BC368 Biochemistry of the Cell II
description
Transcript of BC368 Biochemistry of the Cell II
![Page 1: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/1.jpg)
BC368Biochemistry of the Cell II
BC368Biochemistry of the Cell II
Biological Membranes Chapter 11: Part 1February 10, 2015
![Page 2: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/2.jpg)
“Possibly the decisive step [in the origin of life] was the formation of the first cell, in which chain molecules were enclosed by a semi-permeable membrane which kept them together but let their food in.” J. B. S. Haldane,
1954
Plasma MembranePlasma Membrane
![Page 3: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/3.jpg)
Plasma MembranePlasma Membrane
![Page 4: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/4.jpg)
Membrane is composed of:
A. Lipids Phospholipids Sterols
B. Proteins Integral Peripheral
C. Carbohydrates Glycolipids Glycoproteins
Plasma MembranePlasma Membrane
![Page 5: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/5.jpg)
Plasma MembranePlasma Membrane
Variable components in different membrane types
![Page 6: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/6.jpg)
Membrane LipidsMembrane Lipids
Amphiphilic lipids
Major types: phospholipids, glycolipids, sterols
Glycolipid
sphingosine
glycerophospholipid sphingophospholipid
![Page 7: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/7.jpg)
PhospholipidsPhospholipids
Two classes: glycerophospholipids (aka phosphoglycerides) and sphingophospholipids Fig 10-7
![Page 8: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/8.jpg)
PhospholipidsPhospholipids
Two classes: glycerophospholipids (aka phosphoglycerides) and sphingophospholipids
![Page 9: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/9.jpg)
Two fatty acids; phosphate and polar “head group” on glycerol.
Vary in the FA’s and head group.
Membrane Lipids: 1A. GlycerophospholipidsMembrane Lipids: 1A. Glycerophospholipids
![Page 10: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/10.jpg)
Membrane Lipids: 1B. SphingophospholipidsMembrane Lipids: 1B. Sphingophospholipids
Named for the enigmatic Sphinx
Common in nerve and brain cell membranes
![Page 11: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/11.jpg)
Membrane Lipids: 1B. SphingophospholipidsMembrane Lipids: 1B. Sphingophospholipids
Named for the enigmatic Sphinx
note amidelinkage
Sphingosine replaces glycerol, so only 1 FA tail
![Page 12: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/12.jpg)
Example: sphingomyelin
Membrane Lipids: 1B. SphingophospholipidsMembrane Lipids: 1B. Sphingophospholipids
Head group = phosphocholine or phosphoethanolamine
![Page 13: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/13.jpg)
GlycolipidsGlycolipids
Two classes: glycosphingolipids and galactolipids
Fig 10-7
![Page 14: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/14.jpg)
Membrane Lipids: 2A. GlycosphingolipidsMembrane Lipids: 2A. Glycosphingolipids
Sphingolipids with carbohydrate head group; common on cell surfaces
Examples: cerebrosides and gangliosides
Glucose or galactose
SugarSugar
Ganglioside
![Page 15: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/15.jpg)
Membrane Lipids: 2B. GalactolipidsMembrane Lipids: 2B. Galactolipids
Diglycerides with galatose groups
Common in plant (thylakoid) membranes
![Page 16: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/16.jpg)
Membrane Lipids: 3. SterolsMembrane Lipids: 3. Sterols
Cholesterol and cholesterol-like compounds
![Page 17: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/17.jpg)
Lipid Components of MembranesLipid Components of Membranes
Lipid composition varies across different membranes.
Fig 11-2
![Page 18: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/18.jpg)
Lipid composition varies across the two leaflets of the same membrane.
Lipid Components of MembranesLipid Components of Membranes
![Page 19: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/19.jpg)
Turnover of Membrane LipidsTurnover of Membrane Lipids
Fig 10-16
![Page 20: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/20.jpg)
Defects in Membrane TurnoverDefects in Membrane Turnover
Deposits of gangliosides in Tay Sachs brain
![Page 21: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/21.jpg)
Lipids spontaneously aggregate in water as a result of the Hydrophobic Effect.
Lipid AggregatesLipid Aggregates
![Page 22: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/22.jpg)
Amphiphilic lipids form structures that solvate their head groups and keep their hydrophobic tails away from water.
Above the critical micelle concentration, single-tailed lipids form micelles.
Lipid AggregatesLipid Aggregates
Fig 11-4
![Page 23: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/23.jpg)
Double-tailed lipids form bilayers, the basis of cell membranes.
