Chapter 2

The Chemistry of Life

Section 1: The Nature of Matter

Objectives

• What three subatomic particles make up atoms?

• How are all the isotopes of an element similar?

• What are the two types of chemical bonds?

The Big Idea• Life Depends on chemistry

• Chemical reactions keep you alive

Atom• Basic unit of matter

Democrites

Subatomic particles• Protons - • Neutrons - • Electrons -

Positively charged (+)

Not charged (neutral)

Negatively charged (-)

Bind together to form the nucleus

Electrons Protons

Neutrons

Nucleus

Element• A pure substance that consists

of just one type of atom

6

CCarbon12.011

Atomic number

An elements atomic number = number of protons

Isotope• Atoms of the same element

that differ in the number of neutrons they contain

Nonradioactive carbon-12 Nonradioactive carbon-13 Radioactive carbon-14

6 electrons6 protons6 neutrons

6 electrons6 protons8 neutrons

6 electrons6 protons7 neutrons

6

CCarbon12.011 Mass number

The Sum of protons and neutrons in the nucleus of an atom is its mass number

• The weighted average of the masses of an elements isotope is called its atomic mass

Radioactive isotopes• Can be dangerous

• Can be used practically–Radioactive dating

–Treat cancer

–Kill bacteria

Compounds• A substance formed by the

chemical combination of two or more elements in definite proportions

• Ex) H2O, NaCl

Table Salt

Ionic Bonds• Formed when one or more

electrons are transferred from one atom to another

Sodium atom (Na) Chlorine atom (Cl) Sodium ion (Na+) Chloride ion (Cl-)

Transferof electron

Protons +11Electrons -11Charge 0

Protons +17Electrons -17Charge 0

Protons +11Electrons -10Charge +1

Protons +17Electrons -18Charge -1

• If an atom loses an electron it becomes positive

• If an atom gains an electron it becomes negative

Ions• Positively and negatively

charged atoms

Covalent Bonds• Forms when electrons are

shared between atoms

Molecule• The structure that results when

atoms are joined together by a covalent bond

• Smallest unit of most compounds

Van der Waals Forces• A slight attraction that

develops between the oppositely charged regions of nearby molecules due to unequal sharing of electrons

Homework

1. Describe the structure of an atom.

Atoms are made up of protons and neutrons in a nucleus. Electrons are in constant motion in the space around the nucleus.

2. Why do all isotopes of an element have the same chemical properties

They have the same number of electrons

3. What is a covalent bond?

A bond formed when electrons are shared between atoms

4. What is a compound? How are they related to molecules

A compound is a substance formed by the chemical combination of two or more elements in definite proportions. A molecule is the smallest unit of most compounds

5. How do Van der Waals forces hold molecules together?

When the sharing of electrons are unequal, a molecule has regions that are charged. An attraction can occur between oppositely charged regions of nearby molecules

6. How are ionic bonds and Van der Waals forces similar? How are they different?

In both cases, particles are held together by attractions between opposite charges. The difference is that ionic charges are stronger

Section 2: Properties of Water

Objectives• Why are water molecules polar?

• What are acidic solutions? What are basic solutions?

The Big Idea

• Much of our planet is covered in water

• Water is necessary for life to exist• If life exists on other planets, there

most likely is water present• Water has many properties that

make life possible

Polarity(-)

(+)

The oxygen atom has a stronger attraction for electrons

Hydrogen Bonds• Because of waters partial charges,

they can attract each other and create hydrogen bonds

• Not as strong as covalent or ionic bonds

• Waters ability to create multiple hydrogen bonds gives it many special properties

Cohesion• Attraction between molecules of

the same substance

Adhesion• Attraction molecules of different

substances

Mixture• Material composed of two or more

elements or compounds that are physically mixed but not chemically combined

• Ex.) salt & pepper, earths atmosphere

Solutions• Mixture of two or more

substances in which the molecules are evenly distributed

• Ex.) salt water

• Settles out over time

Solutions

Cl-

Water

Cl-

Na+

Water

Na+

Solute• Substance that is dissolved

• Ex.) salt

Solvent• The substance that does the

dissolving

• Ex.) Water

Suspensions• Mixture of water and non-

dissolved materials

• Ex.) sugar solution, blood

• Separate into pieces so small, they never settle out

The pH scale• Indicated the concentration of

hydrogen ions in a solution

Neutral

Acid

Base

Acids• Any compound that forms H+

(hydrogen) ions in solution

Base• A compound that produces OH-

(hydroxide) ions in solution

Buffers• Weak acids or bases that can

react with strong acids or bases to prevent sharp, sudden pH changes

Homework

1. Use the structure of a water molecule to explain why its polar

Oxygen atom has greater attraction for electrons, therefore the oxygen atom is negative and the hydrogen end is positive

2. Compare acidic and basic solutions in terms of their H+ ion and OH- ion concentrations

Acid have more H+ ions than OH-

ions, and bases have more OH-

ions than H+ ions

3. What is the difference between a solution and a suspension?

In a solution, all components are evenly distributed. In a suspension, un-dissolved particles are suspended

4. What does pH measure?

The concentration of H+ ions in a solution

5. The strong acid hydrogen floride (HF) can be dissolved in pure water. Will the pH of the solution be greater or less than 7?

less than 7

Section 3: Carbon Compounds

Objective• What are the functions of each

group of organic compounds?

