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Chemistry · Class 12 Science

Ch 5Biomolecules — Class 12 Chemistry, concept-first.

Carbohydrates are polyhydroxy aldehydes or polyhydroxy ketones, or larger molecules that yield such compounds on hydrolysis. Many of the simplest ones fit a general formula , which is where the name "carbohydrate" (hydrate of carbon) originally came from, though the name is really a historical accident rather than a st…

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Classification of Carbohydrates

Carbohydrates are polyhydroxy aldehydes/ketones (or compounds that yield them on hydrolysis). They are classified by the number of simple-sugar units released on hydrolysis:

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10.1

Carbohydrates

Carbohydrates are polyhydroxy aldehydes or polyhydroxy ketones, or larger molecules that yield such compounds on hydrolysis.

10.1.1

Classification of Carbohydrates: Aldoses and Ketoses

A monosaccharide is classified as an aldose or a ketose purely on the basis of which kind of carbonyl group it carries.

10.1.2

Monosaccharides: Structures of Glucose and Fructose

Written as a simple open (straight) chain, D-glucose is : an aldehyde group at C1, four successive -bearing carbons (C2 through C5), and a terminal at C6.

10.1.3

D and L Configuration of Monosaccharides

Beyond classifying a sugar as an aldose or ketose, chemists also assign it a configurational label, D or L, that describes the three-dimensional spatial arrangement of its atoms rather than any proper…

10.1.4

Disaccharides: Sucrose as a Non-Reducing Sugar

A disaccharide is formed when two monosaccharide units are joined together by a glycosidic bond, an ether-type linkage formed, in effect, by the loss of one molecule of water between an group of one m…

10.1.5

Polysaccharides: Starch and Cellulose

Starch and cellulose are both natural polysaccharides built entirely from repeating D-glucose units joined together by glycosidic bonds, yet they differ enormously in their physical properties and bio…

10.2

Proteins: Amino Acids and the Peptide Bond

Proteins are the polymers built up from -amino acid monomer units, joined together in long chains by a characteristic amide linkage called the peptide bond.

10.2.1

Primary Structure of Proteins

The primary structure of a protein is simply the specific, precisely ordered sequence in which its amino acids are joined together, one after another, by peptide bonds along the polypeptide chain.

10.2.2

Denaturation of Proteins

Denaturation is the loss of a protein's natural, biologically active three-dimensional shape -- and, along with it, the loss of the protein's normal biological activity -- brought about by physical or…

10.3

Enzymes

Enzymes are biological catalysts -- almost all of them proteins -- produced by living cells to speed up the specific biochemical reactions that keep the cell functioning.

10.4

Nucleic Acids: Composition and Structure of DNA and RNA

Nucleic acids -- deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) -- are polymers built up from repeating monomer units called nucleotides.

Comparing DNA and RNA

DNA and RNA are both polymers of nucleotides, and they share several features in common -- both use adenine, guanine and cytosine among their bases, and both are built on a repeating sugar-phosphate b…

Sample & Board Papers

Sample papers and previous-year board questions for this subject.

+Show 19 questions19 questions
  1. Q1(x) What is a polysaccharide? Explain with an example. (y) What is meant by primary structure of a protein?Preview
  2. Q2Which of the following bases is not present in DNA? (a) Uracil (b) Thymine (c) Guanine (d) CytosinePreview
  3. Q3(i) The following compound is an example of a peptide: H2N-CH(CH2COOH)-C(=O)-NH-CH(CH2-C6H5)-COOCH3 (a dipeptide with a free -CH2COOH side c…Preview
  4. Q4Which of the following bases is not present in RNA? (a) Adenine (b) Guanine (c) Thymine (d) UracilPreview
  5. Q5Give the formula of D-glucose. What does 'D' imply?Preview
  6. Q6Insulin is (a) an amino acid (b) a protein (c) a carbohydrate (d) a lipid **OR** Hydrolysis of protein produces .......... number of amino a…Preview
  7. Q7Optically inactive compound is (a) Aspartic acid (b) Lysine (c) Cystine (d) GlycinePreview
  8. Q8Which of the following bases is absent in RNA? (a) Uracil (b) Thymine (c) Guanine (d) AdeninePreview
  9. Q9(i) Deficiency of which vitamin causes pernicious anaemia? (ii) Between sucrose and maltose, which is a reducing sugar? (iii) Write with che…Preview
  10. Q10In which of the following orders are base, phosphate and sugar arranged in nucleic acid chain? (a) Base-phosphate-sugar (b) Base-sugar-phosp…Preview
  11. Q11(i) What is the monomer of proteins? (ii) What is peptide linkage? Draw the structure of Gly-Ala dipeptide linkage. [1+2]Preview
  12. Q12Which of the following bases is not present in RNA? (a) Uracil (b) Thymine (c) Guanine (d) CytosinePreview
  13. Q13Insulin is (a) an amino acid (b) a carbohydrate (c) a hormone (d) a lipidPreview
  14. Q14(i) Deficiency of which vitamin causes poor coagulation of blood? [1] (ii) Write the structure of zwitterion of alanine. [1] (iii) What do y…Preview
  15. Q15There is a definite sequence of amino acids linked with each other in each polypeptide chain of protein. This sequence of amino acids denote…Preview
  16. Q16Which of the following bases is absent in DNA? (a) Thymine (b) Guanine (c) Uracil (d) AdeninePreview
  17. Q17At isoelectric point structure of glycine is (a) H2N-CH2-COOH (b) H2N-CH2-COO(-) (c) H3N(+)-CH2-COOH (d) H3N(+)-CH2-COO(-)Preview
  18. Q18Glucose and fructose can be distinguished by which of the following reagents? (a) Tollen's reagent (b) Fehling's reagent (c) Br2 / H2O (d) C…Preview
  19. Q19Hydrolysis of sucrose into glucose and fructose is associated with change in specific optical rotation. The phenomenon is known as (a) Mutar…Preview

