Chapter 2. The Chemistry of Life

2.1 The Nature of MatterAtoms Protons (+) Neutrons (0)

Protons and Neutrons have the same mass

Protons and neutrons form the nucleus, the center of the atom

Electrons (-) In constant motion 1/1840 the mass of proton Equal number of electrons

and protons (atoms remain neutral)

Forms electron cloud.

2.1 The Nature of MatterElements Element - a pure

substance that consists entirely of one type of atom

More than 100 elements are known

Elements are represented by a one- or two-letter symbol

Nonradioactive carbon-13 Radioactive carbon-14

6 electrons6 protons6 neutrons

6 electrons6 protons7 neutrons

6

C12.011

2.1 The Nature of MatterElements Atomic Number –

the number of protons in an atom of an element

Mass number – the sum of protons and neutrons in the nucleus of an atom

Radioactive carbon-14

6

CCarbon12.011

Atomic Number

Element Symbol

Atomic Mass

Element Name

2.1 The Nature of MatterIsotopes

Atoms of elements can have different numbers of neutrons Isotopes – atoms of the same element that differ in the

number of neutrons they contain Identified by their mass number Because they have the same number of electrons,

all isotopes of an element have the same chemical properties.

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

6 electrons6 protons6 neutrons

6 electrons6 protons8 neutrons

6 electrons6 protons7 neutrons

2.1 The Nature of MatterRadioactive Isotopes

Some isotopes are radioactive – meaning their nuclei are unstable and break down at a constant rate over time

Radiation can be dangerous, but also have a number of important scientific and practical uses

Examples: Geologists determine the age of rocks and fossils Can treat cancer Kill bacteria that cause food to spoil Can be used as “tracers” to follow the

movements of substances within organisms

2.1 The Nature of MatterChemical Compounds Most elements are

combined with other elements

Compound – a substance formed by the chemical combination of two or more elements in definite proportions

Ex. Water (H20) and table salt (NaCl)

2.1 The Nature of MatterChemical Compounds The physical and

chemical properties of a compound are usually very different from those of the elements from which it is formed

Let’s examine water and table salt…

2.1 The Nature of MatterChemical Bonds

The atoms of compounds are held together by chemical bonds

Bond formation involves the electrons. The electrons that are available to form bonds

are called valence electrons. The main types of chemical bonds are

ionic bonds and covalent bonds.

2.1 The Nature of MatterIonic Bonding Ionic Bond – formed when one or more electrons are

transferred from one atom to another Atoms are electrically neutral Loses an electron – positive charge (cations) Gains an electron – negative charge (anions) Called ionsSodium 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

2.1 The Nature of MatterCovalent Bonding Sometimes electrons are

“shared” instead of transferring Covalent bond – forms when

electrons are shared between atoms

Share two electrons – single covalent bond

Share four electrons – double covalent bond

Share six electrons – triple covalent bond

The structure that results when atoms are joined together by covalent bonds is a molecule,

The molecule is the smallest unit of most compounds.

2.1 The Nature of MatterVan der Waals Forces Atoms do not all have

the same ability to attract electrons

Creates regions that may have a tiny positive or negative charge.

Van der Waals forces – when molecules are close together, a slight attraction can develop between the oppositely charged regions of nearby molecules.

Section 2WATER!

2.2 Properties of WaterThe Water Molecule Earth is called “the

Blue Planet.” How much water covers the earth’s surface?

Water is the single most abundant compound in most living things

Ice is less dense than liquid water.

2.2 Properties of WaterThe Water Molecule - Polarity

A molecule in which the charges are unevenly distributed is called a polar molecule

A water molecule is polar because there is an uneven distribution of electrons between the oxygen and hydrogen atoms.

The negative pole is near the oxygen atoms and the positive pole is between the hydrogen atoms.8 protons

1 proton+

-_

2.2 Properties of WaterThe Water Molecule – Hydrogen Bonds Because of their partial

positive and negative charges, polar molecules can attract to each other.

The attraction between H atom of one water molecule and the O of another is an example of hydrogen bonds.

Hydrogen bonds are NOT as strong as covalent or ionic bonds.

2.2 Properties of WaterThe Water Molecule – Hydrogen Bonds

A single water molecule can be involved in as many as four hydrogen bonds.

Cohesion – an attraction between molecules of the same substance.

Adhesion – the attraction between molecules of different substances.

