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Biochemistry Free and Easy by Kevin Ahern & Indira Rajagopal

Biochemistry Free and Easy by Kevin Ahern & Indira Rajagopal

Welcome to Biochemistry Free and Easy. As biochemistry instructors, we are always delighted when anyone shows an interest in our favorite subject. Helping students understand and enjoy biochemistry is our motivation for writing this book. It is not our intention to provide a comprehensive account of the chemical basis of life. Instead, we have tried to help students understand this fascinating subject by focusing on some key topics and concepts. This pared-down approach can be helpful for novices who might otherwise lose sight of important organizing principles in a sea of detail. The electronic format has also allowed us to provide multimedia links, in the form of video lectures and biochemistry songs to help students learn the subject. Best of all, this format makes it practical for us to distribute the book at no cost to anyone who wishes to learn basic biochemistry.

Biochemistry is a relatively young science, but the rate of its expansion has been truly impressive. This rapid pace of discoveries, which shows no signs of slowing, is reflected in the steady increase in the size of biochemistry text books, most of which top a thousand pages and undergo revisions every couple of years to incorporate new findings. These full-scale texts offer an enormous amount of information and serve as invaluable resources. Those who need the greater level of detail and broader coverage that these books provide have many choices available in any good bookstore.

Cells: The Bio of Biochemistry 

Biochemistry happens inside organisms and possibly, the most obvious thing about living organisms is their astounding diversity. If living things are so varied, it seems reasonable to ask whether their chemistry is, too.

The invention of the microscope opened up a whole new world of microscopic organisms while also providing the first clue that living organisms had something in commonall living things are made up of cells. Some cells are “lone rangers” in the form of unicellular entities, such as bacteria and some protists. Cells are also the building blocks of more complex organisms (like humans, wombats, and turnips).

As increasingly powerful microscopes became available, it was possible to discern that all cells fell into one of two types- those with a nucleus and other sub-cellular compartments like mitochondria and lysosomes, termed eukaryotes, and those that lack such internal compartmentation, the prokaryotes. Some eukaryotes, such as yeast, are unicellular, while others, including animals and plants are multicellular. The prokaryotes may be divided into two very broad categories, the bacteria and the archaeans.

Living organisms are made up of cells, and cells contain many biochemical components such as proteins, lipids, and carbohydrates. But, living cells are not random collections of these molecules. They are extraordinarily organized or "ordered". By contrast, in the nonliving world, there is a universal tendency to increasing disorder. Maintaining and creating order in cells takes the input of energy.

Without energy, life is not possible. It is therefore important that we consider energy first in our attempt to understand biochemistry. Where does energy come from? Photosynthetic organisms can capture energy from the sun, converting it to chemical forms usable by cells. Heterotrophic organisms like ourselves get our energy from the food we eat. How do we extract the energy from the food we eat?

Oxidative Energy

The primary mechanism used by non-photosynthetic organisms to obtain energy is oxidation and carbon is the most commonly oxidized energy source. The energy released during the oxidative steps is “captured” in ATP and can be used later for energy coupling (see below). The more reduced a carbon atom is, the more energy can be realized from its oxidation. Conversely, the more oxidized a carbon atom is, the more energy it takes to reduce it.

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