Answers of Exam Ques.

ANAPLEROTIC REACTIONS · Some of the biosynthetic reactions use intermediates of citric acid cycle,
which results in the decrease in the level of these intermediates in the cycle. · The decreased level of
the intermediates reduces the use of acetyl-Co A for oxidation. So ATP synthesis is hampered. ·
Hence, the intermediates of citric acid cycle are replenished by a different set of reactions known as
“Anaplerotic reactions”. (Anaplerotic = filling up). · Eg: Oxaloacetate, one of the intermediates of the
citric acid cycle is removed for the synthesis of aspartic acid, to be used in the synthesis of proteins.
This causes reduction in the use of acetyl-Co A for oxidation. · Hence, in another set of reaction,
oxaloacetate is produced from pyruvate, by the enzyme pyruvate carboxylase.
activation energy : The energy required by the reactants to undergo the reaction is known as
activation energy. The reactants when heated attain the activation energy. The catalyst (or the
enzyme in the biological system) reduces the activation energy and this causes the reaction to
proceed at a lower temperature. Enzymes do not alter the equilibrium constants, they only enhance
the velocity of the reaction.
allosteric enzyme Some of the enzymes possess additional sites, known as allosteric sites (Greek
: allo-other), besides the active site. Such enzymes are known as allosteric enzymes. The allosteric
sites are unique places on the enzyme molecule. Selected examples of allosteric enzymes
responsible for rapid control of biochemical pathways are Hexokinase ,Phosphofructokinase,
lsocitrate dihydrogen. Pg no.- 101
BETA-OXIDATION OF FATTY ACIDS Oxidation occurs between the α and the ß carbon atoms of the
fatty acid, and hence it is called as “ β -oxidation”, which degrades fatty acids starting at the carboxyl
end to acetylCoA units. Cells lacking mitochondria cannot oxidize fatty acids The oxidation of fatty
acids, occurs in 3 stages,
Activation of fatty acids, in the cytoplasm.

Transfer of activated fatty acids into the mitochondrial matrix.
Oxidation of fatty acids to yield acetyl-CoA.
For example, the oxidation of a molecule of palmitoyl-Co A (which contains 16 carbon units)
to CO2 and H2O yields the following number of ATPs.  Beta oxidation of palmitoyl CoA
yields 7 FADH2, 7 NADH and 8 acetyl CoA.
CODON The three nucleotide (triplet) base sequences in mRNA that act as code words for amino
acids in protein constitute the genetic code or simply codons. The codons are composed of the four
nucleotide bases, namely the purines-adenine (A) and guanine (C), and the pyrimidine-cytosine (C)
and uracil (U). These four bases produce 64 different combinations (43) of three base codons. The
three codons UAA, UAG and UCA do not code for amino acids. They act as stop signals in protein
synthesis.
COENZYME OF PYRUVATE DEHYDROGENASE -The enzyme PDH complex requires 5 coenzymes

thiamine pyrophosphate (TPP), Lipoamide, CoA, FAD & NAD). Pyruvate dehydrogenase complex
catalyzes the conversion of pyruvate to acetyl CoA linking the glycolytic cycle with TCA.
De novo synthesis purines are synthesized from the smaller precursor molecules such as glycine,
aspartic acid, glutamine, CO2 and tetratrahydrofolic acid. This pathway is expensive; Several
reactions require ATP. All enzymes of purine metabolism are found in cytoplasm.  Purine ring
structure is not synthesized as a free base but as a substituent of ribose-5- phosphate, which comes
from 5-phosphoribosyl-1-pyrophosphate (PRPP). The PRPP is formed from ribose 5-phosphate and
ATP. PRPP then donates the ribose 5-phosphate, which serves as base upon which purine structure
is built.
GLYCOLYSIS -Glycolysis occurs in cytosol.  Glycolysis is also known as Embden-mayerhof –Parnas
pathway (EMP or EM Pathway). It has a sequence of 10 enzyme-catalyzed reactions, where one
molecule of glucose (6C) is converted to two molecules of pyruvate (3C). Major function of glycolytic
pathway is the generation of ATP and intermediates for other metabolic pathway , such as,
Synthesis of glycine, serine ,cysteine, Synthesis of fatty acid using acetyl CoA, Glycerol 3-phosphate
etc.Reactions of glycolysis is divided into two phases, preparatory phase and pay off (ATP
generating) phase ( each containing 5 reaction).
holoenzyme. The functional unit of the enzyme is known as holoenzyme which is often
made up of apoenzyme (the protein part) and a coenzyme (non-protein organic part). So
catalytically active enzyme together with its coenzyme and / or metal ions is
called"holoenzyme"
INTEGRATION OF METABOLISM - The purpose of metabolism is to oxidize the food to provide