• Most of the compounds that make up living things contain carbon. In fact, carbon makes up the basic structure, or “backbone,” of these compounds. Each atom of carbon has four electrons in its outer energy level, which makes it possible for each carbon atom to form four bonds with other atoms.

• As a result, carbon atoms can form long chains. A huge number of different carbon compounds exist. Each compound has a different structure. For example, carbon chains can be straight or branching. Also, other kinds of atoms can be attached to the carbon chain.

Section 2-3

Interest Grabber

Life’s backbone

Methane Acetylene Butadiene Benzene Isooctane

Macromolecules “giant molecules”

• Formed by a process called polymerization

Monomers• Smaller units

Polymers• Linked up monomers

Carbohydrates• Compounds made up of carbon,

hydrogen, and oxygen atoms usually in a ratio of 1:2:1

• Main source of energy

• The monomers of starch are sugars

• Single sugar molecules are called monosaccharides

• The large macromolecules formed from monosaccharides are known as polysaccharides

Starch

Glucose

Lipids• Made mostly from carbon and

hydrogen atoms

• Used to store energy

Lipid Glycerol

Fatty Acids

Proteins• Macromolecules that contain

nitrogen as well as carbon, hydrogen, and oxygen

• Proteins are polymers of molecules called amino acids

Amino Acids

General structure Alanine Serine

Carboxyl group

• More than 20 different amino acids, can join to any other amino acid

• The instructions for arranging amino acids into many different proteins are stored in DNA

• Each protein has a specific role• The shape of proteins can be very

important

Proteins

Amino Acids

Nucleic Acids• Macromolecules containing hydrogen,

oxygen, nitrogen, carbon, and phosphorus

Double Helix

Nucleotides• Consists of 3 parts: 5-carbon sugar,

phosphate group and nitrogen base

Nitrogen Base

5-Carbon Sugar

Phosphate group

2 kinds of nucleic acids• RNA (ribonucleic acids) –

contains sugar ribose

• DNA (deoxyribonucleic acid) – contains sugar deoxyribose

Homework

1. Name four groups of organic compounds found in living thingscarbohydrate, lipid, protein, nucleic acids

2. Describe at least one function of each group of organic compoundscarbohydrates – energylipids – store energyproteins – form tissuenucleic acids – transmit hereditary information

3. Compare the structures and functions of lipids and starches

Lipids are made from carbon and hydrogen. Starches are made of carbon, hydrogen and oxygen. They both can be used to store energy

Section 4: Chemical Reactions and Enzymes

Objectives• What happens to chemical bonds

during chemical reactions?

• How do energy changes affect whether a chemical reaction will occur?

• Why are enzymes important to living things?

The Big Idea• Living things are made up of

chemical compounds

• Everything that happens to an organism is based on chemical reactions

Chemical Reactions• A process that changes or

transforms one set of chemicals into another

Reactants• Elements or compounds that

enter into a reaction

Products

• Elements or compounds produced by a chemical reaction

Example Reaction: Getting rid of carbon dioxide

• In the blood

• In the lungs

CO2 + H20 H2CO3 (carbonic acid)

H2CO3 CO2 + H2O

Released as you breathe

Energy in reactions Energy-Absorbing Reaction Energy-Releasing Reaction

Products

Products

Activation energy

Activation energy

Reactants

Reactants

Activation Energy• The energy that is needed to get

a reaction started

Enzymes• Some chemical reactions are too

slow or have activation energies that are too high to make them practical for living tissue

• These chemical reactions are made possible by catalysts

Catalyst• Substance that speeds up the

rate of chemical reactions

• Work by lowering a reactions activation energy

Enzyme• Biological catalysts

• Speed up reactions in cells

• Very specific

• Named for the reaction is catylzes

• Enzyme names always end in -ase

Reaction pathwaywithout enzyme Activation energy

without enzyme

Activationenergywith enzyme

Reaction pathwaywith enzyme

Reactants

Products

Substrates• The reactants of enzyme

catalyzed reactions

• The active site of the enzyme and the substrate have complementary shapes

• Fit like a lock and key

Enzyme Action

Enzyme – substrate complex

Glucose

Substrates

ATP

Substratesbind toenzyme

Substratesare convertedinto products

Enzyme-substratecomplex

Enzyme(hexokinase)ADP

Products

Glucose-6-phosphate

Productsare released

Active site

Regulation of Enzyme Activity

• Enzymes are affected by any variable that affects chemical reactions

1. pH

2. Temperature

3. Concentration

of enzyme

Homework

1. What happens to chemical bonds during chemical reactionsBonds are broken in reactants and new bonds are formed in products

2. Describe the role of energy in chemical reactionssome chemical reactions release energy, and other chemical reactions absorb energy. Energy changes determine how easily a chemical reaction will occur

3. What are enzymes, and how are they important to living things?

Enzymes are biological catylasts. Cells use enzymes to speed up virtually every important chemical reaction that takes place in cells

4. Describe how enzymes work, including the role of the enzyme substrate complex

Substrates, the reactants of an enzyme-catylzed reaction, attach to the enzyme at an active site and form an enzyme – substrate complex. Once the complex is formed, the enzyme helps convert substrate into product

5. A change in pH can change the protein. How might a change in pH affect the function of an enzyme such as hexokinase (hint: think about the analogy of the lock and key)

A change in pH could change the shape of hexokinase. This change would diminish the ability of glucose and ATP to bind to the active site of the enzyme.