Lipid AggregatesLipid Aggregates
Bilayers can form vesicles enclosing an aqueous cavity (liposomes). Fig 11-4
Fig 11-4
![Page 24: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/24.jpg)
Membrane ProteinsMembrane Proteins
Integral proteins (includes lipid-linked): need detergents to remove
Peripheral proteins: removed by salt, pH changes
Amphitropic proteins: sometimes attached, sometimes not
![Page 25: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/25.jpg)
Usually alpha-helical, ~20-25 residues, mostly nonpolar.
Example: glycophorin of the erythrocyte.
Single Transmembrane Segment ProteinsSingle Transmembrane Segment Proteins
Fig 11-8
![Page 26: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/26.jpg)
7 alpha-helix motif is very common.
Example: bacteriorhodopsin
Multiple Transmembrane Segment ProteinsMultiple Transmembrane Segment Proteins
Fig 11-10
![Page 27: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/27.jpg)
Multiple transmembrane segments form β sheets that line a cylinder.
Example: porins.
Beta Barrel Transmembrane ProteinsBeta Barrel Transmembrane Proteins
![Page 28: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/28.jpg)
Fig. 11-14
Attached lipid provides a hydrophobic anchor.
Lipid-Linked Membrane ProteinsLipid-Linked Membrane Proteins
An important lipid anchor is GPI (glycosylated phosphatidylinositol.
![Page 29: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/29.jpg)
On exoplasmic face only
Membrane CarbohydratesMembrane Carbohydrates
![Page 30: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/30.jpg)
An example is the blood group antigens
On exoplasmic face only
Membrane CarbohydratesMembrane Carbohydrates
glycosphingolipids
![Page 31: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/31.jpg)
At its transition temperature (TM), the bilayer goes from an ordered crystalline state to an a disordered fluid one.
Membrane DynamicsMembrane Dynamics
Fig 11-16
![Page 32: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/32.jpg)
Phospholipids in a bilayer have free lateral diffusion.
Membrane DynamicsMembrane Dynamics
Fig 11-17
![Page 33: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/33.jpg)
Phospholipids in a bilayer have restricted movement between the two faces.
Membrane DynamicsMembrane Dynamics
Fig 11-17
![Page 34: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/34.jpg)
Flippases, floppases, and scramblases catalyze movement between the two faces.
Membrane DynamicsMembrane Dynamics
![Page 36: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/36.jpg)
Fluorescent Recovery After PhotobleachingFluorescent Recovery After Photobleaching
Fluorescent tag is attached to a membrane component (lipid, protein, or carbohydrate).
Fluorescence is bleached with a laser.
Recovery is monitored over time.
![Page 37: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/37.jpg)
Fluorescent Recovery After PhotobleachingFluorescent Recovery After Photobleaching
FRAP Movie
![Page 38: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/38.jpg)
Fig. 11-20
Some membrane proteins have restricted movement.
May be anchored to internal structures (e.g., glycophorin is tethered to spectrin).
Protein Mobility in the MembraneProtein Mobility in the Membrane
![Page 39: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/39.jpg)
Fig. 11-21
Lipid rafts are membrane microdomains enriched in sphingolipids, cholesterol, and certain lipid-linked proteins.
Thicker and less fluid than neighboring domains.
Protein Mobility in the MembraneProtein Mobility in the Membrane
![Page 40: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/40.jpg)
Lipid rafts are membrane microdomains enriched in sphingolipids, cholesterol, and certain lipid-linked proteins.
Thicker and less fluid than neighboring domains.
Protein Mobility in the MembraneProtein Mobility in the Membrane
Lipid Rafts
![Page 41: BC368 Biochemistry of the Cell II](https://reader036.fdocuments.in/reader036/viewer/2022070405/56813de1550346895da7b39e/html5/thumbnails/41.jpg)
Nature Reviews Molecular Cell Biology 4, 414-418 (May 2003)
Nature Reviews Molecular Cell Biology 4, 414-418 (May 2003)
Domains of gel/fluid lipid segregation in a model membrane vesicle, which is a mixture of fluid dilaurylphosphatidylcholine phospholipids with short, disordered chains and gel dipalmitoylphosphatidylcholine phospholipids with long, ordered chains. A red fluorescent lipid analogue (DiIC18) partitions into the more ordered lipids, whereas a green fluorescent lipid analogue (BODIY PC) partitions into domains of more fluid lipids. These domains in a model membrane are much larger than the domains of cell membranes.