1. 2.3 Carbon-Based Molecules

2. Carbon is often referred to as the building block of life
*Carbon is often referred to as the building block of life. Carbon atoms are the basis of most molecules that make up living things. The Carbon atom has four unpaired electrons that allow it to form multiple covalent bonds.
*Carbon based molecules have three fundamental structures; straight chain, branched chain, and ring.

3. In many carbon based molecules, small molecules are subunits of an entire molecule. Each subunit is called a monomer. Many monomers linked together are called polymers. Starches for example, are composed of the same polymer, while proteins are composed of different polymers.

4. *There are four main types of carbon-based molecules found in living things. They are carbohydrates, lipids, proteins, and nucleic acids.

5. Carbohydrates
*A monosaccharides is a simple sugars composed of 5 or 6 carbon atoms. Fructose and glucose are 6 carbon atom sugars.
*Two monosaccharide bonded together form a polysaccharide. Starches, cellulose, and glycogen are polysaccharides.

6. Lipids
*Fatty acids are chains of carbon atoms bonded to hydrogen atoms. Three fatty acids bonded to a glycerol molecule are called triglycerides.
*Two types of fats are saturated and unsaturated fats. Saturated fats have the maximum number of single bonded hydrogen atoms. Unsaturated fats contain at least one carbon double bond. Unsaturated fats do not form solids for this reason.
*All cell membranes are made up of lipids called phospholipids. Phopholipids consist of glycerol, two fatty acids, and a phosphate group (PO4-) that is part of the polar head of the molecule. The fatty acids are the nonpolar tails of a phopholipid.
*Cholesterol has a ring structure. The human body uses cholesterols to make steroid hormones.

7. Proteins
*There are three parts of an amino acid. Hydrogen atom, amino group (NH2), and carboxyl group (COOH). Amino acids differ due to the R-group the contain.
*Amino acids form covalent bonds called peptide bonds with each other. The bond is formed between the amino group and the carboxyl group. Amino acids are locked in chains called polypeptides.
*It is the sequence and number of amino acids that determines the type of protein.

8. Nucleic Acids *Two types of nucleic acids are DNA and RNA.
*Nucleic acids have just one function. They make proteins. DNA stores information and RNA helps build the protein.

9. 2.4 Chemical Reactions
*A chemical reaction changes substances into different substances by breaking and forming chemical bonds.
*Two parts of a chemical reaction are the reactants and products. Reactants are the substances changed during the reaction, and the products are the substances made by a chemical reaction.
*Bond energy is the energy required to break a chemical bond.

10. *A reaction that forms product at the same rate the products form reactants is at equilibrium.
*Activation energy is the energy required to put a chemical reaction in motion.
*An exothermic reaction releases heat. An endothermic reaction absorbs heat

11. 2.5 Enzymes
*A catalyst is a substance that decreases the activation energy of a chemical reaction, and as a result increases the reaction rate.
*Enzymes are catalysts for chemical reactions in living things. Enzymes like catalysts are not affected by the chemical reaction itself. Enzymes are proteins that bring substrates together.

12. Substrates are substances that the enzymes act on
Substrates are substances that the enzymes act on. The shape of the enzyme is very important. If the enzyme shape does not fit the substrate, nothing will happen. The combining of the enzyme to the substrate weakens their bonds. The catalyzed reaction forms a product that is released from the enzyme.