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Chemistry · 2026 · 3 marks
CBSE 2026 · Region 2 · Set 2 · Q28
(A) (a) Define the following terms: 2+1 (i) Denaturation as related to proteins (ii) Oligosaccharides (b) On the basis of structure differentiate…
(a)
Define the following terms : $\displaystyle 2+1$
(i)
Denaturation as related to proteins
(ii)
Oligosaccharides
(b)
On the basis of structure differentiate between Amylose and Amylopectin.
(a)
What products would be formed when a nucleotide from DNA containing thymine is hydrolysed ? $\displaystyle \mathbf{1} \boldsymbol{+} \mathbf{1} \boldsymbol{+} \mathbf{1}$
(b)
How will you explain the presence of five -OH groups in glucose molecule which are attached to different carbon atoms ?
(c)
Write the reaction of glucose with HCN.
Marking-scheme solution
.
(a)(i) Loss of biological activity of a native protein due to change in temperature or
chemical change such as pH. / When a protein in its native form, is
subjected to physical change like change in temperature or chemical change
like change in pH, the hydrogen bonds are disturbed. Due to this globules
unfold and helix gets uncoiled and protein loses its biological activity.
(ii)
Carbohydrates that give two to ten monosaccharides units on hydrolysis are
called oligosaccharides.
(b)
Amylose
Unbranched chain of large number
of α − D − (+) glucose units held
together at C1 – C4 linkage
Amylopectin
Branched chain polymer of α − D
− glucose units held together at C1
– C4 linkage and branching occurs
at C1 – C6 linkage.
.
(a)
Thymine, pentose sugar (deoxy ribose), phosphoric acid.
(b)
With acetic anhydride, glucose forms pentaacetate which is a stable
compound which confirms the presence of five −OH groups.
(c)
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CBSE Class 12 Chemistry past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.