More questions

30 Q
+Show 10 questions10 questions
  1. Example 1Classify glucose and fructose as an aldose or a ketose, and explain the basis of this classification.Free
  2. Example 2Write the open-chain (Fischer projection) structure of D-glucose and identify all the functional groups present in it.Free
  3. Example 3Glucose pentaacetate (in which all five $-\text{OH}$ groups are acetylated) does not react with hydroxylamine, $\text{NH}_2\text{OH}$, even…Free
  4. Example 4What is meant by the term 'anomeric carbon'? Using $\alpha$-D-glucose and $\beta$-D-glucose as your example, explain what an anomer is.Preview
  5. Example 5Write the open-chain structure of D-fructose and state the size of ring it forms when it cyclises.Preview
  6. Example 6State the convention used to assign the D and L configuration of a monosaccharide, and use it to explain why glucose is called D-glucose.Preview
  7. Example 7Describe, in general terms, how a glycosidic bond is formed between two monosaccharide units.Preview
  8. Example 8Sucrose does not reduce Fehling's solution or Tollens' reagent, i.e. it is a non-reducing sugar. Explain why, in terms of the glycosidic lin…Preview
  9. Example 9Write the general structure of an $\alpha$-amino acid, and explain what is meant by saying it exists as a zwitterion.Preview
  10. Example 10Glycine and alanine combine to form a dipeptide. Show how the peptide bond is formed between them, and state what small molecule is released…Preview
+Show 20 questions20 questions
  1. Q11Define carbohydrates. On what structural basis are they classified as aldoses or ketoses?Free
  2. Q12What are monosaccharides, oligosaccharides and polysaccharides? Give one example of each that is in your syllabus.Free
  3. Q13What is the anomeric carbon of glucose? Which carbon becomes the anomeric carbon when fructose cyclises, and why is it a different carbon fr…Free
  4. Q14What is mutarotation? Briefly explain why pure $\alpha$-D-glucose and pure $\beta$-D-glucose, dissolved separately in water, both end up sho…Preview
  5. Q15What two monosaccharides are obtained on hydrolysis of sucrose? What is 'invert sugar', and why is it given this name?Preview
  6. Q16Starch is made up of two components. Name them and describe how they differ structurally.Preview
  7. Q17What type of glycosidic linkage joins the glucose units of cellulose, and how does this differ from the linkage in amylose?Preview
  8. Q18Starch and cellulose are both polymers of glucose, yet humans can digest starch but not cellulose. Explain why.Preview
  9. Q19Write the general formula of an $\alpha$-amino acid. Which two functional groups are attached to the same (alpha) carbon?Preview
  10. Q20Why do amino acids generally have much higher melting points than simple carboxylic acids or amines of a similar molar mass, and why are the…Preview
  11. Q21What is a peptide bond? Is it the same as an ordinary amide bond found elsewhere in organic chemistry?Preview
  12. Q22What is meant by the primary structure of a protein? Why is it described as the most fundamental level of a protein's structure?Preview
  13. Q23What is denaturation of a protein? Name three agents or conditions that can cause it.Preview
  14. Q24Boiling an egg turns the transparent, runny egg white into an opaque, solid mass. Explain this observation in terms of protein denaturation.Preview
  15. Q25Does denaturation break the peptide bonds of a protein's primary structure? Explain how denaturation affects a protein's biological activity…Preview
  16. Q26What are enzymes? Explain, using the lock-and-key model, why a given enzyme usually acts only on one particular substrate (or a small family…Preview
  17. Q27What is a nucleotide? Name its three component parts.Preview
  18. Q28Distinguish between DNA and RNA on the basis of (a) the pentose sugar present and (b) the nitrogenous bases present.Preview
  19. Q29State the base-pairing rule that operates between the two strands of DNA. How many hydrogen bonds hold each base pair together?Preview
  20. Q30Describe the double helix structure of DNA proposed by Watson and Crick, and state how the structure of RNA is typically different from it.Preview