The document discusses glycolysis, which is the breakdown of glucose to pyruvate with production of ATP. It occurs in the cytosol of cells and can proceed with or without oxygen present. Under anaerobic conditions, pyruvate is reduced to lactate, while in aerobic conditions pyruvate enters the citric acid cycle in mitochondria to be fully oxidized to CO2 and H2O. Glycolysis is tightly regulated by feedback inhibition and is a key energy producing process, especially under low oxygen conditions like in muscle during exercise. The citric acid cycle further oxidizes acetyl-CoA produced from pyruvate to generate more ATP through oxidative phosphorylation.

1. By – Dr.Piyush Kaushik
MDS
Conservative Dentistry And Endodontics
Email id- drpiyushkaushik7@gmail.com
Whatsapp/call - +918283805023

2.  They are the major source of energy.
 Synthesized by green plants during
photosynthesis from carbon dioxide and
water on absorption of light.
 Fasting blood glucose level in normal
individual is 70-100mg/dl.
 Liver plays a key role in stabilizing glucose
level hence also called glucostat monitor.

3.  Glycolysis
(Embeden Meyerhoff pathway)
It is the oxidation of glucose to lactate and
pyruvate.
 Definition – Glycolysis is defined as the
sequence of reactions converting glucose to
pyruvate and lactate with production of ATP.

4.  Takes place in all cells of the body. Enzymes
of this pathway are present in cytosomal
fraction of the cell.
 Occurs in presence ( pyruvate is the end
product which is converted into water and
CO2 ) or absence of oxygen (lactate is the
end product).
 Major pathway for ATP synthesis in tissues
lacking mitochondria eg. erythrocytes ,
cornea, lens etc

5.  Essential for brain which is dependent on
glucose for energy.
 It is a central metabolic pathway with many of
its intermediates providing branch point to
there pathways. Thus intermediates of
glycolysis are helpful in synthesis of fats and
amino acids.

6.  It is divided into three distinct phases.
Energy investment phase
Splitting phase
Energy generation phase

8.  Fate of pyruvate depends upon presence or
absence of oxygen.
Under anaerobic condition pyruvate is
reduced by NADH to lactate in presence of
enzyme lactate dehydrogenase.
 NADH utilized in this step is obtained from
reaction catalyzed by glyceraldehyde 3
phosphate dehydrogenase.

9.  Formation of lactate allows regeneration of
NAD+ which can be reused by glyceraldehyde
3 phosphate dehydrogenase so that glycolyis
proceeds even in absence of oxygen.
 This is very essential in skeletal muscle
during strenuous exercise where oxygen
supply is limited.
 Glycolyis in erythrocytes leads to lactate
formation since mitochondria which is the
centre for aerobic oxidation is absent.

10.  TOTAL – 10 ATP
 NET TOTAL – 8 ATP in case of malate
aspartate shuttle and 6 ATP in case of
glycerophosphate shuttle.

11.  Hexokinase
 Phosphofructokinase
 Pyruvate kinase
 The reversal of glycolysis with aleternative
arrangement made at three irreversible
stages leads to synthesis of glucose from
pyruvate (gluconeogenesis)

12.  Hexokinase is inhibited by glucose 6
phosphate. This enzyme revents the
accumulation of glucose 6 phosphate due to
product inhibition.
 Phosphofructokinase is the most important
regulating enzymes.
 It catalyzes the rate limiting committed step.

15.  The inhibition of glycolysis by oxygen (aerobic
condition).
 Discovered by Louis Pasteur
 In aerobic conditions level of glycolytic
intermediates from fructose 1-6 biphosphonate
onwards decrease while other accumulates. This
shows that the Pasteur effect is due to inhibition
of enzyme phosphofructokinase.
 The inhibitory effect of ATP ( produced in
presence of oxygen ) and citrate on PFK explains
Pasteur effect.

16.  The phenomenon of inhibition of oxygen
consumption by addition of glucose to
tissues having high aerobic glycolyis.
 This is opposite to Pasteur effect.

19.  Pyruvate is converted to acetyl CoA by
oxidative decarboxylation. This is an
irreversible reaction, catalysed by a
multienzyme complex known as pyruvate
dehydrogenase complex (PDH), which is
found only in the mitochondria. High
activities of PDH are found in cardiac muscle
and kidney.

20.  1 . Lack of TPP (due to deficiency of thiamine)
inhibits PDH activity resulting in the accumulation of
pyruvate.
 2. ln the thiamine deficient alcoholics, pyruvate is
rapidly converted to lactate, resulting in lactic
acidosis.
 3. ln patients with inherited deficiency of
PDH, lactic acidosis (usually after glucose load)
is observed.
 4. PDH activity can be inhibited by arsenic
and mercuric ions. This is brought about by
binding of these ions with -SH groups of lipoic acid.

