Melting point of a fatty acid?

Melting point of a fatty acid?

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What factors determine the melting point of a fatty acid?

  1. Chain length
  2. The number of methylene group
  3. The ionized state of the fatty acid
  4. Its degree of saponification
  5. Its ability to alter the entropy of water

(1) Chain Length

Will definitely affect melting point, as this website explains pretty well:

"Melting point principle: as the molecular weight increases, the melting point increases."

(2) Number of Methylene groups.

This is another way of describing unsaturated from saturated fats. The more saturated a fat is, the straighter it is. Methylene groups cause kinks, which disrupts the Van der Waals forces along the rest of the carbon chain.

As such, from the link above again:

"On the other hand, the introduction of one or more double bonds in the hydrocarbon chain in unsaturated fatty acids results in one or more "bends" in the molecule. The geometry of the double bond is almost always a cis configuration in natural fatty acids. These molecules do not "stack" very well. The intermolecular interactions are much weaker than saturated molecules. As a result, the melting points are much lower for unsaturated fatty acids."

(3) Ionized state of the fatty acid.

This will have a very minor affect. The fatty acid generally has an unpaired ester (-ate at the end) which can have a negative charge. However, from the link above again:

"However, in fatty acids, the non-polar hydrocarbon chain gives the molecule a non- polar character."

So even if the ester had a charge, the negative character is miniscule compared to the intermolecular forces exerted by the non-polar tail. Particularly since the charge can distribute amongst the two oxygen molecules which are conjugated, reducing the reactivity further.

(4) Degree of saponification.

I'm not super-familiar with the degree of saponification, but from a quick overview of the process I'd say this wouldn't affect melting point - counter to my comment. The process of making soap involves only the acidic portion of the fatty-acid triglycerides. That portion of the macromolecule is going to be pretty much the same regardless of the fatty acid, so it will have nearly the same reactivity regardless of its chain length and conjugation.

What will not saponify are usually waxes - which are pretty much fully-saturated hydrocarbon chains with very few (if any) acidic sites. Parafin Wax, for instance, does not saponify, and has the formula ${C_{31}H_{64}}$.

(5) Ability to alter entropy of water.

Like the degree of saponification option above, the ability of a fatty acid to alter the entropy of water correlates to the number of reactive sites throughout the molecule. As-such, unsaturated fats (those with methylene groups) are going to be slightly more reactive as pi-bonds are more reactive than sigma bonds.

So, given that this answer relies on a previous option, it's probably better to go with the previous option.

Ultimately, if I were answering the question I'd choose 1, 2 since the rest either depend on those two or are miniscule. However, beware that it's your question to answer and not mine.

Lipids are a group of diverse macromolecules consisting of fatty acids and their derivatives that are insoluble in water but soluble in organic solvents.

  • Lipids consist of fats , oils , hormones , and certain components of membranes that are grouped together because of their hydrophobic interactions.
  • The lipids are essential constituents of the diet because of their high energy value.
  • These are also essential for the fat-soluble vitamins and the essential fatty acids found with the fat of the natural foodstuffs.
  • Fats combined with proteins (lipoproteins) are essential constituents of the cell membranes and mitochondria of the cell.
  • Lipids occur naturally in living beings like plants, animals, and microorganisms that form various components like cell membranes, hormones, and energy storage molecules.
  • Lipids exist in either liquid or non-crystalline solids at room temperatures and are colorless, odorless, and tasteless.
  • These are composed of fatty acids and glycerol.

Alcohols and Esters

  • The most important and frequently occurring alcohol found in lipids is glycerol. Glycerol is a small organic molecule consisting of three hydroxyls (OH-) groups.
  • Glycerol makes up simple lipids which are esters of fatty acids and glycerol and similar alcohols.
  • The alcohol might be glycerol or other long-chain alcohol. The long-chain alcohols are mostly mono-hydroxy with a single OH group.
  • Depending on the alcohol used, simple lipids consist of fats, oil, or waxes. Fats and oils are esters of fatty acids and glycerol, whereas waxes are esters of fatty acids and long-chain alcohols.
  • The esters of fatty acids are formed after the dehydration reaction between the fatty acids and the alcohol molecules.

Lipids and It&rsquos Types (With Diagram)

Lipids are heterogeneous group of water insoluble compounds which are oily or greasy in consistency but soluble in non-polar solvents like ether, chloroform, benzene etc.

For examples, fatty acids, fats, oils, waxes, certain vitamins and hormones are considered as lipids. Lipids are composed of C, H, O, like carbohydrates but poor in oxygen and therefore require more oxygen for oxidation to release energy.


