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MS1005N General Biochemistry

MS1005N General Biochemistry. Dr Sundus Tewfik s.tewfik@londonmet.ac.uk. LIPIDS 1. Learning outcomes:. Define “lipid” and classify lipids by their chemistry; Draw saturated & unsaturated fatty acids; Illustrate a steroid, a TG and a PL;. 1. More commonly known as fats or oils

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MS1005N General Biochemistry

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  1. MS1005N General Biochemistry Dr Sundus Tewfik s.tewfik@londonmet.ac.uk LIPIDS 1

  2. Learning outcomes: Define “lipid” and classify lipids by their chemistry; Draw saturated & unsaturated fatty acids; Illustrate a steroid, a TG and a PL;

  3. 1. More commonly known as fats or oils 2. Includes many compounds which are poorly soluble in water 3. Many are amphiphiles (meaning that they are soluble in both polar and non-polar solvents)

  4. diethyl ether chloroform methanol benzene 4. some of these are weak amphiphiles eg triglycerides and poorly soluble in water while others are strong amphiphiles eg phospholipids 5. solvents capable of dissolving lipids are called fat solvents and include benzene, diethyl ether, chloroform. A common solvent mixture is chloroform:methanol.

  5. 6. The following classification is one which is often used. There are 5 classes recognised; I fatty acids - these are long chain carboxylic acids RCOOH II acylglycerols, glycerides or neutral fats - these are neutral esters of glycerol and fatty acids Esters; A carboxylic acid contains the -COOH group, and in an ester the hydrogen in this group is replaced by a hydrocarbon group of some kind.

  6. III phosphoacylglycerols or phosphoglycerides - ionic esters of glycerol, fatty acids and phosphate IV lipids (apart from fatty acids) not containing glycerol - includes waxes, polyprenyls, terpenes and steroids

  7. V lipids combined with other biomolecules - such as proteins or carbohydrates Lipoproteins lipopolysaccharides

  8. 7. FATTY ACIDS it is necessary to distinguish between free fatty acids (FFAs) which are not combined with other structures and those fatty acids (FAs) which are found as residues as part of other lipids such as glycerides and phosphoglycerides 8. There are only small amounts of FFAs found in nature the remaining FAs are combined into other structures.

  9. RCOOH RCOO- + H 9. Fatty acids have an ionisable carboxyl group and a nonpolar unbranched hydrocarbon chain • usually possess an even number of carbon atoms (acetyle CoA)

  10. can be saturated (no carbon-carbon double bonds) or unsaturated (possess some carbon-carbon double bonds ) -C=C- • nomenclature (systematic naming) is very important since it aids understanding of structure 6 5 4 3 2 1number of C atom CH3CH2CH2CH2CH2COOH

  11. alkane • the systematic name of the above compound is based on the number of carbon atoms and is related to alkanestructure and the fact that it is a carboxylic acid • (Can you suggest its name?) • it is n-hexanoic acid and it has a common name, • caproic acid

  12. Palmitic acid - saturated stearic acid-Saturated 10. In animal fats the most abundant saturated fatty acids are palmitic acid (C16 ie hexadecanoic acid) and stearic acid (C18 ie octadecanoic acid)

  13. 11. C12, C14 and C20-C28 FAs do occur in animal fats but in much smaller quantities. FAs below C10 occur very rarely in animal fats

  14. 12. Unsaturated FAs contain carbon:carbon double bondsand their names end in enoic as follows

  15. Trans Configuration Cis Configuration 13. How would you name the following unsaturated FA? (Hint - the numbering of the double bond position is taken from the lowest numbered carbon atom involved in the double bond) 16 15-11 10 9 8-2 1number of C atom 14. CH3[CH2]5CH=CH[CH2]7COOH 15. 9- hexadecenoic acid (common name - palmitoleic acid) 16. even this apparently complex systematic name does not define it completely since unsaturated FAs can exist in cis or trans forms ( hint - revise geometric isomerism)

  16. 9 octadecenoic acid Since the trans acids are straighter than their bent cis isomers, they can pack together easier and so have a higher melting point. By selecting a particular hydrogenation catalyst, temperature, stirring speed and pressure, manufacturers can control the precise composition of the margarine to create a particular 'mouth feel', melting range and stability. unlike the cis acids, which occur naturally, the trans acids are artificial and so cannot be metabolised in the human body as efficiently as their isomers. Over the past 3 decades TFAs have been linked to cancer, diabetes, heart disease, low birth rate and obesity.

