Metabolism

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Metabolism

I . Introduction

Now that you are familiar with the structure of prokaryotic cells , we can discuss the activities that allow these microbes to thrive . The life support activity of even the most structurally simple organism involves a large number of complex biochemical reactions . Most , although not all of the biochemical processes of bacteria also occur in eukaryotic microbes and in the cells of multicellular organisms , including humans However , the reactions that are unique to bacteria are fascinating because they allow microorganisms to

do things we cannot do (Neidhardt Holde , 1990 . For example , some bacteria (the chemoautotrophs ) can grow on diets of such inorganic substances as carbon dioxide , iron , sulfur hydrogen gas , and ammonia

This examines some representative chemical reactions that either produce energy (the catabolic reactions ) or use energy (the anabolic reactions ) in microorganisms . We will also look at how these various reactions are integrated within the cell

II . Discussion

A . Catabolic and Anabolic Reactions

We use the term metabolism to refer to the sum of all chemical reactions within a living organism . Because chemical reactions either release or require energy , metabolism can be viewed as an energy-balancing act . Accordingly , metabolism can be divided into two classes of chemical reactions - those that release energy and those that require energy . In living cells , the chemical reactions that release energy are generally the ones involved in catabolism , the breakdown of complex organic compounds into simpler ones . These reactions are called catabolic , or degradative , reactions . On the other hand , the energy-requiring reactions are mostly involved in anabolism , the building of complex organic molecules from simpler ones . These reactions are called anabolic or biosynthetic reactions (Neidhardt Holde , 1990 Anabolic processes often involve dehydration synthesis reactions (reactions that release water ) and require energy to form a new chemical bonds . Examples of anabolic processes are the formation of proteins from amino acids , nucleic acids from nucleotides , and polysaccharides from simple sugars . These biosynthetic reactions generate the materials for cell growth . Catabolic reactions are generally hydrolytic reactions (reactions that use water to break chemical bonds . Chemical bonds store energy when they are broken , chemical energy is released . An example of catabolism occurs when cells break down sugars into carbon dioxide and water

Catabolic reactions furnish the energy needed to drive anabolic reactions . This coupling of energy-requiring and energy-releasing reactions is made possible through the molecule adenosime triphospahte (ATP . ATP stores energy derived from catabolic reactions and releases it later to drive anabolic reactions and perform other cellular work . A molecule of ATP consists of an adenine , a ribose , and three phosphate groups . When the terminal phosphate group is split from ATP , adenosine diphosphate (ADP ) is formed , and energy is released to drive anabolic reactions . Using

to represent a phosphate group , we can write this reaction as (ATP - ADP

energy . Then , the energy from catabolic reactions is used to combine ADP and a

to resynthesize ATP (ADP

br energy - ATP . Thus , anabolic reactions are coupled to ATP breakdown and...