Bloor (1943) coined the term ‘lipid’ and classified them into three types: Simple, Compound and Derived.

Fatty acids are monocarboxylic acids (R-COOH) with long hydrocarbon chains. Fatty acids don’t occur free in nature rather occur as esters in natural fats and oils. The fatty acid is called an acyl group when it is a part of ester. In biological systems, fatty acids usually contain an even number of carbon atoms, typically between 14 and 24. The most common fatty acids have 16-18 carbon and 0-3 double bonds. For example, plamitic (C16), stearic (C18), oleic (C18), linoleic (C18) etc.

Fatty acids are amphipathic molecules because their carboxylic groups (-COOH) are hydrophilic or polar and the hydrocarbon chains are hydrophobic or non-polar. In physiological conditions, fatty acids found in ionized forms. For example, palmitic acid exist in form of palmitate and so on.

The carbon atoms of fatty acids are numbered from the carboxyl carbon (C-l). The C-2 and C3 are called α-carbon and/β-carbon respectively. The methyl carbon at the end is called ω-carbon. Fatty acids are of 2 types, saturated and unsaturated. Saturated fatty acids contain no double bonds (saturated in hydrocarbon chain, e.g., CH3 (CH2)14COOH (palmitic acid), CH3 (CH2)16COOH (stearic acid), CH3 (CH2)18 carboxylic COOH (arachidonic acid) etc. They have higher group melting points and are solid at room temp. Unsaturated fatty acids contain one or more double bonds (unsaturated) in hydrocarbon chain. A double bond in an unsaturated fatty acid has two possible configurations, cis or Trans. The double bonds in most unsaturated fatty acids have the cis orientation that introduces a bend or kink in the hydrocarbon side chain.

Essential Fatty acids (EFA Durr and Burr, 1930):

Bacterial and plants can synthesize all the required fatty acids. But animals can’t synthesize 3 polyunsaturated fatty acids – linoleic, linolenic and arachidonic acids – that are required for growth and synthesis of prostaglandins. If linoleic acids are sufficiently available in the diet then other two EFA can be synthesized from it. EFAs are popularly known as Vitamin F.

Importance of Fatty acids:

1. Fatty acids are fuel molecules, stored as triglycerides in the fat-cells (adipose cells). Under the influence of hormone adrenaline adipose cells hydrolyze the triglycerides into free fatty acids that are released into the blood. The complete oxidations of 3 fatty acids of a triglyceride release 9 Kcal/g, in contrast to carbohydrate and protein that release 4 Kcal/g.

2. They are the building blocks of phospholipids, glycolipids and lipoproteins that found in the biological membranes.

3. Eicosanoids (prostaglandins, thromboxane’s and leukotriene’s) are the polyunsaturated fatty acids, which serve as hormones.

4. Fatty acid derivatives act as intracellular messengers, e.g. IP3 (inositol 1, 4, 5-triphosphate) and DAG (diacylglycerol).

5. Deficiency of EFA (essential fatty acids) in human diet causes sterility, kidney failure, skin lesions like phrenoderma (hard skin), eczema etc.

6. Provide the insight to many diseases like obesity atherosclerosis etc.

7. Hydrogenation of unsaturated fatty acids converts oil to solid fat at room temperature. This is the basis of manufacturing edible vanaspati ghee or margarine from inedible and cheap cotton seed oil.

8. Physicians recommend taking PUFA to those having high blood cholesterol or cardiovascular disease.

9. The cleaning action of soap is due to reduction of surface tension of water by fatty acids

(B) Fats (= True fats, neutral fats, triglycerides or triacylglycerol)

They are the unchanged ester of 3 fatty acids and a gtycerol. When 2 or 1 fatty acids esterified with glycerol, then they are called mono-glycerides respects. In pure fats all the 3 fatty acids are similar e.g tripalmitin, tristearin. In mixed fat (triglyceride) all the three or at least one or 2 fatty adds are dissimilar e.g. butter.

Triglycerides are high efficiency storage fuel. In mammals, triglycerides are deposited in the form of large fat globules in the cytoplasm. In migratory birds, the triglycerides are stored under the skin, in muscle, in abdominal cavity & in liver. About two-thirds of this stored fat is consumed in the long flight over water. Triglycerides store six time as much energy as does glycogen because they are deposited in highly reduced and anhydrous form.

Hence, in evolutionary process triglycerides were selected over glycogen as the major energy reservoir. In a typical 70kg man, triglycerides constitute about 11kg of total body weight with a fuel reserve of 10 5 kcal. If this amount of energy is stored in the form of glycogen, his total body weight would be 55kg greater.

