Biomolecules & DNA/RNA

• A biomolecule is any carbon-based chemical made by a living cell.
• Carbon is the backbone of life because each atom forms four bonds and links into long chains.
• Very large biomolecules are called macromolecules ('macro' = large).
• A polymer is a long chain made by joining many small repeating units called monomers.
• NCERT lists only three macromolecules in living systems: proteins, nucleic acids and polysaccharides – all are polymers.
• Lipids (fats) are NOT true macromolecules; they are smaller but separate out with big molecules because they sit in membranes.
• A homopolymer uses one type of monomer repeated; a heteropolymer uses many different monomers.
• Carbohydrate (polysaccharide) — Simple sugars (e.g. glucose)
• Protein — Amino acids (20 types)
• Nucleic acid (DNA/RNA) — Nucleotides
• Lipid (fat) — Fatty acids + glycerol

A biomolecule is any carbon-based chemical made by a living cell.

Carbon is the backbone of life because each atom forms four bonds and links into long chains.

Very large biomolecules are called macromolecules ('macro' = large).

A polymer is a long chain made by joining many small repeating units called monomers.

NCERT lists only three macromolecules in living systems: proteins, nucleic acids and polysaccharides – all are polymers.

Lipids (fats) are NOT true macromolecules; they are smaller but separate out with big molecules because they sit in membranes.

A homopolymer uses one type of monomer repeated; a heteropolymer uses many different monomers.

• Living bodies are made mostly of a few major elements with smaller amounts of trace elements.
• The four most abundant elements in the human body are oxygen, carbon, hydrogen and nitrogen.
• Bulk minerals like calcium, potassium and sodium are present in larger amounts than trace metals.
• Iron (Fe) is a trace element but vital – it is the metal at the centre of haemoglobin.
• Copper (Cu) and iron are needed only in tiny (micro) amounts compared to sodium and potassium.
• Increasing order of amount (typical 70 kg man): Copper < Iron < Potassium < Sodium.
• Sodium (Na) — Bulk mineral (more)
• Potassium (K) — Bulk mineral
• Iron (Fe) — Trace (less)
• Copper (Cu) — Trace (least)

Living bodies are made mostly of a few major elements with smaller amounts of trace elements.

The four most abundant elements in the human body are oxygen, carbon, hydrogen and nitrogen.

Bulk minerals like calcium, potassium and sodium are present in larger amounts than trace metals.

Iron (Fe) is a trace element but vital – it is the metal at the centre of haemoglobin.

Copper (Cu) and iron are needed only in tiny (micro) amounts compared to sodium and potassium.

Increasing order of amount (typical 70 kg man): Copper < Iron < Potassium < Sodium.

• Carbohydrates are the body's sugars and starches – quick fuel and stored fuel.
• The smallest unit is a simple sugar like glucose; many joined together form a polysaccharide.
• Starch is the storage carbohydrate in plants (e.g. rice, potato).
• Glycogen is the storage carbohydrate in animals (stored in liver and muscle).
• Cellulose is a polysaccharide that builds the tough plant cell wall.
• Chitin forms the exoskeleton of arthropods like insects, crabs and prawns.
• Starch — Energy store — Plants
• Glycogen — Energy store — Animals (liver/muscle)
• Cellulose — Structure — Plant cell wall
• Chitin — Structure — Arthropod shell

Carbohydrates are the body's sugars and starches – quick fuel and stored fuel.

The smallest unit is a simple sugar like glucose; many joined together form a polysaccharide.

Starch is the storage carbohydrate in plants (e.g. rice, potato).

Glycogen is the storage carbohydrate in animals (stored in liver and muscle).

Cellulose is a polysaccharide that builds the tough plant cell wall.

Chitin forms the exoskeleton of arthropods like insects, crabs and prawns.

• A protein is a polymer (long chain) of amino acids.
• There are 20 types of amino acids, so a protein is a heteropolymer.
• Their order is like alphabets making words – sequence decides which protein it is.
• The first amino acid is the N-terminal, the last is the Cterminal.
• Collagen is the most abundant protein in the animal world (skin, bone, connective tissue).
• RuBisCO is the most abundant protein in the whole biosphere (works in photosynthesis).
• Biuret test: NaOH + copper sulphate gives a violet/purple colour if protein is present.

A protein is a polymer (long chain) of amino acids.

There are 20 types of amino acids, so a protein is a heteropolymer.

The first amino acid is the N-terminal, the last is the Cterminal.

Collagen is the most abundant protein in the animal world (skin, bone, connective tissue).

RuBisCO is the most abundant protein in the whole biosphere (works in photosynthesis).

Biuret test: NaOH + copper sulphate gives a violet/purple colour if protein is present.

• Essential amino acids cannot be made by the body and must come from the diet.
• Non-essential amino acids can be made by the body itself.
• Protein-rich foods supply essential amino acids: milk, eggs, fish, meat, pulses (dal), soyabean.
• Egg and milk are 'complete' foods because they contain all essential amino acids.
• Examples of amino acids: alanine, cysteine, proline, tryptophan, lysine.
• Essential — Diet only — Egg, milk, soyabean
• Non-essential — Body makes it — Synthesised internally

Essential amino acids cannot be made by the body and must come from the diet.

Egg and milk are 'complete' foods because they contain all essential amino acids.

