13 topics with concise reviews: definitions, key facts, and class questions.
Energy metabolism is the foundation of biochemistry. This section covers how the cell extracts energy from chemical bonds of nutrients and stores it as the universal "currency" — ATP. We will break down the entire process: from specific and common catabolic pathways to the grand finale in the mitochondria.
Here are the key stages of cellular energy supply: pyruvate oxidative decarboxylation, the tricarboxylic acid (TCA) cycle, and anaplerotic reactions. You will learn how the electron transport chain (ETC) functions, what respiratory control is, and how uncouplers or respiratory chain inhibitors can halt ATP synthesis, redirecting the energy toward thermogenesis.
In classes and exams, the most strictly tested topics are the enzymes and coenzymes of the PDH complex, memorizing the reactions of the Krebs cycle, and the mechanisms of oxidative phosphorylation. Pay special attention to the targets of cyanides and other poisons (ETC inhibitors), as well as brown adipose tissue — these are favorite questions of instructors to test real understanding of the processes.
As a result of dissimilation reactions, complex substances are broken down into simplest compounds. The main ones are carbon dioxide, water, and nitrogenous waste products such as urea.
What is oxidative phosphorylation?
This is the process of synthesizing ATP molecules from ADP and inorganic phosphate, driven by the energy released during the stages of tissue respiration.
Where are the enzymes of the electron transport chain localized?
All major protein complexes of the respiratory chain are densely embedded in the inner mitochondrial membrane, while most dehydrogenases are located in the mitochondrial matrix.
What acts as the main rate-limiting factor of cellular respiration?
The main limiting factor is the concentration of ADP. It is its increase that triggers accelerated NADH oxidation and oxygen consumption.
Why does poisoning with uncouplers accelerate oxygen consumption?
In response to a drop in ADP levels, the body attempts to compensate for the energy deficit. To do this, it maximally accelerates substrate catabolism and the work of the respiratory chain, which requires increased oxygen uptake, although ATP is still not synthesized.
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