1. The fats of animal and plant origin are mixtures of different triglycerides. Plant fats have more unsaturated fatty acids and animal fats have saturated fatty acids. For commercially used fats are different into hard fats (animal fats) and oils (vegetable fats). Fats are solid at room temperature (20°C) but when liquid at 20°C called oils.

2. The property of fat depends upon chain length and their degree of saturation. Short chain length and un-saturation of fatty acids lower the melting point and increase the fluidity.

3. Hydrolysis: Lipases hydrolase the ester bonds so that a triglyceride forms 3 fatty acids and 1 glycerol. It is the basis of fat digestion.

4. Oxidation: On the outer mitochondrial membrane fatty acids first linked to coenzyme A by the enzyme fatty acid thiokinase. This is called fatty acid activation. Subsequently the activated fatty acids enter into the mitochondrial matrix where /β-oxidation (oxidation at /β-carbon) takes place to liberate energy.

5. Saponification: It is the process of formation of soap (metallic salts of fatty acids) by boiling a fat or oil with alkali like KOH, NaOH etc.

6. Saponification number: It is the number of milligrams of KOH required to saponify 1 gm of a given fat or oil. Saponification gives an idea about the molecular weight or chain length of the fatty acids of a fat. A fat having smaller fatty acids have higher saponification.

7. Rancidity: It is the development of unpleasant odour and taste of a fat or oil when kept for a long time, or exposed to air, moisture, heat etc. Rancidity is caused by microbial degradation of fatty acids, hydrolysis of a fat and formation of peroxides at the double bonds. Vegetable fats can be preserved for longer period than animal fat. This is because vegetable fats (oils) contain antioxidants like Vitamin E, Phenols etc. which prevent rancidity.

8. Acid Number: It is the number of milligrams of KOH required to neutralize the free fatty acids present in 1 gm of fat. The acid number indicates the degree of rancidity of a given fat. Higher the acid number, greater is the rancidity or fat.

9. Iodine Number: It is the number of grams of iodine absorbed by 100 gm. of fat. It indicates the degree of un-saturation of fat.

Waxes are esters of long chain fatty acids with monohydric alcohols. The fatty acids and alcohols in the waxes vary from 24 to 36 carbons. Waxes form water-proof coating on the surface of plants and animals.

The well known waxes are as follows:

Secreted from the abdominal glands of worker bees to build honeycombs. It is the ester of palmitic acid and hexacosonol.

ii. Carnauba wax:

It occurs as a coating on the leaves of Carnauba palm tree of Brazil (Copernicia prunifera). It is used in automobile polishes.

iii. Spermaceti (Sperm oil):

It is the hardest known wax obtained from the head of sperm whale. It is used as lubricating wax.

iv. Lanolin (wool fat):

Secreted from the cutaneous glands of fur bearing animals. It is closing similar to sebum.

It is secreted by tuberculosis and leprosy causing bacteria. It is a measure cause of the diseases.

vi. Cerumen (ear wax):

Secreted from the ceruminous glands of external auditory canal.

vii. Paraffin wax:

It is obtained from petroleum. Candles are prepared from paraffin wax and stearic acid.

It is formed by cross-esterification and polymerization of hydroxyl fatty acids. Along with wax (cuticular wax), cut in form cuticle on leaf epidermis which check transpiration. The cuticle is frequently covered by a layer of epicuticular wax.

It is composed of glycerol and phellonic acid. It is found in the walls of cork cells and from Casparian strip of root endodermis. It is water impermeable and checks infection in plants.

(F) Phospholipids (major membrane lipids):

Phospholipids are the esters of fatty acids with glycerol or sphingosine containing an esterified phosphoric acid. The phospholipids derived from glycerol (a 3-C alcohol) are called phosphoglycerides or glycerophospholipids when derived from sphingosine (CI8 amino alcohol), they are called sphingolipids, e.g. sphingomyelins, cerebrosides and gangliosides.

The phosphatidic acid (diaclylglycerol-3 phosphate) is the simplest phosphoglyceride from which others are derived such as phosphatidylcholine (lecithin), phosphatidylethanolamine (cephalin), phosphatidylserine, phosphatidylinositol and plasmalogens.

In phosphatidic acid C-l and C-2 of glycerol are esterified to two fatty acids and the C-3 is esterified to phosphoric acid. The phosphate group of phosphatidic acid becomes esterified to several nitrogenous alcohols like choline, ethanolamine, serine, inositol etc.