Ex. Capillary action.Is this cohesion or adhesion???

Cohesion and Surface Tension.

2.2 Properties of WaterThe Water Molecule – Review1. What kind of bonds

join the atoms in a water molecule?

2. Are the hydrogen atoms bonded to each other?

3. Why is the hydrogen end of the molecule positive and the oxygen end negative?

PG 40

2.2 Properties of WaterSolutions and Suspensions Water is not always pure

– it is often found as a mixture.

Mixture – a material composed of two or more elements, but are not chemically combined.

Ex. Salt and pepper. Two types of mixtures

that can be made from water: solutions and suspensions.

2.2 Properties of WaterSolutions Look below, sodium and chloride ions are attracted

to the polar water molecules. The ions become dispersed in the water, forming a

mixture called a solution. Solutions – evenly distributed throughout the

solution.

Cl-

Water

Cl-

Na+

Water

Na+

2.2 Properties of WaterSolutions Solute – the substance that is dissolved. Solvent – the substance in which the solute dissolves.

What is the solute and solvent in the saltwater solution?

Cl-

Water

Cl-

Na+

Water

Na+

2.2 Properties of WaterSuspensions

Some materials do not dissolve, but when placed in water separate into pieces so small they do not settle out.

These mixtures are known as suspensions.

Ex. Blood

2.2 Properties of WaterAcids, Bases, and pH Water can react to form ions.

H20 H+ + OH-

(water) hydrogen hydroxide ion ion

Water is neutral because the number of positive hydrogen ions produced is equal to the number of negative hydroxide ions produced.

2.2 Properties of WaterThe pH Scale The pH scale is used to indicate

the concentration of H+ ions. Ranges from 0-14 7 - neutral Below 7 – acidic (more H+)

Ex. Hydrochloric acid in the stomach

Above 7 – basic (more OH-) Ex. lye

Each scale represents a factor of ten.

Buffers – weak acids or bases that can react with strong acids or bases to prevent sharp, sudden changes. Ex. Maintain homeostasis

Oven cleaner

Bleach

Ammonia solution

Soap

Sea water

Human bloodPure waterMilkNormalrainfall

Acid rainTomatojuice

Lemon juice

Stomach acid

Neutral

Incr

easi

ngly

Bas

icIn

crea

sing

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cidi

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Section 3MACROMOLECULES!

2.3 Carbon CompoundsThe Chemistry of Carbon Organic chemistry – the study of all compounds that contain bonds

between carbon atoms Why is carbon so important?

Has four valence electrons (forms strong covalent bonds) Can bond with: hydrogen, phosphorus, sulfur, and nitrogen Can also bond with other carbon atoms (form chains of unlimited length) Single, double, or triple covalent bonds Can form large and complex structures.

Methane Acetylene Butadiene Benzene Isooctane

2.3 Carbon CompoundsMacromolecules Macromolecules –

“giant molecules” The smaller units, or

monomers, join together to form polymers. (polymerization)

Four groups of organic compounds found in living things are carbohydrates, lipids, nucleic acids, and proteins.

2.3 Carbon CompoundsMacromolecules

CarbonCompounds

include

that consist of

which contain

that consist of that consist of that consist of

which contain which contain which contain

Carbohydrates Lipids Nucleic acids Proteins

Sugars and starches Fats and oils Nucleotides Amino Acids

Carbon,hydrogen,

oxygen

Carbon,hydrogen,

oxygen

Carbon,hydrogen,oxygen, nitrogen,

phosphorus

Carbon,hydrogen,oxygen,

nitrogen,

2.3 Carbon CompoundsCarbohydrates

Carbohydrates are compounds made up of carbon, hydrogen, and oxygen atoms, usually in a ratio of 1:2:1.

Living things use carbohydrates as a main source of energy.

Plants and some animals use carbohydrates for structural reasons.

Starch

Glucose

What is the monomer? What is the polymer?

2.3 Carbon CompoundsCarbohydrates Simple sugars are called

monosaccharides. Ex. Glucose (simple sugar),

galactose (found in milk), and fructose (found in many fruits)

The large macromolecules formed from monosaccharides are known as polysaccharides. Ex. Glycogen (animal

starch), plant starch (store excess sugar), and cellulose in plants (gives plants strength and rigidity)

2.3 Carbon CompoundsLipids Lipids – are made

mostly from carbon and hydrogen atoms. (composed of glycerol and fatty acids)

Three classes: fats, oils, and waxes Can be used for energy, biological membranes, and waterproof coverings.

