1 Lipids, Biological Membranes and Cellular Transport Fatty Acids Triacylglycerols Polar Lipids...
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Transcript of 1 Lipids, Biological Membranes and Cellular Transport Fatty Acids Triacylglycerols Polar Lipids...
1
Lipids, Biological Membranes and Cellular Transport
Lipids, Biological Membranes and Cellular Transport
Fatty Acids
Triacylglycerols
Polar Lipids
Steroids and Other Lipids
Biomembranes
Biomembrane Transport and Energy Consumption
Fatty Acids
Triacylglycerols
Polar Lipids
Steroids and Other Lipids
Biomembranes
Biomembrane Transport and Energy Consumption
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Types of lipidsTypes of lipids
Fatty AcidsFatty Acids
Saturated Unsaturated
Fatty AcidsFatty Acids
Saturated Unsaturated
AcylglycerolsAcylglycerols
Neutral Phosphoglycerols
AcylglycerolsAcylglycerols
Neutral Phosphoglycerols
NonacylglycerolsNonacylglycerols
Sphingolipids Steroids Waxes
NonacylglycerolsNonacylglycerols
Sphingolipids Steroids Waxes
Complex LipidsComplex Lipids
Lipoproteins Glycolipids
Complex LipidsComplex Lipids
Lipoproteins Glycolipids
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Lipid functionsLipid functions
Cell membrane structureCell membrane structure• Creates a barrier for the cell.• Controls flow of materials.
Energy storageEnergy storage• Fats stored in adipose tissue.
Hormones and VitaminsHormones and Vitamins• Hormones - communication between cells.• Vitamins - assist in the regulation of
biological processes.
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Fatty acid structureFatty acid structure
Long chain monocarboxylic acids
CH3(CH2)nCOOH
Size Range: C12 - C24
Always an even number of carbon.
Saturated - no double bonds.Unsaturated - one or more double bonds.
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Fatty acid structureFatty acid structure
CC
CC
CC
CC
CC
CC
CC
CC
O
OH
C CC
CC
CC
C CC
CC
CC
CC
O
OH
Saturated fatty acid
Unsaturated fatty acid
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Some common fatty acidsSome common fatty acids
Common IUPAC Name MP Formula Lauric n-dodecanoic 44 C11H23COOH
Palmitic n-hexadecanoic 63 C15H31COOH
Stearic n-octadecanoic 70 C17H35COOH
Palmitoleic cis-9-hexadecenoic 0 C15H29COOH
Oleic cis-9-octadecenoic 16 C17H33COOH
Linoleic cis,cis,9,12- 5 C17H31COOH
octadecadienoic
Presence of double bonds reduces melting point.
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React like any other carboxylic acid.
Esterification RCOOH + RROH R-C-ORR + H2O
Hydrolysis
RC-C-ORR + H2O R-C-OH + RROH
Acid-baseRCOOH + NaOH RCOO- Na+ + H2O
Reactions of fatty acidsReactions of fatty acids
O||
O||
O||
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Reactions of unsaturated fatty acids
Reactions of unsaturated fatty acids
• They can undergo the same reactions.• Will also undergo addition.• Most common addition is hydrogenation.
H H | |R-C=C-CH2CH2COOH R-CH2CH2CH2CH2COOH
H2Ni
Used to convert unsaturated vegetable oilsto margarine. Why?Why?
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Neutral acylglycerolsNeutral acylglycerols
Ester of glycerol and a fatty acid.Principal function is energy storage - fat.
C
C
C
H
H
H
H OH
OH
OH
H
R C
O
OH
C
C
C
H
H
H
H OH
OH
O
H
C
O
R
May have 1-3 fatty acids which can each be different. 1 - monoacylglycerol1 - monoacylglycerol
2 - diacylglycerol2 - diacylglycerol3 - triacylglycerol3 - triacylglycerol
+
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Neutral acylglycerolsNeutral acylglycerols
An example of a triacylglycerol.
OH
H
glycerol
O C
O C
O
O C
O
C
C
C
H
H
Hfatty acid
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GlycerophospholipidsGlycerophospholipids
Lipids that contain a phosphate group.
Modified fatModified fatPhosphate replaces one fatty acid chain.
UsesUsesProduction of cell membranes.Emulsifying agents.
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PhosphoglycerolsPhosphoglycerols
Lecithin - phophatidylcholine
Non-polar tail
Polar head
O CO
O CO
C
C
CH2
H
H
H
PO
O
O-
CH2CH2N
H 3 C
H 3 C
H 3 C -O-
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SphingolipidsSphingolipids
SphingolipidsSphingolipids• A type of phospholipid NOT derived from fat.
• Used primarily in nerve tissue - myelin sheath.
• In people, 25% of all lipids are sphingolipids.
CH3(CH2)12CH=CH-CH-OH | C-NH-CH || O
O | ||
CH2-O-P-O-CH2-CH2-N+(CH3)3
|
O-
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Sphingolipid exampleSphingolipid example
Spingomyelin
Sphingosine
Phosphate
CH3(CH2)12CH=CH-CH-OH | C-NH-CH || O
O | ||CH2-O-P-O-CH2-CH2-N+(CH3)3
O-
Fatty acid
Choline
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SteroidsSteroids
Broad class of compounds that all have the same base structure.
