Organic ChemistryChapters 2 and 3

• Organisms are composed of matter– Anything that takes up space and has

mass– An element is a substance that cannot be

broken down to other substances by chemical reactions.

– A compound is a substance consisting of two or more elements combined in a fixed ratio

• Ex. NaCl

• Life requires 25 of the 92 natural elements.– Carbon, oxygen, hydrogen, and nitrogen make

up 96% of living matter– Phosphorus, sulfur, calcium, potassium, and a

few other elements make up the rest of the 4%.

• Trace elements are those required by an organism in only minute quantities.

– An atom is the smallest unit of matter that still retains the properties of an element

• Subatomic particles– Neutrons- neutral, nucleus– Protons- positive, nucleus– Electrons- negative, electron cloud

• Measure the mass of atoms and subatomic particles in daltons– The dalton is the same as the atomic mass unit, or amu)

• Protons and neutrons have masses close to 1 dalton

• Atomic number- number of protons in an element– Written as a subscript to the left of the symbol for the

element. (2He)

• Mass number- sum of protons and neutrons in the nucleus of an atom.– Written as a superscript to the left of an element’s symbol

42He

• Atomic weight- total weight of an atom (including electrons)

• Isotopes– Different forms of atom– Different number of neutrons– Nature- elements occur as a mixture of its

isotopes– Behave identically in chemical reactions– Radioactive isotopes- the nucleus decays

spontaneously, giving off particles and energy.• When the decay leads to a change in the number of

protons, it transforms the atom to an atom of a different element.

– Used to date fossils– Acts as tracers to follow atoms through metabolism– Diagnostic tools

• Energy levels of electrons– Electrons are directly involved in the chemical

reactions between atoms– An atom’s electrons vary in the amount of energy

they possess• Electrons of an atom have potential energy because of

their position in relation to the nucleus.– The more distant the electrons are from the nucleus the

greater their potential energy.– Different states of potential energy that electrons have

are called energy levels, or electron shells.

• Electron configuration and chemical properties

• First shell can hold no more than 2 electrons• Second shell holds a maximum of 8 electrons

– Chemical behavior of an atom depends mostly on the number of electrons in its outermost shell called valence electrons

• Electron orbitals– The three dimensional space where an

electron is found 90% of the time is called an orbital.

• Each electron shell consists of a number of orbitals of specific shapes.

• No more than 2 electrons can occupy the same orbital.

– S shaped orbitals are spherical and hold 2 electrons

– P orbitals are dumbbell shaped

Chemical bonding

• Covalent bonds– Sharing of a pair of valence electrons by two

atoms• Molecule- two or more atoms held together by covalent

bonds• Structural formula H-H

• Molecular formula H2

• Double covalent bond- sharing two pairs of valence electrons

– Nonpolar and polar covalent bonds• Electronegativity- attraction of an atom for the

electrons of a covalent bond– The more electronegative an atom, the more

strongly it pulls shared electrons toward itself.– Nonpolar covalent bond- electrons are shared

equally– Polar covalent bond- one atoms is bonded to a

more electronegative atom, electrons are not shared equally

» Ex. water

• Ionic bond– Two atoms are so unequal in their attraction for valence

electrons that the more electronegative atom strips an electron completely away from its partner.

– a charged atom (or molecule) is called an ion• When the charge is positive, the ion is called at cation• Anion- negatively charged ion

– Ionic bond- attraction between cation and anions– Ionic compounds (salts)- compounds formed by ionic

bonds• Found in nature as crystals of various sizes and shapes

– Ion also applies to entire molecules that are electrically charged.

– Environment affects the strength of ionic bonds.

• Weak chemical bonds play important roles in the chemistry of life– Hydrogen bonds

• Forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom.

– Usually oxygen or nitrogen atoms– Van der Waals interactions

• Enables all atoms and molecules to stick to one another• Occur only when atoms and molecules are very close

together.

• A molecule’s biological function is related to its shape– Molecule has a characteristic size and

shape• Shapes are determined by the positions of the

atoms’ orbitals.

– Determines how most biological molecules recognize and respond to one another.

• Chemical reactions make and break chemical bonds

• Reactants- starting materials• products• Coefficients indicate the number of molecules

involved• All atoms of the reactants must be accounted

for in the products• Some reactions go to completion, but most

reactions are reversible.

