Chemistry Review
Before we get into biology, let's review some basic chemistry. We're doing this because all biomolecules are simply made up of atoms. Therefore a strong grasp of chemistry is crucial in order for us to better understand biological processes.
Elements and Compounds
Elements are considered the purest form of matter. One cannot break down elements into different substances (unless they use nuclear physics).
Compounds are combinations of atoms from different elements, so they can be broken down into different elements using regular chemistry.
For example, pure oxygen gas (O2) is an element cannot be separated into different substances. However, water (H2O) is a compound and can be separated into hydrogen gas (H2) and oxygen gas (O2).
Compounds are combinations of atoms from different elements, so they can be broken down into different elements using regular chemistry.
For example, pure oxygen gas (O2) is an element cannot be separated into different substances. However, water (H2O) is a compound and can be separated into hydrogen gas (H2) and oxygen gas (O2).
Essential Elements
Any element that is considered necessary for life is called an essential element. There are about 25 of them. The 5 most important ones by mass are oxygen, carbon, hydrogen, nitrogen, and calcium. You might find it easier to memorize them using the abbreviation: CHOCaN (Carbon, Hydrogen, Oxygen, Calcium, and Nitrogen).
Some essential elements are needed in very small amounts by organisms, and therefore they are called trace elements. Although they are not consumed in large quantities, we still need them to survive. An example is iron (Fe), all organisms need it in small amounts.
Some essential elements are needed in very small amounts by organisms, and therefore they are called trace elements. Although they are not consumed in large quantities, we still need them to survive. An example is iron (Fe), all organisms need it in small amounts.
The Atom
The atom is composed of three subatomic particles - the proton, the neutron, and the electron.
The proton is a positively charged particle in the nucleus of an atom. The neutron has about the same mass as a proton and it also resides in the nucleus. However, it is not positively charged. In fact, it has no charge at all. On the other hand, the electron is negatively charged, it is much smaller than protons and neutrons, and it moves around the nucleus at nearly the speed of light.
The number of protons determine what element the atom is. For example, only atoms with 7 protons are nitrogen, and all nitrogen atoms must have 7 protons. The number of neutrons and electrons are irrelevant. This so important that we have a special name for the number of protons - the atomic number.
The mass of the atom is called the atomic mass. In order to determine this quantity, knowing the number of protons is not enough. We must also know the amount of neutrons. Each proton or neutron has a mass of 1 amu (this unit is equivalent to the unit Dalton). Therefore, the combined number of protons and neutrons gives the total mass of the atom. Because electrons are so small, they are not taken into consideration when determining the atomic mass.
The proton is a positively charged particle in the nucleus of an atom. The neutron has about the same mass as a proton and it also resides in the nucleus. However, it is not positively charged. In fact, it has no charge at all. On the other hand, the electron is negatively charged, it is much smaller than protons and neutrons, and it moves around the nucleus at nearly the speed of light.
The number of protons determine what element the atom is. For example, only atoms with 7 protons are nitrogen, and all nitrogen atoms must have 7 protons. The number of neutrons and electrons are irrelevant. This so important that we have a special name for the number of protons - the atomic number.
The mass of the atom is called the atomic mass. In order to determine this quantity, knowing the number of protons is not enough. We must also know the amount of neutrons. Each proton or neutron has a mass of 1 amu (this unit is equivalent to the unit Dalton). Therefore, the combined number of protons and neutrons gives the total mass of the atom. Because electrons are so small, they are not taken into consideration when determining the atomic mass.
Bonding
Recall the difference between covalent bonds and ionic bonds. Ionic bonds occur when electrons are transferred completely from one atom to another. This creates two ions which have opposite charges to each other (e.g. Na+ and Cl-). Because they are oppositely charged, the atoms tend to stay close to each other. On the other hand, covalent bonds involve the sharing of electrons between atoms. When electrons are approximately equally shared among the atoms in a bond, it is called a non-polar covalent bond. However, if one atom or atoms are more electronegative (attracts electrons more) than the others, then unequal sharing of electrons will occur. This latter process is called a polar covalent bond. Besides ionic and covalent bonds, you should also know about van der Waals interactions and hydrogen bonds. Because electrons are randomly distributed in a molecule, there will always be random positive and negative charges in different regions of the molecule. These short-lived charges are weak, but in large amounts they can help hold molecules close to each other. These are called van der Waals interactions. Hydrogen bonds occur when a hydrogen atom (bonded to a more electronegative atom so the hydrogen is slightly positively charged) is attracted to a third atom, which is also very electronegative (so it is slightly negative). The slight positive charge from the hydrogen causes it to form a hydrogen bond with the slightly negative third atom.
Because covalent bonds involve the sharing of electrons, they are generally stronger than ionic bonds, which are stronger than hydrogen bonds, which are stronger than van der Waals interactions.
Because covalent bonds involve the sharing of electrons, they are generally stronger than ionic bonds, which are stronger than hydrogen bonds, which are stronger than van der Waals interactions.