HO
Steroid nucleusSteroid nucleus
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CholesterolCholesterol
Associated with hardening of the arteries.
Appears to coat the arteries - plaque formation.plaque formation.
Results in Results in Increased blood pressure from:
Narrowing of arteriesReduced ability to stretch
Clot formation leading to:Myocardial InfarctionStroke
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SteroidsSteroids
Some reproductive hormones.
CH 3
CH 3
O
C
CH 3
O
progesteroneprogesterone
testosteronetestosteroneCH 3
CH 3
OH
O
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SteroidsSteroids
CortisoneCortisoneAssociated with many biological processes:metabolism of carbohydrates, treatment for rheumatoid arthritis, asthma, GI disorders, rashes ...
O
CH3
CH3O OH
C=O
CH2OH
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TerpenesTerpenes
Class of lipids that are all biosynthesized from isoprenes.
Important members include:Important members include:limonene, -carotene, gibberellic acid, squalene, and lycopene.
lycopene - red of tomato, paprika and watermelonlycopene - red of tomato, paprika and watermelon
CH3
H3C CH3CH3 CH3
CH3CH3
H3C
CH3H3C
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Unsaturated fatty acidseicosanoids
Unsaturated fatty acidseicosanoids
EicosanoidsEicosanoids• All are unsaturated.• All have twenty carbons.• Three groups
prostoglandinsprostoglandinsleukotrienesleukotrienesthromboxanesthromboxanes
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ProstaglandinsProstaglandins
Originally isolated from seminal fluid.
All are derived from arachidonic acid.
COOH
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ProstaglandinsProstaglandins
Biological effectsBiological effects• Stimulation of smooth muscles• Regulation of steroid production• Inhibition of gastric secretion• Inhibition of hormone-sensitive lipases• Inhibition / stimulation of plate aggregation• Regulation of nerve transmission• Sensitization to pain• Mediation of inflammatory response
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Blood clottingBlood clotting
Thromboxane AThromboxane A22
Produced by platelets in blood.Stimulates constriction of blood vessels.Aggregation of platelets.
ProstacyclinProstacyclinProduced by cells that line blood vessels.Reverses effects of Thromboxane A2.
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Inflammatory responseInflammatory response
Protective mechanism when tissue is damaged.
Results in swelling, redness, fever, and pain.
Prostaglandins promote this response.
Drugs like aspirin and IbuprofenAnti-inflammatoriesBlock prostaglandin synthesis. Cause reduction in this response.Tylenol - analgesic, not an anti-inflammatory
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Smooth muscle contractionsSmooth muscle contractions
Prostaglandins stimulate contractions in the reproductive system - uterine contractions
DysmenorrheaDysmenorrheaPainful menstruation.
Evidence shows that this may result froman excess of prostaglandins.
Physicians often order Motrin (Ibuprofen)for this.
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Gastrointestinal tractGastrointestinal tract
Prostoglandins will:Prostoglandins will:
Inhibit the secretion of hydrochloric acid in the stomach.
Increase secretion of mucus layer.Protects mucosa from acid invasion.
Aspirin inhibits prostaglandin production.Extended use can result in ulceration ofthe stomach lining. Why?Why?
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Other usesOther uses
In the kidneysIn the kidneys• Cause renal blood vessels to dilate.• Aid in excretion of water and electrolytes.
In the respiratory tractIn the respiratory tract• Produced by WBC in lungs - leukotrienes.• Cause constriction of bronchi - asthma
Other prostaglandins act as bronchodilators.
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Lipid-soluble vitaminsLipid-soluble vitamins
Vitamin A
Vitamin K
H3C CH3
CH3
HO
CH2
H3C
Vitamin D
-(CH=CH-CH=CH)2-CH2-OH|
CH3H3C CH3
CH3
O
O
CH3
CH2
HC C
CH3
(CH2CH CH
CH 3
CH2)2 H2C CH2 CH
CH 3
CH 3
2
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OH
Complex lipidsComplex lipids
Lipids bound to other molecules.
Combination results in a structure.
protein
phospholipid
cholesterol
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Cell and organelle membranes are composed of two layers - lipid bilayers.lipid bilayers.
BiomembranesBiomembranes
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Fluid structure of membranesFluid structure of membranes
Membranes are not static.Membranes are not static.Layers move over each other based on percent of unsaturated fatty acids.
lateral diffusion
rotation
flip-flop
rare
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Mosaic structure of membranesMosaic structure of membranes
ComponentsComponents• Peripheral membrane proteins
bound only to one side of membrane.
• Integral membrane proteinsimbedded within the membrane.
Both types of proteins can move around on surface of cell.
Proteins don’t flip in and out or act like revolving door.
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Mosaic structure of membranesMosaic structure of membranes
globularprotein
carbohydrate
phospholipids
-helixprotein
cholesterol
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Membrane transportMembrane transport
Cell membrane controls passage of materials in and out of cell.
Most transport is controlled by integral membrane transport proteins.
Small molecules, like water, pass through membrane on their own.
