KEY CONCEPT All living things are based on atoms and their interactions.

Living things consist of atoms of different elements. An atom is the smallest basic unit of matter. An element is one type of atom. Hydrogen atom (H) H O Oxygen atom (O)

An atom has a nucleus and electrons. The nucleus has protons and neutrons. Electrons are in energy levels outside nucleus. Oxygen atom (O) Nucleus: 8 protons (+) 8 neutrons outermost energy level: 6 electrons (-) inner energy level: 2 electrons (-)

O A compound is made of atoms of different elements bonded together. water (H2O) O H _ +

A compound is made of atoms of different elements bonded together. water (H2O) carbon dioxide (CO2)

A compound is made of atoms of different elements bonded together. water (H2O) carbon dioxide (CO2) many other carbon-based compounds in living things

Ions form when atoms gain or lose electrons. An ion is an atom that has gained or lost one or more electrons. positive ions negative ions Ionic bonds form between oppositely charged ions. Sodium atom (Na) Chlorine atom (CI) Sodium ion (Na+) Chloride ion (CI-) Na loses an electron to CI ionic bond gained electron

Atoms share pairs of electrons in covalent bonds. A covalent bond forms when atoms share a pair of electrons. multiple covalent bonds diatomic molecules covalent bonds Oxygen atom (O) Carbon atom (C) Carbon dioxide (CO2 )

2.2 Properties of Water KEY CONCEPT Water’s unique properties allow life to exist on Earth.

Life depends on hydrogen bonds in water. 2.2 Properties of Water Life depends on hydrogen bonds in water. Water is a polar molecule. Polar molecules have slightly charged regions. O H _ + Nonpolar molecules do not have charged regions. Hydrogen bonds form between slightly positive hydrogen atoms and slightly negative atoms.

2.2 Properties of Water Hydrogen bonds are responsible for three important properties of water. high specific heat cohesion adhesion

Many compounds dissolve in water. 2.2 Properties of Water Many compounds dissolve in water. A solution is formed when one substance dissolves in another. A solution is a homogeneous mixture. Solvents dissolve other substances. Solutes dissolve in a solvent. solution 78 % Nitrogen 20% Oxygen 1% Other What are the solutes and solvent in the beverage you drink?

2.2 Properties of Water “Like dissolves like.” (Universal Solvent) Polar solvents dissolve polar solutes. Nonpolar solvents dissolve nonpolar solutes. Polar substances and nonpolar substances generally remain separate.

Some compounds form acids or bases. 2.2 Properties of Water Some compounds form acids or bases. An acid releases a hydrogen ion when it dissolves in water. high H+ concentration pH less than 7 more acidic stomach acid pH between 1 and 3

2.2 Properties of Water A base removes hydrogen ions from a solution. low H+ concentration pH greater than 7 bile pH between 8 and 9 more basic

2.2 Properties of Water A neutral solution has a pH of 7. pure water pH 7 Cells have higher H+ concentrations than blood. Which has a higher pH? Why?

2.3 Carbon based Molecules KEY CONCEPT Carbon-based molecules are the foundation of life.

Carbon atoms have unique bonding properties. 2.3 Carbon based Molecules Carbon atoms have unique bonding properties. Carbon forms covalent bonds with up to four other atoms, including other carbon atoms. Carbon-based molecules have three general types of structures. straight chain branched chain ring

2.3 Carbon based Molecules Many carbon-based molecules are made of many small subunits bonded together. Monomers are the individual subunits. Polymers are made of many monomers.

Four main types of carbon-based molecules are found in living things. A phosphate group nitrogen-containing molecule, called a base deoxyribose (sugar) Nucleic Acids

Four main types of carbon-based molecules are found in living things. Carbohydrates are made of carbon, hydrogen, and oxygen in a 1:2:1 ratio.

Four main types of carbon-based molecules are found in living things. Carbohydrates are made of carbon, hydrogen, and oxygen. Carbohydrates include sugars and starches. Monosaccharides are simple sugars. Polysaccharides include starches, cellulose, and glycogen.

