These notes for CBSE Class 11 Biology, Chapter 9, focus on Biomolecules. They define biomolecules as carbon compounds from living tissues, categorizing them into micromolecules (e.g., amino acids, lipids) and biomacromolecules (e.g., proteins, polysaccharides, nucleic acids). The notes detail the structure and types of amino acids, lipids (including fatty acids and glycerol), and phospholipids. They explain nucleosides, nucleotides, and nucleic acids like DNA and RNA. Protein structures (primary, secondary, tertiary, quaternary) and peptide bonds are described. Polysaccharides like starch, cellulose, glycogen, and chitin are covered. The chapter also explains anabolic and catabolic pathways, and the role of enzymes as biocatalysts, including their structure, active sites, and factors affecting their activity like temperature and pH. Enzyme inhibition, classification, and the importance of cofactors (prosthetic groups, co-enzymes, metal ions) are discussed. Finally, the Watson and Crick model of DNA structure is outlined. These notes are ideal for quick revision before exams.
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NCERT Notes For Biology Class 11 Download In PDF
Biomolecules : All the carbon compounds that we get from living tissues.
Micromolecules : Molecules which have molecular weights less than one thou-
sand dalton.
Amino acids : Organic compounds containing an amino group and one car-
boxyl group (acid group) and both these groups are attached to the same carbon
atom called ? ? ? ?
? carbon.
Lipids :
• Water insoluble, containing C, H, O.
• Fats on hydrolysis yield fatty acids.
• Fatty acid has a carboxyl group attached to an R group (contains 1 to 19
carbons).
• Fatty
Acids : Saturated With single bonds in carbon chain. e.g.,
Palmitic acid, butyric acid.
Unsaturated : With one or more double bonds. e.g., oleic acid, linoleic
acid.
Glycerol : A simple lipid, is trihydroxy propane.
• Some lipids have fatty acids esterified with glycerol.
• They can be monoglycerides, diglycerides and triglycerides.
• Phospholipids are compound lipids with phosphorus and a phosphory-
lated organic compound e.g., Lecithin .
Nucleoside : Nitrogenous base + Sugar e.g., Adenosine, guanosine.
Nucleotide : Nitrogenous base + Sugar + Phosphate group. e.g., Adenylic acid,
thymidylic acid.
Nucleic acid : Polymer of nucleotides - DNA and RNA.
Biomacromolecules : Biomolecules with molecular weights in the range of ten
thousand daltons and above; found in acid insoluble fraction.
Lipids are not strictly macromolecules as their molecular weights do not exceed
800 Da but form a part of the acid insoluble pool.
Proteins :
• Are polymers of aminoacids linked by peptide bond.
• Is a heteropolymer.
• For functions of proteins
(a) Primary structure : Is found in the form of linear sequence of amino
acids. First amino acid is called N-terminal amino acid and last amino
acid is called C-terminal amino acid.
(b) Secondary structure : Polypeptide chain undergoes folding or coiling
which is stabilized by hydrogen bonding. Right handed helices are observed. e.g.,
fibrous
protein in hair,
nails.
(c) Tertiary structure : Long protein chain is folded upon itself like a
hollow wollen ball. Gives a 3-dimensional view of protein, e.g., myosin.
(d) Quaternary structure : Two or more polypeptides with their foldings
and coilings are arranged with respect to each other. e.g., Human haemoglobin
molecule has 4 peptide chains - 2a and 2b subunits.
Peptide bond : Formed between the carboxyl (-COOH) group of one amino
acid and the amino (-NH
) group of the next amino acid with the elimination
of water moeity. 2 Polysaccharides : Are long chain of sugars.
(a) Starch : Store house of energy in plant tissues. Forms helical second-
ary structures.
(b) Cellulose : Polymer of glucose.
(c) Glycogen : Is a branched homopolymer, found as storage polysaccharide
in animals.
(d) Insulin : Is a polymer of fructose.
