BIO202 Final Term Current Past Papers

1. Monosaccharides (simple sugars) are those which cannot be hydrolyzed further into simpler forms the backbones of common monosaccharides are unbranched carbon chains in which all the carbon atoms are linked by single bonds. In the open-chain form, one of the carbon atoms is double-bonded to an oxygen atom to form a carbonyl group. Each of the other carbon atoms has a hydroxyl group. If the carbonyl group is at an end of the carbon chain (that is, in an aldehyde group) the monosaccharide is an aldose If the carbonyl group is at any other position (in a ketone group) the monosaccharide is a ketose. Ribose, Glucose and Fructose The simplest monosaccharides are the two three-carbon trioses: ❖ Glyceraldehyde,an aldotriose ❖ Dihydroxyacetone,a ketotriose 2. Disaccharides are those sugars which yield two molecules of the same or different monosaccharides on hydrolysis  Maltose - 2 molecules of glucose on hydrolysis  Lactose – 1 glucose & 1 galactose on hydrolysis  Sucrose – 1 glucose & 1 fructose on hydrolysis 3. A nucleotide is composed of three distinctive chemical sub-units: a five-carbon sugar molecule, a nucleobase—the two of which together are called a nucleoside—and one phosphate group 4. Dehydrogenases remove hydrogen atoms Proteases hydrolyze proteins 5. Two sugars which differ from one another only in configuration around a single carbon atom are termed epimers. Glucose and Galactose are an example of an epimeric pair which differs only with respect to C4. Similarly Glucose and mannose are epimers with respect to C2 6. Glutamate has a pI of 3.22, considerably lower than that of glycine. This is due to the presence of two carboxyl groups, with an average of their pKa values of 3.22 7. Pentose Sugar D-ribose and 2-deoxy D-ribose are the only sugars so far found in the nucleic acids. These aldo pentoses belong to D-family. They are present as Furanose (ring) in the form of βAnomer. The addition of a pentose sugar to a base produces a nucleoside. If the sugar is Dribose, a ribonucleoside is produced. If the sugar is 2-deoxy Dribose, a deoxyribonucleoside is produced 8. Preparing crystalline derivatives of sugars called osazones They are obtained by adding a mixture of phenyl hydrazine hydrochloride and sodium acetate to a sugar solution and heating in water bath for 45 mins. Crystals are formed after the solution is cooled slowly. Reaction involves only the carbonyl carbon and the adjacent carbon. First phenyl hydrazone is formed and then reacts with an additional molecule of phenylhydrazine to form the osazones. 9. An aldose is defined as a monosaccharide whose carbon skeleton has an aldehyde group. They are primarily found in plants. Ketose is a monosaccharide whose carbon skeleton has a ketone group. Only in the presence of reducing sugar, they can isomerize to aldose.

Sugars are linked to the heterocycle by a β -N-glycosidic bond, almost always to the N-1 of a pyrimidine and N-9 of a purine. The N-glycosyl bond is formed by removal of the elements of water a hydroxyl group from the pentose and hydrogen from the base. Thus it is a condensation reaction. Similar to O-glycosidic bond formation in carbohydrates. However N-glycosidic bonds, have Nitrogen atom instead of oxygen linking the two residues.

L fucose is found in the complex oligosaccharide component of glycoprotein and glycolipid rhamnose is found in plant poly saccharide

Pentose any of the class of simple sugars whose molecules contain five carbon atoms, such as ribose and xylose. They generally have the chemical formula C5H10O5. Adenine when combines with pentose the structure is known as Adenosine or deoxyadenosine.

Guanine when combines with pentose the structure is known as Guanosine or deoxyguanosine.

Uric acid is the catabolic end product of purines in human beings

When two or more nucleotides combine together a phosphodiester bond is formed. This bond is formed mainly between the 3´OH group of sugar of one nucleotide and 5´PO4 group of sugar of another nucleotide creating a phosphodiester linkage. By definition, the 5´ end lacks a nucleotide at the 5´ position and the 3´ end lacks a nucleotide at the 3´ position. The sugar and phosphate group is called the backbone of the nucleic acid. The backbones of both DNA and RNA are hydrophilic.

Two types of phosphatases in the body ❖ The one that acts in the alkaline pH is called alkaline phosphatase and ❖ The other which acts at acidic pH is known as acid phosphatase. There may be one, two, or three phosphate groups present in nucleotides. ❖ Nicotinamide adenine dinucleotide phosphate. ❖ Phosphoproteins. ❖ Adenosine triphosphate. ❖ Dihydrogen phosphate.

❖ A nitrogenous base (purine or pyrimidine) ❖ A pentose monosaccharide ❖ One, two, or three phosphate groups

Nitrogenous Bases

The nitrogen-containing bases belong to two families of compounds:

Purines and Pyrimidines

By the attachment of different groups to the rings, different types of pyrimidine and purine are generated.

The nitrogen-containing bases belong to two families of compounds:  Purines  Pyrimidine

Purines

In which include: Adenine (A) and Guanine (G) ❖ Adenine when combines with pentose the structure is known as Adenosine or deoxyadenosine Guanine when combines with pentose the structure is known as Guanosine or deoxyguanosine Adenine is 6-aminopurine

Pyrimidines:

Pyrimidines include: Cytosine (C)—in DNA and RNA, Thymine (T)—only in DNA and Uracil (U) —only in RNA ❖ Cytosine when combines with pentose it becomes deoxycytidine and cytidine ❖ Thymine becomes thymidine and deoxythymidine ❖ Uracil (U) becomes uridine and deoxyuridine depending on the type of sugar. ❖ Cytosine is 2-oxy-4-amino-pyrimidine ❖ Thymine is 2, 4-dioxy-5-methyl-pyrimidine ❖ Uracil is 2, 4-dioxy-pyrimidine ❖ T and U differ by only one methyl group, which is present on T but absent on U Minor Pyramidine Bases: Dihydrouridine (DHU), 5-Methyl Cytadine & 5-HydroxyMethyl Cytadine Unnatural Pyramidine Bases: Fluorouracil (5FU) & 6-Aza Cytosine (AZC)

Xanthine oxidase is a form of xanthine oxidoreductase, an enzyme that generates reactive oxygen species such as superoxide radicals and hydrogen peroxide when it catalyzes the