CHNOPS are the most common elements in living organisms. Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, and Sulfur. These elements make up 98% of living matter on Earth. Why should you study CHNOPS? If you understand the chemical behavior of these 6 elements, you’ll understand almost all of biochemical reactions. CHNOPS make up 99.7% of bacteria. And they make up 97.9% of humans. It takes just 4 elements: Oxygen, Carbon, Hydrogen, and Nitrogen - to make up 96.2% of humans. Let’s start with CARBON. Carbon is about 18% of humans, by mass. We say Earth has carbon-based life forms. Why do we say that? Because of the carbon backbone. Carbon makes up the skeleton of most biological molecules, including Proteins, carbohydrates, lipids, and nucleic acids. Carbon has 4 valence electrons - this lets it make a variety of bonds. 4 single bonds, 2 double bonds, a single bond and a triple bond… So, as a result, you can make lots of different stable structures. Imagine we were talking about legos, or tinker toys. If you can join together a piece in 4 different ways, you could make a lot more structures than something with only one connection or two connections. Silicon has similar chemical behavior. It also has 4 valence electrons. So maybe….we might find a planet one day that had a slightly different start in life, and wound up with silicon-based life forms. Now, HYDROGEN. Hydrogen makes up about 10% of humans. We find Hydrogen in water, H2O, so it’s not surprising it makes up so much of living matter. We are about 60% water. Some organisms are as much as 90% water. We’ll address this idea - how vital water is to life - in another video. Hydrogen is especially active in its ionic form, H+. Acids increase H+ concentration, while Bases decrease H+ concentration. So Hydrogen plays an important part in acid-base behavior, which is involved in a lot of biochemical reactions. NITROGEN. This is an essential component of DNA - think of those nitrogenous bases that make up the rungs of the DNA ladder. Also be on the lookout for nitrogen in amine groups, like on the ends of amino acids. These amine groups confer basic (as opposed to acidic) behavior. Nitrogen makes up about 3% of humans. Nitrogen is also especially abundant in the air that we breathe (about 78%). OXYGEN. Oxygen is also found in water, H2O, so you’d expect a lot of oxygen in living matter. Oxygen makes up about 65% by mass of the human body. We also breathe oxygen, O2. In chemistry, Oxygen is important in oxidizing reactions. It’s going to grab electrons and become negatively charged. Some people think antioxidants are important to slow down our internal oxidizing, or rusting, if you will. PHOSPHORUS is found in the backbone of DNA. Remember the backbone goes “sugar-phosphate-sugar-phosphate.” We also find those phosphate groups in ATP, which is the key form of energy currency in biochemical reactions. Phosphorylation and dephosporylation events are really important in biochemistry. This is often used as a signal or as a trigger for conformation changes in biological molecules. We also find phosphates in phospholipids, which are an important component of cell membranes. Phosphorus makes up about 1% of humans. And finally, SULFUR. Sulfur is found in two amino acids - cysteine and methionine. You’ll learn that amino acids string together to form proteins, and these are 2 of the 20 amino acids. The sulfurs from these amino acids tend to bind together, forming disulfide bridges. This is part of what holds a folded protein together in its final 3D shape. A few organisms use selenium instead of sulfur. But for most organisms, it’s a fundamental part of what makes us. 0.25% of humans are sulfur. Another significant element for humans is CALCIUM. Calcium makes up 1.5% of the human body - almost all of it found in mineral compounds in bones and teeth. But its chemical behavior as an ion is where we see its most dramatic functions, acting - for instance, in neuron signalling and muscle contraction. All the elements used in very small amounts are called TRACE ELEMENTS. These include: Iron - we need that for hemoglobin Sodium and potassium, important as electrolytes, used in signalling/ neuron function. Iodine, needed for your thyroid hormones. I think the details of all the trace elements probably belong in their own video. Next we’ll look at how these elements interact with each other, forming bonds and making the great variety of biological molecules. Here’s a challenge for you - name a biological molecule that contains only the elements in CHNOPS. For example, any given sugar is made up of Carbon, Hydrogen, and Oxygen. Like glucose: C6H12O6. Your job is to find another molecule containing only CHNOPS or a subset of those elements, and write it in the comments. 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