Functions of phospholipids:

1. Phosphatidic acid is an intermediate in the synthesis of triglycerides and phospholipids.

2. Phosphatidic acid is found in bacterial wall and inner mitochondrial membrane.

3. Lecithin acts as a surfactant that lowers the surface tension of lung alveoli. This prevents the collapsing of alveoli.

4. Phosphatidyl inositol 1, 4, 5-bisphosphate (PIP2) is an important phospholipid of cell membrane which hydrolyzed into 2 internal messengers or second messengers in Ca 2+ dependant hormone action. They are IP3 and DAG.

5. Plasmalogens are important phospholipids of brain and muscle.

6. Sphingomyelins occur in myelin sheath that surrounds the axon of neuron.

7. The fluidity of the membrane is regulated in different environments. This is possible by changing the nature of fatty acids in the phosphoglycerides. For example, at low temperature bacterial cell membrane contains more unsaturated fatty acids than the bacteria that grow at high temperatures.

Further, at low temperature organisms maintain fluidity by increasing the phosphoglycerides with more unsaturated fatty acids.

8. Due to amphipathic nature, phospholipids and glycolipids from micelle, lipid bilayer or liposomes (lipid vesicles) in aqueous medium.

These are conjugated lipids which contain fatty acids, alcohol sphingosine and sugar (galactose). The latter replaces one fatty acid molecule.

The glycolipids are components of cell membrane, particularly in myelin sheath of nerve fibers and on outer surfaces of nerve cells. They are components of chloroplast membranes also.

These are also conjugated lipids that contain lipids (mainly phospholipids) and proteins in their molecules.

Lipoproteins are present in cell membranes. Lipids are transported in the blood plasma and lymph as lipoproteins. Lipoproteins occur in the milk and egg yolk.

Steroids are the derivatives of 17-C cyclopentanoperhydrophenanthrene structure that consists of 4 fused saturated rings. Out of 4 rings, A, B & C rings are hexane rings (phenanthrene) and D-ring is cyclopentane ring. The methyl (-CH3) groups occur at C-10 and C-13. A side chain is usual at C-17. The steroid hormones are named as estrane (19C, one angular -CH3 group), androstane (19C, 2 angular – CH3 group), pragnane (21C, with 2 angular side chain and a 2C side chain at C-17).

The steroids are of following types:

When the steroids contain one or more -OH group and no carbonyl group, it is called a sterol, e.g. cholesterol, ergosterol, stigmasterol etc. Cholesterol (C27H45OH) found in plasma membrane of animal cells and mycoplasma. It occurs in animal fats (not in plant fats) in form of cholesteryl ester, here -OH of C-3 esterified with fatty acid. It first isolated from gallstones in 1784. Corticoids cholesterol in synthesized in liver and adrenal cortex. Ergosterol (C28 H48 OH) found in the membrane of yeast and fungi. It is the precursor vitamin D. Stigmasterol and β-sterol is the most common membrane sterols in plants.

(b) Bile acids: e.g. Glycocholic acid and Taurocholic acid.

(c) Sex hormones: Testosterone, Estradiol.

(d) Adrenocortical hormones: Corticosterone

(e) Cardiac glycosides: Stropanthin (from stropanthus), digitoxin (from Digitalis)

(f) Anabolic steroids: Synthetic derivatives of testosterone which are used in promoting growth and repair of tissues.

Importance of Steroids:

1. Cholesterol is the precursor of 5 major steroid hormones- Progesterone, Glucocorticoids and Mineralocorticoids.

2. Cholesterol is the precursor of vitamin-D, ecdysone (moulting hormones) bile salts and bile acids.

3. Cholesterol, ergosterol, stigmasterol and β-sterol are important membrane steroids.

4. Diosgenin, a phytosterol extracted from Dioscorea (Yam plant) and is used in male contraceptive pills.

5. Anabolic steroids increase muscle mass, strength and vigor. They are misused by athletes for body building.

6. Brassinosteroids of brassins derived from compesterol which promote growth and differentiation in plants.

Search Results

In general, fats are organic molecules made up of two parts: glycerin and fatty acids. When we eat fat, the digestive system breaks the bonds between the fatty acids and the glycerin, so these two parts are absorbed into the bloodstream separately.

Fatty acids are the more nutritionally important part of the fat molecule, and they are the ones that determine the chemical differences between different types of fat molecules.

Fatty acids are made up of a long chain of carbon atoms (5, 10 or 18 atoms long, or even longer), with one acidic group (-COOH). This group is why they are called acids.

