WHY even number? Because the body builds fatty acids two carbons at a time (from acetyl-CoA, a 2-carbon unit). So nature keeps adding C2 blocks → even totals.
WHAT makes one "saturated" vs "unsaturated"?
Saturated = no C=C double bonds → chain is straight → packs tightly → solid at room temp (fats, e.g. butter).
Unsaturated = has C=C double bonds → introduces a kink (cis bond) → can't pack → liquid (oils, e.g. olive oil).
Esterification built the bond by removing water. Hydrolysis breaks it by adding water back. With NaOH, the strong base attacks each ester, and the fatty acid leaves as its sodium salt (not the free acid — because base neutralises it):
Biomolecule that is insoluble in water (hydrophobic), due to long hydrocarbon chains.
What two parts make a fatty acid?
A long hydrocarbon tail + a –COOH (carboxylic acid) head.
Why do fatty acids have an even number of carbons?
Built from 2-carbon acetyl units, so they grow in steps of two.
Saturated vs unsaturated — which is solid at room temp and why?
Saturated; straight chains pack tightly → strong van der Waals → higher melting point.
What does a cis double bond do to a fatty acid chain?
Introduces a kink → poor packing → lower melting point → liquid oil.
A triglyceride is made from what + what?
1 glycerol + 3 fatty acids, joined by 3 ester bonds.
How many water molecules are released forming one triglyceride?
3 (one per ester bond).
Why is fat better energy storage than carbohydrate?
Highly reduced (many C–H bonds) and anhydrous → ~9 kcal/g vs ~4 for carbs.
What makes a phospholipid different from a triglyceride?
One fatty acid is replaced by a phosphate group.
What does "amphipathic" mean?
Has both a hydrophilic (polar) head and hydrophobic (nonpolar) tail.
Why do phospholipids form a bilayer in water?
Tails hide from water inward, polar heads face water on both sides.
Define saponification.
Alkaline (NaOH/KOH) hydrolysis of a triglyceride giving soap + glycerol.
What are the products of saponification?
Sodium/potassium salts of fatty acids (soap) + glycerol.
In saponification, why is the product a salt, not the free fatty acid?
NaOH neutralises the released acid to RCOO⁻Na⁺.
Why does saponification go to completion?
The fatty acid is trapped as its salt, so the ester can't reform.
How does soap remove grease?
Amphipathic; tails dissolve in grease, polar heads face water → forms micelles.
Recall Feynman: explain to a 12-year-old
Imagine tiny tadpoles where the head loves water and the tail hates water. In water, the tails huddle together to hide, leaving the heads outside in the water — that's how a cell's skin (membrane) builds itself. Fats are like ropes of greasy tail tied to a tiny knot (glycerol) — great for storing energy because they pack lots of fuel and no water weight. Soap is the same tadpole idea: its tail grabs the grease on your hands, its head holds onto the water, so when you rinse, the grease floats away. And making soap? You take fat, add a strong cleaner (lye/NaOH), and it snips the greasy ropes off the knot — knot becomes glycerol, ropes become soap.
Dekho, lipids ka funda simple hai: ye biomolecules paani mein dissolve nahi hote, kyunki inke paas lambi hydrocarbon chain (greasy tail) hoti hai jo paani se dosti nahi karti. Fatty acid = lamba greasy tail + ek –COOH head. Agar chain mein koi double bond nahi (saturated), to chain seedhi rehti hai, tightly pack hoti hai, isliye solid (jaise ghee, butter). Agar double bond hai (unsaturated), to ek kink/mod aa jaata hai, packing kharab hoti hai, isliye liquid (jaise tel/oil). Yaad rakho: "Sat = Straight = Solid".
Triglyceride banta hai jab 1 glycerol (jiske paas 3 –OH hain) + 3 fatty acids milte hain, ester bond banake. Har ester bond banne par ek paani nikalta hai, to total 3 paani release hote hain — isko condensation kehte hain. Ye body ka best energy store hai kyunki fat mein bahut zyada C–H bonds hote hain aur paani ka weight nahi hota.
Phospholipid bilkul triglyceride jaisa hai, bas ek fatty acid ki jagah phosphate group lag jaata hai. Isse molecule amphipathic ban jaata hai — ek taraf paani-pasand head, doosri taraf paani-nafrat tail. Yahi reason hai ki paani mein ye khud-ba-khud bilayer bana lete hain (tails andar, heads bahar) — yahi humari cell membrane hai.
Saponification matlab fat ko NaOH ke saath todna (alkaline hydrolysis), jisse milta hai soap (fatty acid ka sodium salt) + glycerol. Important point: free fatty acid nahi, balki uska salt banta hai, kyunki NaOH usse neutralise kar deta hai — isiliye reaction poori taraf complete ho jaati hai. Aur soap khud bhi amphipathic hota hai, isliye grease ko micelle bana ke dhota hai. Exam ke liye ye chain yaad rakho: structure → property → state, aur "GFE makes Soap & Glycerol".
