Lipid Concepts Flashcards
List:
The EIGHT main types of lipids.
(As mentioned in BIOL244 lectures).
- Glycerides
- Glycerophospholipids
- Sphingolipids
- Wax
- Terpenes
- Steriods
- Vitamins (some)
- Hormones (some)
Note: Fatty acids are often mentioned alongside lipids, however, they are more of a singular structural component of lipids (often bonded to a glycerol head in a triglyceride).
Give the TWO names for the compound made from ONE glycerol plus THREE fatty acid chains.
Triglyceride OR triacylglycerol.
Triacylglycerol is technically the correct chemical name, but they are often referred to as triglycerides.
How are lipids defined by their solubility?
They are insoluble in polar solvents like water, but are soluble in nonpolar, organic solvents.
They may also be soluble in weakly polar organic solvents.
True or False:
Lipids have diverse structures and properties.
True
(e.g. melting point, state at room temperature etc.)
Which type of fat is typically liquid at room temperature?
Unsaturated (fatty acids)
An example is things like vegetable oil
Which type of fat is typically liquid at room temperature?
Unsaturated (fatty acids)
An example is things like vegetable oil.
The fatty acid chains have naturally-occurring cis double bonds which cause ‘kinks’/bends and decrease the efficiency at which the molecules pack together.
Which type of fat is typically solid at room temperature?
Saturated (fatty acids)
The fatty acid chains have NO double bonds, and so pack together much more tightly, thus leads to more solid structure.
What leads to fatty liver syndrome?
Accumulation of excess lipid droplets in the liver, which leads to chronic inflammation.
These droplets are stored safely in adipocytes.
What (protective) benefit do adipocytes serve?
They allow for the storage of lipid droplets which helps prevent fatty liver syndrome and inflammation from these free fatty acids.
It is also a form of long-term energy storage.
Why are lipids important for normal brain function?
Certain fatty acids contribute towards things like mood regulation, sleep, memory, etc.
This is why mood regulation and anxiety/depression issues arise with starvation.
What are FIVE examples of negative outcomes from too much fat in one’s diet?
- Fatty liver syndrome
- Obesity
- Diabetes (correlated with obesity)
- Heart disease
- Metabolic disorders
List:
FOUR major functions of lipids in the human body.
- Energy source
- Cell membranes
- Regulatory molecules
- Development
Certain hormones and vitamins are key for the final two lised functions.
Define:
Fatty acid
Long, unbranched hydrocarbon chains with a terminal carboxyl.
This COOH head group is polar/charged when deprotonated.
How does an acyl chain differ in structure to a fatty acid?
Fatty acids have a terminal carboxyl (COOH) whilst acyl groups are defined by having the general structure of R-C=O.
An acetyl molecule specifically has its R group as a CH3 (-C(O)CH3).
True or False:
Fatty acids are strong acids.
False
They are weak acids due to the fact they have long hydrophobic carbon chains as well as their polar carboxyl group, which is in its deprotonated form under physiological conditions.
How many carbons make up a ‘short-chain’ fatty acid?
≤ 6
How many carbons make up a ‘medium-chain’ fatty acid?
8 - 12
How many carbons make up a ‘long-chain’ fatty acid?
14 - 24
This size range is considered the most common, and is found in products like meat and fish.
In most animals, what kind of fatty acid chains are more typical?
Even-numbered carbon chains.
However, some marine lifeforms and microorganisms can produce odd-numbered fatty acid carbon chains.
Define:
Saturated fatty acid
NO double bonds in the hydrocarbon chain.
Define:
Unsaturated fatty acid
1 ≥ double bonds in the hydrocarbon chain.
One double bond is called a monounsaturated fat, whilst greater than one is polyunsaturated.
Which type of double bond causes bends in a fatty acid chain, and is the naturally occurring type?
Cis double bonds
Which type of fatty acid double bond can only be artificially produced or synthesised by some bacteria only?
Trans double bond
For example, margarine is manufactured via hydrogenation at high temperatures.
Such chains behave similarily to unsaturated fatty acids in their packing together.
What does each component in the fatty acid shorthand/symbol notation represent?
e.g. oelic acid is 18:1,Δ9
- Before the colon is the number of carbons.
- After the colon is how many double bonds.
- The delta + number tells you which carbon the double bond is positioned at.
In the example, oelic acid has 18 carbons and one double bond positioned at C9 in the chain.
What properties lead to a fatty acid having a higher melting point?