Steroids are also included. Used as a chemical messenger.

What’s the difference between saturated and unsaturated fats???

2.3 Carbon CompoundsLipids

Saturated – fatty acids contain the maximum possible number of hydrogen atoms.

Unsaturated – if there is at least one carbon-carbon double bond in a fatty acid

Polyunsaturated – lipids whose fatty acids contain more than one double bond.

Unsaturated

Saturated

2.3 Carbon CompoundsNucleic Acids

Nucleic acids – are macromolecules containing hydrogen, oxygen, nitrogen, and phosphorus

Nucleic acids are polymers that are composed of monomers called nucleotides.

Nucleotides consist of three parts: a 5 carbon sugar, a phosphate group, and nitrogenous base.

Nucleic acids store and transmit heredity, or genetic, information.

2.3 Carbon CompoundsProteins Proteins – are macromolecules containing hydrogen,

oxygen, nitrogen, carbon, and phosphorus. Proteins are polymers of molecules called amino acids. Amino acids contain an amino group one end and a

carboxyl group on the other.

General structure Alanine Serine

Carboxyl group

Amino group

2.3 Carbon CompoundsProteins

More than 20 amino acids found in nature

Amino acid can bond to any amino acid at the amino group

Instructions for arranging amino acids into a protein is found in DNA.

Uses for proteins: control the rate of reaction (enzymes), regulate cell processes, some are used to form muscle and bone, others transport substances in and out of cells

Van der Waals forces and hydrogen bonds help maintain a proteins shape.

Aminoacids

1. Protein chains.2. Protein can be twisted or folded.3. Protein chain can fold itself.

2.4 Chemical Reactions and EnzymesChemical Reactions Chemical Reactions – a

process that changes, or transforms, one set of chemicals into another.

Reactants – the elements or compounds that enter into a chemical reaction.

Products – the elements or compounds produced by a chemical reaction

Chemical reactions always involve changes in chemical bonds that join atoms in compounds.

2.4 Chemical Reactions and EnzymesChemical Reactions

Ex. Conversion of carbon dioxide to carbonic acid in the human body.

CO2 + H20 H2CO3

H2CO3 CO2 + H20

Reactants Products

2.4 Chemical Reactions and EnzymesEnergy in Reactions

Energy is released or absorbed whenever chemical bonds form or are broken

Chemical reactions that release energy often occur spontaneously.

Chemical reactions that absorb energy will not occur without a source of energy.

Ex. Hydrogen gas burning with oxygen to produce water vapor.

2H2 + 02 2H20

How is energy released??

Living organisms need a constant source of energy to survive!!!!

2.4 Chemical Reactions and EnzymesActivation Energy

Not all chemical reactions that release energy occur spontaneously.

Chemists call the energy needed to get a reaction started the activation energy.

Energy-Absorbing Reaction Energy-Releasing Reaction

How would you compare the energy of the products and reactants in the two types of reactions?

Reactants

Products

Activation EnergyReactants

Activation Energy

Products

2.4 Chemical Reactions and EnzymesEnzymes Some chemical

reactions that are responsible for life are too slow.

These reactions are helped by catalysts

Catalyst – a substance that speeds up the rate of a chemical reaction.

Enzymes – proteins that act as biological catalysts. They speed up chemical reactions in cells.

Reaction pathwaywithout enzyme

Activation energywithout enzyme

Activationenergywith enzyme

Reaction pathwaywith enzyme

Reactants

Products

2.4 Chemical Reactions and EnzymesEnzymes Enzymes end in –ase

(Example. Carbonic anhydrase)

Enzymes are very specific

Enzymes provide a site where reactants can be brought together to react.

The reactants of enzyme-catalyzed reactions are known as substrates.

The substrates bind to a site on the enzyme called the active site.

2.4 Chemical Reactions and EnzymesEnzymes

Glucose

Substrates

ATP

Substratesbind toenzymeSubstrates

are convertedinto products

Enzyme-substratecomplex

Enzyme(hexokinase)

ADP

Products

Glucose-6-phosphate Products

are released Active site

2.4 Chemical Reactions and EnzymesEnzymes Enzymes can be

affected by many different variables.

pH, temperature, etc. Enzymes play an

essential role in regulating chemical pathways, making materials that cells need, releasing energy, and transferring information.