This document discusses intermediary carbohydrate metabolism, specifically glycolysis. It begins with an introduction to glycolysis, noting that it is the degradation of glucose into pyruvate through a series of 10 enzyme-catalyzed reactions. These reactions can occur aerobically, producing pyruvate, or anaerobically, producing lactate. The document then delves into the specific reactions, enzymes, and intermediates involved in both the preparatory and payoff phases of glycolysis. It also discusses the importance of 2,3-bisphosphoglycerate in red blood cells for regulating oxygen release from hemoglobin.

1. INTERMEDIARY METABOLISM
OF CARBOHYDRATES
(DAY:1: INTRODUCTION &
GLYCOLYSIS)
Dr. Ifat Ara Begum
Assistant Professor
Dept. of Biochemistry
Dhaka Medical College
Dhaka

2. INTRODUCTION
It denotes the various biochemical
processes responsible for the
formation, break down and
interconversion of carbohydrates
in living organisms.
The most important carbohydrate
is glucose

3. FATE OF ABSORBED
GLUCOSE

5. METABOLIC PATHWAYS FOR
CARBOHYDRATES
Anabolic pathways: Glycogenesis,
Gluconeogenesis, Lipogenesis,
Uronic acid pathway.
Catabolic pathways: Glycolysis,
Oxidation of pyruvate to acetyl co
A, TCA cycle, Glycogenolysis, HMP
shunt.
Amphibolic pathway: TCA cycle

7. 1. GLYCOLYSIS/ EMBDEN-
MEYERHOF-PARNAS PATHWAY
The stepwise degradation of
glucose (and other simple sugars)
It is unique in that it can function
either aerobically or anaerobically,
depending on the availability of
oxygen and ETC
It is the paradigm (synonym.
model) of metabolic pathways

8. CONTD
This pathway that converts glucose (or
glycogen) into pyruvate in aerobic
condition and lactate in anaerobic
condition.
It is a determined sequence of
ten enzyme-catalyzed reactions.
The intermediates provide entry points
to glycolysis.
most monosaccharides (like
fructose and galactose can be converted
to one of these intermediates.

9. CONTD
Substrate: Glucose/glycogen
Product: Pyruvate (aerobically),
Lactate (anaerobically)
Site: Almost all tissues
Compartment: Cytosol
Nature: Catabolic
Rate limiting enzyme: PFK
Hormonal control: Insulin (+),
Glucagon (-)

10. CONTD
The entire glycolysis pathway can
be separated into two phases:
I. The Preparatory Phase – in which
ATP is consumed and is hence also
known as the investment phase.
The first 5 steps are regarded as
preparatory phase
II.The Pay Off Phase – in which ATP
is produced. The last 5 steps are
regarded as pay off phase

11. I) PREPARATORY PHASE

12. II) PAY OFF PHASE

14. ANAEROBIC GLYCOLYSIS
Occurs in cells lack of
mitochondria like RBC, leucocytes,
renal medulla, lens, cornea.
Here, pyruvate is reduced by
NADH to lactate by LDH.
The NADH utilized in this step is
obtained from the reaction
catalyzed by glyceraldehydes 3
PO4 dehydrogenase .

15. CONTD
C
C
CH3
O−
O
O
C
HC
CH3
O−
OH
O
NADH + H+
NAD+
Lactate Dehydrogenase
pyruvate lactate

16. CONTD
The formation of lactate allows
NAD to be reused by
glyceraldehydes 3 PO4-DH, so that
glycolysis proceeds even in the
absence of O2.
The occurrence of uninterrupted
glycolysis is very essential in
skeletal muscles during strenuous
exercise where O2 supply is
limited.

17. CONTD
Lactate serves as a fuel source for
cardiac muscle as well as brain
neurons.
Astrocytes, which surround and
protect neurons in the brain,
ferment glucose to lactate and
release it.
Lactate taken up by adjacent
neurons is converted to pyruvate
that is oxidized via Krebs Cycle.

18. BASIC PROCESSES INVOLVED IN
GLYCOLYSIS

19. WHY G-6-P IS FORMED?

21. FATE OF G-6-PO4
It is an important compound at the
junction of several metabolic
pathways:
Glycolysis
Gluconeogenesis
Pentose phosphate pathway
Glycogenesis
Glycogenolysis

24. LUEBERING-RAPOPORT
PATHWAY
It is a biochemical pathway in mature
erythrocyte involving the formation of
2.3-bisphosphoglycerate and which
regulates oxygen release from Hb and
delivery to tissues.
It is also called Luebering-Rapoport
shunt.
2,3-BPG combines with Hb and reduces
affinity for O2.

25. CONTD
The normal glycolytic pathway
generates 1,3-BPG, which may be
dephosphorylated by phosphoglycerate
kinase (PGK), generating ATP
But
it may be shunted into the Luebering-
Rapoport pathway,
where bisphosphoglycerate
mutase catalyzes the transfer of a
phosphoryl group from C1 to C2 of 1,3-
BPG, giving 2,3-BPG.

26. CONTD
2,3-BPG, the most concentrated
organophosphate in the
erythrocyte, forms 3-PG by the
action of bisphosphoglycerate
phosphatase.
The concentration of 2,3-BPG varies
inversely with the [H+], which is
inhibitory to catalytic action of
bisphosphoglyceromutase.

28. IMPORTANCE OF 2,3-BPG
When 2,3-BPG binds to deoxyhemoglobin (The
form of hemoglobin without oxygen), it acts
to stabilize the low oxygen affinity state (T
state) of the oxygen carrier.
By selectively binding to deoxyhemoglobin, 2,3-
BPG stabilizes the T state conformation,
making it harder for oxygen to bind
hemoglobin and more likely to be released to
adjacent tissues.
2,3-BPG is part of a feedback loop that can help
prevent tissue hypoxia in conditions where it is
most likely to occur.

29. CONTD
Conditions of low tissue oxygen
concentration such as high altitude (2,3-
BPG levels are higher in those acclimated
to high altitudes), airway obstruction,
or congestive heart failure will tend to
cause RBCs to generate more 2,3-BPG in
their effort to generate energy by allowing
more oxygen to be released in tissues
deprived of oxygen.
Ultimately, this mechanism increases
oxygen release from RBCs under
circumstances where it is needed most.

30. CONTD
This release is potentiated by the Bohr
effect in tissues with high energetic
demands.
Bohr effect is another useful way to
solve the affinity problem of the
hemoglobin, and it is related to the pH
and the CO2.
It’s important to highlight that the
behavior of myoglobin doesn’t work in
the same way, as 2,3-BPG has no effect
on it.