- Unsaturated / less double bonds.
- Longer hydrocarbon chain.
An unsaturated fatty acid is straight-chained, and so molecules pack together more efficiently to increase intermolecular attractions (VdWs) along the hydrocarbon chains.
Longer chains mean greater surface area for intermolecular attractions (VdWs).
True or False:
Fatty acids are considered to have amphipathic properties.
True
This is because they have a hydrophilic head as well as their hydrophobic tail, however the hydrophobic tail dominates.
Define:
Saponification
A reaction that converts esters (can be derived from fatty acids) into soap when combined with an aqueous alkali (e.g. NaOH).
Why are fatty acids typically in their esterified form?
Free fatty acids are toxic and disrupt the pH due to being weak acids.
What are fatty acids typically esterified to?
(Hint: list five key groups)
‘Backbone structures’ containing OH groups, such as…
- Alcohol
- Glycerol
- Sphingosine
- Cholesterol
- Amino acids
What are essential fatty acids?
Fatty acids that cannot be synthesised, but are required for certain biochemical processes, and so must be obtained via diet.
For example, linoelic acid (18 : 2 , Δ9,12), also known as ω-6 as the first double bond occurs at the 6th carbon when you count from the ω end.
Similarily ω-3 (or α-linoelic acid , 18 : 2 , Δ6,9,12) is named for the same reason.
Define:
Glycerides
Esters made up of a polar glycerol ‘head’ and 1-3 non-polar fatty acid chain(s).
Each of the fatty acid chains may be different lengths/types to each other.
The naming is based on the number of chains (mono- , di- , tri- ).
What is the most abundant form of glyceride?
Triglyceride
(i.e. fat)
What are TWO important functions of glycerides?
- Neutralises fatty acids.
- Major long-term energy store in animals.
True or False:
Triglycerides rarely have three identical fatty acid chains.
True
This is simply because there is such a large variety of fatty acid chain types/lengths.
Approximately how much of the stored energy in the human body is from triglycerides?
~85%
Adipocyte triglyceride storage is very efficient and has more calories per gram than carbohydrates or proteins.
And, adipose tissue is only ~15% water, so cells can pack very closely together (whereas muscle is ~80%).
What takes up the most space/mass of an adipocyte?
Large globules of lipid droplets
These squeeze the cytoplasm into a thin layer, and cause the nucleus to be flattened and forced to the periphery.
What is the general structure of a lipid droplet?
A single phospholipid layer with lots of triglycerides contained within.
Which THREE hormones trigger the release of fatty acids from adipocytes?
- Glycogen
- Epinephrine (adrenaline)
- Adrenocorticotropic hormone (ACTH).
These are secreted by other cells.
How can adipose tissue help with thermal regulation?
It acts as insulation and forms layers under the skin, so it helps in trapping heat in cold environments.
What kind of adipose tissue is specialised for heat generation?
Brown adipose
It utilises a protein called thermogenin.
Define:
Adipokines
Hormones secreted by adipocytes which help modulate apetite/satiety, energy expenditure, and related metabolic pathways.
Define:
Glycerophospholipids
Lipids made up of a glyceride with a phosphate group bound to the polar glycerol head group, and two fatty acyl chains.
(e.g. phosphatidic acid).
List:
FOUR key functions of glycerophospholipids.
- Component of cellular membranes.
- Precursors for the biosynthesis of other lipids.
- Influence membrane curvature.
- Signalling roles.
What is an important additional property of the phosphate group on a glycerophospholipid?
It can be esterified with the OH of another polar head group.
For example, choline as a head group in phosphatidylcholine, which is a common constituent of cell membranes.
Which type of esterified glycerophospholipid is commonly found in the outer leaflet of the lipid bilayer?
Phosphatidylcholine
Which type of esterified glycerophospholipid is commonly found in the inner leaflet of the lipid bilayer?
Phosphatidylethanolamine
Ethanolamine is the polar head added to the phosphatidic acid.
Which kind of lipid is uncommon in animals, but common in plant and bacterial membranes?
Glycoglycerolipids
It constitutes about half of the chloroplast membrane lipids.
Define:
Sphingolipids
A type of lipid made up of a sphingoid base and a single, long hydrocarbon tail.
They are major constituents of the plasma membrane.
A sphingoid base is made up of sphingosine (an 18-carbon amino alcohol) - it has an amino group and a terminal hydroxyl.
The fatty acid residue binds to the amine group of the sphingosine via an amide bond.
How are fatty acids bonded to sphingosines in a sphingolipid?
Via an amide bond to the amine group on C2 of the sphingosine.
This is known as a ceramide.
Define:
Ceramide
A central sphingolipid that is made up of a fatty acyl chain bonded to a sphingosine.
It is a precursor for other lipids such as sphingomyelin and glycosphingolipids.
Define:
Sphingosine
A long-chain, unsaturated amino alcohol.
Its backbone is made up of 18 carbons.
How can sphingosine be converted into a signalling molecule?
Through its reversible phosphorylation to form sphingosine-1-phosphate.
Define:
Sphingomyelin
A more complex sphingolipid formed from the esterification of ceramide and a polar phosphorylcholine head group.
In higer animals, sphingomyelin makes up some of the brain and nerve tissue plasma membranes.
It is similar in size and shape to phosphatidylcholine, but they are distinguished by their differing fatty acid components.
Define:
Glycosphingolipid
A more complex sphingolipid formed from the esterification of ceramide and a polar sugar head group.
The type of sugar defines the type of glycosphingolipid.
Define:
Cerebroside
A type of glycosphingolipid in which the sugar head group is a monosaccharide.
(e.g. glucose or galactose)
Define:
Ganglioside
A type of glycosphingolipid in which the sugar head group is a complex oligosaccharide.
(e.g. sialic acid).
Gangliosides are important constituents in muscle and nerve membranes.
Why do gangliosides have large polar heads?
Because they are comprised of complex oligosaccharides.
Define:
Steroids
A broad class of compounds defined by having a steroid nucleus in their base structure.
A steroid nucleus describes three 6C rings with one 5C ring, and an OH attached to one of the 6C rings.
Define:
Steroid nucleus
A base structure of all steroids that is made up of three 6C rings with one 5C ring, and an OH attached to one of the 6C rings.
In animals, which is the most common steroid and the precursor for all other steroids?
Cholesterol
It is comprised of the steroid nucleus with a short branched hydrocarbon tail.
Aside from being a precursor molecule, what is a major function of cholesterol?
It is a constituent of plasma membranes that serves a role in regulating fluidity.
During this, it has amphipathic properties whereby its hydroxyl head orients towards the external aqueous environment, and its hydrophobic regions insert into the membrane.
What does the polar hydroxyl group of cholesterol do when it is part of a membrane.
It forms hydrogen bonds with the hydrophilic heads of adjacent phospholipids.
This combined with the disruption of the close packing of the hydrocarbon tails helps make the membrane more fluid.
How does a cell regulate its level of fluidity in the membrane?
By regulating the level of cholesterol present.
Define:
Glycophospholipid
Lipid molecules found in cell membranes and built on a phosphatidylglycerol core that extend into the extracellular space and may act as anchors for proteins or as signalling tags.
This is imprtant for tissue specificity, cell-cell interactions, and tissue immunity.
Define:
Sphingophospholipid
A lipid with a ceramide backbone and a polar head group made up of phosphate bound to another polar group.
(e.g. choline)
Define:
Terpenes
Lipids formed from ≥ 2 five carbon molecules called isoprene.
These are typically linked ‘head-to-tail’ to form straight chains.
Terpenes are a vast group predominantly produced by plants (but also insects and some animals too).
What is ‘characteristic’ about terpenes?
Their flavour, colour, and/or odour.
How many isoprene units make up a monoterpene?
And how many carbons?
Two
C10
Since there is at least two or more isoprene units required in a terpene molecule - two is the lowest number and where it starts counting from.
Many of these have characteristic odours/flavours, and may have funcitons as defensive agents or pheromones.
How many isoprene units make up a sesquiterpene?
And how many carbons?
Three
C15
How many isoprene units make up a diterpene?
And how many carbons?
Four
C20
One important diterpene includes retinal which is a visual pigment of rhodopsin.
Phytol is a component of chlorophyll.
How many isoprene units make up a triterpene?
And how many carbons?
Six
C30
Which triterpenes are important cholesterol precursors?
Squalene & lanosterol.
Define:
Wax
Esters of long-chain monohydroxy alcohols with long-chain fatty acids.
They are insoluble in water.
What is the general formula of a wax?
R1-C(=O)-O-R2
The fatty acid is R1, and the alcohol is the second R group.
What is a major biological function of wax?
It helps comprise protective coatings to make things water-repellent.
