BIO202 Final Term Solved Papers Fall 2020

Difference between Uracil and thymine? (2 marks)

Uracil has same structure as thymine, but Uracil is demethylated form of thymine which means methyl group is deleted at the 5′ position. The methylation of thymine in DNA makes it more stable than RNA and this protects DNA from attack from enzymes. Uracil is energetically less expensive and thus nature used it in RNA.

Phosphodiester bond (2 marks)

A phosphodiester bond occurs when exactly two of the hydroxyl groups in phosphoric acid react with hydroxyl groups on other molecules to form two ester bonds.

What do you know about kinetic enzymes? (3 marks)

Substrate Concentration Affects the Rate of Enzyme-Catalyzed Reactions

E + S ↔ ES ↔ EP ↔ E + P

A key factor affecting the rate of a reaction catalyzed by an enzyme is the concentration of substrate, [S].However, studying the effects of substrate concentration is complicated because substrate is converted to product and because of reversibility of reactions, e.g. conversion of product back to substrate. One simplifying approach in kinetics experiments is to measure the initial rate (or initial velocity), designated V0, when [S] is much greater than the concentration of enzyme, [E]. The velocity (v) of a reaction is the rate of product formation. Whereas V0 is the initial velocity and is measured as soon as the reactants and enzymes are mixed. At the start of a reaction, [S] is in large excess of [P]. Thus the initial velocity of the reaction will be dependent on substrate concentration. At that time, the concentration of product is very small and, therefore, the rate of the back reaction from P to S can be ignored.

3 Functions of cGMP (3 marks)

cGMP is a common regulator of ion channel conductance, glycogenolysis, and cellular apoptosis. It also relaxes smooth muscle tissues. In blood vessels, relaxation of vascular smooth muscles lead to vasodilation and increased blood flow.

Hydrogenation (2 marks)

Hydrogenation refers to the treatment of substances with molecular hydrogen (H2), adding pairs of hydrogen atoms to compounds (generally unsaturated compounds). These usually require a catalyst for the reaction to occur under normal conditions of temperature and pressure.

Cofactors (2 marks)

Some enzymes require no chemical groups for activity other than their amino acid residues. Whereas some enzymes require molecules other than proteins for enzymic activity. If the non-protein moiety is a metal ion such as Zn2+ or Fe2+ , it is called a cofactor.

RNA (3 marks)

The genetic master plan is contained in the nucleotide sequence of DNA. It is through the ribonucleic acid (RNA)―the "working copies" of the (DNA) ― that the master plan is expressed. RNA is a polymer of ribonucleotides of Adenine, Uracil, Guanine and Cytosine, joined together by 3´-5´phosphodiester bonds. RNA does not contain thymine except in rare cases. The pentose sugar of RNA is D-ribose. Location: RNA is found in the nucleolus, ribosomes, mitochondria, and cytoplasm. The genetic material for some animal and plant viruses is RNA rather than DNA.

VLDL Properties (5 marks)

VLDLs are assembled in the liver composed predominantly of TAGs synthesized in liver and contain some cholesterol and cholesteryl esters • As VLDL pass through the circulation, TAG is degraded and taken up by peripheral tissues in the form of fatty acids, causing the VLDL to decrease in size and become denser, called VLDL remnant. further removal from these remnants produces low-density lipoprotein (LDL) • LDL particles contain much less triacylglycerol than their VLDL predecessors, and have a high concentration of cholesterol and cholesteryl esters • LDLs contain apoB-100 as their major apolipoprotein • they carry cholesterol to extra hepatic tissues that have specific plasma membrane receptors that recognize apoB-100. • apoB-100 receptors internalize the LDL into the cell. • Remaining LDL is endocytosed by Liver cells. • Oxidized LDL can also accumulate in the macrophage cells lining the arteries resulting in the formation of atherosclerosis.

Primary Structure of DNA (5 marks)

Effect of pH on enzyme activity (3 marks)

The pH optimum varies for different enzymes: • The pH at which maximal enzyme activity is achieved is different for different enzymes, and often reflects the [H+] at which the enzyme functions in the body. • For example, pepsin, a digestive enzyme in the stomach, is maximally active at pH 2. whereas other enzymes, designed to work at neutral pH, are denatured by such an acidic environment • Another examples is that there are 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.

What is Lanolin? (2 marks)

Lanolin (or wool fat) is secreted by sheep sebaceous glands and It contains both free and esterified cholesterol, e.g., cholesterol-palmitate • Lanolin secretion helps sheep in reducing water evaporation from the skin. • It is used as industrial lubricant and in cosmetics

Effect of ph in ionization of active site (2 marks)

The concentration of H+ affects reaction velocity in several ways. • First, the catalytic process usually requires that the enzyme and substrate have specific chemical groups in either an ionized or un-ionized state in order to interact. • For example, catalytic activity may require that an amino group of the enzyme be in the protonated form (–NH3 +). • At alkaline pH, this group is deprotonated, and the rate of the reaction, therefore, declines. • Extremes of pH can also lead to denaturation of the enzyme.

Sphingolipids (2 marks)

Sphingosine is an amino alcohol, which is a component of the class of lipids known as sphingolipids • Sphingosine is synthesized in the body in the form of ceramide, to which different moieties are added to form sphingolipids. • Serine and palmitoyl CoA condense to form a product (ketosphinganine) that is reduced. • A very long-chain fatty acid forms an amide with the amino group. a double bond is generated, and ceramide is formed.

Lyases (2 marks)

Theses enzymes catalyze the addition of • NH₃, • H₂O or • CO₂ to double bonds or • the removal of these groups leaving behind double bonds. • Lyases are included in a separate class because they catalyze these reactions by means other than hydrolysis or oxidation.

Bile salt (2 marks)

The bile salts, act to break apart the fat globules in the small intestines and allow them to become more "soluble" for absorption. bile salts (conjugated bile acids) are quantitatively the most important organic components of bile • The primary bile acids are synthesized in the liver from cholesterol • These are cholic acid and chenodeoxycholic acid

Unnatural pyrimidines bases (2 marks)

Fluorouracil (5FU) and 6-Aza Cytosine (AZC)

Sponification (2 marks)

Saponification is a process that involves the conversion of fat, oil, or lipid, into soap and alcohol by the action of heat in the presence of aqueous alkali. Soaps are salts of fatty acids and fatty acids are monomers of lipids that have long carbon chains e.g. sodium palmitate.

Function of mRNA (2 marks)

The members of this class function as messengers to convey the information in a gene to the protein synthesizing machinery. The mRNA carries genetic information from the nuclear DNA to the cytosol, where it is used as a template for protein synthesis.