Lesson 2: The Chemistry of Life
Lesson 2: The Chemistry of Life BIOL 1105
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This 4 page Class Notes was uploaded by Emily Notetaker on Monday September 5, 2016. The Class Notes belongs to BIOL 1105 at Virginia Polytechnic Institute and State University taught by Prof. JI Watkinson in Fall 2016. Since its upload, it has received 63 views. For similar materials see Foundations of Biology in Biology at Virginia Polytechnic Institute and State University.
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Date Created: 09/05/16
Lesson 2: The Chemistry of Life Atoms Atoms are the smallest stable components of cells o All matter is composed of atoms Atoms are made up of smaller components: (which are more unstable and reactive in isolation) o Protons (+ charge) o Neutrons (except for hydrogen which has 1 proton and 1 electron but no neutron) o Electrons (- charge) Atoms are neutral when they have an equal number of protons and electrons Most of the volume of an atom is empty space Electrons mediate interactions with other atoms Atomic Vocabulary Element: Substance consisting of 1 type of atom with the same number of protons Atomic number: The number of protons in an atom o This defines the type of element Mass: The amount of substance Weight: Force exerted by gravity on the substance Atomic mass: The sum of the masses of protons and neutrons in an atom Dalton: Unit of mass o Protons and neutrons each weigh 1 Dalton o Electrons weigh nearly 2,000 times less than 1 Dalton Living Systems The majority of the weight of living systems is composed of: o Carbon (C) o Oxygen (O) o Hydrogen (H) o Nitrogen (N) Organic molecules are carbon-containing Isotopes Definition: Atoms of the same element that have different numbers of neutrons o Ex. Carbon-12 (common) o Carbon-13 o Carbon-14 (rare and unstable) Radioactive Decay Definition: The process by which the nucleus of an unstable atom loses energy by emitting radiation Produces energy Energy is required to move the electron from the nucleus o This produces an electron with greater potential energy An electron moving closer to the nucleus releases energy o This results in less potential energy K, L, M, N are energy levels (quanta or “shells”) Electrons in the outermost energy level (“shell”) are valence electrons o Valence electrons determine an element’s reactive properties o Most contain no more than 8 electrons, making them non- reactive o Elements (such as Sodium) that have just one outer electron are very reactive Octet rule (rule of 8): Atoms tend to completely fill their outer energy levels Ions Definition: Charged atoms resulting when an atom’s proton and electron count differ o Cation: Contains more protons than electrons (+ charge) o Anion: Contains more electrons than protons (- charge) Molecules and Their Bonds Molecule: 2 or more atoms that are chemically bonded together in a stable association o Smallest unit of a chemical compound that can take part in a chemical reaction o Held together by either covalent, ionic, or hydrogen bonding BOND INTERACTION RELATIVE STRENGTH Covalent Sharing of electron Strong pairs Ionic Attraction of opposite charges Hydrogen Sharing of a hydrogen Weak atom Electronegativity: Electrons may not be shared equally o Ex. Oxygen has a greater affinity for electrons than hydrogen does Polar covalent bond: Has an unequal charge distribution o Ex. H2O (H2 creates double the + charge, leaving a smaller – charge from O) Hydrogen bonds o Water readily forms hydrogen bonds (nonpolar molecules cannot form hydrogen bonds with water though) o Life is based on water Individual hydrogen bonds are weak and short-lived, but the combined effect of many hydrogen bonds is substantial Water LIVING CELL Water Small molecules Macromolecules Cohesion: The polarity of water promotes the attraction of water molecules to other water molecules o Water is a liquid at most temperatures on Earth and creates surface tension Adhesion: Water molecules are attracted to other polar molecules o Adhesion of water to charged surfaces drives capillary action Specific heat: The amount of heat required to change 1 gram of a substance by 1 °C o Water has high specific heat because of its tendency to form hydrogen bonds o Substances resist changing temperature when absorbing or losing heat Heat of vaporization: The amount of energy required to change 1 gram of a substance from liquid to gas o Energy is required to break hydrogen bonds to allow conversion from liquid to gas o Water has high heat of vaporization Amphipathic molecules (lipids): Contain a hydrophobic (nonpolar) end and a hydrophilic (polar) end o The hydrophilic sides of the lipid associate with water in a solution o The hydrophobic sides cluster together to “hide” from the water o Lipids then cluster together to form spheres in which: The hydrophobic sides are in the center (away from the water) The hydrophilic sides are on the outside (associating with the water) pH Scale The pH scale measures hydrogen ion (H+) concentration o Logarithmic pH equation: pH= -log[H+] Acid: A higher pH means a lower concentration of hydrogen (H+) ions o Acids dissociate in water to increase H+ o Solutions from a pH of 0 to 6.9 are acidic Base: A lower pH means a higher concentration of hydrogen (H+) ions o Bases dissociate to decrease H+ o Solutions from a pH of 7.1 to 14 are basic Pure water has a neutral pH of 7 Buffer: Resists change in pH o Ex. Blood
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