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Introduction
Before we get into the workings of the cell, we need to know a little bit of chemistry. It's only a little bit, but it is super interesting! (I know you guys are probably giving me a bruh face right now because I'm the one who made the macromolecules page before this one, but I was really excited!!! Let me live my life, haters!)
We'll start our unit with the absolute basics:
Matter is anything that has mass and takes up space
Mass is how much matter an object has
Weight is the effect of gravity on an object
You probably already know that, so let's move on to compounds and molecules. Compounds are bonds of two or more atoms from different elements that are chemically bonded in a fixed ratio. Molecules are two or more atoms chemically bonded together.
Now, you're going to get mad at me, because I said we would be talking about some chemistry... but I also want to tell you about the elements in the human body. So... mwahhahahhaha
Elements of the Human Body
So I didn't want to shamelessly steal from the internet or my biology textbook again so here are all the elements in a list.
Oxygen: 65%
Carbon: 18.5%
Hydrogen: 9.5%
Nitrogen: 3.3%
Calcium: 1.5%
Phosphorus: 1%
Potassium: 0.4%
Sulfur: 0.3%
Sodium: 0.2%
Chlorine: 0.2%
Magnesium: 0.1%
Trace elements: <0.01%
For your information, trace elements are elements that are present in very small quantities, but are vital to your body. Difficiencies in trace elements can be fatal.
Ok guys we can finally get on to actual atoms now 😓
Atoms
In the periodic table, atoms are organized in many ways. Check out the picture to the right. The C in the middle is the symbol for Carbon, which, if you were paying attention, actually makes up 18.5% of our bodies.
Carbon's atomic number is 6. This means it has 6 protons in its nucleus. Its mass number is the sum of the protons and neutrons in its nucleus, which is typically 12. Carbon's atomic mass is the mass of the entire atom. It is usually almost equal to the mass number, with a small amount of weight added from the electrons. Carbon's mass number is 12.010.
Atoms are made of three different kinds of particles - protons, neutrons, and electrons. Protons carry a positive charge and reside in the nucleus of the atom. Protons are like the identity of an element. You can't take a proton away without changing the element itself (on that note, removing protons would involve splitting the nucleus, which is extremely difficult to do). By this, I mean that removing a proton from uranium would turn it into protactinium (which happens in radioactive decay, since uranium is extremely unstable). The element itself changes with the amount of protons.
Neutrons, like protons, sit in the nucleus of an atom. However, they carry no charge, and atoms can have varying numbers of neutrons without changing the identity of the element. Such atoms are known as isotopes - elements with the same number of protons but different numbers of neutrons. Isotopes are marked by their mass number. For example, carbon's isotopes are Carbon-12 (the most common), Carbon-13, and Carbon-14 (used for radiocarbon dating).
Electrons are found in the electron cloud, and they have a negative charge and weigh very little. They orbit the nucleus in shells, which have limits on how many electrons they can store. Electrons cannot reside between shells. The first shell can have 2 electrons. The second shell can have 8, and the third shell can have 8 as well. Usually, atoms have the same number of electrons and protons, but deficiencies or excess amounts of electrons creates ions - atoms with a net charge. Electrons are able to more easily leave atoms than the particles in the nucleus, and every atom wants their valance shell (the outermost shell of an atom) to either be full or empty. Hence, atoms like lithium and sodium are always trying to lose their valance electrons and atoms like fluorine and chlorine are always trying to gain extra valance electrons. Such elements are therefore more reactive. However, atoms like radon that reside in the noble gas column of the periodic table are hardly reactive at all. Their valance shells are full and they are happy and content.
Look at how much you've learned, midget! Though I'm probably shorter than you - I'm only 5'2" and my self-esteem is even shorter 🥲
But you still have MUCH to learn, and you are still pretty stupid. So let's talk about bonds to make you slightly less stupid.
Covalent, Ionic, and Hydrogen Bonds
Covalent bonds are bonds where two or more electrons are shared among atoms. The measure of this attraction for these shared electrons is known as electronegativity. Covalent bonds are very strong bonds between atoms. There are single and double covalent bonds, which is pretty self explanatory - single covalent bonds have a single pair of electrons being shared (they are noted like this: H --- H) while double covalent bonds have two pairs of electrons being shared (O == O). Covalent bonds are the bonds that hold water molecules together - and this is quite a relief, since covalent bonds give water its polarity - a large reason why water is able to support life so well. Polar molecules have an unequal distribution of charges. Basically, the shared electrons spend more time with one atom than the other, creating a net charge on the molecule. Nonpolar molecules are the opposite - they have no net charge and the electrons are shared equally. Water, without its polarity, would not be the solvent of life, so we should be very grateful that this is so. In the cell organelles page, I'll talk more about this in the cell membrane section - it's REALLY REALLY cool!1!!!!
