Lipids and Triacylglycerols

Overview and Structural Classification of Lipids

• Definition and General Properties:

  • Lipids are biomolecules containing fatty acids or a steroid nucleus.

  • The term is derived from the Greek word lipos, meaning "fat".

  • Lipids are nonpolar and insoluble in water, but soluble in organic solvents.

  • They are extracted from biological cells using organic solvents.

• Classification of Lipids:

  • Lipids Containing Fatty Acids:

  • Waxes: Esters formed from a long-chain fatty acid and a long-chain alcohol.

  • Triacylglycerols (Fats and Oils)Grid-structured esters composed of a glycerol backbone esterified to three fatty acid molecules.

  • Glycerophospholipids: Composed of a glycerol backbone esterified to two fatty acids and a phosphate group bonded to an amino alcohol ($\text{PO}_4 - \text{Amino alcohol}$).

  • Prostaglandins: Carboxylic acids containing $20$ carbon atoms, synthesized from fatty acids, featuring a five-carbon ring.

  • Sphingolipids: Built on a sphingosine backbone linked to a fatty acid, a phosphate group, and an amino alcohol.

  • Glycosphingolipids: Built on a sphingosine backbone linked to a fatty acid and a carbohydrate moiety (sugar).

  • Lipids Not Containing Fatty Acids:

  • Steroids: Characterized by a fused four-ring steroid nucleus structure ($3$ cyclohexane rings and $1$ cyclopentane ring). Subcategories include:

    • Cholesterol

    • Bile salts

    • Steroid hormones

Fatty Acid Structure, Nomenclature, and Properties

• General Characteristics of Fatty Acids:

  • Long-chain carboxylic acids featuring an unbranched hydrocarbon tail attached to a terminal carboxyl group ($\text{-COOH}$).

  • Typically contain an even number of carbon atoms, usually ranging from $12$ to $18$ carbon atoms.

  • Highly nonpolar and insoluble in water.

  • Represented structurally using condensed structural formulas or line-bond formulas.

• Saturated Fatty Acids:

  • Contain only single carbon-carbon bonds ($\text{C}-\text{C}$) within the hydrocarbon chain.

  • Hydrocarbon chains are flexible and extended, allowing molecules to fit closely together in a regular, dense pattern.

  • Strong dispersion attractions exist between closely packed fatty acid chains.

  • Require high amounts of energy to overcome intermolecular forces, resulting in high melting points that make them solids at room temperature ($25\,^\circ\text{C}$).

• Common Saturated Fatty Acids:

  • Lauric acid:

  • Carbon count: $12$

  • Common source: Coconut

  • Melting point: $43\,^\circ\text{C}$

  • Condensed formula: $\text{CH}_3-(\text{CH}_2)_{10}-\text{COOH}$

  • Myristic acid:

  • Carbon count: $14$

  • Common source: Nutmeg

  • Melting point: $54\,^\circ\text{C}$

  • Condensed formula: $\text{CH}_3-(\text{CH}_2)_{12}-\text{COOH}$

  • Palmitic acid:

  • Carbon count: $16$

  • Common source: Palm

  • Melting point: $62\,^\circ\text{C}$

  • Condensed formula: $\text{CH}_3-(\text{CH}_2)_{14}-\text{COOH}$

  • Stearic acid:

  • Carbon count: $18$

  • Common source: Animal fat

  • Melting point: $69\,^\circ\text{C}$

  • Condensed formula: $\text{CH}_3-(\text{CH}_2)_{16}-\text{COOH}$

• Unsaturated Fatty Acids:

  • Contain one or more carbon-carbon double bonds ($\text{C}=\text{C}$) along the hydrocarbon chain.

  • Natural unsaturated fatty acids predominantly possess cis double bond configurations.

  • A cis double bond introduces a rigid bend or "kink" in the hydrocarbon chain.

  • "Kinks" prevent fatty acid molecules from packing closely together, weakening intermolecular dispersion forces between chains.

  • Require less energy to separate, leading to significantly lower melting points compared to saturated fatty acids of equivalent chain length. Consequently, they are liquids at room temperature.