- passive transport
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Passive transportPassive transport
DiffusionDiffusionSmall molecules (CO2, O2, H2O) will simply pass through cell membrane.
Entropy is driving force - wants equal concentrations of both sides of membrane.
Membrane is considered selectively permeable to these molecules.
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Facilitated diffusionFacilitated diffusion
PermeasesPermeases - Specific protein transports materials across a membrane.
HCO3_
_Cl
HCO3_
_Cl
HCO3_
_Cl
HCO3_
_Cl
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OsmosisOsmosis
The diffusion of a solvent from a dilute solution through a semipermeable membrane to a more concentrated one.
Semipermeable membranesSemipermeable membranes- only allow small molecules to go
through- cell walls are semipermeable
membranes
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Osmotic pressureOsmotic pressure
Three conditions can exist for cells
- the concentration is the same on both sides - isotonicisotonic
- the concentration is greater on the inside hypertonichypertonic
- the concentration is greater on the outside - hypotonichypotonic
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Cells in ‘high salt’ solutions Cells in ‘high salt’ solutions
If the level of saltin the plasma is toohigh, the cellcollapses.Hypotonic cell,hypertonic solution.
crenationcrenation - water isdrawn out of the cell.
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Cells in ‘low salt’ solutionsCells in ‘low salt’ solutions
If the level of saltin the plasma istoo low, the cellswells and ruptures.Hypertonic cell,hypotonic solution.hemolysishemolysis - water isdrawn into the cell.
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Active transport: ion pumpingActive transport: ion pumping
When a cell must expend energy to move needed materials across the cell membrane.
ATP S ADP + Pi
S
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Examples of membrane transport
Examples of membrane transport
A wide range of proteins are present in and on cell membranes.
The presence of these proteins impart a distinctive set of biological and chemical properties.
ExamplesExamplesGlycophorin A of the erythrocyte membrane.Glucose permease of erythrocyte membrane.Na+ - K+ ATPase pump.Ion-selective channels.
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Erythrocyte membraneErythrocyte membrane
GlycophorinsGlycophorinsA family of glycoproteins that can be extracted from red blood cells using detergents.
Glycophorin AGlycophorin A• 131 amino acid residues and 100
monosaccharides in 16 groups.
• An integral protein of the erythrocyte membrane which penetrates through the bilayer.
• 30 hydrophobic residues act to anchor the protein with a proposed helical structure.
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Glycophorin AGlycophorin A
-COO-
+H N-3
erythrocytemembrane
extracellularfluid
cytoplasm
oligosaccharides
glycophorin A
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Glycophorin AGlycophorin A
Sixty percent of it’s mass is from carbohydrates, with sialic acid being abundant.
Half of the protein extends outside the cell into the extracellular fluid.
While much is known about it’s structure, its biological function has not been found.
The -helicial region may serve as a channel for solute transport.
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Glucose permease oferythrocyte membranes
Glucose permease oferythrocyte membranes
Glucose is the primary fuel for red blood cells.
Facilitated diffusion is used to transport it into the cell - glucose permease.
This permease consists of a single polypeptide chain with almost 500 amino acid residues and 12 hydrophobic domains spanning the membrane.
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Glucose permeaseGlucose permease
Glucose in blood[S] ~ 5 mM
Intercellular glucose[S] ~ 5 mM
Energy-yieldingmetabolism
Erythrocytemembrane
Extracellular fluid
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Glucose permeaseGlucose permease
Transport by glucose permease involves the following steps:
• Binding of the glucose to a specific extracellular site.
• Passage of glucose through the membrane - possibly via a channel formed by the permease.
• Release of glucose on the cytoplasmic side.
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Na+ - K+ ATPase pumpNa+ - K+ ATPase pump
Eukaryotic cells maintain different internal and external levels of Na+ and K+.
SodiumSodiumInside 12 mMOutside 145 mM
PotassiumPotassiumInside 140 mMOutside 4 mM
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Na+ - K+ ATPase pumpNa+ - K+ ATPase pump
An active transport process is used to pump sodium out and bring potassium in.
NaNa++ - K - K++ ATPase pump ATPase pump• Composed of two protein subunits that
span the cell membrane.• The ending asease is used because the
process has characteristics of an enzymatic action.
• ATP is required as the energy source for the ‘coupled reaction.’
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Extracellular side
Cytoplasm
Na+ - K+ ATPase pumpNa+ - K+ ATPase pump
Let’s review the four step process.
membranebilayer
Na+ - K+
ATPasepump
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Na+ - K+ ATPase pumpNa+ - K+ ATPase pump
In the first step, 3 Na+ bind to the cytoplasmic sideof the transporter.
Extracellular side
Cytoplasm
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Na+ - K+ ATPase pumpNa+ - K+ ATPase pump
Enzyme-catalyzed phosphorylation by ATP triggersa conformational change that shifts the sodium ionsoutside the cell.
Extracellular side
Cytoplasm
ATP ADP
P
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Na+ - K+ ATPase pumpNa+ - K+ ATPase pump
Two potassium ions then bind to the extracellular side of the transporter.
Extracellular side
CytoplasmP