UJIAN KIMIA BAHAN ALAM

1.       Fats generally are solid while the oil is liquid phase, however both are equally triglyceride. Explain why the form of two different triglyceride, and point out important factors that determine the form of fat? 

Answer:  

Fats generally are solid  while the  oil is liquid phase because:

• Effect of structure on physical properties

General , as chains become longer and/ or more saturated, the triglyseride is more likely to be a fat (solid)As chains becvome shorter and/or more unsaturated, the triglyseride is more likely to be a oil ( liquid)

• Saturated fatty acids have only single bonds between its constituent carbon atoms, while unsaturated fatty acids having at least one double bond between carbon atoms of the constituent.
• oil has a chain of C1 - C10 while fat has an chain> C10
• Saturated and unsaturated fats differ in their energy content and melting point. Since unsaturated fats contain fewer carbon-hydrogen bonds than saturated fats with the same number of carbon atoms, unsaturated fats will yield slightly less energy during metabolism than saturated fats with the same number of carbon atoms
• Saturated fats can stack themselves in a closely packed arrangement, so they can freeze easily and are typically solid at room temperature

Types	Fats	Oil
Double bond	less	Many
melting point	high	low
phase	Solid	Liquid
source	the animal	The plant generally
Reactivity	not easy Easy rancid	Easy rancid

1.   

         2.    How a primary metabolite can be converted in the secondary metabolites. What is the basic idea and how the machanism could be described?

answer

The most important building blocks employed in the biosynthesis of secondary metabolites are derived from:

1. Acetyl coenzyme A (acetyl-CoA)

The form in which acetate is used in most of its important biochemical reactions is acetyl coenzyme A (acetyl-CoA).

Acetyl-CoA is formed by oxidative decarboxylation of the glycolytic pathway product pyruvic acid.

2. Shikimic acid

Shikimic acid is produced from a combination of phosphoenolpyruvate, a glycolytic pathway intermediate, and erythrose 4-phosphate from the pentose phosphate pathway. 

3. Mevalonic acid

Mevalonic acid is itself formed from three molecules of acetyl-CoA, but the mevalonate pathway channels acetate into a different series of compounds than does the acetate pathway.

4. 1-deoxyxylulose 5-phosphate

Deoxyxylulose phosphate arises from a combination of two glycolytic pathway intermediates, namely pyruvic acid and glyceraldehyde 3-phosphate 

5. Amino acids

Peptides, proteins, alkaloids and many antibiotics are derived from amino acids.

Intermediates from the glycolytic pathway and the Krebs cycle are used in constructing many of them.

the specific reasction
primary metabolite can be converted in the secondary metabolites from  the reaction the fundamental processes of photosynthesis,glycolysis, and theKrebs cycle are tapped off from energy-generating processes to provide biosynthetic intermediates.To make biosynthesis intermediets needs the buillding blocks. By far the most important building blocks employed in the biosynthesis of secondary metabolites are derived from the intermediates acetyl coenzyme A (acetyl-CoA), shikimic acid, mevalonic acid, and methylerythritol phosphate. These are utilized respectively in the acetate, shikimate, mevalonate, and methylerythritol phosphate pathways, Acetyl-CoA is formed by oxidative decarboxylation of the glycolytic pathway product pyruvic acid. It is also produced by the β-oxidation of fatty acids, effectively reversing the process by which fatty acids are themselves synthesized from acetyl-CoA. Important secondary metabolites formed from the acetate pathway include phenols, prostaglandins, and macrolide antibiotics, together with various fatty acids and derivatives at the primary–secondary metabolism interface. Shikimic acid is produced from a combination of phosphoenolpyruvate, a glycolytic pathway intermediate, and erythrose 4-phosphate from the pentose phosphate pathway. The reactions of the pentose phosphate cycle may be employed for the degradation of glucose, but they also feature in the synthesis of sugars by photosynthesis. The shikimate pathway leads to a variety of phenols, cinnamic acid derivatives, lignans, and alkaloids. Mevalonic acid is itself formed from three molecules of acetyl-CoA, but the mevalonate pathway channels acetate into a different series of compounds than does the acetate pathway. Methylerythritol phosphate arises from a combination of two glycolytic pathway intermediates, namely pyruvic acid and glyceraldehyde 3-phosphate by way of deoxyxylulose phosphate. The mevalonate and methylerythritol phosphate pathways are together responsible for the biosynthesis of a vast array of terpenoid and steroid metabolites.
In addition to acetyl-CoA, shikimic acid, mevalonic acid, and methylerythritol phosphate, other building blocks based on amino acids are frequently employed in natural product synthesis. Peptides, proteins, alkaloids, and many antibiotics are derived from amino acids, and the origins of some of the more important amino acid components of these are briefly indicated in Figure 2.1. Intermediates from the glycolytic pathway and the Krebs cycle are used in constructing many of them, but the aromatic amino acids phenylalanine, tyrosine, and tryptophan are themselves products from the shikimate pathway. Ornithine, an amino acid not found in proteins, and its homologue lysine, are important alkaloid precursors and have their origins in Krebs cycle intermediates. Of special significance is the appreciation that secondary metabolites can be synthesized by combining several building blocks of the same type, or by using a mixture of different building blocks. This expands structural diversity and, consequently, makes subdivisions based entirely on biosynthetic pathways rather more difficult. A typical natural product might be produced by combining elements from the acetate, shikimate, and methylerythritol phosphate pathways.