• Primary structure = the exact sequence (order) of amino acids in the chain.
• Secondary structure = the chain coils into a helix or folds into a beta-pleated sheet.
• In proteins only right-handed helices occur.
• Tertiary structure = the whole chain folds like a hollow woollen ball into a 3-D shape.
• Tertiary structure is essential for the biological activity of a protein.
• Quaternary structure = two or more folded chains join into one working unit.
• Haemoglobin (four chains) is the classic example of quaternary structure.
• Primary — Sequence of amino acids
• Secondary — Helix / beta-sheet
• Tertiary — Full 3-D folded shape
• Quaternary — Several chains joined

Primary structure = the exact sequence (order) of amino acids in the chain.

Secondary structure = the chain coils into a helix or folds into a beta-pleated sheet.

Tertiary structure = the whole chain folds like a hollow woollen ball into a 3-D shape.

Quaternary structure = two or more folded chains join into one working unit.

Haemoglobin (four chains) is the classic example of quaternary structure.

• A catalyst speeds up a reaction but is not used up; an enzyme is a biological catalyst.
• Almost all enzymes are proteins; a few RNA enzymes exist, called ribozymes.
• The active site is a pocket where the substrate fits like a key in a lock.
• Enzymes act at the site where they are produced and work at very high speed.
• Most enzymes are denatured (damaged) above ~40°C.
• Exception: thermophilic organisms from hot springs have heat-stable enzymes (stable at 80–90°C).
• Activity depends on temperature, pH and substrate concentration, each with an optimum value.
• Temperature — Optimum near 40°C; denatures if higher
• pH — Each enzyme has an optimum pH
• Substrate conc. — Rate rises then levels off

A catalyst speeds up a reaction but is not used up; an enzyme is a biological catalyst.

Almost all enzymes are proteins; a few RNA enzymes exist, called ribozymes.

The active site is a pocket where the substrate fits like a key in a lock.

Enzymes act at the site where they are produced and work at very high speed.

Exception: thermophilic organisms from hot springs have heat-stable enzymes (stable at 80–90°C).

• Nucleic acids are the instruction manuals of life that store and pass on genetic information.
• A nucleic acid is a polymer of nucleotides.
• Each nucleotide = a nitrogen base + a sugar + a phosphate group.
• The two nucleic acids are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).
• DNA stores the master genetic code; RNA helps read the code and make proteins.
• The sugar is deoxyribose in DNA and ribose in RNA.
• Strands — Double — Single (usually)
• Sugar — Deoxyribose — Ribose
• Bases — A, T, G, C — A, U, G, C
• Role — Stores genes — Makes protein

Nucleic acids are the instruction manuals of life that store and pass on genetic information.

Each nucleotide = a nitrogen base + a sugar + a phosphate group.

The two nucleic acids are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

DNA stores the master genetic code; RNA helps read the code and make proteins.

The sugar is deoxyribose in DNA and ribose in RNA.

• There are four bases in DNA: Adenine (A), Thymine (T), Guanine (G), Cytosine (C).
• In RNA, Thymine is replaced by Uracil (U).
• Purines are double-ring bases: Adenine and Guanine.
• Pyrimidines are single-ring bases: Cytosine, Thymine, Uracil.
• Base-pairing rule: A pairs with T (A–U in RNA) and G pairs with C.
• Pairs are held by hydrogen bonds across the two strands.
• Purine — Adenine, Guanine — Two
• Pyrimidine — Cytosine, Thymine, Uracil — One

There are four bases in DNA: Adenine (A), Thymine (T), Guanine (G), Cytosine (C).

Purines are double-ring bases: Adenine and Guanine.

Pyrimidines are single-ring bases: Cytosine, Thymine, Uracil.

Base-pairing rule: A pairs with T (A–U in RNA) and G pairs with C.

Pairs are held by hydrogen bonds across the two strands.

• DNA has a double-helix shape – two strands twisted like a spiral ladder.
• Chargaff's rule: amount of A = T and amount of G = C.
• The two strands are antiparallel (run in opposite directions).
• Har Gobind Khorana helped synthesise/decode the genetic code; DNA was first synthesised in vitro by Arthur Kornberg.
• The double-helix model of DNA was proposed by Watson and Crick (1953).
• Their model used the X-ray data of Rosalind Franklin and Maurice Wilkins.

DNA has a double-helix shape – two strands twisted like a spiral ladder.

Chargaff's rule: amount of A = T and amount of G = C.

The two strands are antiparallel (run in opposite directions).

Har Gobind Khorana helped synthesise/decode the genetic code; DNA was first synthesised in vitro by Arthur Kornberg.

The double-helix model of DNA was proposed by Watson and Crick (1953).

Their model used the X-ray data of Rosalind Franklin and Maurice Wilkins.

• mRNA = messenger RNA; it carries the code from DNA to the ribosome.
• tRNA = transfer RNA; it brings the correct amino acid to the ribosome.
• rRNA = ribosomal RNA; it forms part of the ribosome (the protein factory).
• A codon is a group of three bases that codes for one amino acid.
• Transcription = DNA copied into mRNA; translation = mRNA read to build protein.
• Stop (non-sense) codons – UAA, UAG, UGA – code for no amino acid and end the chain.
• AUG is the start codon (also codes for methionine).
• mRNA — Carries genetic message
• tRNA — Brings amino acids
• rRNA — Forms the ribosome

mRNA = messenger RNA; it carries the code from DNA to the ribosome.

tRNA = transfer RNA; it brings the correct amino acid to the ribosome.

rRNA = ribosomal RNA; it forms part of the ribosome (the protein factory).

A codon is a group of three bases that codes for one amino acid.

Transcription = DNA copied into mRNA; translation = mRNA read to build protein.

Stop (non-sense) codons – UAA, UAG, UGA – code for no amino acid and end the chain.

AUG is the start codon (also codes for methionine).