  17. 17. In polyunsaturated FAs (PUFAs) the double bonds are usually separated as follows: -[CH=CH-CH2-CH=CH]- divinyl methane structurebut also the following may be found: -[CH=CH-CH=CH]- conjugated diene structure. 18. In animal tissues the most commonly found PUFAs are linoleic acid 18:2 linolenic acid 18:3 arachidonic acid 20:4

  18. 19. Note also that the position of the double bonds can be given in shorthand form, thus oleic acid is 18:1 Δ9 20. The last carbon atom is denoted as ω thus the position of the last (and only) double bond in oleic acid is ω -9 21. What is the ω position of linolenic acid 18:3 Δ9,12,15 ? A. ω-3

  19. 22. TRIACYLGLYCEROLS (OR TRIGLYCERIDES) • commonly occur as storage fats in, for example, adipose tissue; they provide a reservoir of energy • they are neutral fats • they comprise 3 fatty acids combined with glycerol • note that mono and diglycerides also exist as storage fats

  20. CH2OH  CHOH + 3 HOOC[CH2]16CH3  stearic acid CH2OH glyserol esterification CH2O.OC[CH2]16CH3  CHO.OC[CH2]16CH3 + 3H2O  CH2O.OC[CH2]16CH3 tristearin

  21. the reverse of this process is a form of hydrolysis called lipolysis. This may be carried by enzymes called lipases yielding FAs and glycerol. In the case of FAs a process called β oxidation followed by the TCA cycle and oxidative phosphorylation provides a large yield of ATP

  22. Formation of a Triglyceride via Dehydration Synthesis Condensation Reactions (Building of larger molecules) add energy to organic molecules. Hydrolysis Reactions (those that tear apart molecules) release energy from the molecules. http://www.lipidsonline.org/

  23. 23. PHOSPHOACYLGLYCEROLS (OR PHOSPHOGLYCERIDES,GLYCEROPHOSPHOLIPIDS) these are strong amphiphiles they are found in biological membranes

  24. CH2O.OC[CH2]nCH3 O-  CH2 O - P - O-  O- CH3[CH2]nCO.OCH CH2OH  HOCH O-  CH2 O - P - O-  O- + 2 FAs glycerol 3 phosphate usually saturated + 2H2O may be unsaturated What has this got to do with reindeer? phosphatidic acid phosphatidic acid is both an example of a phosphoacylglycerol and a precursor of phosphoacylglycerols.

  25. head tail isoprene polyprenyls 24. LIPIDS (APART FROM FAs) NOT CONTAINING GLYCEROL - these include structures based on isoprene units - lipids which contain the isoprene arrangement are called polyprenyls (terpenes if they are of plant origin) examples include fat soluble vitamins such as vitamin K and vitamin E (α-tocopherol)

  26. Vitamin K Vitamin E (α- tocopherol) other fat-soluble vitamins are A (trans-retinol) and D (cholecalciferol)

  27. 26. STEROIDS these have the characteristic steroid ring structure :- they occur widely in all types of living organisms except prokaryotes versatile group of compounds often found as hormones

  28. 27. The most abundant steroid in the human body is cholesterol (~ 240g per body) which is essential for proper membrane function 28. Cholesterol is often viewed as a ‘bad’ molecule despite having a varied essential and normal roles in the human body. 29. This image stems from a possible correlation between blood cholesterol levels and risk of heart disease. 30. Some cholesterol is converted to other compounds eg bile salts, sex hormones, adrenal hormones and vitamin D (cholecalciferol)

  29. 31. The corticosteroids are products of the adrenal cortex which help regulate the metabolism of electrolytes, proteins and carbohydrates 32. Human sex hormones (and their derivatives) are also steroids - these include testosterone (male sex hormones), and progesterone and œstradiol (female sex hormones)

  30. hydrophilic 33. Bile includes steroids such as taurocholate. This is a bile salt which is an amphipathic steroid (how might this occur?) A. it has a polar and and a non-polar part to its structure 34. These bile salts aid digestion in the small intestine by helping nonpolar lipids mix with the more polar digestive enzymes

  31. Study questions 1. A lipid is a polymer made up of which kind of monomers? a) amino acids                                                     c) nucleotides b) alternating sugar and phosphate groups            d) fatty acids and glycerol 2. A dehydration synthesis reaction is also known as a) a condensation reaction b) a hydrolysis reaction c) an isomeric reaction d) an energy releasing reaction e) monomer formation 3. Which of the following lipids form a bilayer between two watery regions, such as the plasma membrane of a cell? a) steroids    b) neutral fats    c) waxes    d) phospholipids

  32. 5. Which of the following lipids is saturated? 4. Which of the following is Not a lipid? a) steroids    b) fats    c) phospholipids    d) glycogen    e) cholesterol

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