Why Vitamin C Must Be Eaten Often but Vitamin A Can Be Stored
Classify vitamins as fat-soluble or water-soluble and link each to its deficiency disease, then understand the nucleotide structure of DNA and RNA and the roles they play in storing and using genetic information.
Why does the body need vitamins and nucleic acids?
Vitamins are small organic molecules the body needs in tiny amounts but mostly cannot make, and nucleic acids are the giant molecules that store and use genetic information. A shortage of one vitamin can cause night blindness or bleeding gums, and a single change in a nucleic acid can alter a protein.
This lesson covers the classification of vitamins and their deficiency diseases, and the structure and biological roles of DNA and RNA.
This lesson covers the classification of vitamins and their deficiency diseases, and the structure and biological roles of DNA and RNA.
How are vitamins classified, and what diseases does each deficiency cause?
Vitamins are classified by solubility into fat-soluble vitamins A, D, E and K, which the body stores, and water-soluble vitamins B and C, which are mostly excreted and must be taken in regularly; a lack of each causes a specific deficiency disease.
Fat-soluble vitamins — stored in the liver and fatty tissue:
- Vitamin A — carrots, green leafy vegetables, milk and fish liver oil; deficiency causes night blindness and xerophthalmia, a hardening of the cornea
- Vitamin D — made in skin exposed to sunlight, and found in milk and egg yolk; deficiency causes rickets in children and osteomalacia in adults
- Vitamin E — vegetable oils, nuts and wheat germ; deficiency makes red blood cells fragile and weakens muscles
- Vitamin K — green leafy vegetables; deficiency causes delayed blood clotting
Water-soluble vitamins — excreted in urine, apart from vitamin B12:
- Vitamin B1 (thiamine) — whole grains and yeast; deficiency causes beriberi
- Vitamin B2 (riboflavin) — milk, egg white and liver; deficiency causes cracked lips and corners of the mouth
- Vitamin B6 (pyridoxine) — yeast, cereals and milk; deficiency causes convulsions
- Vitamin B12 (cobalamin) — meat, fish, eggs and curd; deficiency causes pernicious anaemia
- Vitamin C (ascorbic acid) — citrus fruits, amla and green vegetables; deficiency causes scurvy, with bleeding gums
Worked example — why cooking destroys vitamin C. Vitamin C dissolves in water and breaks down with heat and air, so vegetables boiled for a long time in water that is then thrown away lose much of it, while quick steaming keeps more.
An everyday example. Amla, the Indian gooseberry, is packed with vitamin C, which is why it appears in murabbas and traditional tonics.
The substance. Vitamin B12 is the exception among water-soluble vitamins — it is stored in the liver, so a deficiency can take a long time to appear.
Fat-soluble vitamins — stored in the liver and fatty tissue:
- Vitamin A — carrots, green leafy vegetables, milk and fish liver oil; deficiency causes night blindness and xerophthalmia, a hardening of the cornea
- Vitamin D — made in skin exposed to sunlight, and found in milk and egg yolk; deficiency causes rickets in children and osteomalacia in adults
- Vitamin E — vegetable oils, nuts and wheat germ; deficiency makes red blood cells fragile and weakens muscles
- Vitamin K — green leafy vegetables; deficiency causes delayed blood clotting
Water-soluble vitamins — excreted in urine, apart from vitamin B12:
- Vitamin B1 (thiamine) — whole grains and yeast; deficiency causes beriberi
- Vitamin B2 (riboflavin) — milk, egg white and liver; deficiency causes cracked lips and corners of the mouth
- Vitamin B6 (pyridoxine) — yeast, cereals and milk; deficiency causes convulsions
- Vitamin B12 (cobalamin) — meat, fish, eggs and curd; deficiency causes pernicious anaemia
- Vitamin C (ascorbic acid) — citrus fruits, amla and green vegetables; deficiency causes scurvy, with bleeding gums
Worked example — why cooking destroys vitamin C. Vitamin C dissolves in water and breaks down with heat and air, so vegetables boiled for a long time in water that is then thrown away lose much of it, while quick steaming keeps more.