Alright, ionic bonds are next. They are also very strong bonds. In ionic bonds, one atom gives an electron to another atom. This creates two ions that are held bonded together by their charges. Remember the sodium and chlorine atoms I mentioned earlier? If you remember, sodium wants to lose its electron while chlorine wants to gain an electron. That's crazy, it's almost like they belong together. It's almost like they're about to turn into table salt 🤯. Sodium (Na) donates its extra electron to chlorine (Cl). They're both happy now, but they still have slightly opposing net charges. Because they helped each other accomplish their dreams, they decide to stick together and bond, creating NaCl, or table salt. Who would've guessed?! Either way, a fascinating component of NaCl is that both of the properties of Na and Cl are changed completely after they bond. Na is a very reactive metal. It's a good conductor of electricity and heat. It's soft and not very dense - it even floats on water. Cl is a yellowish-green gas that reacts violently with hydrogen under light conditions to form hydrochloric acid (which is in your stomach right now). That's wild, bro. Salt is like the most tame substance ever - sometimes I pour it in my hands and lick it like a horse because I like the taste. If you tell me you haven't done that before, you're either in denial and thought you were eating heavily refined sugar or you're a liar.
Alright guys, onto the last bond I'll talk about today. Unlike the other two, this is actually a very weak but very important bond called a hydrogen bond. A great example of this is water. Hydrogen bonds are formed by the force of attraction between a hydrogen molecule with a partial positive charge and another atom or molecule with a particle or full negative charge. I showed a picture of this below. However, I'll go into more depth on it a little bit later on this page!
Water's Life Supporting Properties
Water is an incredible molecule. It is vital to life on Earth, and that is for many reasons. I will go through those reasons with you right now.
Hydrogen Bonds make liquid water cohesive.
Cohesion is the tendency of a molecules of the same kind to stick together. Due to hydrogen bonds, water is cohesive - it sticks to itself. (Water is also adhesive, which is the clinging of one substance to another. Be careful not to confuse them). Cohesion and adhesion are the reasons that water can rise slightly higher than the surface of its cup. Adhesion is also the reason why water rises when it is in contact with a solid.
Water's hydrogen bonds moderate temperature.
Thermal energy is the movement of molecules, and heat is the transfer of thermal energy from one body to another. Temperature is simply heat intensity. Basically, when water evaporates, the surface it leaves behind is cooled (called evaporative cooling). This enables water to moderate temperature.
Hydrogen bonds allow ice to float.
Ice floats because it is less dense than water. In liquid water, hydrogen bonds constantly break and reconnect. The molecules have too much energy. They are much closer to each other. However, when water turns into ice, the molecules have much less energy. The hydrogen bonds stabilize and organize the water into tiny hexagonal crystals, which is less dense than liquid water - enabling ice to float. While this doesn't seem all too significant at first, it's actually vital to life, since it allows to top of a body of water to freeze before the bottom. This insulates the bottom, which is why fish can survive if the top of a pond is frozen over. If this did not happen, ice would freeze and sink to the bottom, freezing the pond from the bottom up, making it very hard for underwater life to survive.
Water is the solvent of life.
Because of water's polarity, water is able to dissolve many things in it. In fact, it is known as the universal solvent because it's able to dissolve more things than any other liquid. For some context, the word solubility is used to describe the ability of a substance to be dissolved in water. A solution is a mixture in which one or more substances are uniformly distributed in another substance. A solute is the substance being dissolved, and a solvent is the substance that the solute will be dissolved into.
Acids and Bases
Alright guys, I just have one more thing to tell you about. We know how water is an extremely good solvent, right? Well, when you dissolve certain things in water, it can become ionized.
This means that it forms acids and bases because of a surplus of either hydronium (H3O+) or hydroxide (OH-) ions. Acids have a high hydronium concentration than hydroxide concentration and bases have a higher hydroxide concentration than hydronium concentration.
The pH scale is used to measure either how basic or how acidic a substance is. It goes from 1-14. The numbers 1-6.9 determine acidity, while the number 7.1-14 determine how basic a substance is. The number 7 marks the neutrality of a substance.
Oh well, that's it for this lesson. I will be working on the cell organelles page this week, and I should have it out soon. I hope to see you in the next one!
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