If you look closely at certain oils and fats such as olive oil, soybean oil, or nut oils, and compare them with others, such as margarine, butter, chicken fat and beef fat (the white stuff found in and around slabs of meat), the most prominent difference you’ll find is that different oils and fats have different states of matter at room temperature. Some oils and fats are liquid at room temperature, and even when kept in the fridge, like olive oil and soybean oil. By contrast, other fats have higher melting temperatures: Butter, margarine and animal fats are solid in the fridge. They become soft solids at room temperature, and melt while cooking.

Beef with fat. Credit: Michael C. Berch, Wikipedia

What causes this difference in melting temperature? The answer is: Mostly how saturated the chemical bonds in the fat molecule are in hydrogen atoms. The more hydrogen atoms a fatty acid has, the more “saturated” it is, and the higher its melting temperature will be.

The following illustrations explain why. In the first illustration, seven molecules of completely saturated fats contain only single covalent bonds between the carbon atoms (represented as the corners of the zigzag line), and each carbon is bound to two hydrogen atoms, neither of which is shown in the illustration.

These linear molecules are able to come close to each other and create a dense structure, which allows for strong intermolecular interactions. The melting point of such a fat would be high.

By contrast, here is an illustration of three unsaturated fat molecules, specifically oleic acid, a main component of olive oil. This fatty acid includes a double covalent bond, represented by a double line:

It’s easy to see that the double bond causes a bend in the carbon chain, and prevents the chains from coming near each other and interacting strongly. In turn, the weak bonds between the molecules make for a lower melting point. This “bent” orientation is called cis in chemical nomenclature, a word derived from Latin.

Oleic acid, shown above, has just one double bond, so it is called “ mono -unsaturated”. Poly- unsaturated fats have multiple double bonds, are even more “bent”, and have even lower melting points.

Saturated fats can impact your health. They tend to build up along the sides of blood vessels, along with other materials, and over time they may clog them, which may cause a heart attack or a stroke, depending on which blood vessel was clogged.

Chemically speaking, saturated fats are very stable, and do not easily react with other molecules or break. Chains of carbons with only single covalent bonds, which make up most of the structure of saturated fatty acids, don’t react with most chemicals. Neither acids nor bases, alcohols, amines, alkali metals or transition metals can break such a chain. In fact, only very strong oxidizers such as chlorine gas, or oxygen in burning reactions, can achieve this.

As a result, saturated fatty acids also oxidize in the body with some difficulty. Thankfully, the acidic group on one end of the fatty acid is quite reactive, and allows for oxidation of the chain by cutting it to pieces, two carbons at a time. By contrast, an unsaturated bond is much more chemically active, and is much more readily oxidized by the body.

Trans fats were invented when chemists discovered a way to prepare an artificial “butter”, named margarine. They found that cheap oils can be reacted with hydrogen gas to give saturated fatty acids, which researchers later discovered may be bad for your health. In recent years, however, researchers found that this reaction creates another class of unsaturated fats, called “trans fats” , which are extremely harmful.

Margarine. Credit: spoospa, Wikipedia

During the manufacturing of margarine, a chemical catalyst is used to make the reaction go faster. It “opens” the double bond and allows the carbon atoms to react with hydrogen. However, sometimes the fatty acid molecule rotates 180 o about the bond, and it closes again without having reacted with a hydrogen atom. The result is a “ trans fat”, a fatty acid which has a double bond but doesn’t have a “bent” structure, as the following figure shows:

This linear molecule looks a lot like a saturated fat, and shares the property of a high melting point, but has a big problem: Trans double bonds are very rare in nature and the human body has a hard time reacting with them. As a matter of fact, all the enzymes in the human body which react with fatty acids and break them down are capable of reacting only with “bent”, cis fatty acids. Hence, trans fats build up in the body and can cause a lot of damage.

Dr. Avi Saig
Department of Neurology and Davidson Institute of Science Education
Weizmann Institute of Science

Article translated from Hebrew by Aviv J. Sharon, M.Sc. student at the Weizmann Institute of Science.

Note for Surfers
If you find the explanations unclear or have further questions, please drop us a line on the forum. We welcome your comments, suggestions and feedback.

Lipid Peroxidation

Lipid peroxidation is a potentially damaging mechanism if left to continue without regulation. When electrons are taken from cell membrane lipids, peroxidation occurs. Reactive oxygen species (ROS) react to produce an unstable fatty acid radical (a fatty acid missing electrons in its valence shell) and water.

To become more stable as is required under the octet rule, the fatty acid radical reacts with oxygen. Even so, even these radicals are unstable and they continue to react – usually with each other. This chain of events only halts when the molecule becomes stable (non-radical). Lipid peroxidation is a snowball effect that can only be halted by antioxidants.

