BIOCHEMISTRY-- SEMESTER-- 1 TOPIC—LIPIDS—CLASSIFICATION AND FUNCTIONS VIDEO LECTURE 1&2 (PART 1& PART 2)
Overview of the Unit:
Lipids are a group of organic compounds that are insoluble in water (hydrophobic) but soluble in organic solvents
Most membrane lipids are amphipathic small molecules having polar head group and non-polar tail group
Functions of lipids:
1. Lipids are the major constituents of Membrane structure.
2. Lipids are energy giving food substances; each gram of lipid provides nearly nine kilo calories of energy. They also act as storage forms of food and stored in adipose tissue.
3. They help in the digestion of food in the form of bile salts and required for the absorption of fat soluble vitamins
4. The steroid hormones are lipids
5. They act as insulating material and protect the animals that live in low temperatures
Fatty acids: Fatty acid is a carboxylic acid with a long aliphatic chain which can be either saturated or unsaturated
Fatty acids that have carbon–carbon double bonds are known as unsaturated. Fatty acids without double bonds are known as saturated.
Saturated fatty acids
Palmitic acid CH3(CH2)14COOH
Stearic acid CH3(CH2)16COOH
Arachidic acid CH3(CH2)18COOH Unsaturated fatty acids
Oleic CH (CH ) CH=CH(CH ) COOH acid 3 2 7 2 7
Linoleic CH (CH ) CH=CHCH CH=CH(CH ) COOH acid 3 2 4 2 2 7
α -
Linolenic CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOH acid
Arachido CH3(CH2)4CH=CHCH2CH=CHCH2CH=CHCH2CH=CH(C NIST nic acid H2)3COOH
Classification of lipids:
Lipids are classified as the following
Simple lipids: Also called as triglycerides and are chemically tri esters of fatty acids and glycerol. Triglycerides are the main constituents of body fat in animals, as well as vegetable fat. These are of two types
1. Simple Tri acyl glycerides: consists of the same type of three fatty acids attached to the three OH groups of glycerol. Tristearin, triolein, tripalmitin, 2. Mixed tri acyl glycerides consist of three different types of fatty acids attached to the three OH groups of glycerol. Distearo-olein
Waxes: A wax is a simple lipid which is an ester of a long-chain alcohol and a long chain fatty acid. Waxes are found in nature as coatings on leaves and stems.
Ex. Carunba wax, bees wax. spermaceti found in the head of sperm whale.
Compound lipids
Esters of fatty acids with alcohol, containing non-lipid Group (PO4, Nitrogenous base, or sugar). Compound Lipids are Further Classified as: Phospho-lipids Ex: Phosphatidylethanolamine (cephalin) (PE), Phosphotidyl choline,
Phosphatidylinositol ((PI) plasmalogens, Spingolipids.
Glyco-lipids: Proteo-lipids (lipo-proteins) Sulpho-lipids Phosphatidic acid (PA): The simplest glycerophospholipid is phosphatidic acid (PA) It consists of glycerol, phosphate, and 2 fatty acyl chains in ester linkages
Different types of phospholipids are
1. Phosphatidylethanolamine (cephalin) (PE)
Phosphotidyl choline:
Phosphoinositides: Phosphatidylinositol ((PI
Phosphatidylserine (PS)
Functions of phospholipids: They are the
1. Major constituents of all cell membranes
2. Components of bile
3. Anchor some proteins in membranes
4. Act as signal mediators
5. Components of lung surfactant
6. Components of lipoproteins
Plasmalogens:
Plasmalogens have an ether-linked hydrocarbon chain at C-1 of glycerol, instead of ester- linked fatty acid
Platelet-activating factor (PAF) is a plasmalogen (a phosphatidalcholine) with an acetyl group at C-2 of glycerol
It has potent physiologic actions (platelet activation; inflammatory responses; bronchoconstriction)
SPINGO LIPIDS:
These are the simplest spingogycolipids They consist of a ceramide with a single sugar residue at the 1-hydroxyl moiety. The sugar residue can be either glucose or galactose Galactosylceramide is the principal glycosphingolipid in brain tissue. Glucosylceramide is found at low levels in animal cells such as the spleen, erythrocytes.
A ganglioside is a molecule composed of a glycosphingolipid (ceramide and oligosaccharide) with one or more sialic acids (e.g. n-acetylneuraminic acid, NANA) linked on the sugar chain
The oligosaccharide groups on gangliosides extend well beyond the surfaces of the cell membranes, and act as distinguishing surface markers that can serve as specific determinants in cellular recognition and cell-to-cell communication.
These carbohydrate head groups also act as specific receptors for certain pituitary glycoprotein hormones and certain bacterial protein toxins such as cholera toxin.