– Factors affecting the rate of reaction• Concentration of reactants• Concentration of products• Chemical equilibrium- point at which the

reactions offset one another exactly– Does not mean that the reactants and products are

equal in concentration

Water

• Polar– Oxygen is more electronegative than hydrogen, electrons

spend more time closer to oxygen– Shaped like a wide V– Properties of water arise from attractions between polar

molecules

• Cohesion– Water molecules stick to each other as a result of

hydrogen bonding.– Contributes to the transport of water against

gravity in plants.– Adhesion- clinging of one substance to another

• Adhesion to the walls of the vessels helps counter the downward pull of gravity

– Surface tension- measure of how difficult it is to stretch or break the surface of a liquid.

• Water has a greater surface tension that most liquids.

• Stabilizes Temperature– Water stabilizes air temperatures by

absorbing heat from air that is warmer and releasing the stored heat to air that is cooler.

– Heat and temperature• Anything that moves has kinetic energy

– Faster a molecule moves, the greater its kinetic energy• Heat is a measure of the total quantity of kinetic energy

due to molecular motion in a body of matter• Temperature measures the intensity of heat due to the

average kinetic energy of the molecules.• Whenever two objects of different temperature are

brought together, heat passes from the warmer to the cooler body until the two are the same temperature.

• Celsius Scale• Calorie- amount of heat energy it takes to raise the

temperature of 1g of water by 1 degree C• Kilocalorie• Joule- one joule equals 0.239 cal( cal=4.184J)

– Specific heat• The amount of heat that must be absorbed or lost for 1g

of that substance to change its temperature by 1°C– 1 calorie per gram per degree C (1cal/g/°C)

• Relatively high specific heat

– Evaporative cooling• Evaporation (vaporization) - transformation from a liquid

to a gas– Some evaporation occurs at any temperature

• Heat of vaporization- quantity of heat a liquid must absorb for 1 g of it to be converted from the liquid to the gaseous state.

– Water has a high heat of vaporization– Helps moderate Earth’s climate

• Evaporative cooling– As a liquid evaporates, the surface of the liquid remains

behind cools down– Hottest molecules are the most likely to leave as a gas

• Expansion upon freezing– Less dense as a solid than as a liquid.– Due to hydrogen bonding– Important factor in the fitness of the

environment

• Solvent– solution

• Liquid that is a completely homogeneous mixture of two or more substances

• Solvent- dissolving agent; solute- substance that is dissolved

• Aqueous solution- water is the solvent– Not a universal solvent but a very versatile

solvent due to its polarity– Hydration shell- sphere of water molecules

around each dissolved ion. – Can dissolve ionic compounds and polar

molecules that are water soluble (sugars)

– Hydrophobic and hydrophilic substances• Hydrophilic- has an affinity for water

– Used even if doesn’t dissolve because molecules are too large

• Hydrophobic-substances that do not have an affinity for water

– Non-ionic and nonpolar– Repeal water

– Solute concentration• Most of the chemical reactions that occur in organisms

involve solutes dissolved in water• Calculate the concentrations of solutes dissolved in

aqueous solutions– A mole is equal in number to the molecular weight of a

substance– Molecular weight is the sum of the weights of all the

atoms in a molecule.– Advantage of measuring in moles is that a mole of one

substance has exactly the same number of molecules as a mole of another substance.

– The number of molecules in a mole (Avogadro’s number) is 6.02 x 1023

– Molarity- the number of moles of solute per liter of solution

Dissociation of Water

• Hydrogen ion- single proton with a charge of +1• Hydroxide ion- water molecule that lost a proton

(OH-) and has a charge of -1• Proton binds to the other water molecule, making a

hydronium ion (H3O+)• Easier to think of it as the dissociation of water into

a hydrogen ion and a hydroxide ion• Hydrogen and hydroxide ions are very reactive

– Changes in their concentrations can drastically affect a cell’s proteins and other complex molecules.

– Pure water : concentrations are equal

• pH– Acids and bases

• Acids increase the hydrogen ion concentration of a solution (ex. HCl)

• Bases reduce hydrogen ion concentration– Some bases reduce directly by accepting hydrogen

ions (Ammonia, NH3)– Other bases reduce the hydrogen ion concentration

by dissolving to form hydroxide ions, which then combine with hydrogen ions to form water (NaOH)

• HCl is a strong acid and NaOH is a strong base because they dissociate completely.

