BIO152Lecture 3: Water, Carbon, and Macromolecules

Sept. 17, 2013

Prof. Rawle

@FiRawle #BIO152

Announcements• Evolution survey now available on Blackboard.

• Please note these slides are summary slides of chapters 2 and 3 in your text. We will not be covering all of these slides in class, but you are expected to know this material. Most of this material should be review from high school.

Ch 2: Key Concepts

Molecules form when atoms bond to each other. Chemical bonds are based on electron sharing. The degree of electron sharing varies from nonpolar covalent bonds to polar covalent bonds to ionic bonds.

Water is essential for life. Water is highly polar and readily forms hydrogen bonds. Hydrogen bonding makes water an extremely efficient solvent.

Energy is the capacity to do work or supply heat, and can be (1) a stored potential or (2) an active motion. Chemical energy is a form of potential energy, stored in chemical bonds.

Chemical reactions tend to be spontaneous if they lower potential energy and increase entropy (disorder). An input of energy is required for nonspontaneous reactions to occur.

Most of the important compounds in organisms contain carbon. Key carbon containing molecules formed early in Earth’s history.

Basic Atomic Structure

• Atoms are composed of:• Protons – positively charged particles• Neutrons – neutral particles• Electrons – negatively charged particles

• Protons and neutrons are located in the nucleus.

• Electrons are found in orbitals surrounding the nucleus.

Elements – The Building Blocks of Chemical Evolution

• Every different atom has a characteristic number of protons in the nucleus, called the atomic number.

• Atoms with the same atomic number have the same chemical properties and belong to the same element.

• The mass number is the number of protons + neutrons of the most common isotope.

• Forms of an element with different numbers of neutrons are isotopes.

Electron Arrangement around the Nucleus

• Electrons move around atomic nuclei in specific regions called orbitals.• Each orbital can hold up to two electrons.

• Orbitals are grouped into levels called electron shells. • Electron shells are numbered, with smaller numbers closer

to the nucleus. • The electrons in the outermost shell are called valence

electrons.

• Elements commonly found in organisms have at least one unpaired valence electron. The number of unpaired electrons in an atom is its valence.

Chemical Bonding

• Unfilled electron orbitals allow formation of chemical bonds, and atoms are most stable when each electron orbital is filled.

• Covalent bond: Each atom’s unpaired valence electrons are shared by both nuclei to fill their orbitals.

• Ionic bond: Electrons are transferred from one atom to another.

Substances held together by ionic or covalent bonds are called molecules.

Covalent Bonds

• Electrons are not always shared equally. An atom in a molecule with a high electronegativity will hold the electrons more tightly and have a partial negative charge (δ–), whereas the other atom will have a partial positive charge (δ+).

• Differences in electronegativity dictate how electrons are distributed in covalent bonds.

• Nonpolar covalent bond: Electrons are evenly shared between two atoms and the bond is symmetrical.

• Polar covalent bond: Electrons are asymmetrically shared.

Ions and Ionic Bonds

• An atom or molecule that carries a charge is called an ion.• Cation: An atom that loses an electron and becomes positively charged.• Anion: An atom that gains an electron and becomes negatively charged.

• The resulting attraction between oppositely charged ions is an ionic bond.

The Electron-Sharing Continuum

The degree to which electrons are shared in chemical bonds forms a continuum, from equal sharing in nonpolar covalent bonds, to unequal sharing in polar covalent bonds, to the transfer of electrons in ionic bonds.

How Many Bonds Can an Atom Have?

• The number of unpaired electrons determines the number of bonds an atom can make.

• Atoms with more than one unpaired electron can form multiple single bonds or double or triple bonds.

2-20Figure 2.9 The Geometry of Methane and Water.

Representing Molecules

• The shape of a simple molecule is governed by the geometry of its bonds.

• Molecular formulas indicate the numbers and types of atoms in a molecule (e.g., H2O, CH4).

• Structural formulas indicate which atoms are bonded together and whether the bonds are single, double, or triple bonds.

• Ball-and-stick models and space-filling models show 3D geometry.

Chemical Reactions

• Chemical reactions occur when:1. One substance is combined with another. • Atoms are rearranged in molecules, or small molecules combine to form larger

molecules.

2. One substance is broken down into another substance. • Molecules are split into atoms or smaller molecules.

• In most cases, chemical bonds are broken and new bonds form.

