8-28 Membrane Structure/Function

Question 0

What are the 3 types of polar groups that make up phosphoGlycerides polar head ?

Answer 0

[ Choline + Phosphate + Glycerol ]all make up the Polar Head of Phosphoglycerides

Question 1

List and Describe main molecules within a cell plasma membrane

Answer 1

1. Amphiphillic Phospholipids (polar phosphate head/non-polar tails)
   - ->length & saturation of fatty acid tails dictates membrane fluidity
2. PhosphoGlycerides=has cis db “kink” that prevents other phosglycrds from packing too tightly! –>3 DIFFERENt TYPES of polar head groups
3. Cholesterol=INC RIGIDITY of membrane and DEC permeability of bilayer to water soluble molecules. Present in Lrge amounts!

Question 2

What is the plasma membranes composition in regards to lipids and proteins?

Answer 2

50% Lipids /// 50% Proteins (Proteins range from 25%-75%)

Question 3

Hydrophobic molcules can ___-____ which is energetically _____ because……

Answer 3

Hydrophobic and Phospholipids SELF-AGGREGATE (come together has a group) within water because it’s more energetically favorable!

Water won’t have to move all of itself to form around hydrophobic stuff

Question 4

Why are plasma membranes so stable and able to survive within an aqueous environment despite hydrophobic interior

Answer 4

Lipid Bilayers (and lipid micelles) All SEAL OFF into a sealed compartment to protect edges from water via strong hydrophobic interactions between the tails =more energetically favorable

Question 5

1) What makes Plasma Membranes so stable?
2) INC Cholesterol = ____[INC/dec] membrane rigidity
3) What’s the weird property of Cholesterol??
4) What 2 things does membrane fluidity depend on?

Answer 5

Hydrophobic interactions provide GREAT PLASTICITY to plasma membranes and prevent rupture.

2) INC Cholesterol = INC membrane rigidity (it becomes more rigid)
3. CHoles makes membranes rigid physically BUT still INC membrane fluidity and thus INC lateral mobility of membrne proteins

4. membrne fluidity//lipid mobility depend on [Lipid Composition] and [Transition Temperature]

Question 6

Transition Temperature

2) Lower Transition Temperature= ___[higher/lower] membrane fluidity
3) What two things are responsible for TT?

Answer 6

Temperature at which the membrane freezes!
2)LOWER TT = HIGHER membrane fluidity
[they freeze at lower temp so stays fluid for longer]
3)a-More cis db kinds will DEC tail packing–>DEC TT DEC TT <–INC fluidity

Question 7

What are Lipid Rafts? [2]

Answer 7

Spontaneous/Non-random formed Cholesterol and Sphingolipid rich regions. transient “cliques” that form between different types of phospholipids
2)microdomains that move/localize signaling receptor proteins during cell-to-cell contact (VERY IMP for PROTEIN MOVEMENT)!

Question 8

Glycosylated Lipids (or GLYCOLIPIDS) are found ______

Answer 8

Glycolipids are found on the exterior side of the Plasma membrane FACING THE WATER–>are receptors

Question 9

What is the functional significance of the hydropathy index?

Answer 9

identifies protein transmembrane spanning regions (i.e.alpha-helix proteins) by analyzing hydrophobicity of the protein seq.
(should be high since it has to traverse all the way thru membrane)

Question 10

Describe Galectin 3 (Gal3)

Answer 10

Gal3 localizes to clean up pathological agents after they’ve ruptured a defense agent (phagosome/endosome/lysosome). Gal3 binds to sugars that are normally only inside the cell. If agent blows up, sugars will be available for Gal3 to bind.

Question 11

Describe the mechanism behind cell signaling from phosphatidylinositol

Answer 11

1) phosphatidylserine on the inner side of the Plasma Membrane gives a [-] charge to inner leaflet compared to outer
2) Phospholipase C cleaves inositol phospholipids to generate relay Signal and scaffold for protein Kinase C

Question 12

1) What 3 “anchor” methods are used by membrane proteins to half-way embed into the plasma membrane?
2) What is the purpose of this?

Answer 12

1) myristoylation=Protein+myrstrol group connects to a hydrophobic anchor
2) Palmityol anchor=adds protein to palmityol group and cysteine residue
3) farnesyl anchor=adds protein to cysteine and prenyl group

ALL GROUPS THE PROTEIN ARE ATTACHED TO WILL CONNECT TO A HYDROPHOBIC “ANCHOR” THAT’S HALF-WAY EMBEDDED IN PLASMA MEMBRANE. (Used by many receptors to be “right next door” to the TRANSmembrane receptors so they can receive message from outside w/out actually being outside)

Question 13

Beta Barrel transmembrane proteins are used a lot in _____-

Answer 13

Beta Barrel TRANSPORT IONS/PROTEINS/BIG MOLECULES

Question 14

• Membrane Proteins move laterally within the PM to ______
• *How do you measure this lateral movement of TM proteins?
• **What molecule could play a large role in how fast proteins move?

Answer 14

• Polarize the cell so that it can respond to toxins/pathogens/movmnt
• *FRAP (Fluorescence recovery after photobleaching) measures how fast a protein will move to recover a bleached area.
• *Fast recovery=HIGH Protein mobility

***Lipid Rafts “cholesterol-sphingolipid boats” are what some TM proteins are connected to=help to move those proteins to damaged/bleached area

Question 15

1) Lipid Rafts are often the point of _________
2) How are viruses related to this?
3) Why are Dendritic Cells a problem in regards to viruses?

Answer 15

1)Lipid Rafts often cell-to-cell contact between WBC
2) Viruses developed ability to BUD FROM LIPID RAFTS so when
cell-to-cell contact occurs, virus will bud from out of nowhere and infect new cells

3)Dendritic Cells pick up pathogens and present to B and T cells but keep them intact in a compartment. Virions hide out in tht compartment and attack the B and T when Dendrtc goes to present!

Question 16

C-Actin

Answer 16

Sits right below the Plasma membrane as a scaffolding protein for the PM to sit on.
2)Helps to coordinate cell-to-cell contact/synapses and the ultimate movement of the entire cell

Question 17

Sialic Acid

Answer 17

Glycolipid used as a receptor on ALL cells

Question 18

What is PS protein?

2)How does it work?

Answer 18

PS(normally on inner leaf of plasma membrane) tells macrophages to eat a cell

2)when it’s time to kill a cell, the transporter that removes PS from exterior leaf of plasma membrane is deactivated and scramblase enzyme starts to flip phospholipids inside out so PS on outside now.