• Common Unsaturated Fatty Acids:

  • Monounsaturated Fatty Acids (contain exactly one $\text{C}=\text{C}$ double bond):

  • Palmitoleic acid:

    • Carbon count: $16$

    • Common source: Butter

    • Melting point: $0\,^\circ\text{C}$

    • Condensed formula: $\text{CH}_3-(\text{CH}_2)_5-\text{CH}=\text{CH}-(\text{CH}_2)_7-\text{COOH}$

  • Oleic acid:

    • Carbon count: $18$

    • Common source: Olives, corn

    • Melting point: $13\,^\circ\text{C}$

    • Condensed formula: $\text{CH}_3-(\text{CH}_2)_7-\text{CH}=\text{CH}-(\text{CH}_2)_7-\text{COOH}$

  • Polyunsaturated Fatty Acids (contain two or more $\text{C}=\text{C}$ double bonds):

  • Linoleic acid:

    • Carbon count: $18$

    • Common source: Soybeans, sunflowers

    • Melting point: $-9\,^\circ\text{C}$

    • Condensed formula: $\text{CH}_3-(\text{CH}_2)_4-\text{CH}=\text{CH}-\text{CH}_2-\text{CH}=\text{CH}-(\text{CH}_2)_7-\text{COOH}$

  • Linolenic acid:

    • Carbon count: $18$

    • Common source: Corn

    • Melting point: $-17\,^\circ\text{C}$

    • Condensed formula: $\text{CH}_3-(\text{CH}_2-\text{CH}=\text{CH})_3-(\text{CH}_2)_7-\text{COOH}$

  • Arachidonic acid:

    • Carbon count: $20$

    • Common source: Meat, eggs, fish

    • Melting point: $-50\,^\circ\text{C}$

    • Condensed formula: $\text{CH}_3-(\text{CH}_2)_3-(\text{CH}_2-\text{CH}=\text{CH})_4-(\text{CH}_2)_3-\text{COOH}$

• Melting Point Comparison Analysis:

  • An $18$-carbon saturated fatty acid (Stearic acid) has a melting point of $69\,^\circ\text{C}$.

  • An $18$-carbon monounsaturated fatty acid with one double bond (Oleic acid) drops to a melting point of $13\,^\circ\text{C}$.

  • An $18$-carbon polyunsaturated fatty acid with two double bonds (Linoleic acid) drops further to $-9\,^\circ\text{C}$.

  • An $18$-carbon polyunsaturated fatty acid with three double bonds (Linolenic acid) has a melting point of $-17\,^\circ\text{C}$.

  • Rule: As the number of cis double bonds increases, the number of kinks increases, decreasing the close-packing efficiency and lowering the melting point.

Essential Fatty Acids and Prostaglandins

• Prostaglandins:

  • Hormone-like substances synthesized in low concentrations in almost all mammalian tissues.

  • Possess $20$ carbon atoms derived from polyunsaturated fatty acids such as arachidonic acid.

  • Structural features include a cyclopentane ring, hydroxyl groups ($\text{-OH}$) at carbon $11$ ($\text{C}11$) and carbon $15$ ($\text{C}15$), and a trans double bond at carbon $13$ ($\text{C}13$).

  • Biological functions: Synthesized locally at sites of tissue damage; mediate inflammatory responses, induce fever, and stimulate pain receptors.

  • Medical inhibition: Nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin, ibuprofen, and naproxen block the enzymatic conversion of arachidonic acid into prostaglandins, relieving pain, inflammation, and fever.

• Omega-6 and Omega-3 Fatty Acids:

  • Classified according to the position of the first double bond counting from the methyl ($\text{CH}_3-$) end, designated as the omega ($\omega$) carbon.

  • Omega-6 Fatty Acids:

  • First double bond occurs at carbon $6$ ($\text{C}6$) from the methyl end.

  • Prevalent in vegetable oils.

  • Example: Linoleic acid ($\text{CH}_3-(\text{CH}_2)_4-\text{CH}=\text{CH}-\dots$).

  • Omega-3 Fatty Acids:

  • First double bond occurs at carbon $3$ ($\text{C}3$) from the methyl end.

