1.3 membrane structure

Question 1

Phospholipid description

Answer 1

It has a polar charged hydrophilic phosphate head, and a non-polar hydrophobic tail

Question 2

What happens when you put phospholipids in water

Answer 2

an emergent property is that: the phospholipids will rearrange themselves so that the hydrophilic phosphate heads are in contact with the water. They can rearrange into a bilayer sheet, a micelle, or liposome.

Question 3

Protiens

Answer 3

• integral proteins are permanently embedded in the membrane, and can go all the way in and be polytopic, or only penetrate one layer and be monotopic.
• Peripheral proteins have a temporary relationship with the membrane, and can be monotopic or attach to the membrane surface.

Question 4

glycoprotiens

Answer 4

• Glycoproteins are proteins that have an oligosaccharide chain attached to them
• They are important for cell recognition in the nervous system and hormone receptors

Question 5

How do phospholipid molecules move

Answer 5

phospholipid molecules can move by each other laterally but not vertically.

Question 6

describe protein functions

Answer 6

transport - protein channels ( faciliated) and protein pump (energy)
receptors - peptide based hormones like insulin
anchorage - cystoskeleton filaments and extracellular matrix
cell recognition - MHC proteins and antigens
intracellular joining - tight junction and plasmodesmata
enzymatic activity - metabolic pathways (electron transport chain)

Question 7

Cholesterol

Answer 7

Cholesterol impacts membrane fluidity and flexibility by making phospholipids pack more tightly.

• Cholesterol is a lipid but its carbon rings make it a steroid.
• Cholesterol has a polar hydroxyl group which attaches to the phosphate head
• cholesterol has a non-polar hydrophobic tail which attaches to lipid tails.

Question 8

Why is it important to regulate membrane fluidity

Answer 8

membrane has to be fluid enough for the cell to move
membrane has to be fluid enough for materials to pass through it
if a membrane is too fluid, it can not regulate the materials passing through it

Question 9

Membrane- fluid or solid

Answer 9

The phosphate head is said to be solid, the lipid tails are liquid, so a phospholipid is know as fluid

Question 10

How does cholesterol affect the membrane

Answer 10

cholesterol makes phospholipids pack more tightly together and restricts the movement of phospholipids and other molecules, and this decreases membrane fluidity

cholesterol disrupts the natural packing of phospholipids hydrocarbon tails, preventing lipid tails from crystalizing and becoming solid. therefore increases the membrane flexibility

cholesterol reduces the permeability to hydrophilic molecules/ ions like sodium and hydrogen

Question 11

tracie

Answer 11

Transport - protein channel (facilitated) and protein pump (energy)
Receptors - peptide based hormones (insulin)
Anchorage - cytoskeleton filaments and extracellular matrix
Cell Recognition - MHC proteins and antigens
Intracellular joining - tight junctions and plasmodesmata
Enzymatic activity - metabolic pathways (electron transport chain)

Question 12

Singerson - fluid mosaic model

Answer 12

Components of the fluid mosaic model:

• phospholipid forms a bilayer, phospholipids are fluid and can move laterally
• integral proteins can penetrate the membrane surface
• peripheral proteins were bound to the inner or outer layer of the membrane
• Proteins could move laterally/freely along the membrane
• fluid mosaic model

Question 13

what proved the fluid mosaic model right?

Answer 13

Fluorescent antibody tagging:

• red and green fluorescent markers tagged antibodies that would bind to membrane
• membrane proteins of some cells were marked either red or green
• two cells were fused together
• within 40 minutes, the red and green marks were seen to be mixed throughout the membrane
• this showed the proteins and phospholipids were free to move along the membrane and were not bound to the outside of it.

biochemical technique:

• membrane proteins were found to vary in size and be globular in shape.
• therefore membrane proteins could not form a continuous layer around the peripheral, and instead were fluid throughout the model
• membrane proteins were found to be amphipathic, and therefore parts of them penetrated the membrane surface.

Question 14

david donnelson model -components - evidance -what it explained

Answer 14

components:
- a protein lipid bilayer sandwich
- phosphate heads face outside of bilayer lipid tails were on the inside
- membrane proteins coated the peripheral of the membrane
- membrane proteins could not penetrate the membrane

why did they believe it:

• an electron micrograph was taken that showed two dark opposite lines with a lighter area between it
• phospholipids stain light proteins stain dark

what it explained:
- how membranes could be such a strong barrier despite being so thin

Question 15

what proved david donnelson wrong

Answer 15

2 issues with the model:

• membranes were not all identical and symmetrical
• Proteins are amphipathic

freeze fracture evidence:

• a membrane was coated in nitrogen and cut with a knife to reveal the inner layers
• proteins were found embedded throughout the membrane on different sides.

Question 16

attraction between hydrophobic tails causes

Answer 16

Stability to membrane

/ Stability to membrane between hydrophilic heads and water;