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Biomolecules of life > Week 4 - lipids and cell membranes part 2 > Flashcards

Week 4 - lipids and cell membranes part 2 Flashcards

1
Q

What is the structure of bacteriorhodopsin?

A
  • 7 TM helices
  • protein uses light energy to transport protons form inside to outside, generating a proton gradient to used to form ATP
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2
Q

Describe the amino acid sequence of bacteriorhodopsin

A
  • seven alpha-helical regions (mostly hydrophobic)
  • charged residues in red in between
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3
Q

Whats the structure of porin?

A
  • channel forming b-strands off porin
  • sugars and amino acids can passively diffuse through the hydrophilic pore
  • amino acid primary structure arranged alternating - hydrophobic parts in contact with membrane, hydrophilic parts lie inside of barrel
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4
Q

How is prostaglandin H2 synthasase 1

A
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5
Q

Describe the structure of membrane proteins

A
  • parts of the protein that interact with the hydrophobic parts of the membrane have non-polar side-chains
  • structures within the membrane are regular so that all hydrogen bonds are established
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6
Q

name the bond energy of covalent bonds

A

Ca. 100 kcal/mol

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7
Q

Name the bond energy of electrostatic bonds

A

Ca. 10-40 kcal/mol

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8
Q

Name the bond energy of hydrogen bonds

A

Ca. 1-10 kcal/mol

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9
Q

Name the bond energy of hydrophobic (van der waals) bonds

A

Ca. 0.1-2 kcal/mol

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10
Q

How to predict transmembrane helices accurately form the aa sequence?

A

Hydrocarbon core of membrane is typically 30 A wide, length that can be traversed by 20 residue aloha helix
- hydropathy plot - calc of hydrophobicity index

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11
Q

What is the most hydrophobic amino acid in nature?

A

Phenolalanine

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12
Q

What is the most hydrophilic amino acid found in nature?

A

Argenine

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13
Q

Was the hydropathy plot valid for detecting beta strands?

A

No, beta strand structure you have alternating hydrophilic/ hydrophobic energy - fluctuations in energy, not high enough

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14
Q

What can be used to observe the rapid lateral diffusion of lipids and many membrane proteins?

A

Fluorescence recovery after photobleaching (FRAP)

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15
Q

Explain the experiment for FRAP

A
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16
Q

What does the rate of recovery of fluoresence depend on?

A

Lateral mobility of the fluoresence-labelled componenet, diffusion constant D

17
Q

Name the formula used to calculate rate of diffusion

A

S= (4Dt)1/2
S - average distance traversed in time t
D- diffusion constant

18
Q

What is the average time of diffusion in phospholipid molecules?

A

2 mm in 1 sec (D= 1mm^2 1s-1)

19
Q

Protein rhodopsin

A
20
Q

Fibronectin

A
21
Q

How much slower is transverse diffusion for a lipid?

A

About 109 times

22
Q

Is transverse diffusion ever observed for a protein? Whats the result?

A

NO, membrane asymmetry can be perserved for long periods

23
Q

What factors affect membrane fluidity?

A
  • transition form solid-like to fluid-like depends on the length of fatty acid chains and their degree of unsaturation
  • saturated are more rigid
  • a cis-bond lowers Tm
24
Q

Stearate

A
25
Q

Oleate

A
26
Q

What is the membrane fluidity in bacteria like?

A
  • regulate the fluidity of their membranes by varying the number of double bonds and the length of their fatty acid chains
  • ratio of saturated/ unsaturated fatty acid …
27
Q

How does the membrane fluidity in animals differ?

A
  • cholesterol is key regulator
  • different shape of cholesterol disrupts interaction between fatty acid chains
  • may form specific complexes with lipid rafts
    -these may bring together proteins participating in single transduciton pathways
28
Q

What is the membrane protein orientation like ?

A
  • unique, after synthesis, they are inserted asymmetrically - do not rotate
29
Q

What is the orientation of lipids?

A
  • asymmetrically distributed as a consequence of their biosynthesis, not usually absolute, except for glycolipids
30
Q

RBC

A
31
Q

Bacteria

A
32
Q

Perociomes

A
33
Q

Mitochondira

A
34
Q

Nucleus

A
35
Q

What do membranes do in eukaryotic cells?

A

Compartmentalisation

36
Q

What is the function of receptor-mediated endocytosis?

A
  • key role in cholesterol metabolism
  • cholesterol released form low lipoprotein complex and stored or used for membrane biosynthesis
  • protein degraded
37
Q

What can exploit endocytosis?

A

Viruses, some bacteria to invade
- reverse process is a key step in release of neurotransmitter

Biomolecules of life (10 decks)

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