Ian lipids in membrane 1

Question 1

when is a chimeric cell formed?

Answer 1

when 2 cells are merged together

Question 2

describe experiment 1: demonstrating diffusion using chimeric cells?

Answer 2

• UNPOLARISED cell, as POLARITY (having defined membrane areas) PREVENTS DIFFUSION
• When the cells are merged together, diffusion of memb proteins can be monitored
• At first, the proteins are split into hemispheres, but then CONTINUOUS DIFFUSION LATERALLY–> each type of cell protein becomes EVENLY DISPERSED
• DEMONSTRATES: MEMBRANE FLUIDITY- can diffuse w/out restriction in
• In cells such as epithelial/endothelial cells (POLAR) membranes are not this fluid due to TIGHT JUNCTIONS, at top of cell O LIMIT the diffusion of membrane proteins. Polarised cells also have CYTOSKELETAL ELEMENTS

Question 3

which part of the cholesterol prevents movement of surrounding ph.lip?

Answer 3

the ORGANIC CHAINS of cholesterol

Question 4

why does RBC require more cholesterol than liver cell membranes?

Answer 4

• RBC is forced through capillaries smaller than it

O to not be damaged, cholesterol provides MECHANICAL STRENGTH

Question 5

what is the function of cholesterol in nerve cells?

Answer 5

• gives MECHANICAL STRENGTH to the fragile nerve cell

- prevents the muscle being crushed

Question 6

inner membranes have more or less cholesterol?

Answer 6

less (they require less strength and more fluidity)

Question 7

how much cholesterol do bacteria have in their cell membranes?

Answer 7

0% ad they have cell walls to get mechanical strength and fluidity limitation

Question 8

PHOSPHATIDYLETHANOLAMINE has an overall charge of what?

where is PHOSPHATIDYLETHANOLAMINE found normally?

Answer 8

negative

- found on INNER LEAFLET of membranw

Question 9

PHOSPHATIDYLETHANOLAMINE % is higher where? what does it suggest?
highEST where? why?

Answer 9

liver and RBC, suggests having a negative charge on the inside of membrane is IMPORTANT
HIghest in mitochondria -Negative charge important for creating a proton concentration

Question 10

phosphatidylcholine is found in high conc where?

Answer 10

• More in liver cell

- SIGNIFICANTLY MORE in MITOCHONDRIA and ER

Question 11

give 2 functions of glycolipids

Answer 11

• Immune recognition

- Receptor complexes

Question 12

what is the cholesterol: phospholipid ratio in RBC?

Answer 12

~1:1

Question 13

Experiment 2: Creating artificial membranes-Lipid Rafts

Answer 13

• Artificial membrane containing cholesterol (stained red) and phospholipids
• Initially cholesterol is EVENLY SPREAD, over time it moves and concentrates in areas (LIPID RAFTS)
• In an artificially made membrane, cholesterol location goes from evenly spread, to being concentrated in lipid rafts and back again.
• Variable changed: TEMPERATURE (BUT no other factors)
• In a normal membrane there would be PROTEINS, which provide support
• Accessory proteins accelerate the formation of lipid bilayer
• Lipid raft can be maintained using CALMODULIN protein
• Protein molecules are SIGNIFICANTLY LARGER the other components
• STOPPING A RECEPTOR WORKING:
• Can destabilise lipid rafts, and allow great lateral diffusion O cells can TOLERISE themselves to constant stimulation
• Individual components of receptors can be diffused apart in the membrane

Question 14

what are the roles of glycolipids?

Answer 14

• They can act as ANOCHORING PROTEIN
• act as SIGNALLING POINTS
• act as IMMUNE RECOGNITION sites
• receptor associated molecules (increase stability)

Question 15

liver SER roles?

Answer 15

• manufactures lipids, which has no hydrophilic areas
• these lipids are pumped in BETWEEN MEMBRANE LEAFLETS of the SER
• O as the volume between the leaflets increases (due to pumping lipids in), more PHOSPHOLIPIDS are required to account for the stretch in the membrane

Question 16

Experiment 3: FACS (fluorescence activated cell sorting) and Apoptosis

Answer 16

• Purpose of FACS plot is to demonstrate what stage of their lifecyle they are in, this can be viable, early apoptotic, late apoptotic, or necrotic.
Propidium iodide is a vital dye, meaning that fluorescence indicates that the cell mitochondria is not working, thus suggesting cell death will proceed.
• In a viable cell, propidium iodide will be pumped OUT of the cell using an ATP dependent pump, the ATP is generated using the working mitochondria, therefore if
proidium iodide is not pumped of the cell, it binds to DNA, causing fluorescence. Propidium iodide dyes RED
• In apoptotic cells, scramblase and floppases will move the phospholipids phosohatidylserine and phosphatidylethanolamine (irrelevant) to the outer leaflet of the membrane,
causing the membrane to be not asymmetric. P.serine acts as a signal for apoptosis to occur. Annexin V is an antibody-like molecule, that is coupled with FITC (fluorescent molecule).
• Annexin V has the ability to bind to phosphatidylserine, which can cause the fluorescence of FITC when bound with p.serine. Because of this, Annexin V can be used to indicate the abundance of apoptotic cells, and what stage of apoptosis the cells are at, as the molecule binds to P.serine molecules that have been moved to the outer leaflet of the
plasma membrane, causing fluorescence.