An everyday example. Amla, the Indian gooseberry, is packed with vitamin C, which is why it appears in murabbas and traditional tonics.
The substance. Vitamin B12 is the exception among water-soluble vitamins — it is stored in the liver, so a deficiency can take a long time to appear.
What are the structure and biological roles of DNA and RNA?
DNA and RNA are nucleic acids — polymers of nucleotides, each made of a pentose sugar, a nitrogenous base and a phosphate group; DNA, a double helix, stores genetic information, while RNA, usually single-stranded, uses that information to make proteins.
Building blocks:
- Nucleoside = pentose sugar + nitrogenous base
- Nucleotide = nucleoside + phosphate group
- Nucleotides join through phosphodiester links, forming a sugar-phosphate backbone
Sugars and bases:
- DNA contains 2-deoxyribose and the bases adenine (A), guanine (G), cytosine (C) and thymine (T)
- RNA contains ribose and the bases A, G, C and uracil (U) in place of thymine
- A and G are two-ringed purines; C, T and U are one-ringed pyrimidines
Structure of DNA:
- Two antiparallel strands twist into a right-handed double helix
- Bases pair by hydrogen bonds: A with T through two hydrogen bonds, and G with C through three
- So in any DNA the amount of A equals T and G equals C, and the two strands are complementary
Types and roles of RNA:
- Messenger RNA carries the genetic code from DNA to the ribosome
- Transfer RNA brings the correct amino acid to the ribosome
- Ribosomal RNA forms part of the ribosome, where proteins are made
Biological roles. Replication copies DNA so genetic information passes to daughter cells, and protein synthesis transcribes DNA into messenger RNA, which is translated into a protein.
Worked example — base pairing. If one DNA strand reads 5'-ATGCCA-3', its partner reads 3'-TACGGT-5'. A DNA sample that is 30 per cent adenine is also 30 per cent thymine, leaving 40 per cent shared equally by guanine and cytosine, at 20 per cent each.
An everyday example. Forensic laboratories in India identify people through DNA profiling, which relies on the sequence of bases that differs between individuals.
The substance. The extra -OH group on ribose makes RNA less stable than DNA — which suits RNA's short-lived working roles and DNA's long-term storage.
Building blocks:
- Nucleoside = pentose sugar + nitrogenous base
- Nucleotide = nucleoside + phosphate group
- Nucleotides join through phosphodiester links, forming a sugar-phosphate backbone
Sugars and bases:
- DNA contains 2-deoxyribose and the bases adenine (A), guanine (G), cytosine (C) and thymine (T)
- RNA contains ribose and the bases A, G, C and uracil (U) in place of thymine
- A and G are two-ringed purines; C, T and U are one-ringed pyrimidines
Structure of DNA:
- Two antiparallel strands twist into a right-handed double helix
- Bases pair by hydrogen bonds: A with T through two hydrogen bonds, and G with C through three
- So in any DNA the amount of A equals T and G equals C, and the two strands are complementary
Types and roles of RNA:
- Messenger RNA carries the genetic code from DNA to the ribosome
- Transfer RNA brings the correct amino acid to the ribosome
- Ribosomal RNA forms part of the ribosome, where proteins are made
Biological roles. Replication copies DNA so genetic information passes to daughter cells, and protein synthesis transcribes DNA into messenger RNA, which is translated into a protein.
Worked example — base pairing. If one DNA strand reads 5'-ATGCCA-3', its partner reads 3'-TACGGT-5'. A DNA sample that is 30 per cent adenine is also 30 per cent thymine, leaving 40 per cent shared equally by guanine and cytosine, at 20 per cent each.
An everyday example. Forensic laboratories in India identify people through DNA profiling, which relies on the sequence of bases that differs between individuals.
The substance. The extra -OH group on ribose makes RNA less stable than DNA — which suits RNA's short-lived working roles and DNA's long-term storage.
Exam tip
What earns full marks on vitamins and nucleic acids?
Match every vitamin to both a source and a deficiency disease, and compare DNA with RNA under four headings: sugar, bases, strands and role.
