Cell Membranes

Question 0

What is the function of a cell surface membrane?

Answer 0

Cell surface membranes surround all cells, controlling what enters and leaves. Membranes also divide up the cytoplasm of eukaryotic cells into separate compartments.

Question 1

What can the cell membrane be known as? (Two names)

Answer 1

• Cell surface membrane

- Cell plasma membrane

Question 2

Define: Fluid Mosaic model, why is it called this?

Answer 2

Fluid: Phospholipids are liquid
Mosaic: Proteins are similar to small pieces of tile surrounded by phospholipids, which in turn are like the cement holding everything together.

Question 3

Define: Hydrophobic

Answer 3

Not attracted to water. The hydrophobic tails of the phospholipid bilayer are facing inwards, away from the water.

Question 4

Define: Hydrophillic

Answer 4

Attracted to the water. The hydrophilic heads of the phospholipid bilayer are facing outwards, towards the water.

Question 5

Define: Phospholipid bilayer (What are its components?)

Answer 5

A phospholipid layer contains hydrophobic tails and hydrophilic heads. There are two of these layers, hence the name, bilayer.

Question 6

Define: Partially permeable or Selectively permeable

Answer 6

Selectively permeable means that only certain components are allowed through the membrane.

Question 7

What are the functions of phospholipids? What are they permeable and impermeable to?

Answer 7

• To form a bilayer barrier between cytoplasm and the cell exterior
• The are fluid so components move around within the membrane
• Permeable to non polar molecules like oxygen and fatty acids
• Permeable to small polar molecules like ethanol, H2O and CO2
• Impermeable to ions and large polar molecules like sugars

Question 8

What is the function of cholesterol?

Answer 8

• To stabilise the phospholipid bilayer by binding to polar heads and non polar tails of phospholipids
• To control fluidity by preventing phospholipids at low temperatures and becoming too fluid at high temperatures
• Reduces the permeability to water, ions and polar molecules

Question 9

What are the functions of proteins in the cell surface membrane?

Answer 9

• They are transmembrane proteins acting as channels and carriers
• They are receptors for chemicals made by other cells: Hormones

Question 10

What are the functions of Glycolipids and Glycoproteins?

Answer 10

• They are carbohydrate chains only found of the exterior surface of cell membranes
• They act as receptors for signalling molecules and for drugs
• They act as cell surface markers that identify the cells to others (cell surface antigens)
• They are involved in cell adhesion

Question 11

Why are there membranes within cells? What do they do?

Answer 11

• Membranes within cells divide the cell into compartments where functions can occur more efficiently
• They isolate harmful enzymes in lysosomes
• They provide a large surface area for holding the enzymes and coenzymes for forming ATP in mitochondria and chloroplasts
• They provide a large surface for pigments such as chlorophyll
• They surround vesicles that transport mitochondria between parts of the cell