2.3 Carbon based Molecules Carbohydrates can be broken down to provide energy for cells. Some carbohydrates are part of cell structure. Polymer (starch - storage) Starch is a polymer of glucose monomers that often has a branched structure. Polymer (cellulose – cell structure) Cellulose is a polymer of glucose monomers that has a straight, rigid structure monomer

2.3 Carbon based Molecules Lipids are nonpolar molecules that include fats, oils, and cholesterol. Consist of Carbon, Hydrogen & Oxygen Many contain carbon chains called fatty acids. Fats and oils contain fatty acids bonded to glycerol. Triglyceride

2.3 Carbon based Molecules Lipids have several different functions. broken down as a source of energy & insulation make up cell membranes used to make hormones

2.3 Carbon based Molecules Fats and oils have different types of fatty acids. saturated fatty acids unsaturated fatty acids

2.3 Carbon based Molecules Phospholipids make up all cell membranes. Polar phosphate “head” Nonpolar fatty acid “tails” Phospholipid

2.3 Carbon based Molecules Proteins are polymers of amino acid monomers Carbon, Hydrogen, Oxygen & Nitrogen Twenty different amino acids are used to build proteins in organisms.

2.3 Carbon based Molecules Proteins are polymers of amino acid monomers. Twenty different amino acids are used to build proteins in organisms. Amino acids differ in side groups, or R groups. Amino acids are linked by peptide bonds.

2.3 Carbon based Molecules Proteins differ in the number and order of amino acids. Amino acids interact to give a protein its shape. hydrogen bond Hemoglobin Incorrect amino acids change a protein’s structure and function.

2.4 Chemical Reactions Nucleic acids are polymers of monomers called nucleotides.

2.5 Enzymes Nucleic acids are polymers of monomers called nucleotides. Nucleotides are made of a sugar, phosphate group, and a nitrogen base. A phosphate group nitrogen-containing molecule, called a base deoxyribose (sugar)

2.5 Enzymes Nucleic acids are polymers of monomers called nucleotides. Nucleotides are made of a sugar, phosphate group, and a nitrogen base. DNA stores genetic information. DNA RNA builds proteins. RNA

2.4 Chemical Reactions KEY CONCEPT Life depends on chemical reactions.

Bonds break and form during chemical reactions. Chemical reactions change substances into different ones by breaking and forming chemical bonds. Reactants are changed during a chemical reaction. Products are made by a chemical reaction. CO2 + H2O H2CO3

CO2 + H2O H2CO3 2.4 Chemical Reactions Bond energy is the amount of energy that breaks a bond. Energy is added to break bonds. Energy is released when bonds form. A reaction is at equilibrium when reactants and products form at the same rate. CO2 + H2O H2CO3

Chemical reactions release or absorb energy. Activation energy is the amount of energy that needs to be absorbed to start a chemical reaction.

2.4 Chemical Reactions Exothermic reactions release more energy than they absorb. Reactants have higher bond energies than products. Excess energy is released by the reaction.

2.4 Chemical Reactions Endothermic reactions absorb more energy than they release. Reactants have lower bond energies than products. Energy is absorbed by the reaction to make up the difference.

2.5 Enzymes KEY CONCEPT Enzymes are catalysts for chemical reactions in living things.

A catalyst lowers activation energy. 2.5 Enzymes A catalyst lowers activation energy. Catalysts are substances that speed up chemical reactions. decrease activation energy increase reaction rate

2.5 Enzymes Enzymes allow chemical reactions to occur under tightly controlled conditions. Enzymes are catalysts in living things. Enzymes are needed for almost all processes. Most enzymes are proteins.

2.5 Enzymes Disruptions in homeostasis can prevent enzymes from functioning. Enzymes function best in a small range of conditions. Changes in temperature and pH can break hydrogen bonds. An enzyme’s function depends on its structure.

2.5 Enzymes An enzyme’s structure allows only certain reactants to bind to the enzyme. substrates active site substrates (reactants) enzyme Substrates bind to an enzyme at certain places called active sites.

2.5 Enzymes The lock-and-key model helps illustrate how enzymes function. substrates brought together bonds in substrates weakened Substrates bind to an enzyme at certain places called active sites. The enzyme brings substrates together and weakens their bonds. The catalyzed reaction forms a product that is released from the enzyme.