🧬 Nucleic Acids, Enzymes, Vitamins, and Lipids

Why These Biomolecules Matter in Agriculture

When a plant pathologist uses PCR to detect a virus in a potato sample, the technique relies on the biochemistry of nucleic acids. When a seed scientist tests lipase activity to assess seed viability, they are measuring enzyme function. When a nutritionist promotes biofortified crops rich in Vitamin A (golden rice, orange-fleshed sweet potato), they are applying knowledge of vitamins. And when an oilseed breeder improves the fatty acid profile of mustard, they are working with lipids. These four biomolecule classes underpin much of agricultural science.

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Enzymes

Enzymes are special classes of proteins that act as biological catalysts — they speed up chemical reactions without being consumed.

Feature	Detail
First enzymatic activity discovered by	Buchner (Zymase from yeast — the first enzyme found)
Term "enzyme" coined by	W. Kuhne (1878)
Lock and key model	Proposed by Fisher; introduced by Koshland

Characteristics of Enzymes

• Specific, proteinaceous, colloidal in nature.
• Sensitive to temperature and pH (each enzyme has an optimum).
• Do not change the equilibrium of a reaction — only speed it up.
• Work by lowering the activation energy.

Agricultural example: Amylase enzymes in germinating barley break down starch into maltose — the basis of the malting industry. Cellulase enzymes are used in biofuel production from crop residues. Lipase activity in stored oilseeds indicates rancidity (important for seed quality testing).

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Vitamins

• The term vitamin was introduced by Funk.
• Vitamins mainly act as cofactors for enzymatic activity.

Classification of Vitamins

Type	Vitamins	Key Feature
Water soluble	Vitamin B complex & Vitamin C	Excreted easily; not stored in body
Fat soluble	Vitamin A, D, E, K	Stored in body fat and liver

Agricultural connection: Biofortification breeding programmes target vitamin content in crops:

• Vitamin A → Golden Rice (beta-carotene enriched), orange-fleshed sweet potato
• Vitamin C → Amla (Indian gooseberry), guava
• Vitamin E → Sunflower and wheat germ oil

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Nucleic Acids

Nucleic acids are polymers of nucleotides joined by phosphodiester bonds.

Functions:

1. Transmission of hereditary characters from parents to offspring.
2. Synthesis of proteins.

Types: DNA (Deoxyribose Nucleic Acid) and RNA (Ribose Nucleic Acid).

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Components of Nucleic Acids

Component	Examples
Sugar	Ribose (RNA) or Deoxyribose (DNA)
Phosphate group	Phosphoric acid
Nitrogenous bases	Purines (A, G) and Pyrimidines (T, C, U)

Term	Definition
Nucleoside	Sugar + Nitrogenous base
Nucleotide	Nucleoside + Phosphate group

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Nitrogenous Bases

Type	Bases	Ring Structure
Purines	Adenine (A), Guanine (G)	Double ring
Pyrimidines	Thymine (T), Cytosine (C), Uracil (U)	Single ring

Base Pairing Rules (Chargaff's Rules):

• Adenine (A) pairs with Thymine (T) — 2 hydrogen bonds
• Guanine (G) pairs with Cytosine (C) — 3 hydrogen bonds
• In RNA, Thymine is replaced by Uracil (A pairs with U)

Mnemonic: Pure As Gold = Purines are Adenine and Guanine.

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DNA (Deoxyribonucleic Acid)

Feature	Detail
Sugar	Deoxyribose (pentose)
Location	Nucleus, Chloroplast, Mitochondria
Function	Protein synthesis; hereditary material
Status	Hereditary material in almost all organisms

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RNA (Ribonucleic Acid)

Feature	Detail
Sugar	Ribose
Location	All living cells (mostly in cytoplasm)
Function	Coding, decoding, gene expression; protein synthesis via translation

Types of RNA

Type	Full Name	Function
tRNA	Transfer RNA	Carries amino acids to ribosome
mRNA	Messenger RNA	Carries genetic code from DNA to ribosome
rRNA	Ribosomal RNA	Structural component of ribosomes (most abundant)

Agricultural relevance: RNA viruses cause many major crop diseases — rice tungro, tomato spotted wilt, potato virus Y. Detection of these viruses using RT-PCR (Reverse Transcriptase PCR) is based on understanding RNA structure.

