Module 8 ~ Lipids

What are the structural characteristics of Lipids?

• a defining feature of insolubility in water

• lower in weight than other biomolecules

• form aggregates rather than polymers

What are the functional characteristics of lipids?

• energy storage

• structural components of membranes

• active roles: signaling (intracellular and extracellular, and enzyme co-factors & vitamins

What does a fatty acid look like?

• hydrocarbon with a carboxylic head: the head is the first carbon

• differ in length and degree

• usually an even number of C’s (12-24)

What is the significance of double bonds within fatty acids?

• saturated have NO double bonds

• unsaturated = one double

• poly = multiple

• double = cis and separated by a methylene group

Which three points of potential variability does fatty acid nomenclature address?

• length

• presence/absence of double bonds

• location of double bonds

Which type of chains have a stronger association through hydrophobic and van der Waals interactions?

• longer more than shorter

• saturated more than unsaturated (4×4’s packed neatly)

What is the melting temperature a reflection of in fatty acids?

• length and degree of saturation of the hydrocarbon tails

• double bonds have a greater influence than the length of the tail on the fatty acid associations

• inc length = inc melting temp

• saturated + long = solid

• unsaturated: the more double bonds the more liquid

What are fatty acids required for energy stored as?

• triacylglycerols

What is the name of the intracellular space of energy storage in animal tissues?

• adipocytes

What do shorter hydrocarbons mean in terms of double bonds?

• more double bonds and more fluidity

What are ester linkages?

• what joins the three fatty acids to a glycerol backbone

• remove the polar carboxyl group to make a more hydrophobic molecule

How much more energy is in fats than carbs on a gram basis?

• 6 times

What is low oxidation state?

• less oxygenated fuels burn more efficiently

• more energy in bacon (fats) than in a bagel

What is hydration state?

• lipids are hydrophobic with limited interaction with water providing a compact, dehydrated energy storage form

• like the jelly powder vs making the jello: water makes it heavy

What is saponification?

• treating fats with a base

  • making soap from fat

• treatment of fat with a strong base breaks the ester linkages to release free fatty acids

What do micelles do?

• work in detergents and soap to capture hydrophobic molecules because of its hydrophilic head and phobic tail

What is olestra?

• taste and looks like fat, but can’t be processed by our digestive system

• eight fatty acids linked to a sugar group

• causes loose stools

What do waxes serve as?

• esters of long-chain fatty acids and long chain alcohols

• insoluble and high melting temp (60-100 C)

• on leaves, fruits, animal skin and feathers

What do membrane bilayers do?

• define cells and regulate the composition of the intracellular environment

• spontaneous

How can membrane lipids be classified?

• based on their backbone (glycerol or sphingosine)

• by polar head group (phospho. vs glyco)

What is the most abundant lipids in membranes?

• glycerophospholipids

What is the make-up of glycerophospholipids?

• a glycerol backbone with a phosphate at the C3 position (Glycerol 3-phosphate)

• Glycerol-3Phosphate + 2 fatty acids = phosphatide or diacylglycerol 3-phosphate

In glycerophospholipids, which is the point of attachment for a variety of polar head groups?

• the phosphate group

How can the polar head groups in glycerophospholipids differ?

• their charge: positive, negative, or neutral

• have specialized functions above and beyond just polar head groups

What does phosphatidylserine do?

• healthy cell, they are positioned inside and pointing inside the cell

• cancerous, infected: they become pointed outside and triggers programed cell death (apoptosis)

What does phosphatidylinositol do?

• involved in intracellular signal transduction and messenger

Why do some plants use sugar and sulfate polar head groups instead of phosphate?

• sometimes its a limiting resource

• conserve use of phosphate for more critical applications such as nucleic acids

• these are called galactolipids or sulfolipids

What are spingolipids?

• derived from sphingosine, a long chain amino alcohol

• structurally similar to monoacly glycerol

How is ceramide formed?

• single fatty acid linked by amide bond (amino and carboxyl) to form ceramide

  • structurally similar to diacylglycerol

What are the common sphingolipids?

• sphingomyelins: phosphocholine

• cerebrosides: sing sugar, glycosphingolipid

• gangliosides: multiple sugar, glycosphingolipids

What determine blood types?

• glycosphingolipids pointing out for the cell to recognize them

What do membrane lipids of extremophiles often contain?

• ether linkages

• branch points within the hydrocarbon tails

• membrane spanning hydrocarbon tails composed from a single molecule

What are sterols?

• structural membrane lipids

• contain four fused ring steroid nucleus: 3 -six carbon rings and a 5 carbon D ring

• rigid and nearly planar

• precursors for many biologically active products

• base in cholesterol

What is cholesterol?

• serves for mediating membrane fluidity and serving as a precursor of steroid hormones and bile salts

• is breaking the movement and breaking the crowd in smaller groups, dampening movement of fluidity

What are some active roles of lipids?

• intracellular signaling molecules

• hormones

• enzyme factors

• enzyme cofactors

• pigments

• vitamins

What are eicosanoids?

• paracrine hormones: localized and specific

• derivatives of fatty acids: arachidonic acid, is the precursor for other classes

What are the three types of eicosanoids and what are their roles?

• Prostaglandins

  • constrictions of blood vessels, fever and inflammation

• Thromboxanes

  • involved in blood clot formation

• Leukotrienes

  • smooth-muscle contraction: produced in a different pathway

What can block fever and blood clot formation?

• Aspirin, but doesn’t block Leukotrienes because it has a specific pathway

What do steroid hormones do?

• hydrophobic oxidized sterol derivatives

• carried through blood stream by carrier proteins

• Pass through plasma membrane to bind receptors in the nucleus

• alter patterns of gene expressions and metabolism

How do phosphatidylinositols act as intracellular signal?

• have 4,5 biphosphate on the inner membrane face

• takes info that’s outside and convert it to intracellular responses

• receptor causes the reaction inside

What signaling molecule does phosphatidylinositols have

• the phospholipase C

  • triggers cleavage of the polar head group to produce inositol to release calcium which in turn activates specific protein kinases, the body diffuses and does so as well (not redundant, a safety feature)

*has a domino effect

What are vitamins?

• four lipids: ADEK

• all contain rings and long aliphatic side chains

• highly hydrophobic

• differ widely in their functions

What does Vitamin D do?

• regulates calcium uptake and deposition

• obtain from diet or produced endogenously

• endogenous production (body does it by itself) ONLY through exposure of UV light

What is associated with insufficient and excessive of Vit D?

• insufficient = skeletal defects (Rickets)

• excessive = calcification of soft tissues

Where is Vit A obtained from?

• liver, egg yolks, and milk products

*some animals have sufficient Vit A in their livers to present a danger to humans if they were to consume them

What are the three forms of Vit A?

• alcohol (retinol)

• aldehyde (retinal): light sensitive compound with a role in vision, “red eye” in photos results from retinal

• retinoic acid

What is vitamin E?

• a reducing reagent that scavenges oxygen free radicals

• may prevent damage to fatty acid in membranes

• often used as an additive in cosmetics

What does the deficiency of Vitamin E cause?

• scaly skin, muscular weakness and sterility

What is Vitamin K?

• required for the synthesis of blood coagulation proteins

• was used as rat poison where is caused rodents to suffer uncontrolled bleeding

• now given to individuals who suffer excessive blood clotting