Lipids: Study Notes

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Lipids:

Lipids are esters of fatty acids with alcohol; they are insoluble in water and soluble in a number of non polar organic solvents like ether, benzene and chloroform.

Lipids form colloidal complex and get dispersed uniformly in water in the form of minute droplets. The complex is known as emulsion.

Fatty acids

Fatty acids are organic acid having hydrocarbon chains that end in a -COOH group attached to an R-group.

Formation of Lipids

• Glycerol has three hydroxyl (-OH) groups, all of which can condense with a fatty acid. Usually all three undergo condensation reactions and the lipid formed is therefore called a triglyceride.
• Triglycerides are the commonest lipids in nature and are further classified as fats or oils, according to whether they are solid (fats) or liquid (oils) at 20°C.
• Triglycerides are non-polar. They do not form hydrogen bonds with water molecules and therefore do not dissolve in water they are hydrophobic.
• Their tails vary in length according to the particular fatty acids used. A major function of lipids is to act as energy stores. They have a higher calorific value than carbohydrates.

CLASSIFICATION:

ACYLGLCEROL:

It is estimated that a person of average size contains approximately 16 kg of fat which is equivalent to 144000 Kcal of energy which takes a very long time to deplete.

There are 2 type of acylglycerol:

1. Saturated Acylglycerol contain saturated fatty acids i.e. they contain one or more than one double bond.They are solid at ordinary temperature, mostly found in animals. E.g. Stearin found in beef and mutton
2. Unsaturated Acylglycerol contain unsaturated fatty acids i.e. they contain one or more than one double bond. They are liquid at ordinary temperature. They are found in plant also called oil.E.g., Linolin found in cotton seed contains linoleic acid.

WAXES:

• Waxes are simple lipids having one molecule of fatty acid forming ester bond with one molecule of long chain alcohol. E.g. Bee's wax
• Waxes are found as protective covering on stem, stalks, leaves, petals, fruit, skin, fur, feather etc.

PHOSPHOLIPIDS:

• It is similar to triacylglycerol or oil except that one fatty acid is replaced by phosphate group.
• The phospholipids molecule consist of 2 ends which are called hydrophilic (water loving) end (head) & hydrophobic (water fearing) end (tail).
• Phospholipids are present in all living cells frequently associated with membranes & are related to vital function such as regulation of cell permeability & transport processes.

TERPENOIDS:**

• Terpenoid is built up of isoprenoid (C5H8) units. Steroids, carotenoids & terpenes are the important classes of it.
• They help in oxidation & reduction process as terpenes
• Some are components of essential oils of plants e.g. menthol, camphor, mint etc.
• Plant pigment like carotene, xanthophylls is also the form of terpenoids.

TERPENES:

• This group of lipids is based on isoprenoid unit.
• Small sized terpenes are volatile in nature & produce special fragrance.
• Some of these are use in perfumes e.g.
• Myrcene from oil of bay àGeranoil from rose
• Limonene from lemon oil à Menthol from peppermint oil
• Derivatives of some terpenes are found in Vitamin A.
• They are also important constituents of chlorophyll molecules as well as intermediate compound for cholesterol biosynthesis.
• In nature they are utilized in the synthesis of rubber & latex.

STEROIDS:

• Steroids consist of three 6-carbon rings (A, B, C) & one 5(D) carbon ring
• These rings are fused together as shown below with total 17-C atoms called steroid nucleus

Examples: Most important steroid is cholesterol, a component of animal cell membrane & a precursor for the synthesis of a no. of steroids, sex hormones such as testosterone, progesterone & estrogen.

CAROTENOIDS:

• Carotenoids consist of fatty acid like carbon chain which are conjugated by double bonds & carrying 6-membered carbon ring at each end.
• These compounds are pigments producing red, orange, yellow, cream & brown colors in plants
• Carotene, Xanthophyll

Nucleic Acid:

Nucleic acids are the polymers of nucleotides.They form the genetic material of all living organisms.

Structure of nucleotides: A nucleotide has three components, a 5-carbon sugar, a nitrogenous base and phosphoric acid.

Sugar: The sugar has five carbon atoms therefore it is a pentose. Those containing ribose (C5H10O5) are called ribonucleic acids or RNA and those containing deoxyribose (ribose with an oyxgen atom removed from carbon atom 2, C5H10O4) are called deoxyribonucleic acids or DNA)

Nucleoside: Nitrogen base + Sugar

Adenine + sugar = Adenosine

Guanine + sugar = Guanosine

Cytosine + sugar = Cytidine

Thymine + sugar = Thymidine

Uracil + sugar = Uridine

CLASSIFICATION OF NUCLEIC ACID:

1. MONONUCLEOTIDE comprises one nucleotide molecule.E.g. ATP.
2. DINUCLEOTIDE comprises of two nucleotides.
3. POLYNUCLEOTIDE is a long chain nucleic acid molecule that consists of large no. of nucleotide

Nicotinamide adenine dinucleotide (NAD).

• Nicotinamide is a vitamin constituent. The two nucleotides are linked by phosphate of one another.
• It carries electron & work with dehydrogenase enzyme.
• It removes 2 hydrogen atoms from its substrate. (2H+ & 2e-)
• Both electrons & one hydrogen ion are passed to NAD which reduces it to NADH.

Ribonucleic Acid (RNA):

• • Translation:During Translation, mRNA connects to the ribosome. Two other types of RNA, tRNA (transfer) and rRNA (ribosomal), interpret the mRNA information, translating it into a specific sequence of amino acids that aids in protein synthesis.
  • Ribonucleic Acid (RNA):RNA, like DNA, is a string of nucleotides. RNA is composed of ribonucleotides, which include ribose sugar and nitrogenous bases A, G, C, and U. Unlike DNA, RNA substitutes Thymine with Uracil.

There are three types of RNA:

Messenger RNA (mRNA)

• Single-stranded
• Length varies depending on gene size
• Carries genetic information as codons (triplets of nucleotides)
• Involved in protein synthesis
• Percentage of Cellular RNA: 3 to 4%

Transfer RNA (tRNA)

• Smallest RNA, consisting of 70-90 nucleotides
• Single-stranded but forms duplex regions
• Transfers specific amino acids to ribosomes
• Contains anticodons that are complementary to codons
• Approximately 60 types in total, with 45 types in human cells
• Percentage of Cellular RNA: 10 to 20%

Ribosomal RNA (rRNA)

• Located in ribosomes
• Largest type of RNA
• Facilitates the formation of peptide bonds during protein synthesis
• Percentage of Cellular RNA: 80%

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