When the process is not stopped, damage occurs in structures that contain lipids. This is most commonly the membranes of our cells. Lipid peroxidation is known to play a role in cancer development.

II. Compound Lipids:

In contrast to simple lipids, the complex lipids contain elements like phosphorus, sulfur, nitrogen, etc. Besides these elements, carbon, hydrogen and oxygen which are present in all lipids. Among the complex lipids, phospholipids resemble the simple lipids most closely in their structure.


Phospholipids are a major constituent of the cell membranes of most of the organisms. In a phospholipid molecule, two hydroxyl groups of glycerol are esterified with carboxyl groups of long-chain fatty acids as in case simple lipids. In contrast, the third hydroxyl group of glycerol is esterified with phosphoric acid. Such a lipid is called a phosphatide. In most of the phospholipids, phosphoric acid is further linked to an organic group (R). This chemical constitution makes the phospholipid molecule amphipathic, with a non-polar, water-insoluble part (the fatty acids) and a highly polar, water-soluble part (the rest of the molecule).

Picture Source-

Important functions of lipids

(1) They serve as food reserve in both plants and animals. Hibernating animals store extra fat before the onset of cold weather. Migratory birds also do the same before migration.

(2) Fats function as concentrated food because as compared to carbohydrates, they yield more than twice energy/unit weight (9.3:4.5 kcal/gm).

(3) Fats can be converted to carbohydrates. Therefore, fats stored in oilseeds (e.g., Groundnut, Mustard, Castor, Sun­flower, Cotton, and Coconut) provide not only energy but also raw materials for the growth of the embryo.

(4) In spores and seeds, lipids help in thermal insulation, protect them from ultraviolet radiations and loss of water.

(5) Vitamin A, D, E and vitamin K are soluble in fats. And latter not only act as their carriers but also prevent vitamin from oxidation.

(6) In animals, fat occurs as droplets inside the cells called adipocytes. Adipocytes of cold-blooded or poikilothermic animals have a higher amount of unsaturated fatty acids as compared to warm-blooded or homoeothermic animals.

Fatty or adipose tissue makes an insulating layer below the skin of animals for protection against low temperature. The whale has a very thick layer of subcutaneous fats called blubber. Animals live in colder regions also have a thick fatty layer for insulation (Polar Bear is the example).

(7) Subcutaneous fat surrounds off the body contours of animals and human beings. The fats produce a shock-absorbing cushion around eyeballs, gonads, kidneys and other vital organs in the animal.

(8) Edible oils secreted from many seeds are used in cooking purposes. Animal fats present in milk from where we yield butter and ghee.

(9) Plant oils are used as a low amount of cholesterol fat. They are also hydrogenated to form vegetable oil or ghee.

(10) Soap was previously manufactured from animal fat. Nowadays, plant fats are used for this purpose.

(11) Drying oils which having unsat­urated fatty acids are used in the paint industry.

(12) Waxes make a protective layer on the animal fur. They prevent the floating leaves of aquatic plants against wetting and submerge. In land plants, they lower the rate of transpiration.

(13) Myelin sheath around nerve fibres takes place in insulation.

14) Phospholipids, glycolipids and sterols are the substances of cell membranes.

(15) Fragrance of many plant products is due to fat-like components which are called terpenes.

(16) In birds, oils from preen gland is used to lubricate feathers and protect them from wetting. Hair is similarly lubricated in mammalian skin. It protects their felting. The skin also helps to moisturise.

(17) Desert animals employ fat as a source of metabolic water, e.g., Kangaroo Rat, Camel. Kangaroo or Desert Rat does not drink water. Stored fat in its hump of camel uses for obtaining metabolic water during extreme desiccating conditions.

MCQ on Fatty Acids with Answer Key (Biochemistry MCQ-9)

(1). Most commonly occurring fatty acids in nature are:
a. Even number of carbon atoms in an un-branched chain of 12 – 24 carbons
b. Odd number of carbon atoms in an un-branched chain of 12 – 24 carbons
c. Even number of carbon atoms in a branched chain of 12 – 24 carbons
d. Odd number of carbon atoms in a branched chain of 12 – 24 carbons

(2). In most of the naturally occurring mono-unsaturated fatty acids, the double bonds will be placed between ____________.
a. C6 – C7
b. C7 – C8
c. C8 – C9
d. C9 – C10

(3). Which of the following molecule acts as a sugar carrier in animals?
a. Warfarin
b. Ubiquinone
c. Plastoquinone
d. Dolichol

