1. Chapter 2: Chemistry of Life
Sections 1-5

2. Atoms, Ions, and Molecules
Atom: the smallest basic unit of matter.
All atoms have the same basic structure.
Protons (+), electrons (-), and neutrons (no charge)
Protons and neutrons make up the center of the atom called the atomic nucleus
Electrons make up the outer shell of the atom
Element: one particular type of atom
It can’t be broken down by ordinary chemical means
The difference between elements is the amount of protons they have

3. Atoms, Ions, and Molecules
91 elements occur naturally on Earth; 25 are found in organisms
Carbon, Oxygen, Nitrogen, and Hydrogen make up 96% of the human body.
The other 4% is Calcium, Phosphorus, Potassium, Sulfur, and Sodium
Atoms of elements are often linked together when they are found in organisms.
Compound: a substance made of atoms of different elements bonded together in a certain ratio.
Most common compounds are Water (H2O) and Carbon Dioxide (CO2)

4. Atoms, Ions, and Molecules
Properties of compounds are normally different from the properties of the elements that make them up.
For example: Water, Diamonds, Sugars, and Proteins
Ion: an atom that has gained or lost an electron(s).
Ions happen so that the outermost electron shell can be full.
Ionic compounds (compounds made of only ions) easily dissolve in water
Ionic Bonds: a bond formed through the electrical force between oppositely charged ions. (NaCl)

5. Atoms, Ions, and Molecules
Sometimes atoms don’t give up or gain electrons, but they share.
Covalent Bond: forms when atoms share a pair of electrons
These bonds are normally very strong (CO2)
Molecule: 2 or more atoms held together by covalent bonds

6. Properties of Water
Water expands as it freezes and it becomes less dense as it becomes solid.
Water is a polar molecule (one area is slightly more positive and the other is slightly more negative)
Polar molecules form when atoms in molecules have unequal pulls on the electrons they share.
Nonpolar molecules don’t have charged regions.
Hydrogen Bond: an attraction between a slightly positive hydrogen and a slightly negative atom, normally oxygen or nitrogen.

7. Properties of Water Hydrogen bonds are found in DNA
Typical hydrogen bonds are 20 times weaker than typical covalent bonds
In water, however, they are very strong
Hydrogen bonds are responsible for 3 very important traits of water:
High Specific Heat
Cohesion: the attraction among molecules of a substance.
Adhesion: the attraction among molecules of different substances
Many compounds dissolve in water

8. Properties of Water
One substance dissolves in another makes a solution
Solution: A mix of substances that is the same throughout (homogenous)
2 parts to a solution: Solvent: the substance that is present in the greater amount and that dissolves the other substance; Solute: a substance that dissolves in the solvent
Concentration is the amount of solute dissolved in a certain amount of solvent (ex: Kool-Aid)
Polar and ionic molecules dissolve in water; nonpolar (oil and fat) do not

9. Properties of Water
Some compounds break up into ions when they dissolve in water.
Acid: a compound that releases a proton (H+) when it dissolves in water
Bases: compounds that remove H+ ions from a solution
The amount of H+ ions are measured using the pH scale.
0-14
0 is the most acidic = large amount of H+
14 is the most basic = very little H+
7 is neutral = neither acidic or basic

10. Properties of Water
pH is regulated by buffers inside of organisms like humans
Buffers are compounds that can bind to H+ ions when the concentration increases and can release when it decreases
Buffers help maintain homeostasis

11. Carbon-Based Molecules
Carbon = the building block of life
Atomic structure gives it bonding properties that are unique
Can form covalent bonds with up to 4 other atoms
Carbon can be in straight chains, branched chains, and rings
Chains can bond with rings to form very large complex molecules
Each subunit in the complete molecule is a monomer.
Monomers link together to make polymer: a large molecule, or macromolecule, made of many monomers bonded together
All monomers could be the same = starches
Monomers could be different = proteins

12. Carbon-Based Molecules
Living things are made of 4 types of carbon-based molecules:
Carbohydrates, Lipids, Proteins, and Nucleic Acids
Carbohydrates: molecules composed of carbon, hydrogen, and oxygen. Includes sugar and starches.
Carbs are a source of usable energy for cells and are very important for plant cell structure.
Most basic carbs are simple carbs aka monosaccharides
They are either 5 or 6 carbon atoms
Ex: Fructose (6), Glucose (6)

13. Carbon-Based Molecules
2 simple sugars combined together make a disaccharide like table sugar
More than 2 simple sugars together make a polysaccharide like glycogen and cellulose
Lipids: nonpolar molecules that include fats, oils, and cholesterol.
Contain chains of carbon atoms bonded to oxygen and hydrogen atoms
Some lipids are used as usable energy and some are part of cell structure