STEROIDS s
Steroids are lipids containing a steroid nucleus (core structure) The steroid nucleus is a fused ring system consisting of three cyclohexane rings and one cyclopentane ring The rings are designated A, B, C and D Attachment of different groups to the core steroid structure leads to a wide variety of steroid compounds, including cholesterol, bile salts and steroid hormones
C D
A B
Cholesterol is the highly studied small molecule in biology. Thirteen Nobel Prizes have been awarded to scientists who devoted major parts of their careers to cholesterol Cholesterol is the most abundant steroid in animals Plants have very small amounts (but have related compounds) It’s a major component of cell membranes, and affects the fluidity of the membrane due to its bulky structure It is a precursor for biosynthesis of many other steroids Cholesterol is called a sterol because it contains an alcohol group We can obtain cholesterol from our diet (animal products), but our liver can also synthesize all the cholesterol that we need The liver synthesizes more cholesterol when dietary intake is low Excessive blood cholesterol is associated with atherosclerosis and formation of gallstones
CHOLESTEROL IS THE BIOSYNTHETIC SOURCE OF ALL STEROID HORMONES
Five major classes of hormones Progestins (regulate events during pregnancy and are precursors to all other steroid hormones) Androgens (male sexual characteristic development and maintenance) Estrogens (female sexual characteristics development and maintenance) Glucocorticoids (promote gluconeogenesis, and in certain doses suppress inflammation rxns) Mineralocorticoids (regulate ion balance in kidney) Bile acids and bile salts are synthesized from cholesterol in the liver
They are stored in the gall bladder and released into the upper small intestine to help break down fats and oils (like soaps) by the process called emulsification.
UNIT WISE STUDENT ASSIGNMENTS:
1. Classification of lipids
2. Phospholipids
3. Saturated and unsaturated fatty acids
4. Sphingolipids
5. Glycolipids
6. Cholesterol
7. Membrane structure
8. Composition of plasma membrane
9. Membrane transport
QUESTION BANK FOR THE UNITS
Ten marks questions
1. Discuss about the classification of lipids in detail.
2. Give the structure and functions of cholesterol in detail.
3. Explain about the membrane structure by fluid mosaic model
4. Discuss about the membrane transportation in detail.
5. Write about the structure and functions of phospholipids
Five Marks questions
1. Saturated and unsaturated fatty acids
2. Essential fatty acids
3. Neutral fats
4. Sphingolipids
5. Structure of cholesterol 6. Functions of cholesterol
7. Diagram of plasma membrane
8. Active transport
Two mark questions
1.Simple triacylglycerides
2.Mixed triacylglycerides
3.Cerebrocides
4.Plasmalogens
5.Cephalin
6. Phosphatidic acid
7. Lyso phospholipid
8.Endo and exocytosis
9.Osmosis
10.Bile salts
11.Steroid hormones
12.Facilitated diffusion
Student seminar topics: 1. FLUID MOSAIC MODEL OF MEMBRANE
2. CHOLESTEROL-THE KEY COMPOUND
3. MEMBRANE A BOUNDARY FOR TRANSPORTATION Quiz questions
1. Example for polyunsaturated fatty acid 2. Fats are formed by the condensation of ------3. The double bond in cholesterol exists between the carbon atoms ---- 4. The fluid mosaic model was proposed by – 5. The Kink in unsaturated fatty acids is due to the – 6. The fatty acids that are not synthesized in our body and has to be taken in diet---- 7. The compound that helps in the maintenance of fluidity of plasma membrane---
8. Cholesterol is an------
9. Amphipathic lipids contain ----
10. Cephalin contains
11. The lipid present in the axon membrane of nerve cell
12. The difference in the blood groups is due to the difference in the ----- components of cell membrane
13. Example for bile salts
14. Emulsification is due to the formation of ----
15. Ceramide consist of----
16. The ATPase that helps in the maintenance of eukaryotic membrane potential
17. Define osmosis
18. Facilitated diffusion is the diffusion through----
19. The transportation process that requires energy for the movement of solute molecules
20. In the process of phagocytosis the engulfed particles are digested in sacs called-----
\
1 linolenic acid, arachidonic acid
2. Fatty acids and alcohol
3.5&6
4. Singer &Nicolson
5. Unsaturation
6. Essential fatty acids
7. Cholesterol
8. Alcohol
9. Polar head group and nonpolar tail group.
10. Phospotidic acid & choline
11. Sphigomyelin
12.Glycoprotein
13. Sodium taurocholate &Sodium glycocholate
14. Micelles
15. Sphingosine alcohol +Fatty acid
16. Sodium potassium ATPase
17. The movement of a solvent from low concentration to high concentration through semipermeable membrane is called osmosis
18. Transporter protein 19. Active transport
20. Phagolysosomes.