(4). The best source of trans fatty acid in diet is ____________.
a. Vegetables
b. Ground nut
c. Dairy products
d. Fruits

(5). LDL and HDL are commonly known as __________ and ________ respectively.
a. Good cholesterol and bad cholesterol
b. Bad cholesterol and good cholesterol
c. Assimilatory cholesterol and oxidative cholesterol
d. Oxidative cholesterol and assimilative cholesterol

(6). The solubility of fatty acids in water ________________
a. Increase with increase in chain length and fewer the double bonds
b. Increase with increase in chain length and increase in double bonds
c. Decrease with chain length and decrease with number of double bonds
d. Decrease with chain length and increase with double bonds

(7). At room temperature (25oC), a fat with saturated fatty acid of 12 – 20 carbon have:
a. Liquid consistency
b. Solid consistency
c. Cannot be predicted

(8). Carbon atoms in fatty acid are __________ than those of sugars.
a. Less reduced
b. More reduced
c. Less oxidized
d. More oxidized

(9). In naturally occurring unsaturated fatty acids, the double bonds are in _______ conformation.

a. Cis conformation
b. Trans conformation
c. A mixture of cis and trans conformation
d. Cis and trans conformation alternatively

(10). Increased dietary uptake of trans fatty acid causes blood level __________

a. Increase of HDL
b. Increase of LDL
c. Increase of LDL and decrease of HDL
d. Increase of HDL and decrease of LDL

(11). Which of the following is a cyclic fatty acid?

a. Cerebronic acid
b. Ricinoleic acid
c. Chaulmoorgic acid
d. Oleic acid

(12). Which of the following is NOT an essential fatty acid?

a. Linoleic acid
b. LInolenic acid
c. Arachidonic acid

(13). Which of the following statement is true?

a. Cholesterols are present in both plants and animals
b. Sterol is the only type of cholesterol in plants
c. Cholesterol is not found in plants
d. Cholesterol is completely absent in liver cells of cold blood animals

(14). Heart attach possibility in women is fewer than men. The probable reason for this may be ______.

a. Blood HDL level in female is more than male
b. Blood HDL in female is less than male
c. Blood of female individuals do not contain HDL
d. Blood of female individuals do not contain LDL

(15). At room temperature (25oC) an unsaturated fatty acid will have ___

a. Liquid consistency
b. Solid consistency
c. Waxy consistency
d. Cannot be predicted

(16). Which of the following statement is true?

A. Sodium salt of higher fatty acid is called soft soaps
B. Potassium salt of higher fatty acid is called soft soaps
C. Sodium salt of higher fatty acid is called hard soaps
D. Potassium salt of higher fatty acid are called hard soaps

(17). The number of OH groups in fatty acids can be expressed as:

a. Polenske number
b. Reichert-Meissl number
c. Acetyl number
d. Iodine number

(18). The triterpenoid which acts as the precursor of all animals sterols:

a. Lanosterol
b. Cholesterol
c. Cycloartenol
d. Isoprenoids

(19). The precursor of all fungal sterols is _______.

a. Lanosterol
b. Cholesterol
c. Cycloartenol
d. Isoprenoids

(20). The triterpenoid which acts as the precursor of almost all plant sterols:

a. Lanosterol
b. Cholesterol
c. Cycloartenol
d. Isoprenoids

(21). A sterol present in the plasma membrane of fungi and protozoans instead of cholesterol is ________________

a. Lanosterol
b. Cholesterol
c. Ergosterol
d. Cycloartenol

(22). The sterol which acts as the precursor of Vitamin D2 (provitamin D2) is:

a. Colcalciferol
b. Lanosterol
c. Cholesterol
d. Ergosterol

(23). Which of the following is an example for phytosterol?

a. β-sitosterol
b. Campesterol
c. Brassicasterol
d. All of these
e. None of these

(24). A naturally occurring fatty acid with C-C triple bond in the hydrocarbon chain:

a. Digitoxin
b. Oubain
c. Nemotinic acid
d. None of these

(25). Which of the following is NOT an omega-6 fatty acid?

a. Alpha-linolenic acid
b. Linoleic acid
c. Eicosadienoic acid
d. Arachidonic acid

More Biochemistry MCQs

Answer key and explanations:

1. Ans. (a). Even number of carbon atoms in an un-branched chain of 12 – 24 carbons

Fatty acids with odd number of carbon, branched chain and more than 24 carbon atoms do occurs in nature but very rarely.

In majority of naturally occurring mono-unsaturated fatty acids, the double bond is between C9 and C10 of the hydrocarbon chain.