  • Prevalent in cold-water fish oils and plant sources.

  • Examples:

    • Linolenic acid ($\text{CH}_3-\text{CH}_2-\text{CH}=\text{CH}-\dots$)

    • Eicosapentaenoic acid (EPA)

    • Docosahexaenoic acid (DHA)

• Structural Formula Examples for 10-Carbon Fatty Acids:

  • Saturated 10-carbon fatty acid:     $\text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{COOH}$

  • Monounsaturated omega-3 10-carbon fatty acid:     $\text{CH}_3-\text{CH}_2-\text{CH}=\text{CH}-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{COOH}$

  • Monounsaturated omega-6 10-carbon fatty acid:     $\text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{CH}_2-\text{CH}=\text{CH}-\text{CH}_2-\text{CH}_2-\text{COOH}$

Waxes and Triacylglycerols (Fats and Oils)

• Waxes:

  • Esters formed from a long-chain saturated fatty acid and a long-chain alcohol.

  • Found on plant leaves and stems as a waterproof coating that minimizes water evaporation and protects against insects.

  • Representative Waxes:

  • Beeswax:

    • Structural formula: $\text{CH}_3-(\text{CH}_2)_{14}-\text{C}(=\text{O})-\text{O}-(\text{CH}_2)_{29}-\text{CH}_3$

    • Biological source: Honeycomb

    • Applications: Candles, shoe polish, wax paper

  • Carnauba wax:

    • Structural formula: $\text{CH}_3-(\text{CH}_2)_{24}-\text{C}(=\text{O})-\text{O}-(\text{CH}_2)_{29}-\text{CH}_3$

    • Biological source: Brazilian palm tree

    • Applications: Polishes for furniture, automobiles, floors, and shoes

  • Jojoba wax:

    • Structural formula: $\text{CH}_3-(\text{CH}_2)_{18}-\text{C}(=\text{O})-\text{O}-(\text{CH}_2)_{19}-\text{CH}_3$

    • Biological source: Jojoba plant

    • Applications: Candles, soaps, cosmetic formulations

• Triacylglycerols (Fats and Oils):

  • Major storage form of energy in biological systems.

  • Formed via esterification: Three hydroxyl groups ($\text{-OH}$) of glycerol react with the carboxyl groups ($\text{-COOH}$) of three fatty acid molecules, producing three ester bonds and eliminating three water molecules ($3\,\text{H}_2\text{O}$).

$\text{Glycerol} + 3\text{ Fatty Acids} \xrightarrow{\text{Esterification}} \text{Triacylglycerol} + 3\,\text{H}_2\text{O}$

• Example: Reaction of glycerol with three stearic acid molecules yields glyceryl tristearate (commonly named tristearin).

• Physical Differences Between Fats and Oils:

  • Fats:

  • Solid at room temperature ($25\,^\circ\text{C}$).

  • Prevalent in animal products (e.g., meat, whole milk, butter, cheese, beef tallow).

  • Contain predominantly saturated fatty acid chains that allow compact molecular packing.

  • Oils:

  • Liquid at room temperature ($25\,^\circ\text{C}$).

  • Prevalent in plant seeds and fruits (e.g., olive, corn, canola, soybean, sunflower, safflower).

  • Rich in unsaturated fatty acids with cis double bonds, preventing tight packing.

  • Example: Olive oil contains high proportions of oleic acid ($18$-carbon monounsaturated), forming glyceryl trioleate (triolein).

• Fatty Acid Composition and Melting Points of Fats and Oils:

  • Beef tallow: Melting point $42\,^\circ\text{C}$; ~$50\%$ saturated, ~$48\%$ monounsaturated, ~$2\%$ polyunsaturated.

  • Butter: Melting point $32\,^\circ\text{C}$; ~$64\%$ saturated, ~$32\%$ monounsaturated, ~$4\%$ polyunsaturated.

  • Coconut oil: Melting point $25\,^\circ\text{C}$; ~$92\%$ saturated, ~$6\%$ monounsaturated, ~$2\%$ polyunsaturated.