Quantifying Molecules

• The molecular weight of a molecule is the sum of the mass numbers of all the atoms in the molecule.

• One mole, or 6.022 1023 molecules, has a mass equal to the molecular weight expressed in grams.

• The concentration of a substance in a solution is typically expressed as molarity (M), which is the number of moles per liter.

Why Is Water Such an Efficient Solvent?

• Life is based on water because water is a great solvent.

• The covalent bonds in water are polar because oxygen has a greater electronegativity than hydrogen.• Oxygen has a partial negative charge. • Hydrogen has a partial positive charge.

• Hydrogen bonds are the weak electrical attractions between the partially negative oxygen of one water molecule and the partially positive hydrogen of a different water molecule.• Can also form between a water molecule and another polar molecule.

Water and Hydrogen Bonds

• Ions and polar molecules stay in solution because of their interactions with water’s partial charges. These atoms and molecules are said to be hydrophilic.

• Uncharged and nonpolar compounds do not dissolve in water and are said to be hydrophobic.

Hydrogen bonding makes it possible for almost any charged or polar molecule to dissolve in water.

Correlation of Water’s Structure and Properties

• Water is unique due to its small size, bent shape, highly polar covalent bonds, and overall polarity.

• Water also has several remarkable properties, largely due to its ability to form hydrogen bonds. Water is:

1. Cohesive

2. Adhesive

3. Denser as a liquid than a solid

4. Able to absorb large amounts of energy

A Closer Look at the Properties of Water

• Cohesion – binding between like molecules • Results in high surface tension

• Adhesion – binding between unlike molecules

• Water expands as it changes from a liquid to a solid.• This is why ice floats!

• Water has an extraordinarily large capacity for absorbing heat.• High specific heat• High heat of vapourization

Acid–Base Reactions and pH

• Proton [hydrogen ion (H+)] concentration is the basis of the pH scale.• pH expresses proton concentration in a solution.

• The pH of pure water is 7. • Acids have a pH of less than 7.• Bases have a pH of greater than 7.

• In acid–base reactions, a proton donor (acid) transfers a proton to a proton acceptor (base).

The pH Scale and Buffers

• The pH scale is logarithmic: pH = −log [H+]

• Greater H+ concentration – lower pH – more acidic • Lower H+ concentration – higher pH – more basic/alkaline

• Buffers are compounds that minimize changes in pH.

Chemical Evolution Theory

• Simple molecules present on ancient Earth reacted to create larger, more complex molecules.

• This may have happened in:• The atmosphere• Deep-sea vents

How Do Chemical Reactions Happen?

• Chemical reactions have reactants and products. For example:

CO2(g) + H2O(l) H2CO3(aq)

• Chemical equilibrium occurs when the forward and reverse reactions proceed at the same rate and the quantities of reactants and products remain constant.

• Endothermic reactions must absorb heat to proceed, but exothermic reactions release heat.

What Is Energy?

Energy is the capacity to do work or supply heat. This capacity exists in one of two ways—as a stored potential or as an active motion.

Potential Energy and Kinetic Energy

• Stored energy is called potential energy. An object’s position determines its ability to store energy. For example:• Electrons in an outer shell (farther from the positively

charged nucleus) have more potential energy than do electrons in an inner shell.

• The energy of movement is called kinetic energy or thermal energy, which is measured as temperature.• Low-temperature objects have slower molecules than high-temperature

objects.

Heat and the First Law of Thermodynamics

• Heat is the thermal energy transferred between objects of different temperatures.

• The first law of thermodynamics states that energy is conserved—it cannot be created or destroyed, but it can be transferred or transformed.

What Makes a Chemical Reaction Spontaneous?

Chemical reactions are spontaneous if they proceed on their own, without any continuous external influence such as added energy.

• The spontaneity of a reaction is determined by two factors:1. The amount of potential energy• Products of spontaneous reactions have less potential energy than the reactants.

2. The degree of order• Products of spontaneous reactions are less ordered than the reactants.

The Second Law of Thermodynamics

• Entropy (S) is the amount of disorder in a group of molecules.

• The second law of thermodynamics states that entropy always increases. • In other words, chemical reactions result in products with less ordered

(usable) energy.

• In general, physical and chemical processes proceed in the direction that results in lower potential energy and increased disorder.

