Bioenergetics

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MBM 110: MEDICAL
BIOCHEMISTRY
Lecture 1;
-Bioenergetics and Biological oxidation
Lecturer: Dr. Biwott Felix K.
Contacts: Email; fekiott@gmail.com
Mobile No: 0697-529-032
KIUT
1st Semester, 2023/2024

2. Bioenergetics
• Also known as biochemical thermodynamics
• It deals with the study of energy changes in living cell
(transfer and utilization).
• The reactions are broadly classified as exergonic
(energy releasing) and endergonic (energy
consuming).
• It is concerned with the initial and final states of
energy component of the reactants and not the
mechanism of chemical reactions.
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• The energy actually available to do work (utilizable) is
known as free energy.
• Changes in the free energy (△G) are valuable in predicting
the feasibility of chemical reactions.
• The reactions can occur spontaneously if they are
accompanied by decrease in free energy.
• During a chemical reaction, heat may be released or
absorbed. Enthalpy (△H) is a measure of the change in
heat content of the reactants, compared to products.
• Entropy (△S) represents a change in the randomness or
disorder of reactants and products. Entropy attains a
maximum as the reaction approaches equilibrium.
Free energy

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• Hundreds of reactions simultaneously take place in a
living cell, in a well-organized and integrated manner.
• The entire spectrum of chemical reactions, occurring
in the living system, are collectively referred to as
metabolism.
• A metabolic pathway (or metabolic map) constitutes
a series of enzymatic reactions to produce specific
products.
• The term metabolite is applied to a substrate or an
intermediate or a product in the metabolic reactions.
Metabolism

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• Broadly divided into two categories
1. Catabolism : The degradative processes concerned with
the breakdown of complex molecules to simpler ones,
with a concomitant release of energy.
2. Anabolism : The biosynthetic reactions involving the
formation of complex molecules from simple precursors.
Metabolism

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• It traps the energy of the biomolecules in the form of ATP
and generates the substances (precursors) required for the
synthesis of complex molecules.
• Catabolism occurs in three stages
1. Conversion of complex molecules into their building
blocks : Polysaccharides are broken down to
monosaccharides, lipids to free fatty acids and glycerol,
proteins to amino acids.
2. Formation of simple intermediates : The building
blocks produced in stage (1) are degraded to simple
intermediates such as pyruvate and acetyl CoA.
Catabolism

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3. Final oxidation of acetyl CoA : Acetyl CoA is completely
oxidized to CO2, liberating NADH and FADH2 that
finally get oxidized to release large quantity of energy (as
ATP). Krebs cycle (or citric acid cycle) is the common
metabolic pathway involved in the final oxidation of all
energy-rich molecules. This pathway accepts the carbon
compounds (pyruvate, succinate etc.) derived from
carbohydrates, lipids or proteins.
Catabolism

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Stages for catabolism

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Anabolism
• For the synthesis of a large variety of complex
molecules, the starting materials are relatively few.
These include pyruvate, acetyl CoA and the
intermediates of citric acid cycle.
• Besides the availability of precursors, the anabolic
reactions are dependent on the supply of energy (as
ATP or GTP) and reducing equivalents (as NADPH +
H+).
• The anabolic and catabolic pathways are not reversible
and operate independently.

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Types of metabolic reactions
• The biochemical reactions are mainly of four types
1. Oxidation-reduction.
2. Group transfer.
3. Rearrangement and isomerization.
4. Make and break of carbon-carbon bonds.
• These reactions are catalysed by specific enzymes—
more than 2,000 known so far.