question 4

what is meant by “fluid” in fluid mosaic model?

Answer 4

phospholipids and proteins moving freely and laterally within the phospholipid bilayer.

Question 5

what is meant by “mosaic” in fluid mosaic model?

Answer 5

protein and cholesterol (animals only) molecules that are randomly embedded and scattered among the phospholipid molecules, resulting in mosaic arrangement of components.

Question 6

types of proteins found in cell membrane

Answer 6

1. channel protein: allows passage of specific ion/molecules across membrane
2. carrier protein: allows passage of specific ion/molecules across membrane
3. enzymes
4. receptors: specific binding sites that bind to chemical messengers to relay a message into cell
5. glycoproteins: cell recognition and cell adhesion, protein + carbohydrate

Question 7

what affects fluidity of membrane?

Answer 7

1. increases at high temperature
2. increases due to unsaturated fatty acids
3. decreases due to saturated fatty acids
4. cholesterol increases membrane fluidity at low temperature but decreases at high temperature

Question 8

ways molecules/ions can pass through the cell surface membrane

Answer 8

1. simple diffusion (passive)
2. facilitated diffusion (proteins, passive)
3. active transport (active)

Question 9

simple diffusion allows what to pass through membrane

Answer 9

• small molecules
• lipid soluble substances
• non-polar/ non hydrophillic

Note: water and glycerol** are polar. large polar molecules cannot cross cell membrane as they are hydrophillic. water and glycerol can cross however because they are small

Question 10

what happens in facilitated diffusion

Answer 10

• passive process, down a concentration gradient, with the help of transport proteins (channel and carrier)
• transport proteins are very specific. they transport specific substances

Question 11

how do CHANNEL proteins help with facillitated diffusion

Answer 11

provides a hydrophillic passage for specific hydrophillic molecules to move across hydophobic core of cell membrane.

• etc: aquaporins facillitate passage of water molecules

Question 12

how do CARRIER proteins help with facilitated diffusion

Answer 12

change in shape triggered by the binding and release of specific molecule at binding site shields molecules from hydrophobic core

Question 13

what happens in active transport across cell membrane

Answer 13

• against concetration gradient –> low concentration to high concetration
• energy from hydrolysis of ATP is required.
• cells that constantly transport molecules using active transport require a lot of energy, hence they have large number of mitochondria
• carrier proteins required

Question 14

process of active transport

Answer 14

1. molecule is present in higher concentation inside cell
2. molecules have to be actively transported into cell with the help of carrier proteins
3. hydrolysis of ATP provides carrier protein with energy needed to change its shape to transport molecule across cell membrane