- Fat-soluble: A, D, E, K; water-soluble: the B group and C
- A: night blindness; D: rickets; K: poor clotting; B1: beriberi; B12: pernicious anaemia; C: scurvy
- Nucleotide = sugar + base + phosphate; nucleoside = sugar + base
- DNA: deoxyribose, thymine, double helix; RNA: ribose, uracil, usually a single strand
The trap. Calling a nucleoside a nucleotide. A nucleoside has no phosphate group; adding phosphate makes it a nucleotide.
- Fat-soluble: A, D, E, K; water-soluble: the B group and C
- A: night blindness; D: rickets; K: poor clotting; B1: beriberi; B12: pernicious anaemia; C: scurvy
- Nucleotide = sugar + base + phosphate; nucleoside = sugar + base
- DNA: deoxyribose, thymine, double helix; RNA: ribose, uracil, usually a single strand
The trap. Calling a nucleoside a nucleotide. A nucleoside has no phosphate group; adding phosphate makes it a nucleotide.
Did you know
Why can people in sunny India still lack vitamin D?
The skin makes vitamin D when ultraviolet light from the Sun falls on it, so it seems surprising that vitamin D deficiency is common even in a sunny country.
Spending most of the day indoors, covering most of the skin, air pollution that blocks ultraviolet rays, and darker skin, which needs longer exposure to make the same amount, all reduce how much vitamin D the body produces.
Because vitamin D is fat-soluble, the body can store it, so regular time in sunlight and foods such as milk and eggs help keep levels up.
Spending most of the day indoors, covering most of the skin, air pollution that blocks ultraviolet rays, and darker skin, which needs longer exposure to make the same amount, all reduce how much vitamin D the body produces.
Because vitamin D is fat-soluble, the body can store it, so regular time in sunlight and foods such as milk and eggs help keep levels up.
Exam relevance
How do JEE Main and NEET test vitamins and nucleic acids?
Biomolecules is a recurring chapter in both JEE Main and NEET, and vitamins and nucleic acids are its memory-based sections.
What gets asked. Fat-soluble and water-soluble vitamins with their deficiency diseases, differences between DNA and RNA, nucleosides versus nucleotides, base pairing and complementary strands, and the three types of RNA and their roles.
Question types. Mostly match-the-column questions pairing vitamins with diseases, plus single-correct questions on nucleic acid structure.
Why it matters later. Nucleic acid structure is the foundation of Molecular Basis of Inheritance in NEET Biology, and base-pair hydrogen bonding links back to Chemical Bonding and Molecular Structure.
The trap that costs marks. Saying the body cannot store any water-soluble vitamin — vitamin B12 is stored in the liver.
What gets asked. Fat-soluble and water-soluble vitamins with their deficiency diseases, differences between DNA and RNA, nucleosides versus nucleotides, base pairing and complementary strands, and the three types of RNA and their roles.
Question types. Mostly match-the-column questions pairing vitamins with diseases, plus single-correct questions on nucleic acid structure.
Why it matters later. Nucleic acid structure is the foundation of Molecular Basis of Inheritance in NEET Biology, and base-pair hydrogen bonding links back to Chemical Bonding and Molecular Structure.
The trap that costs marks. Saying the body cannot store any water-soluble vitamin — vitamin B12 is stored in the liver.
Key takeaways
What must you be able to do from this lesson?
- Vitamins: fat-soluble A, D, E and K, stored in the body, and water-soluble B and C, needed regularly, each linked to a deficiency disease
- Nucleotides: a pentose sugar, a nitrogenous base and a phosphate, joined by phosphodiester links
- DNA and RNA: deoxyribose, thymine and a double helix for storing information; ribose, uracil and single strands for making proteins
If a DNA sample contains 18 per cent guanine, what percentage of it is adenine?
- Nucleotides: a pentose sugar, a nitrogenous base and a phosphate, joined by phosphodiester links
- DNA and RNA: deoxyribose, thymine and a double helix for storing information; ribose, uracil and single strands for making proteins
If a DNA sample contains 18 per cent guanine, what percentage of it is adenine?