(e) Chitin : Chemically modified sugar (amino-sugars) N-acetyl galac-
tosamine. Form exoskeleton of arthropods.
Anabolic pathways : Lead to formation of more complex structure from a sim-
pler structure with the consumption of energy. e.g., Protein from amino acids.
Catabolic pathway : Lead to formation of simpler structure from a complex
structure. e.g., Glucose ? Lactic Acid.
Enzymes : Are biocatalysts.
• Almost all enzymes are proteins.
• Ribozomes - Nucleic acids that behave like enzymes.
• Has primary, secondary and tertiary structure.
• Active site of an enzyme is a crevice or pocket into which substrate
fits.
• Enzymes get damaged at high temperatures.
• Enzymes isolated from thermophilic organisms (live under high temperatures)
are thermostable.
• Enzymes accelerate the reactions many folds.
• Enzymes lower the activation energy of reactions.
• ES ES EP EP
+??+
where E = Enzyme, S = Substrate, P = Product.
Factors affecting enzyme activity :
(a) Temperature : Show highest activity at optimum temperature. Activity
declines above and below the optimum value.
(b) pH : Enzymes function in a narrow range of pH. Highest activity at
optimum pH.
(c) Concentration of substrate : The velocity of enzymatic reaction rises
with increase in substrate concentration till it reaches maximum ve-
). Further increase of substrate does not increase the rate
of reaction as no free enzyme molecules are available to find with
additional substrate.
locity V max
Enzyme inhibition : When the binding of a chemical shuts off enzyme
activity, the process is called inhibition and chemical is called inhibitor.
Competitive inhibition : Inhibitor closely resembles the substrate in its
molecular structure and inhibits the enzyme activity. E.g., inhibition of succinic
dehydrogenase by malonate.
Oxidoreductase/dehydrogenases : Catalyse oxidoreduction between 2 sub-
strates.
Transferases : Catalyse transfer of a group between a pair of substrates.
Hydrolases : Catalyse hydrolysis of ester, ether, peptide, glycosidic, C-C,
P-N bonds.
Lyases : Catalyse removal of groups from substrates by mechanisms other
than hydrolysis.
Isomerases : Catalyse inter-conversion of optical, geometric or positional
isomers.
Ligases : Catalyse linking together of 2 compounds.
Cofactors : Non-protein constituents found to the enzyme to make it cata-
lytically active. Protein portion of enzyme is called apoenzyme.
Cofactors :
• Prosthetic groups : Are organic compounds tightly bound to
apoenzyme. E.g., haem in peroxydase and catalase.
• Co-enzymes : Organic compounds which has transient association with
enzyme. E.g., NAD, NADP.
• Metal ions : Required for enzyme activity. Form coordination bond with
side chains at active site and with substrate.
E.g., zinc is a co-factor for
enzyme carboxypeptidase.
18. Nucleic acids : Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
DNA structure (Watson and Crick Model) : DNA is a right handed, double
helix of two polynucleotide chains, having a major and minor groove. The two
chains are antiparallel, and held together by hydrogen bonds (two between A and
T and three between C and G). The backbone is formed by sugar-phosphatesugar
chain. The nitrogen bases are projected more or less perpendicular to this
backbone and face inside.
Biomolecules are all the carbon compounds that we obtain from living tissues.
Micromolecules have molecular weights less than one thousand daltons, while biomacromolecules have molecular weights in the range of ten thousand daltons and above.
The four levels of protein structure are primary, secondary, tertiary, and quaternary structure.
Enzymes are biocatalysts, and almost all enzymes are proteins. They accelerate reactions and lower activation energy.
Enzyme activity is affected by temperature, pH, and substrate concentration.
Cofactors are non-protein constituents that are required for an enzyme to be catalytically active. They can be prosthetic groups, co-enzymes, or metal ions.
DNA is a right-handed, double helix of two antiparallel polynucleotide chains held together by hydrogen bonds between nitrogenous bases (A-T and C-G), with a sugar-phosphate backbone.
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