Gibbs Free-Energy Change

• The Gibbs free-energy change (ΔG) determines whether a reaction is spontaneous or requires energy.

ΔG < 0 is an exergonic spontaneous reaction.

ΔG > 0 is an endergonic reaction that requires energy input.

ΔG = 0 is a reaction that is at equilibrium.

Temperature and Concentration Affect Reactions

• Breaking and forming bonds depends on collisions between substances.• This allows electrons to interact.

• The rate of a reaction depends upon the number of collisions.

• The number of collisions is dependent on the temperature and concentration of the reactants:• Higher temperature more collisions faster reaction• Higher concentration more collisions faster reaction

Energy Inputs and the Start of Chemical Evolution

• Formation of formaldehyde (H2CO) and hydrogen cyanide (HCN) is the first step in chemical evolution and requires energy input.

• Photons are packets of light energy emitted by the Sun.

• High-energy photons can break molecules apart by knocking electrons away from valence shells. The resulting free radicals have unpaired electrons and are extremely unstable and highly reactive.

Chemical Energy Is a Form of Potential Energy

• Significant amounts of H2CO and HCN could form under the temperature and concentration conditions that were likely on ancient Earth.• These products have more potential energy than the reactants.

• Potential energy stored in chemical bonds is called chemical energy.

• Thus: solar energy (energy of the Sun) was converted into chemical energy (in H2CO and HCN).

The Importance of Carbon

Carbon has great importance in biology because it is the most versatile atom on Earth. Because of its four valence electrons, it can form many covalent bonds. With different combinations of single and double bonds, an almost limitless array of molecular shapes is possible.

• The formation of carbon–carbon bonds was an important event in chemical evolution.

Functional Groups: Determinants of Chemical Behaviour

• The carbon atoms in an organic molecule furnish the skeleton that gives the molecule its overall shape.

• Amino and carboxyl groups: Attract or drop a proton, respectively

• Carbonyl groups: Sites of reactions that link molecules into larger, more-complex compounds

• Hydroxyl groups: Act as weak acids

• Phosphate groups: Have two negative charges

• Sulfhydryl groups: Link together via disulfide bonds

Canadian Research 2.1 The Carbon-Rich Tagish Lake Meteorite

• Most asteroids land in oceans and unpopulated regions and are never found, but in January 2000 a meteorite landed near Atlin, BC.

• Fortunately when fragments were collected they were handled with gloves and were quickly frozen.

• This meteorite was unusual because:• It contained carbonaceous chondrites that date from the birth of our solar

system.• It contained a lot of organic molecules, including amino acids.

Canadian Research 2.1 The Carbon-Rich Tagish Lake Meteorite

• Carbon like most other atoms is created within older stars by thermonuclear reactions fusing helium nuclei together.

• The meteorite was analyzed by Peter Brown from the University of Western Ontario and others.

• They found the asteroid contained:• 3.7% carbonate minerals such as FeCO3 and

• 1.7% other types of carbon-containing molecules.

• Because the overall carbon content of this meteorite is unexpectedly high, this meteorite may be very old. The Tagish Lake meteorite may be the most primitive object ever studied in a laboratory.

Ch 2 Summary

• You should be able to• Determine which molecule would be more stable in your blood: one with

an ionic bond or one with a covalent bond. • Describe why water is such an excellent solvent.• Describe why buffers are important• Determine which chemical reactions would tend to be spontaneous or not• Describe the process of chemical evolution• Draw the different functional groups• Predict how a molecule with a functional group might behave

Ch 3: Key Concepts

Most cell functions depend on proteins.

Amino acids are the building blocks of proteins. Amino acids vary in structure and function because their side chains vary in composition.

Proteins vary widely in structure. The structure of a protein can be analyzed at four levels that form a hierarchy—the amino acid sequence, substructures called α-helices and β-pleated sheets, interactions between amino acids that dictate a protein’s overall shape, and combinations of individual proteins that make up larger, multiunit molecules.

In cells, most proteins are enzymes that function as catalysts. Chemical reactions occur much faster when they are catalyzed by enzymes. During enzyme catalysis, the reactants bind to an enzyme’s active site in a way that allows the reaction to proceed efficiently.

Revisiting the Theory of Chemical Evolution

• Modern life arose through a series of endergonic chemical reactions.