14. Carbon-Based Molecules
Fats and oils are 2 of the most common lipids
Fats and oils have a very similar structure
Both are made with glycerol bonded to fatty acids
Fatty Acids: chains of carbon atoms bonded to hydrogen atoms
Saturated and Unsaturated
Many lipids have 3 fatty acids bonded to a glycerol = triglyceride
All cell membranes are made of mostly phospholipids = 1 glycerol , 2 fatty acids, and 1 phosphate group
Cholesterol is a fatty acid that has a ring structure
Body needs it for cell membranes, steroid hormones (estrogen, testosterone)

15. Carbon-Based Molecules
Protein: a polymer made of monomers called amino acids
One or more polypeptides
Differ in the number and order of amino acids
Specific sequence determines type and function
Sulfur atoms help make covalent bonds and shape the protein
Amino Acids: molecules that contain carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur
Organisms use 20 different amino acids to make proteins
Our body makes 12 of the amino acids
Form covalent bonds called peptide bonds
Peptide bonds tie amino acids together to make polypeptides

16. Carbon-Based Molecules
The detailed instructions to build the proteins are stored in long carbon based molecules
Nucleic Acids: polymers that are made up of monomers called nucleotides
Nucleotides are composed of a sugar, a phosphate group, and a nitrogen base
2 types: RNA and DNA
They have just one function
Work together to make proteins
DNA has the info to make amino acids; RNA puts them together to make the proteins

17. Chemical Reactions
Chemical Reactions: change substances into different substances by breaking and forming chemical bonds.
Oxygen is used in the human body to help breakdown Glucose (C6H12O6) into a usable form of energy
Reactants: the substances changed during a chemical reaction (O2 and Glucose)
Products: the substances made by a chemical reaction (CO2 and H2O)
Reactants are on the left and products are on the right
Reactants  Products
This particular reaction is called Cellular Respiration

18. Chemical Reactions
For the products to be made bonds have to be broken in the reactants and then made in the products
Energy is first added to break the bonds in the molecules of O2 and Glucose
Bond Energy: the amount of energy that will break a bond between 2 atoms
Bond energy is never the same; different atoms = different bond energy
Energy is released when bonds form (like when H2O and CO2 are made)
Energy released = bond energy

19. Chemical Reactions
Some reactions will keep taking place until all of the reactants are used up
Many reactions in organisms are reversible; They move in both directions simultaneously
Blood does this to carry CO2
CO2 combines H2O to make Carbonic Acid (H2CO3)
Your body does this to get rid of CO2 waste from your cells
When a reaction takes place at an equal rate in both directions, the reactant and product concentrations stay the same
Equilibrium: when both the reactants and products are made at the same rate

20. Chemical Reactions All chemical reactions involve a change in energy
Some energy must be absorbed by the reactants in any chemical reaction
Activation Energy: the amount of energy that needs to be absorbed for a chemical reaction to start
It’s like the energy you would need to push a rock up a hill
Exothermic chemical reaction releases more energy than it absorbs.
Extra energy is given off as heat or light
Example: Cellular Respiration

21. Chemical Reactions
Endothermic chemical reactions absorb more energy than it releases.
Example: Photosynthesis
If products have higher bond energy than reactants the reaction is endothermic.
Energy has to be absorbed to make up for the difference.

22. Enzymes
Activation energy starts off a chemical reaction and then the reaction continues on it’s own at a certain rate
Normally the activation energy comes from an increase in temperature
Can still take a long time
Catalyst: a substance that decreases the activation energy needed to start a chemical reaction and, as a result, also increases the rate of the chemical reaction.
With a catalyst less energy is needed to start the reaction and products form faster
Catalysts are not reactants or products because they are not changed or used up

23. Enzymes
Reactions in the human body normally need to take place quickly so they need a catalyst
Enzymes: catalysts for chemical reactions in living things
They lower the activation energy and increase the rate of chemical reactions
They do not change the chemical equilibrium, they reduce the time it takes to reach equilibrium.
They are involved in almost every process in organisms.
Almost all enzymes are proteins

24. Enzymes Each enzyme also depends on its structure to function properly
Conditions like temperature and pH can affect the shape and function of the enzyme
Temperatures higher than normal body temperature can make enzymes lose their function and start to break apart.
Structure is important because each enzyme allows only certain reactants to bind to the enzyme.
Substrates: the specific reactants that an enzyme acts on
Like a key fits into a lock

25. Enzymes
Substrates come together with an enzyme at a certain place which is the active site.
Enzyme brings the substrates together and weakens the bonds
Catalyzed reaction forms a product that is released from the enzyme