This could be leaves, stems, fruit (plants), or even fur and skin (animals).
What substance from a Brazilian palm tree is used to generate a high gloss finish on things such as automobiles, floors, shoes, and boats?
A hard wax called carnauba wax.
What is lanolin?
A wool wax used in cosmetics.
Which TWO lipid classes are important for chemical signalling in and on cells?
Glycerophospholipids & sphingolipids.
For example, their breakdown can generate secondary chemical signals that act locally (on same cell or neighbouring), usually by triggering reaction cascades.
Define:
Lipid aggregates
Due to their significant hydrophobicity, lipids in polar solvents such as water will associate (aggregate) in a way that minimises exposure of their hydrophobic regions and orients their hydrophilic regions to be in contact with surrounding polar solvent molecules.
For example, monolayers, bilayers, and micelles.
In aqueous solutions lipids…
…form orderly structures spontaneously.
Rarely does a lipid exist as a monomer in a polar solvent.
Define:
Monolayer
(of lipids)
A single layer of lipids on the surface of an aqueous solution.
Define:
Bilayer
(of lipids)
A formation of lipids in which there are two layers, each having the hydrophilic (head) regions oriented outwards towards the polar solvent and the hydrophobic (tail) regions oriented inwards between the two layers.
This is the most stable structure for phospholipids, and makes up cell membranes.
Define:
Micelle
(of lipids)
Spherical structures formed by single-tailed lipids in an aqueous solution.
For example, fatty acids or monoacylglycerol etc.
Define:
Critical Micelle Concentration (CMC)
The minimum concentration of fatty acids/single-tailed lipids in an aqueous solution required for micelles to begin forming.
At lower concentrations, such lipids/fatty acids will instead form monolayers.
Why do phospholipids tend to form bilayers rather than micelles?
They have two fatty acyl chains, which don’t pack together as well as monoacylglycerols or single fatty acids in a micellular formation.
What are the TWO majour fat sources for fatty acid catabolism?
Dietary & adipose tissue.
Modern diets tend to be high in fat.
What must occur before fatty acid catabolism processes commense?
Fatty acids need to be transported to the appropriate cells for catabolism.
(e.g. heart, liver, muscle)
What kind of fatty acid chains are included in dietary fat?
Long chain
(i.e. about 16 - 20 carbons)
Where does the breakdown of fats FIRST start occuring during digestion?
Hydrolysis of dietary triglycerides by acid-stable lipases in the stomach.
However, this is not very effective and only a small amount is hydrolysed.
What happens to the partially hydrolysed fat after it leaves the stomach and enters the duodenum?
Large amounts of lipases (and estarases) contained within pancreatic fluid continue to hydrolyse the fats into monoglycerides and fatty acids.
This is assisted by bile secretions from the gall bladder, which emulsify fat globules to further promote hydrolysis.
Bile is made up of compounds derived from cholesterol, and is synthesised in the liver, and stored in the gall bladder.
What is bile comprised of?
Compounds derived from cholesterol.
For example cholic acid.
Identify:
The function of bile.
Surfactant/detergent/emulsifier.
It emulsifies fat globules and promotes hydrolysis of these into monoglycerides and fatty acids via pancreatic lipases and esterases.
Where is bile synthesised, stored, and then excreted?
It is synthesised in the liver, stored in the gallbladder, and excreted from there into the small intestine.
Define:
Mixed micelle
Aggregates of lipolytic products formed in the small intestines, which act as a lipid shuttle that carries these compounds to absorptive cells (to then become chylomicrons).
They are typically comprised of monoglycerides, fatty acids, bile, phospholipids, cholesterol, and protein.
At which carbon positions do pancreatic lipases cleave fatty acids from?
C1 & C3
The monoglycerides are further hydrolysed by intestinal lipases in the small intestine.
Define:
Chylomicron
A lipoprotein aggregate formed in the cells of the small intestine.
It is the largest, lowest density, highest in triglycerides, and lowest in protein of the lipoproteins.
What activates lipoprotein lipase to hydrolyse triglycerides of chylomicrons and release fatty acids?
The binding apolipoprotein II on the surface of the chylomicron.
The lipprotein lipase is anchored to the surface of endothelial cells.
What are the TWO fates of fatty acids released by lipoprotein lipase hydrolysing the triglycerides of chylomicrons?
- Diffuse into endothelial cells and then enter capillaries proximal to liver, muscle, or adipose tissues for absorbtion and then energy production.