1. Production of small organic compounds• i.e., formaldehyde (H2CO), hydrogen cyanide (HCN)

2. Formation of mid-sized molecules from these small compounds• i.e., amino acids, simple sugars• These molecules combined with ocean water to form

“prebiotic soup.”

3. Mid-sized building blocks combine to form large molecules. • i.e., proteins, complex carbohydrates

4. Life became possible when one of these large molecules self-replicated.

Early Origin-of-Life Experiments

Could the first steps of chemical evolution have occurred on ancient Earth?

• To find out, Stanley Miller combined methane (CH4), ammonia (NH3), and hydrogen (H2) in a closed system with water, and applied heat and electricity as an energy source.

• The products included hydrogen cyanide (HCN) and formaldehyde (H2CO), important precursors for more-complex organic molecules and amino acids.

• In more recent experiments, amino acids and other organic molecules have been found to form easily under these conditions.

The Structure of Amino Acids

All proteins are made from just 20 amino acid building blocks.

• All amino acids have a central carbon atom that bonds to NH2, COOH, H, and a variable side chain (“R-group”).

• In water (pH 7), the amino and carboxyl groups ionize to NH3

+ and COO–, respectively—this helps amino acids stay in solution and makes them more reactive.

The Nature of Side Chains

The 20 amino acids differ only in the unique R-group attached to the central carbon. The properties of amino acids vary because their R-groups vary.

Functional Groups Affect Reactivity

• R-groups differ in their size, shape, reactivity, and interactions with water.

1. Nonpolar R-groups: hydrophobic; do not form hydrogen bonds; coalesce in water

2. Polar R-groups: hydrophilic; form hydrogen bonds; readily dissolve in water

• Amino acids with hydroxyl, amino, carboxyl, or sulfhydryl functional groups in their side chains are more chemically reactive than those with side chains composed of only carbon and hydrogen atoms.

Monomers and Polymers

• Many mid-size molecules, such as amino acids and nucleotides, are individual units called monomers. They link together (polymerize) to form polymers, such as proteins and nucleic acids.

• Macromolecules are very large polymers made up of many monomers linked together.

• Thus, proteins are macromolecules consisting of linked amino acid monomers.

Assembling and Breaking Apart Polymers

• Polymerization requires energy and is nonspontaneous.

• Monomers polymerize through condensation (dehydration) reactions, which release a water molecule.

• Hydrolysis is the reverse reaction, which breaks polymers apart by adding a water molecule.

• In the prebiotic soup, hydrolysis is energetically favourable and thus would predominate over condensation. However, polymers clinging to a mineral surface are protected from hydrolysis, and thus polymerization of the amino acids into proteins may have occurred spontaneously.

The Peptide Bond

• Condensation reactions bond the carboxyl group of one amino acid to the amino group of another to form a peptide bond.

• A chain of amino acids linked by peptide bonds is called a polypeptide.

• Polypeptides containing fewer than 50 amino acids are called oligopeptides (peptides).

• Polypeptides containing more than 50 amino acids are called proteins.

Polypeptide Characteristics

• Within the polypeptide, the peptide bonds form a “backbone” with three key characteristics:

1. R-group orientation• Side chains can interact with each other or water.

2. Directionality • Free amino group, on the left, is called the N-terminus.• Free carboxyl group, on the right, is called the C-terminus.

3. Flexibility• Single bonds on either side of the peptide bond can rotate, making the

entire structure flexible.

What Do Proteins Do?

Proteins are crucial to most tasks required for cells to exist:• Catalysis – enzymes speed up chemical reactions.• Defence – antibodies and complement proteins attack pathogens.• Movement – motor and contractile proteins move the cell or molecules

within the cell.• Signalling – proteins convey signals between cells.• Structure – structural proteins define cell shape and comprise body

structures.• Transport – transport proteins carry materials; membrane proteins

control molecular movement into and out of the cell.

Canadian Research 3.1 Designing New Proteins

• Scientists use proteins as tools in experiments, such as the green fluorescent protein from jellyfish which is used to make different parts of a cell visible.

• Some scientists are now designing their own proteins.

• Researchers, Brian Bryksa, Yasumi Horimoto, and Rickey Yada, from the University of Guelph have created a new protein from a combination of a cow protein that kills harmful bacteria and a pig enzyme that works in the stomach and cuts up other proteins.

• The new protein is designed to travel to the location of a bacterial infection - the enzyme portion will cut the hybrid protein in two- this releases the antimicrobial portion to fight the

bacteria

• This protein may be used in human or agriculturally important plants or animals.

