Biomolecules:

 All the carbon compounds that we get from living tissues can be called
‘biomolecules’
Components of living cells:
 The acid insoluble fraction, has only four types of organic compounds
i.e., proteins, nucleic acids, polysaccharides and lipids. They are called
biomacromolecules.
 These classes of compounds with the exception of lipids, have molecular
weights in the range of ten thousand daltons and above .
 Lipid is still considered a biomacromolecule since it is present in acid
insoluble pool. The lipids ruptured cell walls form large vesicles which
aren’t dissolved by the acid.
 The components of cells are given below:

Secondary Metabolites:

AMINO ACIDS:
 Amino acids are organic compounds containing an amino group and
an acidic group as substituents on the same carbon i.e., the α-carbon.
Hence, they are called α-amino acids. They are substituted methanes.
 There are four substituent groups occupying the four valency positions.
These are hydrogen, carboxyl group, amino group and a variable group
designated as R group. Based on the nature of R group there are many
amino acids.
 The R group in these proteinaceous amino acids could be a hydrogen
(the amino acid is called glycine), a methyl group (alanine), hydroxy
methyl (serine), etc
 Based on number of amino and carboxyl groups, there are acidic (e.g.,
glutamic acid), basic (lysine) and neutral (valine) amino acids. Similarly,
there are aromatic amino acids (tyrosine, phenylalanine, tryptophan).
 Btw glutamic acid is also called glutamate.
PROTEINS:
 Proteins are polypeptides. They are linear chains of amino acids linked
by peptide bonds.
 Each protein is a polymer of amino acids. As there are 20 types of amino
acids (e.g., alanine, cysteine,proline, tryptophan, lysine, etc.), a protein is
a heteropolymer and not a homopolymer.
 Collagen is the most abundant protein in animal world
 Ribulose bisphosphate Carboxylase-Oxygenase (RuBisCO) is the most
abundant protein in the whole of the biosphere


STRUCTURE:
 The sequence of amino acids i.e., the positional information in a protein
– which is the first amino acid, which is second, and so on – is called the
primary structure (Figure 9.3a) of a protein.
 The bond btw 2 amino acids are called peptide bonds.
 The first amino acid is also called as N-terminal amino acid. The last
amino acid is called the C-terminal amino acid.{from the left}
  A protein thread does not exist throughout as an extended rigid rod. The
thread is folded in the form of a right hand helix(eg of secondary
structure)(aka alpha helix)
 . In addition, the long protein chain is also folded upon itself like a
hollow woolen ball, giving rise to the tertiary structure. Eg enzymes
 Quartenary structures are a combo of more than 1 of the above
mentioned structures.
 Eg:Adult human haemoglobin consists of 4 subunits.Two of these are
identical to each other. Hence, two subunits of α helix and two subunits
of β plated sheet(another 2ndry structure) together constitute the
human haemoglobin.
POLYSACCHARIDES:
 Polysaccharides are long chains of sugars. They are threads (literally a
cotton thread) containing different monosaccharides as building blocks.
 The monosaccharides are linked by glycosidic bond. a polysaccharide the
individual monosaccharides are linked by a glycosidic bond. This bond is
also formed by dehydration. This bond is formed between two carbon
atoms of two adjacent monosaccharides In a nucleic acid a phosphate
moiety links the 3’-carbon of one sugar of one nucleotide to the 5’-
carbon of the sugar of the succeeding nucleotide.
 In a polysaccharide chain (say glycogen), the right end is called the
reducing end and the left end is called the non-reducing end.
 Various eg are given below:
1. cellulose is a polymeric polysaccharide consisting of only one type
of monosaccharide i.e., glucose.
2. Starch is a variant of this but present as a store house of energy in
plant tissues.
3. Animals have another variant called glycogen.
4. Inulin is a polymer of fructose.
 Exoskeletons of arthropods, for example, have a complex polysaccharide
called chitin. These complex polysaccharides are mostly homopolymers.
LIPIDS:
Lipids are generally water insoluble. They could be simple fatty acids. A fatty
acid has a carboxyl group attached to an R group. The R group could be a
methyl (–CH3 ), or ethyl (–C2H5 ) or higher number of –CH2 groups (1
carbon to 19 carbons). For example, palmitic acid has 16 carbons including
carboxyl carbon. Arachidonic acid has 20 carbon atoms including the
 carboxyl carbon. Fatty acids could be saturated (without double bond) or
unsaturated (with one or more C=C double bonds). Another simple lipid is
glycerol which is trihydroxy propane. Many lipids have both glycerol and
fatty acids. Here the fatty acids are found esterified with glycerol. They can
be then monoglycerides, diglycerides and triglycerides. These are also
called fats and oils based on melting point. Oils have lower melting point
(e.g., gingelly oil) and hence remain as oil in winters. Some lipids have
phosphorous and a phosphorylated organic compound in them
NUCLEOTIDES:
 Thet are polynucleotides.
 For nucleic acids, the building block is a nucleotide. A nucleotide has three
chemically distinct components. One is a heterocyclic compound, the
second is a monosaccharide and the third a phosphoric acid or phosphate.
 the heterocyclic compounds in nucleic acids are the nitrogenous bases
named adenine, guanine, uracil, cytosine, and thymine.
 Adenine and Guanine are substituted purines while the rest are substituted
pyrimidines.
 The sugar found in polynucleotides is either ribose(in RNA) and ) or
2’deoxyribose.
Structure of DNA:
 one of the secondary structures exhibited by DNA is the famous Watson-
Crick model. This model says that DNA exists as double helix. The two
strands of polynucleotides are antiparallel i.e.,run in the opposite direction.
The backbone is formed by the sugarphosphate-sugar chain.
 The nitrogen bases are projected more or less perpendicular to this
backbone but face inside. A and G of one strand compulsorily base pairs
with T and C, respectively, on the other strand.
 There are two hydrogen bonds between A and T and three hydrogen bonds
between G and C.
 Each strand appears like a helical staircase. Each step of ascent is
represented by a pair of bases. At each step of ascent, the strand turns 36°.
One full turn of the helical strand would involve ten steps or ten base pairs.
 One full turn of the helical strand would involve ten steps or ten base pairs.
 The pitch is 34Å. The rise per base pair is 3.4Å.
METABOLISM:
 Together all the chemical reactions in the cell are called metabolism.
 metabolic reactions do not occur in isolation but are always linked to some
other reactions. In other words, metabolites are converted into each other
in a series of linked reactions called metabolic pathways.
 . The called biosynthetic pathways or anabolic pathways. The latter
constitute degradation and hence are called catabolic pathways.
 Eg of catabolic pathway is respiration.
 The most important form of energy currency in living systems is the bond
energy in a chemical called adenosine triphosphate (ATP)
LIVING STATE:
 the blood concentration of glucose in a normal healthy individual is 4.2
mmol/L– 6.1 mmol/L.
 the living state is a non-equilibrium steadystate to be able to perform work.
ENZYMES:
 catalysts which hasten the rate of a given metabolic conversation are also
proteins. These proteins with catalytic power are named enzymes.
 Almost all enzymes are proteins. There are some nucleic acids that behave
like enzymes. These are called ribozyme.
 . Rate of a physical or chemical process refers to the amount of product
formed per unit time.
 Rate can also be called velocity if the direction is specified. Rates of physical
and chemical processes are influenced by temperature among other
factors. A general rule of thumb is that rate doubles or decreases by half for
every 10°C change in either direction.
 Catalysed reactions proceed at rates vastly higher than that of uncatalysed
ones.eg: In the absence of any enzyme this reaction is very slow, with about
200 molecules of H2CO3 being formed in an hour. However, by using the
enzyme present within the cytoplasm called carbonic anhydrase, reaction
speeds dramatically with about 600,000 molecules being formed every
second. The enzyme has accelerated the reaction rate by about 10 million
times.
ENZYME ACTION:
 During the state where substrate is bound to the enzyme active site, a new
structure of the substrate called transition state structure is formed.