- Bind to albumin and be transported via the bloodstream to more distant cells.
What is the purpose of linking CoASH to fatty acids upon entering a cell?
It activates the fatty acid and essentially labels it for degredation before it is transported into the mitochondria.
Which enzyme catalyses the binding of CoASH to a fatty acid in the cytoplasm?
Acyl-CoA synthetase
As the enzyme name suggests, this requires ATP.
What is the difference between short-chain and long-chain fatty acids in regards to transport into the mitochondria for β-oxidation?
Short-chain fatty acids may be transported directly as free fatty acids, while long-chain fatty acids CANNOT.
Identify:
The enzyme, substrate, end product, and any other important byproducts/reactants of the first reaction for long-chain fatty acid transport into the mitochondria.
(Not including the step of adding CoA via acyl-CoA synthetase)
- Carnitine acytransferase I
- Acyl group of the fatty acyl-CoA is transferred to the OH of carnitine to form acylcarnitine, which then diffues into the mitochondrial intermembrane space.
Identify:
The enzyme, substrate, end product, and any other important byproducts/reactants of the second reaction for long-chain fatty acid transport into the mitochondria.
(Not including the step of adding CoA via acyl-CoA synthetase)
- Acylcarnitine translocase
- Transports acylcarnitine into matrix.
- This is coupled with the transport of carnitine from the matrix to the cytosol.
This enzyme is found on the inner mitochondrial membrane.
Identify:
The enzyme, substrate, end product, and any other important byproducts/reactants of the third reaction for long-chain fatty acid transport into the mitochondria.
(Not including the step of adding CoA via acyl-CoA synthetase)
- ## Carnitine acyltransferase II
What is the control point of fatty acid oxidation / β-oxidation?
Acyl-CoA transport into the mitochondria.
(Specifically, at carnitine acyltransferase I)
What molecule inhibits carnitine acyltransferase I?
Malonyl-CoA
(i.e. a precursor to fatty acid synthesis)
Which enzyme catalyses the conversion of acetyl-CoA to malonyl-CoA?
Acetyl-CoA Carboxylase (ACC)
List:
The FOUR overarching steps leading to energy production with fatty acids as a substrate.
(Hint: how does it connect to other ATP generating metabolic pathways)
- Activation (forms fatty acyl-CoA)
- Transport (into mitochondria via carnitine for LCFA)
- β-oxidation (in mitochondria)
- TCA cyle (metabolite acetyl-CoA fed into this)
List:
The FOUR main reactions of β-oxidation.
- Oxidation
- Hydration
- Oxidation
- Cleavage
It is called β-oxidation since the βC is oxidised to allow for multiple rounds of cleavage.
Identify:
The enzyme, substrate, end product, and any other important byproducts/reactants of β-oxidation reaction I.
- Acyl-CoA dehydrogenase
- Oxidation (dehydrogenation) of acyl-CoA in which the Cα-Cβ bond is converted to a trans double bond to form trans-Δ2-enoyl-CoA.
- Coupled with the reduction of the FAD prosthetic group to FADH2.
Acyl-CoA DH has different isoforms depending on the lenght of the fatty acyl-CoA chain.
The 2e- of FADH2 can then be taken to the ETC via ETF (electron-transferring flavoprotein) to ubiquinone (Q).
Identify:
The enzyme, substrate, end product, and any other important byproducts/reactants of β-oxidation reaction II.
- Enoyl-CoA hydratase
- Stereospecific hydration of the trans double bond (Cα=Cβ) to yield L-β-hydroxyacyl-CoA.
Identify:
The enzyme, substrate, end product, and any other important byproducts/reactants of β-oxidation reaction III.
- L-β-hydroxyacyl-CoA dehydrogenase
- Oxidation (dehydrogenation) of L-β-hydroxyacyl-CoA to L-β-ketoacyl-CoA.
- Coupled with reduction of NAD+ to NADH.
It can now undergo cleavage between the alpha and beta carbon.
The NADH can deposit its electrons to the ETC.
Identify:
The enzyme, substrate, end product, and any other important byproducts/reactants of β-oxidation reaction IV.
- Thiolase
- Cleavage of the Cα-Cβ bond and attachement of CoASH to the shorter fragment to release acetyl-CoA, whilst the main chain is shortened by 2C before enetering the next round of oxidation.
This occurs via a fatty acyl-CoA enzyme-cysteine thiolester intermediate.