  • Olive oil: Melting point $-6\,^\circ\text{C}$; ~$10\%$ saturated, ~$84\%$ monounsaturated, ~$6\%$ polyunsaturated.

  • Canola oil: Melting point $-10\,^\circ\text{C}$; ~$5\%$ saturated, ~$65\%$ monounsaturated, ~$30\%$ polyunsaturated.

  • Soybean oil: Melting point $-16\,^\circ\text{C}$; ~$13\%$ saturated, ~$30\%$ monounsaturated, ~$57\%$ polyunsaturated.

  • Sunflower oil: Melting point $-18\,^\circ\text{C}$; ~$9\%$ saturated, ~$24\%$ monounsaturated, ~$67\%$ polyunsaturated.

  • Safflower oil: Melting point $-18\,^\circ\text{C}$; ~$8\%$ saturated, ~$19\%$ monounsaturated, ~$73\%$ polyunsaturated.

  • Corn oil: Melting point $-20\,^\circ\text{C}$; ~$15\%$ saturated, ~$51\%$ monounsaturated, ~$34\%$ polyunsaturated.

Chemical Reactions of Triacylglycerols

• Hydrogenation:

  • Addition reaction where double bonds in unsaturated fatty acids react with hydrogen gas ($\text{H}_2$) in the presence of a metal catalyst such as nickel ($\text{Ni}$) or platinum ($\text{Pt}$).

  • Converts $\text{C}=\text{C}$ double bonds into $\text{C}-\text{C}$ single bonds.

  • Increases the saturation level and melting point of liquid plant oils, converting them into semi-solid or solid products like margarine and shortening.

  • Example: Hydrogenation of glyceryl trioleate yields glyceryl tristearate:

$\text{Glyceryl trioleate (triolein)} + 3\,\text{H}_2 \xrightarrow{\text{Ni}} \text{Glyceryl tristearate (tristearin)}$

• Formation of Trans Fats during Hydrogenation:

  • During commercial partial hydrogenation, some double bonds undergo catalytic isomerization rather than saturation, converting natural cis double bonds into trans double bonds.

  • Trans fatty acids adopt a linear structure similar to saturated fatty acids, leading to close packing and altered biological behavior.

  • Health implications: Trans fats raise low-density lipoprotein (LDL, "bad") cholesterol levels while lowering high-density lipoprotein (HDL, "good") cholesterol levels, increasing cardiovascular disease risk.

  • Foods containing trans fats typically state "partially hydrogenated vegetable oil" on product ingredient labels.

• Olestra: Artificial Fat Substitute:

  • Synthesized by esterifying sucrose with eight long-chain fatty acids.

  • Too bulky to fit into the active sites of human digestive lipase enzymes, preventing breakdown in the gastrointestinal tract.

  • Passes through the body unabsorbed and un-metabolized, providing zero calories while retaining the mouthfeel of natural fats in snack products.

• Acid or Enzymatic Hydrolysis:

  • Ester bonds in triacylglycerols are cleaved by water ($3\,\text{H}_2\text{O}$) in the presence of an acid catalyst ($\text{H}^+$) or biological enzymes (lipases).

  • Yields one molecule of glycerol and three free fatty acid molecules.

  • Example: Hydrolysis of glyceryl tripalmitate (tripalmitin):

$\text{Glyceryl tripalmitate} + 3\,\text{H}_2\text{O} \xrightarrow{\text{H}^+\text{ or lipase}} \text{Glycerol} + 3\text{ Palmitic acid}$

• Saponification (Base Hydrolysis):

  • Reaction of a triacylglycerol with a strong aqueous base such as sodium hydroxide ($\text{NaOH}$) or potassium hydroxide ($\text{KOH}$) under heat.

  • Splits the ester bonds to produce glycerol and the alkali metal salts of fatty acids, which are commonly known as soaps.