 3.Hormone progesterone is essential for the survival of the pregnancy. These hormones are drived from a streoid biognetically. Explain the logic of chemical reactions which may occur in the formation of progesterone. 

BIOSYNTHESIS PROGESTERONE

To get the hormone progesterone which is needed by mammals. like all other steroid hormones, synthesized from pregnenolone, which in turn comes from cholesterol. This is a step in the formation reaction of progesterone Cholesterol  undergoes double oxidation to produce 20,22-dihydroxycholesterol.

1.  This vicinal diol is then further oxidized with loss of the side chain starting at position C-22 to produce pregnenolone. This reaction is catalyzed by cytochrome P450scc.
2.  The conversion of pregnenolone to progesterone takes place in two steps. 

·         First, the 3-hydroxyl group is oxidized to a keto group  

·         second, the double bond is moved to C-4, from C-5 through a keto/enol tautomerization reaction. This reaction is catalyzed by 3beta-hydroxysteroid dehydrogenase/delta(5)-delta(4)isomerase.

Progesterone in turn  is the precursor of the mineralocorticoid aldosterone, and after conversion to 17-hydroxyprogesterone (another natural progestogen) of cortisol and androstenedione. Androstenedione can be converted totestosterone, estrone and estradiol.

 In laboratory

the synthesis begins with reacting the phosphonium salt  with phenyl lithium to produce the phosphonium ylide . The ylide  is reacted with an aldehyde to produce thealkene . The ketal protecting groups of  are hydrolyzed to produce the diketone , which in turn is cyclized to form the cyclopentenone. The ketone of  is reacted with methyl lithium to yield the tertiary alcohol , which in turn is treated with acid to produce the tertiary cation . The key step of the synthesis is the π-cation cyclization of  in which the B-, C-, and D-rings of the steroid are simultaneously formed to produce . This step resembles the cationic cyclization reaction used in the biosynthesis of steroids and hence is referred to as biomimetic. In the next step the enol orthoester is hydrolyzed to produce the ketone . The cyclopentene A-ring is then opened by oxidizing with ozone to produce . Finally, the diketone  undergoes an intramolecular aldol condensation by treating with aqueous potassium hydroxide to produce progesterone.

4. Many alkaloids are toxic to other organism. They often have pharmacological effects and are used as medications, as recreational drugs, or in entheogenic rituals. Describe in outline the process of biosynthesis of an alkalois compound and describe the functions groups which play an important role in the biological activities

.BIOSYNTHESIS OF ATROPINE

 The biosynthesis of atropine starting from L-Phenylalanine first undergoes a transamination forming phenylpyruvic acid which is then reduced to phenyl-lactic acid. Coenzyme A then couples phenyl-lactic acid with tropine forming littorine, which then undergoes a radical rearrangement initiated with a P450 enzyme forming hyoscyamine aldehyde. A dehydrogenase then reduces the aldehyde to a primary alcohol making (-)-hyoscamine, which upon racemization forms atropine.

 

Biosynthesis of atropine starting from L-Phenylalanine