1 Lipids, Biological Membranes and Cellular Transport Fatty Acids Triacylglycerols Polar Lipids Steroids and Other Lipids Biomembranes Biomembrane Transport.

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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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Unsaturated fatty acidsUnsaturated fatty acids

trans

ciscis, cis

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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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LecithinLecithin

Polar headNon-polar tail

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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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SteroidsSteroids

CholesterolCholesterol

Principal membrane lipid for fluidity.

HO

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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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OH

HO OH

COOH

O

HO OH

COOHOH

HO OH

COOH

EE11

FF11

FF22

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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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DiffusionDiffusion

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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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Semipermeable membraneSemipermeable membrane

Na+

Cl-

Na+

Na+

Cl-

Cl-

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OsmosisOsmosis

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Measurement ofosmotic pressureMeasurement of

osmotic pressure

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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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IsotonicIsotonic

A red blood celland plasma havethe sameosmotic pressure

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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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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


Let’s review the four step process.

membranebilayer

Na+ - K+

ATPasepump

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In the first step, 3 Na+ bind to the cytoplasmic sideof the transporter.

Extracellular side

Cytoplasm

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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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Two potassium ions then bind to the extracellular side of the transporter.

Extracellular side

CytoplasmP

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Enzyme-catalyzed hydrolytic elimination of thephosphoryl group returns the transporter to itsoriginal shape, moving the potassium into the cell.

Extracellular side

CytoplasmP

1 Lipids, Biological Membranes and Cellular Transport Fatty Acids Triacylglycerols Polar Lipids Steroids and Other Lipids Biomembranes Biomembrane Transport.

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