Canadian Research 3.1 Designing New Proteins

What Do Proteins Look Like?

Proteins can serve diverse functions in cells because they are diverse in size and shape as well as in the chemical properties of their amino acids.

• All proteins have just four basic levels of structure: primary, secondary, tertiary, and quaternary.

Primary Structure

• A protein’s primary structure is its unique sequence of amino acids.

• Because the amino acid R-groups affect a polypeptide’s properties and function, just a single amino acid change can radically alter protein function.

Secondary Structure

• Hydrogen bonds between the carbonyl group of one amino acid and the amino group of another form a protein’s secondary structure.

• A polypeptide must bend to allow this hydrogen bonding, forming:• -helices

• -pleated sheets

• Secondary structure depends on the primary structure.

• Some amino acids are more likely to be involved in -helices; others, in -pleated sheets.

• The large number of hydrogen bonds in a protein’s secondary structure increases its stability.

Canadian Research 3.2 Spider Silk Proteins

• Spiders produce several types of silk, one type is dragline silk, which a spider uses in case it falls. This silk is six times stronger than a steel fibre of the same diameter.

• Its strength is due to the structure of its proteins. They comprise mostly β-pleated sheets, and it is the sum total of all the backbone-to-backbone hydrogen bonds that gives the material its strength.

• Efforts are under way to mass-produce spider-silk proteins for use as surgical sutures, bullet proof vests, and other applications requiring a strong yet lightweight material.

Canadian Research 3.2 Spider Silk Proteins

• Spiders anchor themselves and use dragline silk as a safety line.

• Is the dragline silk strong enough to stop a spider from falling?

• Scenario 1 - dragline failed >50%

• Scenario 2 - dragline failed 90%

Canadian Research 3.2 Spider Silk Proteins

• When researchers tested the strength of the silk, they found that it wouldn’t be able to stop a spider from falling.

• However, draglines rarely break when spiders fall - why?

• Spiders have a couple of tricks:• As they fall they continue to release new silk• Within their spinnerets, they have internal friction brakes and as they

produce their new silk, they put on their brakes.

Tertiary Structure

• The tertiary structure of a polypeptide results from interactions between R-groups or between R-groups and the peptide backbone. • These contacts cause the backbone to bend and fold, and contribute to the

distinctive three-dimensional shape of the polypeptide.

• R-group interactions include hydrogen bonds, hydrophobic interactions, van der Waals interactions, covalent disulfide bonds, and ionic bonds.

R-group Interactions That Form Tertiary Structures

• Hydrogen bonds form between hydrogen atoms and the carbonyl group in the peptide-bonded backbone, and between hydrogen and negatively charged atoms in side chains.

• Hydrophobic interactions within a protein increase stability of surrounding water molecules by increasing hydrogen bonding.

R-group Interactions That Form Tertiary Structures

•van der Waals interactions are weak electrical interactions between hydrophobic side chains.

•Covalent disulfide bonds form between sulphur-containing R-groups.

•Ionic bonds form between groups that have full and opposing charges.

Quaternary Structure

• Many proteins contain several distinct polypeptide subunits that interact to form a single structure.

• The bonding of two or more subunits produces quaternary structure.

Summary of Protein Structure

• Note that protein structure is hierarchical. • Quaternary structure is based on tertiary structure, which is based in

part on secondary structure. • All three of the higher-level structures are based on primary structure.

• The combined effects of primary, secondary, tertiary, and sometimes quaternary structure allow for amazing diversity in protein form and function.

Folding and Function

• Protein folding is often spontaneous, because the hydrogen bonds and van der Waals interactions make the folded molecule more energetically stable than the unfolded molecule.

• A denatured (unfolded) protein is unable to function normally.

• Proteins called molecular chaperones help proteins fold correctly in cells.

Prions and Protein Folding

• Prions are improperly folded forms of normal proteins that are present in healthy individuals.• Amino acid sequence does not differ from a normal protein, but shape is

radically different.

• Prions can induce normal protein molecules to change their shape to the altered form.

An Introduction to Catalysis

• Catalysis may be the most fundamental of protein functions.