– pH scale• In any aqueous solution, the product of the H+

and OH- concentrations is constant at 10-14. • The pH scale, which ranges from 0 to 14,

compresses the range of H+ and OH- concentrations by employing logarithms

– The pH of a solution is defined as the negative logarithm (base 10) of the hydrogen ion concentration.

– pH declines as H+ concentration increases.– Acids are below 7, bases are above 7– Most biological fluids are within the pH 6 to pH 8

range.

– Buffers• Internal pH of most living things is close to 7• Buffers are substances that minimize changes in the

concentrations of H+ and OH- in a solution. – Work by accepting hydrogen ions from the solution when

they are in excess and donating hydrogen ions to the solution when they have been depleted.

• Acid precipitation– Uncontaminated rain has a pH of about 5.6 allowing the

formation of carbonic acid from carbon dioxide and water– Acid precipitation refers to rain, snow, or fog that is more

acidic than 5.6– Caused primarily by the presence in the atmosphere of

sulfur oxides and nitrogen oxides– Effect of acids in lakes and streams is most pronounced in

the spring, as snow begins to melt.– Direct effects on forests and other terrestrial life is

controversial

Organic Compounds

Carbon

• Compounds containing carbon are said to be organic– Organic chemistry- branch of chemistry that specializes in

the study of carbon compounds

• Versatile building blocks– carbon usually completes its valence

shell by sharing elections with other atoms in four covalent bonds.

• Tetravalence is one facet of carbon’s versatility that makes large, complex molecules possible.

• Variation in carbon skeletons contributes to diversity– Carbon chains form the skeletons of most organic

molecules• Can vary in length and may be straight, branched, or arranged

in closed rings

– Hydrocarbons are organic molecules consisting only of carbon and hydrogen

• Hydrophobic (bonds between C and H are nonpolar)• Store a relatively large amount of energy

– Isomers• Same molecular formula but different structures and

different properties• Structural isomers

– Differ in the covalent arrangements of their atoms– Location of double bonds

• Geometric isomers– Same covalent partnership, but differ in their spatial

arrangements

• Enantiomers– Mirror images of each other– Usually one isomer is biologically active and the other is

inactive.– Important in pharmaceutical industry

Functional Groups

• Functional groups– Components of organic molecules that are most commonly

involved in chemical reactions– Each functional group behaves consistently from one

organic molecule to another, and the number and arrangement of the groups help give each molecule its unique properties.

– Six functional groups most important in the chemistry of life are:

• Hydroxyl• Carbonyl• Carboxyl• Amino• Sulfhydryl• Phosphate

– All are hydrophilic, increasing solubility in water

• Hydroxyl group– A hydrogen atom is bonded to an oxygen

atom, which in turn is bonded to the carbon skeleton of the organic molecule

– Compounds containing hydroxyls are called alcohols.

• Names end in –ol (ex. Ethanol)• Abbreviated as –OH or –HO

– is polar

• Carbonyl Group– Consists of a carbon atom joined to an

oxygen atom by a double bond– Aldehyde- carbonyl on end of compound

• proponal

– Ketone- carbonyl anywhere else in compound

• Acetone– Acetone and proponal are isomers

• Carboxyl– Oxygen atom is double-bonded to a carbon atom

that is also bonded to a hydroxyl group (-COOH)– Called carboxylic acids or organic acids

• Ex. Formic acid, acetic acid

– Source of hydrogen ions

• Amino Group – Consists of a nitrogen atom bonded to 2

hydrogen atoms and to the carbon skeleton (-NH2)

– Called amines• Ex. Glycine

– Also has a carboxyl group– Most organic compounds have 2 or more different

functional groups– Compounds having both amino and carboxyl

groups are called amino acids

• Sulfhydryl Group– sulfur atom bonding to an atom of

hydrogen (-SH)– Called thiols

• Phosphate group– Have a phosphate ion covalently attached

by one of its oxygen atoms to the carbon skeleton.

– One of functions is to transfer energy between organic molecules

Polymer Principles

• Most macromolecules are polymers– A polymer is along molecule consisting of many similar or

identical building blocks linked by covalent bonds.• Repeating units that serve as building blocks of a polymer are

small molecules called monomers.

