Cell membrane

Question 1

What are all cells surrounded by?

Answer 1

Cell surface membrane (eukaryotic)
Plasma membrane (prokaryotic)

Question 2

What are the 2 biochemical components for cell membranes?

Answer 2

Protein molecules
Phospholipids

Question 3

How are phospholipids arranged?

Answer 3

As a bilayer
One sheet of phospholipid molecules opposite another

Question 4

What is the actual width of the cell membrane?

Answer 4

7-8 nm

Question 5

What happens when the phospholipids form bilayers?

Answer 5

Hydrophilic heads point outwards = interacts with the tissue fluid/blood plasma that surrounds the cell & cytoplasm inside the cell
Hydrophobic tails point inwards = towards the inside of the membrane

Question 6

Explain why the hydrophilic heads point outwards and the hydrophobic tails point inwards when the phospholipids form bilayers

Answer 6

Tails repel water present in the cytoplasm and extracellular fluid
Heads are attracted to the water

Question 7

How do cell membranes appear under the electron microscope?

Answer 7

Double line

Question 8

Why is the stain used on the cell membrane water-soluble?

Answer 8

Associates with the hydrophilic phospholipids heads appear dark

Question 9

Are all proteins in the membrane globular or fibrous?

Answer 9

Globular proteins

Question 10

Where can globular proteins be found in the membrane?

Answer 10

On the surface of the bilayer
Partly embedded (extrinsic)
Extending completely across both phospholipid layers (intrinsic/transmembrane)

Question 11

Describe & explain the position of the charged, or hydrophilic, parts of the protein, in relation to the phospholipids

Answer 11

Charged parts of the protein are attracted to the phosphate heads
Uncharged parts of the proteins associate with the non-polar fatty acid tails of the phospholipids

Question 12

Where are carbohydrates found in the cell?

Answer 12

Pointing out of the outside of the cell
Attached to either proteins (glycoproteins)
Or attached to the phospholipids (glycolipids)

Question 13

How are glycoproteins and glycolipids formed?

Answer 13

Through glycosylation
Collectively known as the glycocalyx

Question 14

What is a glycoprotein?

Answer 14

Polypeptide with a side chain made of carbohydrates

Question 15

What are the function of glycoproteins?

Answer 15

Act as receptor molecules
Act as antigens for cell recognition

Question 16

Where is cholesterol present?

Answer 16

Between the phospholipids in animal cell membranes

Question 17

Why is the model called the fluid mosaic?

Answer 17

Fluid : individual phospholipids molecules can move around relative to one another
Mosaic : proteins embedded in the bilayer vary in size and shape and are arranged in a random pattern

Question 18

What is the main function of the cell membrane?

Answer 18

Aid d transport of certain substances into/out of cells
E.g. to obtain oxygen & remove carbon dioxide

Question 19

What is the function of phospholipids?

Answer 19

Form a selective bilayer
Allows non-polar or uncharged molecules through
Prevents the passage of polar or charged molecules

Question 20

What is the function of extrinsic proteins?

Answer 20

Associated with 1 layer only
May act as receptors for hormones

Question 21

What is the function of intrinsic proteins?

Answer 21

Act as carriers or channels
Allow the passage of charged or polar molecules
E.g. glucose

Question 22

What is the function of glycocalyx?

Answer 22

Act as cell-to-cell recognition
E.g. wbc in an immune response
Important in cell adhesion and acting as receptors

Question 23

What is the function of cholesterol?

Answer 23

Controls membrane fluidity