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Topics in Depth

The Theme of Order in Energy Flow and Enzymes

What makes your cells amazing is that they use heat energy to produce order. See what we did there? Brought the biology back full circle—that's Shmoop. One thing that will become clear as we investigate different topics in biology is that a cell’s precious life is completely dependent on the transfer of one type of energy to another. The main chemical energy carrier of the cell is ATP, short for adenosine triphosphate, and cells convert energy from ATP to many things, including

  • Mechanical energy to move organelles (read: the machinery of the cell)
     
  • Electrical energy to move ions against a concentration gradient
     
  • Thermal energy to release heat

In fact, one of the most important energy transfer events, perhaps the most important transfer event, for life on our planet is the biological process called photosynthesis, which occurs in most plants, algae, and some bacteria. Photosynthesis is the process wherein light energy from the sun is converted into chemical energy to make organic compounds, or food (mainly sugars), for the organism.

Behold, the different types of energy in context! We think our friend needs to work on his upper body strength.

Photosynthetic organisms make their own nutrients, but animals like us depend completely on taking in organic compounds from our environment (delicious food). Eating isn’t that bad, right? In fact, it’s quite a tasty experience as long as the food is good. But, our need to find food outside our bodies means that photosynthesis also fuels our existence, albeit a little less directly.

Through a fundamental life process called respiration, organisms, including plants, obtain their energy from the organic compounds they consume. To do this, said organisms allow their carbon and hydrogen compounds to combine with oxygen in the environment to produce carbon dioxide (CO2) and water (H2O). This actually happens in numerous steps through a number of biochemical reactions collectively known as a cell’s metabolism. These different biological reactions can be grouped together into pathways. A key feature of a metabolic pathway is that each intermediate is used in the next step, which eventually results in the production of the final product.

A pathway can be thought of as individual reactions that each work toward a common goal. Take, for example, this lump of brown clay.

What an adorable little monkey.

Metabolism can be further divided into two opposing biological processes called anabolism and catabolism. Catabolism refers to the processes, or catabolic pathways, by which cells break down food into smaller molecules, in turn releasing energy. This energy is used in anabolism, or anabolic pathways, to build new and larger molecules. More specifically, the smaller molecules generated in catabolic pathways are used in anabolic pathways as building blocks to create large molecules such as proteins, lipids, and DNA.

In this way, anabolic and catabolic pathways are interdependent. During the chemical reactions that comprise a cell’s metabolism, electrons are transferred from one chemical reaction to another.

  • When electrons are removed from one biological molecule, that molecule is said to be oxidized
  • When electrons are transferred to a biological molecule, that molecule is said to be reduced.

All in all, together anabolic and catabolic pathways generate the order that drives life. We will discuss metabolic pathways in further detail, as well as the enzymes that make them possible, later on in this unit. We bet you can't wait.

Here is a simple demonstration of how food molecules, cell components, and biological molecules all relate through catabolic and anabolic pathways.

Is anybody else getting a Perfection flashback after scoping out those particle synthesis building blocks? Just us then. Great.

Ready for a random question? Good. How do the processes going on inside a cell contribute to the rest of the universe? We have just informed you that when you eat your double bacon cheeseburger, your body uses catabolic pathways to take the energy from the food and convert it into useful chemical molecules and cellular order. It turns out that some of this energy from the breakdown of food is also released back into the environment as heat, CO2, and H2O, which in turn adds to the increasing disorder of the universe. Didn't see that coming, didya? Universe, 2, You, 0.

Brain Snack

Some organisms possess the ability to convert chemical energy into light energy. An example? The firefly.

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