Chemistry for Biology Why study chemistry in biology? Think about what you are made of. If we completely broke you down, you would end up a pile of Elements (or atoms). -elements are the simplest chemical units that exist. They cannot be broken down by ordinary chemical means like dissolving in water and melting in fire. -gold is an element. What happens if you take a gold bracelet and apply heat to it? Your body is mainly Carbon, Hydrogen, Oxygen and Nitrogen. -see Figure 2.3 on pg. 22 of your book. You are approximately 96% these four elements.

Elements are composed of 3 parts: Protons- located in the center of the atom. These particles carry a POSITIVE charge. Neutrons Neutrons- also located in the center of the atom. These particles carry NO charge. Electrons- these particles are located outside the nucleus in orbitals. Electrons carry a negative charge. They are “held” in their orbits by the opposite charge of the protons in the nucleus.

Elements are arranged on the Periodic chart. This is like a dictionary for elements. Large numbers represent the atomic number as well as the number of protons in an element. Smaller numbers are the atomic mass. Symbols come from the element’s Latin name.

Many facts can be learned about an atom from the Periodic Chart. 1. The number of protons is = to the atomic number. example: Oxygen is #8 and has 8 protons. 2. The atomic mass minus the atomic number = the number of neutrons. example: Oxygen atomic mass is (atomic number) = 8 neutrons. What happens if we change the number of protons?? (change the element entirely) What happens if we change the number of neutrons?? (change the mass of the element) Form an isotope of the element when we change the mass. Isotopes have the same # of protons but different # of neutrons and different atomic mass.

Isotopes are common in nature. Called “radioactive” because they emit a charge. They are used for many purposes. Medical Uses: Put in dyes to help with CAT and PET scans and MRI’s. Dye is injected or put in a drink. (Barium is popular) Other Uses: Used to trace chemical pathways in organisms. Radio- active Oxygen used to study photosynthesis in plants. Used to “date” fossils and bones…”carbon dating”. Bad Isotopes cause problems: Chernobyl nuclear meltdown…many people have cancer. Cesium mimics elements that build bone, but breaks bones down instead of building them up.

Different brain scans when cocaine is present in blood and not present in blood. Three Mile Island Nuclear Power Plant

Elements join to form Compounds. -compounds are two or more elements joined in a fixed ratio. -most chemicals in nature are found in compounds because elements alone are “unstable”. -common compounds like H 2 O and Na + Cl - are part of your everyday routines. -the elements in salt are very dangerous alone…but joined to form the compound, they are harmless. rations/Sodium/images/Sodium Lump.jpg m/Experiments/how_to/Im ages/Chlorine_gas.jpg

s/nature/9.a.Ionicbond-nacl.gif Compounds are joined together by Bonds. Two basic types of bonds are found in abundance in biological systems. Ionic Bonds– these bonds occur when one element gives it’s electrons to another element creating a charge between the two elements causing them to bond. “Opposites attract.” Example: salt is made of Na and Cl… Na completely donates one electron to Cl thus making Na + and Cl – which bonds them together. (Figure 2.8, pg. 25)

Covalent Bonds– these bonds occur when two or more elements share electrons. Because the sharing is =, there is no charge created. Example: Oxygen that you breathe is really 2 O atoms held together by a covalent bond. This is drawn like O=O. The single bars represent one covalent bond each. Thus, oxygen can be written as O 2. (Figure 2.9, pg. 26) content/uploads/2011/01/Covalent-Bond1.gif

Hydrogen Bonds are also important in biology…particularly between adjacent water molecules. The positive charge of the H + has a special affinity for the negative charge of the O - and so the molecules have a very special arrangement. Not very strong alone, but when combined with many other H bonds in a sheet of water make for a very strong compound. img/biology/chemistry/hydrogen-bonds.jpg hydrogenbond.gif

Water is the single most important compound on the planet. Your cells are 70-95% water. Life began in the water…and evolved there for ~3 billion ybp before moving on to land. Earth is 75% water…one of the reasons we can live here. Chemical structure of water is simple: 2 atoms of Hydrogen covalently bonded to one atom of Oxygen. Water is slightly charged…thus we say it is a polar molecule. The hydrogen end is slightly + in charge, the oxygen end is slightly – in charge. This charge creates hydrogen bonds between two water molecules creating “sheets” of water with cool properties.

Water has 4 unique properties that make it essential for life. 1.Water molecules are cohesive. They stick to each other. They also take different shapes according to the container they are in. --think about all the times water changes shape before it finally ends up in your cells. --cohesion of water molecules allows insects to walk on water. --water molecules move from the roots of plants up through the stem and finally evaporate out the leaves by cohesion. (see Fig. 2.12, pg. 29)

2.Water can help moderate temperatures. --since water has the ability to soak up large amounts of heat and then slowly release it during periods of cold, water can help keep the temperature of an area within a reasonable set of limits. --water is also responsible for moderating body temperature during overheating. How does it do this? water1.jpg

3.Ice is less dense than liquid water. In other words …ICE FLOATS!!... --when water starts to get cooler, individual molecules move apart, creating “pockets” of air in a crystal that weighs less than the liquid it forms from…so it can float!! Why is this important to life? What would happen if all the oceans, rivers, ponds and lakes froze from the bottom up? Would they ever thaw completely out? What about organisms that live in them? Ice also creates an insulating layer to keep water below it warm.

4.Water is a Universal Solvent. --water will mix with just about anything. --creates an Aqueous Solution. --examples are numerous…blood, tea, soda (polar) Water won’t mix with petrols…oil containing products. --paint that is oil based, gasoline, grease on your dishes or clothing, vinegar/salad oil (non-polar) **SOAP DOES NOT DISSOLVE OIL** Soap is an important additive to water in order to remove oil. Soap has unique properties because it has both a polar and non-polar end to its molecule. The polar end will attach to water, the non-polar end to oil, forming a micelle of water and oil just long enough to remove oil from the object.

Life is constantly changing it’s chemical composition. This is largely due to chemical reactions taking place. In a reaction, there are reactants and products. Reactants are what enter the process and products are what come out at the end. Think of it like baking a cake…what goes in is very different from what comes out!! But it is all still there at the end!! Water is formed by combining Hydrogen and Oxygen… 2 H 2 + O 2 = 2 H 2 O. This equation is also balanced meaning that the ingredients are equal on both sides of the equation. Nothing is lost and nothing is created.

Water monitors pH of many living things. pH is the measure of potential Hydrogen…or the number of hydrogen atoms present in a solution. When water breaks apart it produces an H+ and an OH- Solutions are rated on a pH scale ranging from Acids go from Pure water is neutral at 7.0 Bases go from These numbers are determined by the amount of hydrogen the solution has. Lots of hydrogen means an acid is formed, Lots of OH means a base is formed. Neutral substances have equal amounts of H and OH.

pH Scale ranks common substances according to their acid and base content. Each jump on the scale represents 10 x more or less hydrogen atoms than the previous substance.

Acid rains cause many problems for the environment. Many plants are acid intolerant, so a build-up of acid in the soil can cause them to die. Plants that are acid tolerant will take over the soil and may limit the food supply for other organisms. Acid rain run-off can raise the pH of lakes, rivers, and streams in an ecosystem, effecting the entire aquatic food chain. Recreation can also be affected by acid rain. Car paint peels off, marble statues erode.