energy in the form of ATP.  Some molecules obtained during metabolism are also converted to
new cellular materials and essential components.  Another important function is the processing of
waste products to facilitate their excretion. www.drvet.in  Animals take food at periodic intervals,
they do not eat continuously. After a meal, blood is loaded with glucose, triacylglycerol and amino
acids, which are absorbed from the intestine. From the blood these nutrients are taken into tissues
so that blood levels are quickly returned to normal level. The tissues store the excess food and use
these stores when the animals are fasted. There are regulatory mechanisms, which direct
compounds through metabolic pathways involved in storage and utilize them as fuel when required.
 Hormones (like insulin, glucagon and catecholamines), concentration of available nutrients and
the energy needs of the body control the mechanisms.
Isoenzymes (isozymes) are The multiple forms of an enzyme catalysing the same reaction are
isoenzymes or isozymes. They, however, differ in their physical and chemical properties which
include the structure, electrophoretic and immunological properties, Km and Vmax values, pH
optimum, relative susceptibility to inhibitors .and degree of denaturation. s. Different tissues may
contain different isoenzymes and these isoenzymes may differ in their affinity for substrates and
they may be inhibited by different concentrations of inhibitors Eg. LDH has five distinct isoenzymes
LDH1, LDH2, LDH3, LDH4 and LDH5.
Km is the Michaelis constant = (k1 + k2)/k1. Km is the substrate concentration required to produce
a reaction rate equal to half the Vmax. Km measures the affinity of the enzyme for the substrate. A
low Km indicates high affinity and vice versa. o Km does not vary with the enzyme concentration.
KATAL - . One kat denotes the conversion of one mole substrate per second (mol/sec). Activity may
also be expressed as millikatals (mkat), microkatals ( µ kat) and so on. The SI unit of enzyme activity
is the katal (kat).
 One katal is the transformation of 1.0 mole of substrate to product per second.
o 1 U = 1 µ mol / min
o 1 katal = 1 mol / sec
o 1 U = µ kat / 60 = 16.67 nkat.
Ketosis i ketonemia and ketonuria is commonly referred to as ketosis Smell of acetone in breath is a
common feature in ketosis. Ketosis is most commonly associated with starvation and severe
uncontrolled diabetes mellitus. '. Excess utilization of fats coupled with deficiency of carbohydrates
leads to ketosis.
MITOCHONDRIAL SHUTTLE SYSTEM Inner mitochondrial membrane is impermeable to certain
important compounds like NAD+/NADH/ NADP+/NADPH, Coenzyme-A and oxaloacetate.
 NADH is generated in the glycolytic process in cytosol (in the reaction catalyzed by
glyceraldehyde-3-phosphate dehydrogenase).
 It has to be transported across the mitochondrial membrane to get re-oxidized to NAD+ via the
respiratory chain in mitochondria.
 As the inner membrane is impermeable to NADH, they are transported through special transport
system called “shuttle system”.
 Such special systems carry the reducing equivalents (NADH) from the cytosol to mitochondrial
matrix by an indirect route.
 There are 2 common and important shuttle systems, viz.
, o Malate-aspartate shuttle, and
o Glycerol 3-phosphate shuttle.

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Answers of Exam Ques.

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ANAPLEROTIC REACTIONS · Some of the biosynthetic reactions use intermediates of citric acid cycle,

Activation of fatty acids, in the cytoplasm.

COENZYME OF PYRUVATE DEHYDROGENASE -The enzyme PDH complex requires 5 coenzymes

INTEGRATION OF METABOLISM - The purpose of metabolism is to oxidize the food to provide

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