Title: Chapter 9 (part 2)
1Chapter 9 (part 2)
2Triacylglycerols (TAG)
- Fats and oils
- Impt source of metabolic fuels
- Because more reduced than carbos, oxidation of
TAG yields more energy (16 kJ/g carbo vs. 37 kJ/g
TAG) - Americans obtain between 20 and 30 of their
calories from fats and oils. 70 of these
calories come from vegetable oils - Insulation subcutaneous fat is an important
thermo insulator for marine mammals
3Olestra
- Olestra is sucrose with fatty acids esterified to
OH groups - digestive enzymes cannot cleave fatty acid groups
from sucrose backbone - Problem with Olestra is that it leaches fat
soluble vitamins from the body
4Head
Tail
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6rubber
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8The reason rubber is elastic and gutta percha is
plastic
Rubber forms an amorphous structure
Gutta-percha forms crystalline arrays
9Steroids
- Based on a core structure consisting of three
6-membered rings and one 5-membered ring, all
fused together - Triterpenes 30 carbons
- Cholesterol is the most common steroid in animals
and precursor for all other steroids in animals - Steroid hormones serve many functions in animals
- including salt balance, metabolic function and
sexual function
10cholesterol
- Cholesterol impt membrane component
- Only synthesized by animals
- Accumulates in lipid deposits on walls of blood
vessels plaques - Plaque formation linked to cardiovascular disease
11Steroids
12Many steroids are derived from cholesterol
13Membranes
- Barrier to toxic molecules
- Help accumulate nutrients
- Carry out energy transduction
- Facilitate cell motion
- Modulate signal transduction
- Mediate cell-cell interactions
14The Fluid Mosaic Model
- The phospholipid bilayer is a fluid matrix
- The bilayer is a two-dimensional solvent
- Lipids and proteins can undergo rotational and
lateral movement - Two classes of proteins
- peripheral proteins (extrinsic proteins)
- integral proteins (intrinsic proteins)
15The Fluid Mosaic Model
16Motion in the bilayer
- Lipid chains can bend, tilt and rotate
- Lipids and proteins can migrate ("diffuse") in
the bilayer - Frye and Edidin proved this (for proteins), using
fluorescent-labelled antibodies - Lipid diffusion has been demonstrated by NMR and
EPR (electron paramagnetic resonance) and also by
fluorescence measurements - Diffusion of lipids between lipid monolayers is
difficult.
17fusion
After 40 minutes
18Flippases
- Lipids can be moved from one monolayer to the
other by flippase proteins - Some flippases operate passively and do not
require an energy source - Other flippases appear to operate actively and
require the energy of hydrolysis of ATP - Active flippases can generate membrane asymmetries
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20Membranes are Asymmetric
In most cell membranes, the composition of the
outer monolayer is quite different from that of
the inner monolayer
21Membrane Phase Transitions
- Below a certain transition temperature, membrane
lipids are rigid and tightly packed - Above the transition temperature, lipids are more
flexible and mobile - The transition temperature is characteristic of
the lipids in the membrane
22Phase Transitions
- Only pure lipid systems give sharp, well-defined
transition temperatures - Red pure phospholipid
- Blue phopholipid cholesterol
23Structure of Membrane Proteins
- Integral (intrinsic) proteins
- Peripheral (extrinsic) proteins
- Lipid-anchored proteins
24Peripheral Proteins
- Peripheral proteins are not strongly bound to the
membrane - They can be dissociated with mild detergent
treatment or with high salt concentrations
25Integral Membrane Proteins
- Integral proteins are strongly imbedded in the
bilayer - They can only be removed from the membrane by
denaturing the membrane (organic solvents, or
strong detergents) - Often transmembrane but not necessarily
- Glycophorin, bacteriorhodopsin are examples
26Seven membrane-spanning alpha helices, connected
by loops, form a bundle that spans the bilayer in
bacteriorhodopsin. The light harvesting
prosthetic group is shown in yellow. Bacteriorhodo
psin has loops at both the inner and outer
surface of the membrane. It displays a common
membrane-protein motif in that it uses alpha
helices to span the membrane.
27Lipid-Anchored Proteins
- Four types have been found
- Amide-linked myristoyl anchors
- Thioester-linked fatty acyl anchors
- Thioether-linked prenyl anchors
- Glycosyl phosphatidylinositol anchors
28Amide-Linked Myristoyl Anchors
- Always myristic acid
- Always N-terminal
- Always a Gly residue that links
29Thioester/ester-linked Acyl Anchors
- Broader specificity for lipids - myristate,
palmitate, stearate, oleate all found - Broader specificity for amino acid links - Cys,
Ser, Thr all found
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31Thioether-linked Prenyl Anchors
- Prenylation refers to linking of "isoprene"-based
groups - Always Cys of CAAX (CCys, AAliphatic, Xany
residue) - Isoprene groups include farnesyl (15-carbon,
three double bond) and geranylgeranyl (20-carbon,
four double bond) groups
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