Dolichol is an alcohol functional group containing long chain organic compound made up of many isoprene units. Dolichol has important function in N-glycosylation of proteins in the form of dolichol phosphate. Dolichol also functions as membrane anchor point for the formation of oligosaccharides.

5. Ans. (b). bad cholesterol and good cholesterol

6. Ans. (c). Decrease with chain length and decrease with number of double bonds

Fatty acids are partially soluble in water. The partial solubility is due to presence of hydrophilic COOH group at the tip the hydrocarbon chain. The hydrocarbon chains are completely insoluble in water. When the fatty acids are of shorter length, it will be more soluble in the water since the chain length reduction reduces the hydrophobic interactions of hydrocarbons.

7. Ans. (b). Solid consistency

Saturated fatty acids do not have double bounds and hence molecules can be packed compactly. When unsaturation is present in the fatty acids, due to double bonds there will be kinks in the fatty acid chains and this hinders the compact packing of fatty acid residues. Since the molecules are not compactly packed in the unsaturated fats, they acquire a liquid consistency.

Carbon atoms in fatty acids are more reduced than those in sugars. This is why fatty acids are more energy rich than sugars.

10. Ans. (c). Increase of LDL and decrease of HDL

11. Ans. (c). Chaulmoorgic acid

Chaulmoorgic acid is a cyclic fatty acid obtained from Chaulmoorgra seeds. Chaulmoorgic acid is used in the treatment of leprosy.

12. Ans. (d). Arachidonic acid

Arachidonic acid is a poly unsaturated ω fatty acid. It is not an essential fatty acid. Arachidonic acid is synthesized from linoleic acid in the body. If there is any inability to convert linoleic acid to arachidonic acid, it becomes a conditionally essential fatty acid.

Essential fatty acids: (EFAs) are fatty acids in humans which are very essential for the normal functioning of the body and it is not synthesized in the cells. They should be obtained from the diet. Only two fatty acids are essential to human, they are alpha linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid).

13. Ans. (c). Cholesterol is not found in plants

Cholesterol is not found in plants but other sterols do occurs in plants.

14. Ans. (a). Blood HDL level in Female is more than male

15. Ans. (a). Liquid consistency

Nemotinic acid is a rare fatty acid with C-C triple bond. Santalbic acid which is present in the sandal wood oil also contains one triple bond.

25. Ans. (a). Alpha-linolenic acid

Alpha linolenic acid is an omega 3 fatty acid.

The answer key is prepared with best of our knowledge.
Please feel free to inform the Admin if you find any mistakes in the answer key..


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What is the Difference between saturated and unsaturated fatty acids?

Firstly, saturated fatty acids are where all the carbon atoms have single bonds between them making the lipid saturated as no more hydrogens can be added. Having no double bond means the fatty acid is straight, and so they can pack closely together (e.g. in triglycerides and phospholipids) meaning they are usually solid at room temperature and are called fats. These usually have a higher melting point as the van der waals forces between them are stronger as they are closer together, meaning it takes more energy to break the bond/ force. On the other hand, unsaturated fatty acids are where there is a double bond between one or more of the carbon atoms in the hydrocarbon chain. This leads to them being unsaturated as the double bond can effectively ‘fold out’ so another hydrogen is able to be added to the molecule. Having one double bond means that the fatty acid is monounsaturated, having many means it is polyunsaturated. These double bonds cause the fatty acid chain to ‘kink’ meaning the fatty acids can’t pack as closely together, which results in more fluidity. This causes the triglycerides to be liquid at room temperature, thus an oil. Having the bend in the hydrocarbon chain means there are weaker van der waals forces between the molecules, and so leading to a lower melting point.

Increase of Unsaturated Fatty Acids (Low Melting Point) of Broiler Fatty Waste Obtained Through Staphylococcus xylosus Fermentation

The increasing rise in the production of meat around the world causes a significant generation of agro-industrial waste--most of it with a low value added. Fatty wastes have the potential of being converted into biodiesel, given the overcome of technological and economical barriers, as well as its presentation in solid form. Therefore, the aim of this work was to investigate the capacity of Staphylococcus xylosus strains to modify the chemical structure of chicken fatty wastes intending to reduce the melting points of the wastes to mild temperatures, thereby breaking new ground in the production of biodiesel from these sources in an economically attractive and sustainable manner. The effects in time of fermentation and concentration of the fat in the medium were investigated, assessing the melting point and profile of fatty acids. The melting temperature showed a decrease of approximately 22 °C in the best operational conditions, due to reduction in the content of saturated fatty acids (high melting point) and increase of unsaturated fatty acids (low melting point).


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