Factors Affecting Enzyme Activity:
 Enzymes generally function in a narrow range of temperature and
pH(Figure 9.7). Each enzyme shows its highest activity at a particular
temperature and pH called the optimum temperature and optimum pH.
Activity declines both below and above the optimum value.

 With the increase in substrate concentration, the velocity of the

enzymatic reaction rises at first. The reaction ultimately reaches a
maximum velocity (Vmax) which is not exceeded by any further rise in
concentration of the substrate.
INHIBITION:
 When the binding of the chemical shuts off enzyme activity, the process
is called inhibition and the chemical is called an inhibitor.
 When the inhibitor closely resembles the substrate in its molecular
structure and inhibits the activity of the enzyme, it is known as
competitive inhibitor. Due to its close structural similarity with the
substrate, the inhibitor competes with the substrate for the substrate
binding site of the enzyme. Consequently, the substrate cannot bind and
as a result, the enzyme action declines, e.g., inhibition of succinic
dehydrogenase by malonate which closely resembles the substrate
 succinate in structure. Such competitive inhibitors are often used in the
control of bacterial pathogens.

Classification and Nomenclature of Enzymes:

 Enzymes are divided into 6 classes each with 4-13 subclasses and named
accordingly by a four-digit number.
 Oxidoreductases/dehydrogenases: Enzymes which catalyse
oxidoreduction of substrate.
 Transferases: Enzymes catalysing a transfer of a group, G (other than
hydrogen)
 Hydrolases: Enzymes catalysing hydrolysis of ester, ether, peptide,
glycosidic, C-C, C-halide or P-N bonds
 Lyases: Enzymes that catalyse removal of groups from substrates by
mechanisms other than hydrolysis leaving double bonds.
 Isomerases: Includes all enzymes catalysing inter-conversion of optical,
geometric or positional isomers.
 Ligases: Enzymes catalysing the linking together of 2 compounds, e.g.,
enzymes which catalyse joining of C-O, C-S, C-N, P-O etc. bonds.
Co Factors: