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Biology · Cell: Structure and Function · Chapter notes

Biomolecules · Class 11 NEET Notes

Class 11 notes on Biomolecules for NEET: carbohydrates, proteins and amino acids, nucleic acids, enzymes and metabolism, grouped the way the questions group them.

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In short

Biomolecules is a chapter of names and numbers, so it rewards organised revision far more than long reading. Everything a cell is made of falls into four families: carbohydrates, proteins, nucleic acids and lipids, plus the enzymes that run the reactions between them. Learn them grouped, because that is how NEET asks about them.

Contents
  1. ·How to Read This
  2. 1Analysing What a Cell Is Made Of acid soluble and insoluble
  3. 2Carbohydrates monomer to polymer
  4. 3Proteins and Amino Acids and the four structural levels
  5. 4Nucleic Acids the third great polymer
  6. 5Enzymes how they work, and what changes them
  7. 6Metabolism the living state is never at equilibrium
  8. ★Biomolecules · Fact Sheet
0

How to Read This

  • This chapter is mostly recall, so the marks go to whoever revises the lists, not who reads the most.
  • Blue marks a defining fact. Red marks a number or a trap.
  • Read the points, study the two diagrams, then use the fact sheet the night before.
1

Analysing What a Cell Is Made Of

  • Grind a tissue with acid, then filter. What passes through is the acid soluble pool.
  • Acid soluble: all the small molecules, with molecular weight under about 1000 daltons. Amino acids, sugars, nucleotides, lipids.
  • Acid insoluble: the big polymers. Proteins, nucleic acids, polysaccharides.
  • Lipids are an oddity. Their molecular weights are small, so they belong with the small molecules, but they appear in the insoluble fraction because they sit inside membrane fragments.
  • Water is the most abundant chemical in any living organism, at about 70 to 90 percent.
  • Among the macromolecules, protein is the most abundant.
2

Carbohydrates

  • Monosaccharides: glucose, fructose, galactose, ribose. They cannot be hydrolysed further.
  • Disaccharides: sucrose is glucose plus fructose, lactose is glucose plus galactose, maltose is two glucose.
  • Polysaccharides: starch and glycogen store energy, cellulose and chitin give structure.
  • Cellulose has no helix and holds no iodine, which is why plant fibre does not stain blue. Starch does form a helix, and holds iodine to give the blue colour.
  • Inulin is a polymer of fructose. Chitin makes the insect exoskeleton.
3

Proteins and Amino Acids

  • An amino acid has an amino group, a carboxyl group, a hydrogen and an R group, all on the same carbon.
  • There are 20 amino acids in proteins, and the R group is what distinguishes them.
  • Amino acids are zwitterions: at neutral pH both the amino and carboxyl groups are ionised.
  • Essential amino acids cannot be made by the body and must come from food.
Sequence, then local folding, then the whole 3D shape, then several chains together.THE FOUR LEVELS OF PROTEIN STRUCTUREPRIMARYthe sequence of amino acidsSECONDARYhelix or pleated sheetTERTIARYfolded into a 3D shapeQUATERNARYseveral chains togetherHaemoglobin has four chains, so it has quaternary structure. Myoglobin has one, so it stops at tertiary.
Sequence, then local folding, then the whole 3D shape, then several chains together.
  • Amino acids join by a peptide bond, formed by removing water.
  • Primary is the sequence. Secondary is the helix or pleated sheet.
  • Tertiary is the folded 3D shape. Quaternary is several chains together.
  • Haemoglobin has four chains, so it shows quaternary structure. Myoglobin has one, so it stops at tertiary.
  • Collagen is the most abundant protein in the animal world. RuBisCO is the most abundant on Earth.
4

Nucleic Acids

  • A nucleotide has three parts: a nitrogen base, a pentose sugar and a phosphate group.
  • Nucleoside is base plus sugar. Add the phosphate and it becomes a nucleotide. That distinction is examined.
  • Purines are adenine and guanine, with two rings. Pyrimidines are cytosine, thymine and uracil, with one.
  • DNA has deoxyribose and thymine. RNA has ribose and uracil.
  • The backbone is sugar and phosphate, joined by phosphodiester bonds.
5

Enzymes

  • Enzymes are almost all proteins. The exceptions are ribozymes, which are RNA.
The substrate fits the active site, forms a complex, then leaves as product.ENZYME ACTION: LOCK AND KEY, THEN INDUCED FITenzyme with its active sitesubstrateenzyme-substrate complexEnzymes lower the ACTIVATION ENERGY. They never change the equilibrium position,and they are not used up in the reaction.
The substrate fits the active site, forms a complex, then leaves as product.
  • Enzymes lower the activation energy. They do not change the equilibrium position, and they are not used up.
  • Rate rises with temperature to an optimum, then falls sharply as the protein denatures.
  • Each enzyme also has an optimum pH.
  • Competitive inhibitor: resembles the substrate and binds the active site. Malonate against succinate dehydrogenase is the standard example.
  • Cofactors: prosthetic groups are tightly bound, coenzymes are loosely bound and often vitamins, and metal ions are the third kind.
  • The protein part alone is the apoenzyme. With its cofactor it is the holoenzyme.
6

Metabolism

  • Every living thing runs thousands of chemical reactions, all of them enzyme catalysed.
  • Anabolic pathways build and consume energy. Catabolic pathways break down and release it.
  • The living state is a steady state, not equilibrium. Reaching equilibrium would mean death.
  • That steady state is maintained only by a constant input of energy, which is why metabolism never stops.

★ Biomolecules · Fact Sheet

Every rule for revision day.

THE TWO FRACTIONS

Acid soluble: small molecules

Acid insoluble: the polymers
Lipids sit oddly in insoluble.

MOST ABUNDANT

Water, in any organism

Protein, among macromolecules
RuBisCO, on Earth.

DISACCHARIDES

Sucrose: glucose + fructose

Lactose: glucose + galactose
Maltose: glucose + glucose.

POLYSACCHARIDES

Starch and glycogen store

Cellulose and chitin build
Only starch holds iodine.

AMINO ACIDS

20 in proteins

The R group distinguishes them
Zwitterions at neutral pH.

PROTEIN LEVELS

Primary: sequence

Secondary: helix or sheet
Tertiary: 3D. Quaternary: many chains.

HAEMOGLOBIN

Four chains, so QUATERNARY.

Myoglobin has one chain,
so it stops at tertiary.

NUCLEOTIDE

Nucleoside = base + sugar

Nucleotide = that + phosphate
Purines A and G, two rings.

ENZYMES

Lower the ACTIVATION energy

Never shift the equilibrium
Ribozymes are RNA, not protein.

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