• Reactions take place when:• Reactants collide in precise orientation • Reactants have enough kinetic energy to overcome repulsion between the

electrons that come in contact during bond formation

An Introduction to Catalysis

• Enzymes perform two functions:

1.Bring substrates together in precise orientation so that the electrons involved in the reaction can interact

2.Decrease the amount of kinetic energy reactants must have for the reaction to proceed

Activation Energy and Rates of Chemical Reactions

• The activation energy (Ea) of a reaction is the amount of free energy required to reach the intermediate condition, or transition state.

• Reactions occur when reactants have enough kinetic energy to reach the transition state. • The kinetic energy of molecules is a function of their temperature.

• Thus, reaction rates depend on:• The kinetic energy of the reactants • The activation energy of the particular reaction (the free energy of the

transition state)

Catalysts and Free Energy

• A catalyst is a substance that lowers the activation energy of a reaction and increases the rate of the reaction.

• Catalysts lower the activation energy of a reaction by lowering the free energy of the transition state.

• Catalysts do not change ΔG and are not consumed in the reaction.

Enzymes

• Enzymes are protein catalysts and typically catalyze only one reaction.

• Most biological chemical reactions occur at meaningful rates only in the presence of an enzyme.

Enzymes:1. Bring reactants together in precise orientations

2. Stabilize transition states

• Protein catalysts are important because they speed up the chemical reactions that are required for life.

How Do Enzymes Work?

• Enzymes bring substrates together in specific positions that facilitate reactions, and are very specific in which reactions they catalyze.

• Substrates bind to the enzyme’s active site.

• Many enzymes undergo a conformational change when the substrates are bound to the active site; this change is called an induced fit.

• Interactions between the enzyme and the substrate stabilize the transition state and lower the activation energy required for the reaction to proceed.

The Steps of Enzyme Catalysis

• Enzyme catalysis has three steps: 1. Initiation

• Substrates are precisely oriented as they bind to the active site.

2. Transition state facilitation• Interactions between the substrate and active site R-groups lower the

activation energy.

3. Termination• Reaction products are released from the enzyme.

3-106Figure 3.21 Enzyme Action C an Be Analyzed as a Three-Step Process.

Do Enzymes Act Alone?

• Some enzymes require cofactors to function normally. These are either metal ions or small organic molecules called coenzymes.

• Most enzymes are regulated by molecules that are not part of the enzyme itself.

Enzyme Regulation

• Competitive inhibition occurs when a molecule similar in size and shape to the substrate competes with the substrate for access to the active site.

• Allosteric regulation occurs when a molecule causes a change in enzyme shape by binding to the enzyme at a location other than the active site. • Allosteric regulation can activate or deactivate the enzyme.

What Limits the Rate of Catalysis?

• Enzymes are saturable; in other words, the rate of a reaction is limited by the amounts of substrate present and available enzyme.• The speed of an enzyme-catalyzed reaction increases

linearly at low substrate concentrations.• The increase slows as substrate concentration increases• The reaction rate reaches maximum speed at high substrate

concentrations.

• All enzymes show this type of saturation kinetics. • At some point, active sites cannot accept substrates any

faster, no matter how large the concentration of substrates gets.

Physical Conditions Affect Enzyme Function

• Enzymes function best at some particular temperature and pH.• Temperature affects the movement of the substrates and enzyme.• pH affects the enzyme’s shape and reactivity.

Rate of Enzyme-Catalyzed Reactions

• To summarize, the rate of an enzyme-catalyzed reaction depends on:

1. Substrate concentration

2. The enzyme’s intrinsic affinity for the substrate

3. Temperature

4. pH

Was the First Living Entity a Protein?• Several observations argue that the first self-replicating

molecule on Earth was a protein:

1. Amino acids were abundant in the prebiotic soup.

2. Proteins are the most efficient catalysts known.

3. A self-replicating molecule had to act as a catalyst for the assembly and polymerization of its copy.

• However, the first self-replicator probably needed to have a mold or a template—something not found in proteins.

© 2014 Pearson Canada, Inc.Chapter 2 3-116

Summary• You should be able to

• Draw an amino acid and indicate the variable R group• Predict how a protein is composed of mostly acidic and polar R groups

would interact with water.• Describe how the four levels of protein structure affect the shape and

function of a protein.• Describe the major functions of proteins in a cell.• Describe how enzymes are regulated.• Predict how a change in pH will affect an enzyme.• Predict what would happen to a cell if one enzyme in a crucial pathway

was not correctly regulated.