Chapter 10 / 10.2 Proteins

Proteins – quick and clear notes 🧬

1. Why proteins matter

Proteins are the most plentiful biomolecules in living things. You meet them daily in milk, cheese, pulses, peanuts, fish, and meat. They build body tissues, keep reactions running, and power growth. The name comes from the Greek proteios, meaning “primary.” :contentReference[oaicite:0]{index=0}

2. Building blocks: α-amino acids

General formula – each has an amino and a carboxyl group on the same carbon: \( \mathrm{RCH(NH_2)COOH} \). Only the α-type appears after protein hydrolysis. :contentReference[oaicite:1]{index=1}
Trivial names often hint at taste or source (e.g., glycine tastes sweet 😊). :contentReference[oaicite:2]{index=2}
Essential amino acids (starred in the book) must come from food; the rest are non-essential. :contentReference[oaicite:3]{index=3}
Based on –NH₂ and –COOH counts: more amino → basic, more carboxyl → acidic, equal → neutral. :contentReference[oaicite:4]{index=4}

3. Handy properties

Colourless crystals with high melting points; they dissolve well in water.
They act like salts because they exist as a zwitter ion: \( \mathrm{^{+}H_3NCHRCOO^{-}} \). This gives them amphoteric super-powers (they can react with acids and bases). :contentReference[oaicite:5]{index=5}
All natural α-amino acids (except glycine) are chiral and usually found in the L-form. :contentReference[oaicite:6]{index=6}

4. Peptide link & chain sizes 🔗

A peptide bond is an amide, \( \mathrm{-CO-NH-} \), formed when the –COOH of one amino acid meets the –NH₂ of another, releasing water 💧. Two amino acids make a dipeptide, e.g.

\(\text{Gly} + \text{Ala} \;\longrightarrow\; \text{Gly–Ala} + \mathrm{H_2O}\)

Add a third for a tripeptide, keep going for a polypeptide, and once you pass ~100 residues (> 10 000 u) you have a full-fledged protein! :contentReference[oaicite:7]{index=7}

5. Two big shape families 🧵🎈

Fibrous – long, parallel chains held by H-bonds / S–S bridges; tough and water-insoluble (keratin in hair, myosin in muscle). :contentReference[oaicite:8]{index=8}
Globular – chains fold into compact spheres; usually water-soluble (insulin, albumin). :contentReference[oaicite:9]{index=9}

6. Four levels of structure 📏

Primary – exact amino-acid sequence; swap one residue and you change the protein! :contentReference[oaicite:10]{index=10}
Secondary – local folding: right-handed α-helix or zig-zag β-pleated sheet, both stabilised by backbone H-bonds. :contentReference[oaicite:11]{index=11}
Tertiary – overall 3-D folding, fixed by H-bonds, disulphide links, van der Waals and ionic attractions, giving fibrous or globular shapes. :contentReference[oaicite:12]{index=12}
Quaternary – how separate chains (sub-units) fit together (think of the four chains in haemoglobin). :contentReference[oaicite:13]{index=13}

7. Denaturation – shape collapse 😵

Heat or pH change breaks stabilising bonds, uncoils helices, and the protein loses its function (egg white solidifying or milk curdling). The primary chain survives. :contentReference[oaicite:14]{index=14}

8. Enzymes – protein superheroes 🦸🏻‍♂️

Almost all enzymes are globular proteins. They speed reactions by slashing activation energy. Example: maltase turns maltose into two glucose units:

\(\mathrm{C_{12}H_{22}O_{11} + H_2O \xrightarrow{\text{maltase}} 2\,C_6H_{12}O_6}\)

Names usually end in “-ase.” :contentReference[oaicite:15]{index=15}

Important Concepts for NEET 🔑

Essential vs non-essential amino acids – know which must come from food. :contentReference[oaicite:16]{index=16}
Zwitter-ion nature gives amino acids their salt-like behaviour and high melting points. :contentReference[oaicite:17]{index=17}
Peptide bond formation and the jump from dipeptide to full protein. :contentReference[oaicite:18]{index=18}
The four structural levels (primary → quaternary) and the forces that hold each level together. :contentReference[oaicite:19]{index=19}
Denaturation – loss of secondary/tertiary structure but not the primary chain (egg-white test!). :contentReference[oaicite:20]{index=20}