– Condensation reaction- monomers are connected by a reaction in which two molecules are covalently bonded to each other through loss of a water molecule

• Specifically a dehydration reaction because the molecule lost is water

• One molecule provides a hydroxyl group (-OH) while the other provides a hydrogen (-H)

• Cell must expend energy • Process occurs only with the help of enzymes

– Polymers are disassembled to monomers by hydrolysis

• Reverse of dehydration• Break with water

• Polymer variety– Each cell has thousands of different kinds

of macromolecules– Molecules are constructed from only 40 to

50 common monomers and some others that occur rarely.

• Key is arrangement

Carbohydrates

• Include both sugars and their polymers– Simplest- monosaccharide (single sugar)– Disaccharides- double sugars– Polysaccharides- many sugars

• Monosaccharides– Have molecular formulas that are some multiple of CH2O.

• Glucose is the most common– Has a carbonyl group and multiple hydroxyl groups

– Classifying sugars• Depending on location of the carbonyl group, a sugar is either

an aldose (aldehyde sugar) or a ketose (ketone sugar)– Glucose is an aldose, fructose (structural isomer of glucose) is a

ketose

• Most names for sugars in end –ose• Size of carbon skeleton

– Ranges from three to seven carbons long» Glucose, fructose, and other sugars that have six carbons

are called hexoses. Trioses (3 carbon sugars) and pentoses (five carbon sugars) are also common.

• Spatial arrangement of their parts around asymmetric carbons– Ex. Glucose and galactose (differ only in placement of parts)

– Most sugars form rings– Monosaccharides are major nutrients for

cells– Functions

• major fuel for cellular work• Carbon skeletons serve as raw materials for

the synthesis of other types of small organic molecules such as amino acids and fatty acids

• Disaccharides– Two monosaccharides joined by a

glycosidic linkage• Glycosidic linkage is a covalent bond formed

between two monosaccharides by a dehydration reaction.

• Polysaccharides– Are macromolecules, polymers with a few

hundred to a few thousand monosaccharides joined by glycosidic linkages.

– Some serve as storage material, hydrolyzed as needed to provide sugar for cells

– Others serve as building material for structures that protect the cell or the whole organism

– Architecture and function of a polysaccharide are determined by its sugar monomers and my the positions of its glycosidic linkages.

– Storage polysaccharides• Starch is a storage polysaccharide of plants

– Consists mainly of glucose monomers– Most of monomers are joined by 1-4 linkages

(number 1 carbon to number 4 carbon)– Angle of these bonds makes the polymer helical.

» Simplest form of starch, amylose, is unbranched

» Amylopectin, a more complex form of starch, is a branched polymer with 1-6 linkages at the branch points.

– Plants store starch as granules within cellular structures called plastids, including chloroplasts

– Starch represents stored energy– Most animals have enzymes that can hydrolyze plant starch

• Animals store a polysaccharde called glycogen– Humans and other vertebrates store glycogen mainly in liver and

muscle cells– Hydrolysis of glycogen in these cells releases glucose when the

demand for sugar increases.– Stored fuel cannot sustain an animal for long– Glycogen bank is depleted in about a day unless it is

replenished by consumption of food

– Structural polysaccharides• Organisms build strong materials from structural

polysaccharides• Cellulose is a major component of the though walls that

enclose plant cells– Two different ring structures for glucose

» Alpha (α) and Beta (β)– In cellulose, all of the glucose molecules are in the β

configuration– , a cellulose molecule is straight (never branched), and its

hydroxyl groups are free to hydrogen bond with the hydroxyls of other cellulose molecules lying parallel to it.

– In plant cell walls, parallel cellulose molecules held together in this way are grouped into units called microfibrils.

– Enzymes that digest starch by hydrolyzing α linkages are unable to hydrolyze the β linkages of cellulose.