21.  Citric acid cycle essentially involves the
oxidation of acetyl CoA to CO2 and H2O. This
cycle utilizes about two thirds of total oxygen
consumed by the body.
 The citric acid cycle is the final common
oxidative pathway for carbohydrates , fats
and amino acids.
 Krebs cycle is the most important
central pathway connecting almost all the
individual metabolic pathways (either directly
or indirectly).

22.  The citric acid cycle was proposed by Hans
Adolf Krebs in 1937, based on the studies of
oxygen consumption in pigeon breast
muscle.
 The enzymes of TCA cycle are located in
mitochondrial matrix, in close proximity to the
electron transport chain.

24.  The TCA cycle basically involves the
oxidation of acetyl CoA to COz with
simultaneous regeneration of oxaloacetate.
As such there is no net consumption of
oxaloacetate or any other intermediate in the
cycle.

25.  Requirement of O2 by TCA cycle
There is no direct participation of oxygen in Krebs
cycle. However, the cycle operates only under
aerobic conditions. This is due to the fact that
NAD+ and FAD (from NADH and FADH2,
respectively) required for the operation of the
cycle can be regenerated in the respiratory chain
only in the presence o f 02. Therefore citric acid
cycle is strictly aerobic in contrast to glycolysis
which operates in both aerobic and anaerobic
conditions.

26.  During the process of oxidation of acetyl CoA
via citric acid cycle,4 reducing equivalents (3 as
NADH and one as FADH2) are produced.
Oxidation of 3 NADH by electron transport
chain coupled with oxidative phosphorylation
results in the synthesis of 9 ATP, whereas FADH2
leads to the formation of 2 ATP. Besides there is
one substrate level phosphorylation .Thus a total
of twelve ATP are produced from one acetyl CoA.

28. 1.Citrate synthase is inhibited by ATP, NADH, acetyl
CoA and succinyl CoA.
 2. lsocitrate dehydrogenase is activated by ADP, and
inhibited by ATP and NADH.
 3. alpha-Ketoglutarate dehydrogenase inhibited by
succinyl CoA and NADH.
 4. Availability of ADP is very important for the citric
acid cycle to proceed. This is due to the fact that
unless sufficient levels of ADP are available, oxidation
(coupled with phosphorylation of ADP to ATP) of
NADH and FADH2 through electron transport chain
stops. The accumulation of NADH and FADH2 will
lead to inhibition of the enzymes (as stated above)
and also limits the supply of NAD+ and FAD which
are essential for TCA cycle to proceed.

29.  It is both catabolic and anabolic hence called
amphibolic.
 It is involved in gluconeogenesis , transamination
and deamination.
 Oxaloacetate and alpha ketoglutarate – synthesis
of glutamate and aspartate.
 Succinyl CoA- synthesis of porphyrins and heme.
 3. Mitochondrial citrate is transported to the
cytosol, where it is cleaved to provide acetyl CoA
for the biosynthesis of fatty acids, sterols etc.

30.  When a molecule of glucose (6 carbon)
undergoes glycolysis,2 molecules of pyruvate
or lactate (3 carbon) are produced. Pyruvate is
oxidatively decarboxylated to acetyl CoA (2
carbon) which enters the citric acid cycle and
gets completely oxidized to CO2 and H2O.

31.  The synthesis of glucose from noncarbohydrate
compounds is known as gluconeogenesis. The
major substrates/precursors for gluconeogenesis
are lactate, pyruvate, glucogenic amino acids,
propionate and glycerol.
 Gluconeogenesis occurs mainly in the cytosol,
although some precursors are produced in
mitochondria.Gluconeogenesism ost ly takes
place in liver (about 1 kg glucose synthesized
everyday) and, to some extent, in kidney matrix
(about one-tenth of liver capacity

32.  Brain , CNS , testes , kidney medulla and
erythrocytes are dependent upon glucose for
supply of energy.
 Only source to supply energy to skeletal
muscles under anaerobic conditions.
 In case of fasting, gluconeogenesis must
occur to meet the basic requirement of body
of glucose.
 Certain metabolites eg lactate glycerol and
propionate are cleared from blood by
gluconeogenesis.

34. Lactate produced by active skeletal muscle is
a major precursor of gluconeogenesis . Under
anaerobic conditions, pyruvate is reduced to
Lactate by lactate dehydrogenase (LDH)

35.  Glycogen is the storage form of glucose ,
stored mostly in liver and muscles.
 Function of glycogen – Maintain blood glucose
level
 It is the fuel reserve of the body as -:
Glycogen can be rapidly mobilized
 Glycogen can generate energy in the absence
of oxygen
 Brain depends on continuous glucose supply
(which mostly comes from glycogen.)

36. It is regulated by
3 mechanisms -:
1) Allosteric
regulation
2) Hormonal
Regulation
3) Influence of
calcium
Allosteric regulation