Basics of human metabolism

I found quite good flow diagram in the book Principles of anatomy and physiology, 7-th edition. It covers the  basics of metabolism, mainly the view of certain key molecules involved in it. There could be dozens of similar ones, which would involve different molecules on different pathways, because in the essence, the flow diagram is about the depicting one or more pathways of certain molecules in the body.

The metabolic pathway is defined as a series of chemical reactions that take place somewhere in the body. It can be cyclical or straightforward, and it can be executable in one direction or in both directions. The total sum of all metabolic pathways in the body is called metabolic network. 

So with the pathways, they have their starts and ends, and maybe even some milestones and/or dimension changes along the way. Good flow diagram brings all this information in simple, graphical way of covering the knowledge about human body, and systems involved within it.

This diagram focuses on chemical pathways of food that breaks down to proteins, carbohydrates and fats. Their further broke-down equivalents are amino acids, glucose and triglycerides respectively. But mainly it focuses on three key molecules, which serves as intermediates in human metabolism, and those are Acetyl co-enzyme A, Pyruvic acid, and Glucose 6-phosphate.

The last one is the ring of glucose with addition of phosphate group on sixth carbon in the chain. This altered glucose molecule, also called phosphorylated glucose, can be then used for energy into Krebs cycle, energy for DNA production, or to convert it to Pyruvic acid, the second intermediate molecule.

This one, in turn, can be used for production of alanine amino acid, or by aerobic and anaerobic reactions, to energy (ATP) with lactic acid, or to convert it to another intermediate molecule - Acetyl co-enzyme A. And this molecule can enter Krebs cycle, or to be converted to ketone bodies, cholesterol, or fatty acids. I hope it's all clear from the picture.

Each component or even word in this diagram could be enough to write about for the separate post. In whole, this is the representation of human metabolism, or at least one possible side from which it can be viewed. Plus the metabolism itself could be topic for whole books, and it is. It can be divided by particular substances into fat metabolism, protein metabolism, or carbohydrate metabolism. Or simply the metabolism of any other substance with its own characteristic pathway and chemical changes along the way.

PROCESSES

Some parts of diagram, or words, describe a process, like for example glycolysis, aerobic reactions, or Krebs cycle. So in this case, glycolysis would mean breaking down of glucose rings down to the Pyruvic acid. Aerobic reactions would be those that require oxygen for successful execution, and anaerobic reaction are on the other hand those that don't, and can work without the oxygen.

Krebs cycle represent many different reactions involving many different substances. But just to give you a hint, there is 9 steps or chemical reactions in cyclic manner, which starts and ends with the same substance - Acetyl co-enzyme A. Those then involve 9 different enzymes, 9 substrates and end products for each step. Again, each of these processes could be picked up and fill the text for the whole chapter.

So the topic is complex, and thank God there are such a things as simplifiers of it in the form of flow diagrams. The way I see it, the understanding of processes within our bodies is priceless and irreplaceable. Moreover, it cost nothing these days as there are tons of websites and library books dedicated to bringing the light on the topic. So you can watch, read, think, learn, understand and I'll see you next time around.

ATP - cell's rechargeable battery

ATP, or adenosine triphosphate, could be put in an analogy of a mini rechargeable battery that cells are using to feed the energy for many different processes within the body. It contains three basic parts.  The adenine molecule, sugar molecule (ribose), and three phosphate groups - which are really one phosphorus atom surrounded by four oxygen atoms.

The energy we talk about here is in the form of high-energy bond between those phosphate groups. When they separate, the energy is released, and then used. To put back on that last phosphate group, and therefore recharging it, it requires the energy which the body needs to get from the food we eat. This principle is explained on this picture.

 

When you take away that last phosphate group, you create the molecule called ADP - adenosine diphosphate (only 2 phosphate groups). That would be the representation of empty battery in this analogy. Rotating those two chemical reactions, then provides the means of an empty and full battery, which are moving from the place of using up to the place of recharging it. And back again and again cyclically.

 

For example, one molecule of glucose can bring up the production of as much as 38 ATPs, provided there is an oxygen present in the process. This is called an aerobic respiration. In the absence of oxygen, however, only two ATPs can be made - the process called anaerobic respiration. For more detailed view of how and where ATPs are made in the body, this flow diagram does a great job.

 

Here you can see that some ATPs are made in mitochondrion, some in the cytosol, and some in the gut - where happens the basic breaking down of food from the meals we eat. In the gut, the proteins, complex carbohydrates, and lipids are digested into the final products, which are in form of amino acids, glucose, fatty acids, and glycerol respectively.

 

First round of freshly made ATPs is happening in the cytosol, where the glucose and the glycerol are used for creating it. Cytosol is semi-fluid matrix inside of the cells, in which all the organelles are suspended. Mitochondrion is a special organelle for making ATPs and many other functions. There in the middle, there is a cyclical sequence of chemical reactions called TCA, or Krebs cycle (or citric acid cycle). This represents the biggest system for ATP production in the body.