• Chitin– Another important structural polysaccharide used by

arthropods to build exoskeletons

Lipids

• Does not include polymers

• Grouped together because they share one important trait: little or no affinity for water

• Hydrophobic behavior is based on molecular structure

• Consist mostly of hydrocarbons

• Fats store large amounts of energy– Constructed from two kinds of smaller molecules: glycerol

and fatty acids• Glycerol is an alcohol with three carbons, each containing a

hydroxyl group• A fatty acid has a long carbon skeleton, usually 16 or 18

carbon atoms in length with a carboxyl group at one end.– The nonpolar C-H bonds in the hydrocarbon chains of fatty acids

make the molecule hydrophobic.• Making a fat, three fatty acids each join to a glycerol by an

ester linkage– Ester linkage- a bond between a hydroxyl group and a carboxyl

group– Called a triacylglycerol or triglyceride

• Fatty acids vary in length and the number and locations of double bonds

– Saturated fats» No double bonds between the carbon atoms

composing the chain, then as many hydrogen atoms as possible are bonded to the carbon skeleton

» Most animal fats are saturated » Solid at room temperature

– Unsaturated fats» Has one or more double bonds, formed by the

removal of hydrogen atoms from the carbon skeleton» Fats of plants and fishes» Usually liquid at room temperature and often referred

to as oils» Kinks where double bonds are located prevent the

molecules from packing closely enough together to solidify

• Major function of fats is energy storage– A gram of fat stores more than twice as much

energy as a gram of a polysaccharide, such as starch.

– Humans and other mammals stock their long term food reserves in adipose cells which swell and shrink as fat is deposited and withdrawn from storage.

» Adipose tissue also cushions such vital organs as the kidneys and a layer of fat beneath the skin insulates the body

• Phospholipids– Similar to fats, but only have two fatty acid tails rather than three– Phospholipids show ambivalent behavior toward water

• Their tails, which consist of hydrocarbons, are hydrophobic and are excluded from water

• The phosphate group and its attachments form a hydrophilic head that has an affinity for water.

• micelle, a phospholipid droplet with the phosphate heads on the outside, in contact with water; hydrocarbon tails restricted to the water free interior of the micelle

– At the surface of a cell, phospholipids are arranged in a bilayer• Hydrophilic heads are on the outside, hydrophobic tails point toward

the interior• Forms a boundary between the cell and its external environment• Major components of cell membranes

• Steroids– Lipids characterized by a carbon skeleton

consisting of four fused rings– Different steroids vary in the functional groups

attached to this ensemble of rings. – Cholesterol

• Common component of animal membranes and is also the precursor from which other steroids are synthesized.

– Many hormones, including vertebrate sex hormones, are steroids produced from cholesterol

Proteins• Used for structural support, storage, transport of

other substances, signaling from one part of the organism to another, movement, and defense against foreign substances.

• As enzymes, proteins regulate metabolism by selectively accelerating chemical reactions in the cell

• All proteins are polymers constructed from the same set of 20 amino acids.– Polymers of amino acids are called polypeptides– A protein consists of one or more polypeptides folded and

coiled into specific conformations

• Polypeptides– Amino acids are organic molecules possessing

both carboxyl and amino groups.• α carbon attached to:

– Amino group, carboxyl group, hydrogen atom, and a variable group symbolized by R

• The R group, also called the side chain, differs with the amino acid

– Physical and chemical properties of the side chain determines the unique characteristics of a particular amino acid.

» Nonpolar, hydrophobic» Polar, hydrophilic» Electrically charged (either acidic or basic)

– Amino acids are joined by catalyzing a dehydration reaction

• Resulting bond is a peptide bond.• Repeated to form a polypeptide• At one end of the polypeptide is a free amino

group, and at the opposite end is a free carboxyl group.

– Chain has an amino end (N-terminus) and a carboxyl end (C-terminus)

• Protein function– A functional protein is not just a

polypeptide chain, but one or more polypeptides precisely twisted, folded, and coiled into a molecule of unique shape.

• Amino acid sequence determines the 3-D shape (conformation)

• A protein’s specific conformation determines how it works

• Function of a protein depends on its ability to recognize and bind to another molecule

– Four levels of Protein Structure• Primary Structure

– Unique sequence of amino acids– Like the order of letters in a very long word– Determined by inherited genetic information– Even slight changes can affect a protein’s conformation

and ability to function

• Secondary structure– Segments of the polypeptide chain repeatedly coiled or

folded– Result of hydrogen bonds at regular intervals along the

polypeptide backbone» α helix- delicate coil held together by hydrogen

bonding between every 4th amino acid» β pleated sheet-two or more regions of the

polypeptide chain lie parallel to each other. Hydrogen bonds between the parts of the backbone in the parallel regions hold the structure together

• Tertiary structure– Consists of irregular contortions from interactions

between side chains (R groups) of the various amino acids.

