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Researchers link digestive tract Researchers link digestive tract cancer to cell oxygen deficiency The enzyme succinate dehydrogenase processes oxygen to supply energy to the cell. It is embedded in the outer membrane of mitochondria, cellular structures which supply energy to the cell. The researchers found that some patients with GIST (Gastrointestinal stromal tumor) had mutations in the genes for the B and C subunits of the enzyme. Cancer of the digestive tract is linked to a shutdown in an enzyme – succinate dehydrogenase, that helps supply oxygen to cells. Let's explore more about cellular respiration and its importance.

Learning Objectives

After completing the topic, the student will be able to:

  • Predict what happens if cell does not undergo cellular respiration and appreciate the importance of this phenomenon.
  • Define cellular respiration and understand the basic principles of it.
  • Understand how catabolic pathways yield energy by oxidizing organic fuels.
  • Define and describe the terms – glycolysis, citric acid cycle and electron transport chain.
  • Understand and explore the basic principles of oxidation and reduction (redox reactions).
  • Examine how glycolysis harvests chemical energy by oxidizing glucose to pyruvate.
  • Evaluate how citric acid cycle completes the energy‐yielding oxidation of organic molecules.
  • Examine how during oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis.
Living cells Living cells require energy from outside sources The giant panda in this figure obtains energy for its cells by eating plants
Cellular Respiration

Cellular respiration is the set of the metabolic reactions and processes that occurs in the cells of living organisms for conversion of biochemical energy from nutrients into adenosine triphosphate (ATP), and then release of waste products.

The reactions of respiration include catabolic reactions, which break large molecules into smaller ones, releasing energy. Respiration is one of the key ways where a cell gains useful energy for its cellular activity. Cellular respiration is considered an exothermic redox reaction chemically, but technically, cellular respiration is a combustion reaction.

We all need energy to function and we get this energy from food we eat. The most efficient way for cells to harvest energy stored in food is through cellular respiration, a catabolic pathway for the production of adenosine triphosphate (ATP).

ATP, a high energy molecule, is expended by working cells. Cellular respiration occurs both in prokaryotic cells and eukaryotic cells. Living cells require transfusions of energy from outside sources to perform their many tasks– for example, assembling polymers, pumping substances across membranes, moving and reproducing.

Cellular respiration- Citric acid cycle One of the key pathways in Cellular respiration- Citric acid cycle Citric acid cycle – The biochemical hub of the cell
Mechanism of cellular respiration

The energy stored in the organic molecules of food ultimately comes from the sun. During process of respiration, the whole of energy contained in respiratory substrates is not released all at the time. It is released slowly in several steps of reactions controlled by different enzymes.

As we know, important life processes, such as synthesis of proteins, fats and carbohydrates, require a certain expenditure of energy. Where does this energy come from, how is it stored, and how is it made available to the living cell, are some of the questions, which are to be answered by process of respiration. The reaction that occurs in common respiration of glucose may be summed up as follows:

Glucose + Oxygen Carbon Dioxide + Water + Energy

C6H12O6+6O2 6CO2+6H2O+Energy

In this chapter, we consider how cells harvest the chemical energy stored in organic molecules and use it to generate ATP, the molecule that drives most cellular work. After presenting some basics about respiration, we will focus on the three key pathways of respiration: Glycolysis, the Citric acid cycle, and oxidative phosphorylation.