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Lipids

Lipids are organic compounds containing hydrogen, carbon, and oxygen atoms that form the structural framework of cell membranes and serve as energy reserves.

• Lipids are defined as esters of glycerol and fatty acids (triglycerides).
• Include: fats, waxes, sterols, fat-soluble vitamins, monoglycerides, and phospholipids.

Types of Lipids

Type	Composition	Key Role
Triglycerides	Glycerol + 3 fatty acids	Energy storage (oils in seeds)
Phospholipids	2 fatty acids + Glycerol + Phosphate group	Cell membrane structure (polar lipids)
Glycolipids	Glycerol + Fatty acids + Carbohydrates	Cell recognition

Agricultural connection: The oil content and fatty acid composition of oilseed crops (groundnut, mustard, sunflower, soybean) are primary breeding targets. High oleic acid varieties are preferred for better shelf life and heart health.

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Vitamins — Deficiency Diseases and Agricultural Sources

Vitamin	Chemical Name	Deficiency Disease	Rich Agricultural Source
Vitamin A	Retinol	Night blindness, Xerophthalmia	Carrot, Papaya, Mango
Vitamin B₁	Thiamine	Beriberi	Whole grains, Legumes
Vitamin B₃	Niacin	Pellagra	Groundnut, Meat
Vitamin B₉	Folic acid	Megaloblastic anaemia	Green leafy vegetables, Pulses
Vitamin C	Ascorbic acid	Scurvy	Amla, Citrus, Guava
Vitamin D	Calciferol	Rickets, Osteomalacia	Sunlight, Fish liver oil
Vitamin E	Tocopherol	Reproductive failure	Vegetable oils, Wheat germ
Vitamin K	Phylloquinone	Haemorrhage	Green leafy vegetables, Soybean

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Dietary Fibre

• Defined as the sum of lignin and polysaccharides that are not digested by human digestive enzymes.
• Important for digestive health.

Agricultural note: High-fibre crops include whole grains (oats, barley), pulses, and millets. Breeding for appropriate fibre content is important for both human nutrition and animal fodder quality.

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Summary Cheat Sheet

Concept / Topic	Key Details
Enzyme definition	Biological catalysts; special class of proteins
First enzymatic activity	Discovered by Buchner (Zymase from yeast)
Term "enzyme" coined by	W. Kuhne (1878)
Lock and key model	Proposed by Fisher; introduced by Koshland
Enzymes work by	Lowering activation energy; do NOT change equilibrium
Enzyme nature	Proteinaceous, colloidal, specific to substrate
Term "vitamin" coined by	Funk
Vitamins act as	Cofactors for enzymatic activity
Fat-soluble vitamins	A, D, E, K (mnemonic: ADEK)
Water-soluble vitamins	B complex & C; excreted easily, not stored
Nucleic acids	Polymers of nucleotides joined by phosphodiester bonds
Nucleoside	Sugar + Nitrogenous base
Nucleotide	Nucleoside + Phosphate group
Purines	Adenine (A) & Guanine (G) — double ring
Pyrimidines	Thymine (T), Cytosine (C), Uracil (U) — single ring
A–T base pairing	2 hydrogen bonds
G–C base pairing	3 hydrogen bonds
RNA vs DNA bases	Uracil replaces Thymine in RNA
DNA sugar & location	Deoxyribose; in nucleus, chloroplast, mitochondria
DNA function	Hereditary material; protein synthesis
tRNA	Carries amino acids to ribosome
mRNA	Carries genetic code from DNA to ribosome
rRNA	Structural component of ribosomes; most abundant RNA
Lipids definition	Esters of glycerol and fatty acids (triglycerides)
Phospholipids	2 fatty acids + glycerol + phosphate; form cell membranes
Dietary fibre	Lignin + non-digestible polysaccharides
Vitamin A deficiency	Night blindness, Xerophthalmia — source: Carrot, Papaya, Mango
Vitamin B₁ deficiency	Beriberi — source: Whole grains, Legumes
Vitamin B₃ deficiency	Pellagra — source: Groundnut, Meat
Vitamin C deficiency	Scurvy — richest source in India: Amla
Vitamin D deficiency	Rickets, Osteomalacia — source: Sunlight
Vitamin K deficiency	Haemorrhage — source: Green leafy vegetables, Soybean