METABOLISM! The making and breaking of molecules, a topic of which there is MUCH to say as you can see in this giant wall chart showing just *some* of the interconnected pathways that are taking place microscopically inside of you and me! note: *almost* all of that chart is taking place in your body. Some of it, like photosynthesis only takes place in certain organisms. sorry for mis-speaking

Today I thought I’d talk you through some of the basic fundamental concepts of metabolism, including some easily-confusing topics like how ATP stores energy and what some of the terminology like anabolism, metabolism, and proton mean. Yes, you got me to do another video, but today there are no animations other than text-revealing in figures but I use some of my graphics to illustrate my points. I will also but some brief details here for those who prefer reading. And you can find a super long post on metabolism from a few weeks ago, with lots of info about glycolysis and oxidative phosphorylation here: 

So here goes an intro: Your body’s main form of energy storage and transfer is a molecule called ATP – Adenosine TriPhosphate. Much more on it here, and more details below: but basically it has 3 phosphate groups (phosphorus surrounding by 4 oxygens) stuck together – and each of those phosphates is negatively charged. Since opposites charges repel, they want to get apart from each other so, like clamping together a stiff spring, it takes energy to keep them bonded together (we call this chemical potential energy)- if you let one go (split ATP into ADP + Pi) you release energy, and you can use that energy to do things (like build proteins and stuff)⠀

Your body can take all sorts of different fuel sources (sugars, fats, proteins) and – like using different currencies and denominations to purchase arcade tokens – generate ATP from them, which can be “spent” for all sorts of things in sort of “point of sale” transactions. Making ATP from food is called catabolism. You might be more familiar with the term metabolism – and catabolism’s part of that (the breakdown part), but the term “metabolism” also encompasses anabolism which is the building part. ⠀

One form of catabolism is called glycolysis – which is a process used to break down sugars. But that’s not where the big ATP payout from sugars comes from – it’s just the starting part! Where next? Different methods of ATP-making have different “broker’s fees” – so if you start with the same fuel input you can get different ATP outputs depending on which catabolic process you take. The best bang for your buck (or I guess it’d be more like buck for your bang…) is from aerobic respiration. As the “aerobic” implies, this requires oxygen. In aerobic respiration, most of the energy you produce from sugar doesn’t come from glycolysis – though you still start there, and then go through the citric acid cycle where you can pick up some more – but the big payoff comes from something called “oxidative phosphorylation” (ox-phos) that occurs in “mini-cells” inside your cells called mitochondria (the citric acid cycle happens here too, but glycolysis happens in the general cell interior (cytoplasm). 

The pathways are interconnected so you can take parts from catabolism & use them for building things (anabolism) and different broken-down things can enter pathways at different points – so although I’m gonna talk in terms of glucose (blood sugar) catabolism, different molecules can enter at different points in the process (i.e. most of this doesn’t just apply to glucose!)⠀

ATP’s great, but it’s only part of the story. Another main player in the energy transfer pathway is Nicotinamide Adenine Dinucleotide (NAD⁺) and it’s cousin NADP⁺ (just add phosphate) and their reduced forms NADH & NADPH. But if ATP’s cellular energy money, NADH is more like an energy IOU! NAD comes from vitamin B3 (niacin) and other places and by accepting (in the NAD⁺) form & transporting electrons (in its NADH form), NADH can take energy IOUs in the form of electrons up the electron transport chain of command to the bank boss to demand those energy “arcade tokens” (ATP molecules) in a process called oxidative phosphorylation (ox-phos).  Put these these energy-making processes together: glycolysis, citric acid cycle (TCA) (or other initial breakdown process) to generate NADH and ATP followed by a trip to the mitochondria for oxidative phosphorylation.

Mitochondria are often called the “powerhouses” of the cell because they’re where electron-to-ATP conversion occurs in a process called oxidative phosphorylation which consists of an  electron transport chain (ETC) and chemiosmosis. Basically it consists of molecules (NADH or FADH₂) passing electrons up & up and up the chain of command, pumping out protons as they go, until they reach ATP synthase which is a bit like a hydraulically-powered ATP-making factory – similarly to how waterfalls can be used to turn a wheel, proton “falls” can be used to turn a biochemical motor to get ADP to add a P to make ATP.⠀Put all that together you get an overall energy-making process referred to as cellular respiration. ⠀

note: I’m the Student Ambassador for the IUBMB (International Union of Biochemistry and Molecular Biology) and I talked their president-elect, Alexandra Newton, into giving me one of these giant metabolic charts. Well actually she offered – no arm pulling involved! Thanks again almost-president-Newton! Be sure to follow the IUBMB if you’re interested in biochemistry! They’re a really great international organization for biochemistry.⠀ 

more on topics mentioned (& others) #365DaysOfScience All (with topics listed) 👉   ⠀

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