  • Example: Saponification of glyceryl tripalmitate with sodium hydroxide:

$\text{Glyceryl tripalmitate} + 3\,\text{NaOH} \rightarrow \text{Glycerol} + 3\text{ Sodium palmitate (soap)}$

ADDITIONAL NOTES

Lipids

- one of the amjor biomolecule which has the characteristic of being hydrophobic

- main component of out cell to create semioermeable layer

- our plasma membrane is built with this

» for example virus structure—they are made of protein capsules not lipid capsules so they are ahrd to eliminate

- plasma membrane does not let water in—it has a selection—the selection of entry and exit made it possible by the lipids—so lipids is essential for life

structure of lipid

triglycerols

- one of main lipids in our body

- glycerol structure attached with three fatty acid

— like an achor

— can be converted back to glucose

» fats can be sugar becasue it has glycerols and it contains carbons attached fatty acids and it is hydrophobic

- most of our lipis contain two fatty acid tail

» lipids is first discovered when they burn animal and found a waterlike substance but does not mix with water

» organic solvents are alcohol methanol methane exane

» to handle lipid you need alcohol because it can be hydrated

prostalglandins is one of the component of sexual hormone a precursor needed

waxes is what you put in your hair

fats and oil - cooking oils essence oils what people use to scent a room

steroids example is cholesterol glucos]=corticoid stresss hormones which can be produced by lipid soluble hormones

fatty acids is the subunit of lipids

from the acids we can derive prostalglandins and also waxes triglycerol and glycerophospholipids

» dofferences

- waxes contain long chain of alcohol

- has oh group—oh funcitonal group

dpuble bond oxygen with carbon is carbonyl

glycerolphospolipid vs triglycerl

- it has phosphate group and amino alcohol which contains H2OH

- posphate without oxygen is called phosporus

- posphate is positive

sphingolipids

- can also be found in the plasma mebrane but abundance cannot compare glycerol phospolipid

aphingio vs clyco

- sphin contains NH2 amino group with phosphate

- only difference is the backbone is not a glycerol but a sphingiocine

- glyco alsa has the same backbon ebut does not contain phosphate amino alcohol but they contain sugar

steroids

- contain aromatic ring

- three aromaric rings and one pentameric rings

- smells good but stressful

cholesterol

- derived from the steroids

- can be turned into steroids—they are interchangable—called latachalier principle

bile salts

- important for emulsuficaiton

- can be seen in galbladder

- melt down fats

camola healthiest oil and also olive oil

unsaturated is the healthy one

fi;ipino use coconut oil which is super saturated

oil oof animal is saturated and in plants is unsaturated

usually oil depends on extraction—the harder it is to extract is more expensive

you will know if a substance is ssaturater od unsaturated in structure—if it has kinks or double bonds it is unsaturated

unsaturated is more helathy beacuase if lipid has kinks then they wont aggregate so they would not compress and in your ody they are less likely to do so also unlike saturated

margarine vs butter healthiness

- depends on perspective of person

- marg is more liquified

- but butter is more natural then marg

in chemistry based health you look at the structure and function

- for the heart its margarine but for reprodcutive health cholesterol and such you will prefer butter

medical science vs natural science

- med science you have a lot of consideration—it can be bad here it can be good there type shi

- in nat what is bad for health it is bad ofr health no consideration

fatty acids

- always end with methyl group—chemical strucutre CH3

- they are insoluble in water

ch2 usually has hydorgen in their valence based on this they are hydrophobic because hydrogen repulse H2O

But in OH dehydrsation happens

lipids or fats x alcohol or soju is a good combination however in moderation

liver will be overworked

dehydration happens

if you remove hydrogen on lipid surface then it becomes open for access to enzyme

lipids are hydrocarbons beause they are carbons containing hydorgen or protons

saturated fatty acid

- dont have kinks

- reason why they easily aggregate and create physical chracteristic of hihg melting point

- easily become solidify because theyre lipid tails is attracted to each other

- example is stearic acid—its melting point is 69°C so we need that to melt it down if you eat it you can not melt it even you exercise and heat up

- forms as asteroclerosis

- if they were not emulsified in gal bile so they get left n the blood causing dyspedidemia which rises your fat on blood and it stays there until it hardens

reason why in cold countries cardiovascukar is one of the leaning helath disesa

they rarely have diabetis

but in philippines both is prominent

you can define the type of acids based on the number of their carbon

the longer the dtructure the higher the melting point

golden standard of identifying a molecule is their structure

kinks = unsaturated

sys vs trans

sys is plateau

why is unsaturated much healthy

- they are assymetric so they create weaker bonds

- the lookalike the molecules euqals more electron tobe shared

hydrophobic interaction

- pressure where two hydrophobic creating a tension like van der waal interaction like london dipersion force

- but not all weak are weak if you put many weak together they can be strong

- saturatde fats can harden in your stomach

how we break down fats

we have glycerol and fatty acids

they are cut apart in digestive and is put inside the channels seperately

once inside cell they are gonna be formed again

eterocytes before blood

fats san be dumped with feces

if your poop is shiny and if there is a thin translucent layer between the water then thats fats

if you have many galstones then body has difficulties in emulsifying

more kinks = faster melting because they dont aggregate

the carbon numnber can tell us the location of the kinks

prostaglabdins

molecular transmittor

nociceptors or pain receptors is rich with this

if a woman gives birth this rises

ewe can use paracetamol to prevent forming of prostalglandins

omega 6

first kink

can be found is fishes

whoever the carbon that first create double boond then we will account the atroberts something on that saud carbon

omega 3

we have many kink

DHA is the fastest to melt

the huge space will lower their melting point

palm oil can be sautrated or unsaturated because palm trees vary

enzymes we can inhibit

the number of kinks differ

elongates = longer carbons

detchaturaze = higher kinks

can form DHA whihc is good for the heart

waxes

first discovered in plants

water slides off gabby leaf because it is full of wax

plastic starts from wax

waxes in sperm of male is caused by polyester shirts

fats and oils

good scents

olive oil

- not for egg

very unsaturated

they can easily be separated despite themselves

melting point and freezing point

in oil we usually talk about melting point

most of the oil is unsaturated because its mostly fron plants

fats of animals smells bad

bacteria can be mixed easily with oills of animals becasue animals are vector of bacteria

bacteria stays in animals especially mammals

hair follicle has sebaceous gland so it is fav of bacteria

reason why some people smell bad

our metabolism is enzyme—they break down the bonds through dehydration synthesis addition of water

we lose out double bonds then we get lonepair of electrons—tehy can interact with another with appropriate charge

most kind of reation is assidted by enzyme

the enzyme work on it

from saturated converted to unsaturatd by assisted enzyme

enzyme conttains alkaline group that contain protons in surface of thei carbons

they can easily donate these protons

it vanish when hydrogen attack the carbon then it get displaced

then well have lone pair then the lone pair will create the disk

if it create

in chemistry anything is possible as long as you can create the proper structure

cis vs strans

LDL low density lypoproteins

HDL is more healthy

LDL should be prpocessed by your body to become HDL

If you have metabolic problem for example you dont have insulin you cant properly dtore fatty droplets then it goes to blood and becomes fat

fats is sstill important because after carbphydrated bpdy take energyy to fats

most of the time diabetes is genetics because they lack specific type of enzymes or proteins that can break don or signal our body to release insulin

MONGD

maturity onset of the glut diabetes because even at young age there are signs of disabetes

genetics of disease start in family when one person started it

if they dont have history of high blood but does now the next gen can inherit it

cis to tarns conversion

cant be replaced by hydrogen oro double bond will be lost becasue of lost of free electrons

double bond is stronger than single stiff

if its stiff even pushed by other molecules down it will not bent

but if you lose double bond then it easily get disturbed

alkin alkane alkine

triple bond is stronger but is uncommon in nature beauces in biologyv all molecules should be repurposable

all molecules use energy

if you die all your molecule will go to the environment what we call GTE Global Thermal Equilibrium

the reason why the body goes cold becaseu energy goes from high to low

our body has high temp but the reason our temp stays is becasue we have constant input of energy like eating

if you dont eat your temp willl match the envirmonment then you die—physics call entrophy

soap is made of animal oils

if you scrub it on your skin the oil traps the bacteria then when you wash oil will come with water

high glycerol and fatty acids palsma mebrane will be torn and well have coagulation

omega 3 = third carbon form tial

omega 6 = sixth carbon from tial which is first double bond

memorize types of acid