» Hydrophobic interaction» Disulfide bridges- form where 2 cysteine

monomers are brought close together by the folding of the protein.

» Hydrogen bond» Ionic bond

• Quaternary Structure– The overall protein structure that results from the

aggregation of two or more polypeptide chains.

– Protein conformation• Depends on the physical and chemical conditions of the

protein’s environment– If the pH, salt concentration, temperature, or other aspects of the

environment are altered, the protein may unravel and lose its native conformation, called denaturation

» is biologically inactive» Most proteins become denatured when transferred from an

aqueous environment to an organic solvent (ether or chloroform)

» Chemicals that disrupt the hydrogen bonds, ionic bonds, and disulfide bridges that maintain a protein’s shape.

» Excessive heat» When a protein in a test-tube solution has been denatured

by heat or chemicals, it will often return to its functional shape when the denaturing agent is removed.

• Chaperonins (chaperone proteins)– Protein molecules that assist the proper folding of other

proteins– Do not specify the correct final structure of a polypeptide– Keep the new polypeptide segregated from “bad

influences” in the cytoplasmic environment while it fold spontaneously.

– Determining the structure of a protein• X-ray crystallography

– Main method used to determine 3-D shape– Depends on the diffraction (deflection) of an x-ray beam

by the individual atoms in a crystal of protein

Nucleic Acids

• The amino acid sequence of a polypeptide is programmed by a unit of inheritance known as a gene– Genes consist of DNA which is a polymer

belonging to the class of compounds known as nucleic acids

• Nucleic Acids store and transmit hereditary information– Two types of nucleic acids

• DNA • RNA

– DNA• Is the genetic material that organisms inherit from their

parents• Consists of hundreds or thousands of genes• Encoded within the structure is the information that

programs all the cell’s activities.

– RNA• DNA directs the synthesis of messenger RNA (mRNA).• The mRNA molecule then interacts with the cell’s

protein-synthesizing machinery to direct the production of a polypeptide

• DNARNAprotein• Eukaryotic cell

– Ribosomes are located in the cytoplasm– DNA- nucleus– mRNA conveys the genetic instructions for building

proteins from the nucleus to the cytoplasm• Prokaryotic cells

– Lack nuclei– Use RNA to send a message from the DNA to the

ribosomes and other equipment of the cell that transalt the coded information into amino acid sequences.

• Nucleic Acid Structure– Are polymers of nucleotides

• Nitrogenous base• Pentose sugar (5 Carbon)• Phosphate group

– Types of nitrogenous bases• Pyrimidine

– Has a six membered ring of carbon and nitrogen atoms– Cytosine– Thymine– Uracil

• Purines– Larger, with the six membered ring fused to a five membered

ring – Adenine– Guanine

• Adenine , Guanine, and Cytosine are found in both types of Nucleic acid

– Thymine is only found in DNA– Uracil- RNA

– Pentose sugar• Ribose in RNA• Deoxyribose in DNA

– Lacks an oxygen atom on its number 2 carbon

– Nucleoside monophosphate- or nucleotide– Polynucleotide- nucleotides are joined by covalent bonds

called phosphodiester linkages between the phosphate of nucleotide and the sugar of the next

• Results in a backbone with a repeating pattern of sugar-phosphate units

– The sequence of bases along a DNA (or mRNA) polymer is unique for each gene.

• Number of possible base sequences is limitless• Linear order of bases in a gene specifies the amino acid

sequence (Primary structure) of a protein

• Inheritance is based on replication of the DNA double helix– RNA molecules consist of a single polynucleotide chain– DNA has 2 polynucleotides that spiral around an imaginary

axis to form a double helix• 1953 Watson and Crick• Sugar-phosphate backbones are the outside of the helix• Nitrogenous bases are paired in the interior• Polynucleotides are held together by hydrogen bonds

between the paired bases and by van der Waals interactions between the stacked bases.

– A goes with T– G goes with C– Both strands are complementary to each other

• Genes (DNA) and their products (proteins) document the hereditary background of an organism.– DNA sequences determine amino acid

sequences of proteins– Siblings have greater similarity in their DNA and

proteins than do unrelated individuals of the same species

– Two species that appear to be closely related based on fossil and anatomical evidence should also share a greater proportion of their DNA and protein sequences than do more distantly related species.