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Biomolecules

Short Answer Type

181.

Which vitamin is called ascorbic acid? What are its physiological functions? Which disease is caused by the deficiency of this vitamin?

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182. What do you understand by a vitaminoses? Name the defeiciency disease caused due to lack of Vitamin A and K.

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183.

Explain the following:
Glucose responds Fehling solution and osazone, it does not react with Schiff’s base and sodium bisulphite.

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184.

Explain the following:
Glucosides react neither with Fehling solution nor with Tollen's reagent. They also do not allow mutarotation.

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185.

Explain the following:
Although fructose does not have an aldehydic group, it reacts with Fehling solution.

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186.

What is melting temperature (T_m) of DNA? A DNA molecule with more number of GC base pairs than AT base pairs has higher T_m than the one with lesser number of GC base pairs than AT base pairs. Explain why?

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187.

What are forces holds the two strands of DNA together in a double-helix structure? Draw structure to show the bonding between adenine and thymine, and between guanine and cytosine.

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188.

'DNA replication is semi-conservative'. Explain.

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189.

What is transcription with reference to protein synthesis? How does it take place?

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Long Answer Type

190. What happens when D-glucose is treated with following reagents?
(i) Acetic anhydride
(ii) Hydroxylamine
(iii) Tollen’s reagents
(iv) Fehling solution
(v) Phenyl hydrazine.

(i) Acetylation of glucose with acetic anhydride gives glucose petnaacetate which confirms the presence of five -OH groups.

(ii) Glucose reacts with hydroxylamine to give monoxime. This reaction confirms the presence of a carbonyl group.

(iii) Glucose reduce ammonical silver nitrate (Tollen’s reagent) to metallic silver.

(iv) Glucose reduces Fehling’s solution and gives brick red precipitate due to formation of cuprous oxide (Cu₂O):

(v) D-glucose reacts with phenylhydrazine to give glucose phenylhydrazone which is soluble in water. If excess of phenylhydrazine is used, dihydrazone, known as glucosazone is formed.