الأيض وATP

It's professor Dave, let's talk about metabolism and ATP. One of the most incredible things about your body is the way it takes the food you eat and turns it into the energy that allows you to think, and move your body. This is an overwhelmingly complex set of processes which can be collectively referred to as metabolism, which is simply when enzymes transform certain molecules into other molecules through multi-step pathways. So let's learn how this works. First, metabolic pathways can be of two varieties. They can be catabolic, where larger molecules are broken into smaller pieces, releasing energy in the process, or they can be anabolic, where small molecules are assembled into larger one, which requires energy to occur. We can call these ones biosynthetic pathways, because these are the ways that nature synthesizes molecules. The most incredible thing to consider is that while it is tempting to view these pathways as though the enzymes are tiny factory workers, performing their tasks with complete sentience, it is actually the case that every single reaction in the pathway occurs simply because it is thermodynamically favorable. Enzymes recognize their substrate because of electrostatic attractions in the active site and the reactions they catalyze are fundamentally no different than the simple reactions between small molecules that we learned in organic chemistry. There's nucleophile and an electrophile in proximity, so reaction occurs. This means that everything we will discuss is just consequence of the electromagnetic force operating on biomolecules, nothing more than plus and minus. Although these sets of metabolic pathways occur spontaneously in every cell in your body, some of the reactions involved are endothermic, and require energy input to happen. The cellular currency of energy that will be used to facilitate such reactions is called adenosine triphosphate, or ATP. ATP is essentially just an RNA nucleotide. Notice the adenine base, the ribose sugar and phosphate groups. The only difference is that in nucleic acid like RNA, each nucleotide has one phosphate, but here there are three, and it is these phosphate groups that give ATP its energy-storing properties. There is an abundance of negative charge on these phosphates, and we know that like charges repel one another, so there is lot of potential energy stored in this part of ATP, kind of like compressed spring. Just the way compressed spring wants to expand, releasing the stored potential energy and converting it into kinetic energy, these phosphates want to come apart, so when ATP undergoes hydrolysis and transfers one phosphate group to something else during an enzymatic reaction, thus becoming adenosine diphosphate, or ADP, it releases some of that potential energy which can then be converted into the energy needed to promote reaction, or pump ions across membrane against the concentration gradient, or any number of other things. ADP can then be phosphorylated to become ATP again, so this back and forth between the two forms is the method that nature has discovered to provide energy for cellular processes. Next we will look at the specific reactions that have to occur in order to generate energy for our bodies to use. Thanks for watching, guys. Subscribe to my channel for more tutorials, and as always, feel free to email me: