Menu 1 Energy and Enzymes. Menu 2 Menu – Energy and Enzymes Instructions Instructions Energy Energy Chemical Bonds Chemical Bonds ATP ATP Catabolic.

Energy and EnzymesEnergy and Enzymes

Before you begin…Before you begin…

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Forms of EnergyForms of Energy

These forms of energy are important to life:– chemical– radiant (examples: heat, light)– mechanical– electrical

Energy can be transformed from one form to another.

Chemical energy is the energy contained in the chemical bonds of molecules.

Radiant energy travels in waves and is sometimes called electromagnetic energy. An example is visible light.

Photosynthesis converts light energy to chemical energy.

Energy that is stored is called potential energy.

Laws of ThermodynamicsLaws of Thermodynamics

1st law: Energy cannot be created or destroyed.– Energy can be converted from one form to another.

The sum of the energy before the conversion is equal to the sum of the energy after the conversion.

– Example: A light bulb converts electrical energy to light energy and heat energy. Fluorescent bulbs produce more light energy than incandescent bulbs because they produce less heat.

2nd law: Some usable energy dissipates during transformations and is lost.– During changes from one form of energy to another,

some usable energy dissipates, usually as heat. The amount of usable energy therefore decreases.

Energy is required to form bonds.Energy is required to form bonds.

Atoms or molecules

EnergyEnergy

+ Energy Larger molecule

The energy that was used to form the bonds is now stored in this molecule.

Energy is released when bonds are Energy is released when bonds are broken.broken.

EnergyEnergy

When bonds break, energy is released. It may be in a form such as heat or light or it may be transferred to another molecule.

ATP (Simplified Drawing)ATP (Simplified Drawing)

A Base (adenine)

Sugar (ribose)

3 phosphate groups

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ATP Stores EnergyATP Stores Energy

The phosphate bonds are high-energy bonds.

Energy

ADP + Pi + Energy

Breaking the bonds releases the energy.

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ADP + Pi

EnergyEnergy(from glucose or other high-energy compounds)

ATP is RecycledATP is Recycled

ATP (Adenosine Triphosphate) is an energy-containing molecule used to supply the cell with energy. The energy used to produce ATP comes from glucose or other high-energy compounds.

ATP is continuously produced and consumed as illustrated below.

ADP + Pi + Energy ATP + H2O(Note: Pi = phosphate group)

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ATPATP

ATP ADP + Pi

Energy

ATPATP

Energy from breaking bonds in this molecule is used to form ATP.

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ATPATPATP ADP + Pi

Energy

The energy in ATP can be used to form bonds in other molecules.

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O P O P O P O CH2

O- O- O-

ATP (Adenosine Triphosphate)ATP (Adenosine Triphosphate)

3 phosphate groups

Base (adenine)

Ribose

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PhosphorylationPhosphorylation

ATP is synthesized from ADP + Pi. The process of synthesizing ATP is called phosphorylation.

Two kinds of phosphorylation are illustrated on the next several slides.– Substrate-Level Phosphorylation– Chemiosmotic Phosphorylation

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Substrate-Level PhosphorylationSubstrate-Level Phosphorylation

ADPHigh-energy molecule

A high-energy molecule (substrate) is used to transfer a phosphate group to ADP to form ATP.

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This bond will be broken, releasing energy.

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The energy released will be used to bond the phosphate group to ADP, forming ATP.

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Enzyme

An enzyme is needed.

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Breaking this bond will release energy.

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The energy will be used to form this bond.

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Low-energy molecule ATP

The energy has been transferred from the high-energy molecule to ADP to produce ATP.

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Mitochondrion StructureMitochondrion Structure

Cristae Matrix

Intermembrane Space

This drawing shows a mitochondrion cut lengthwise to reveal its internal membrane.

Outside

Intermembrane Space

Matrix

This drawing shows a close-up of a section of a mitochondrion.

Matrix (inside)

ChemiosmoticChemiosmoticPhosphorylationPhosphorylation

Matrix (inside)

Pumps within the membrane pump hydrogen ions from the matrix to the intermembrane space creating a concentration gradient.

Outside

Intermembrane Space

Matrix

Matrix (inside)

This process requires energy and will be discussed in the chapter on cellular respiration.

Outside

Intermembrane Space

Matrix

Matrix (inside)

A high concentration of hydrogen ions in the intermembrane space creates osmotic pressure.

Outside

Intermembrane Space

Matrix

Matrix (inside)

Osmotic pressure forces the hydrogen ions through this protein (called ATP synthase) as they return to the matrix.ChemiosmoticChemiosmotic

Outside

Intermembrane Space

Matrix

ADP + Pi

ATP synthase produces ATP by phosphorylating ADP. The energy needed to produce ATP comes from hydrogen ions forcing their way into the matrix as they pass through the ATP synthase (due to osmotic pressure).

Matrix (inside)

Osmotic pressure forces the hydrogen ions through this protein (ATP synthase) as they return to the matrix. ChemiosmoticChemiosmotic

Outside

Intermembrane Space

Matrix

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Chemiosmotic PhosphorylationChemiosmotic Phosphorylation

Chemiosmotic phosphorylation (previous slide) is used by the mitochondrion to produce ATP. The energy needed to initially pump H+ ions into the intermembrane space comes from glucose. The entire process is called cellular respiration and will be discussed in a later chapter.

The chloroplast also produces ATP by chemiosmotic phosphorylation. The energy needed to produce ATP comes from sunlight.

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Chloroplast StructureChloroplast Structure

The chloroplast is surrounded by a double membrane.

Molecules that absorb light energy (photosynthetic pigments) are located on disk-shaped structures called thylakoids.

The interior portion is the stroma.

Thylakoids

Double membraneStroma

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H+H+ H+

H+H+H+H+

A Thylakoid (see previous slide)A Thylakoid (see previous slide)

In order to synthesize ATP, hydrogen ions must first be pumped into the thylakoid. This process requires energy.

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H+H+ H+

H+H+H+H+

A ThylakoidA Thylakoid

A concentration gradient of hydrogen ions is established. The osmotic pressure from this gradient can be used as an energy source for producing ATP.

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H+H+ H+

H+H+H+H+

ADP + Pi

Chemiosmotic PhosphorylationChemiosmotic Phosphorylation

ATP synthase produces ATP by phosphorylating ADP. The energy comes from hydrogen ions forcing their way into the stroma as they pass through the ATP synthase under pressure (osmotic pressure).

Osmotic pressure forces hydrogen ions through this protein (ATP synthase) as they return to the stroma.

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We have just discussed two different forms of phosphorylation:– Substrate-level phosphorylation– Chemiosmotic phosphorylation

We saw that chemiosmotic phosphorylation occurred in both the mitochondria (during cellular respiration) and in the chloroplast (during photosynthesis). These two processes are sometimes given separate names:– Oxidative phosphorylation (in mitochondria)– Photophosphorylation (in chloroplast)

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Catabolic and Anabolic ReactionsCatabolic and Anabolic Reactions

The energy-producing reactions within cells generally involve the breakdown of complex organic compounds to simpler compounds. These reactions release energy and are called catabolic reactions.

Anabolic reactions are those that consume energy while synthesizing compounds.

ATP produced by catabolic reactions provides the energy for anabolic reactions. Anabolic and catabolic reactions are therefore coupled (they work together) through the use of ATP.

Diagram: next slide

ATP ADP + Pi

Energy

An anabolic reaction

A catabolic reaction

Catabolic and Anabolic Reactions

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Anabolic Reactions

Anabolic reactions consume energy.

Substrates(Reactants)

Products

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Catabolic reactions release energy.

Catabolic Reactions

Substrate(Reactant)

When bonds are broken, energy is released.Menu

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Activation EnergyActivation Energy

Activation Energy

In either kind of reaction, additional energy must be supplied to start the reaction. This energy is called activation energy.

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Activation EnergyActivation Energy

Activation Energy

An example of activation energy is the spark needed to ignite gasoline.

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Enzymes Lower Activation EnergyEnzymes Lower Activation Energy

d Activation energy without enzyme

Activation energywith enzyme

Enzymes lower the amount of activation energy needed for a reaction.

Substrate

Enzyme

Active Site

Enzyme-Substrate ComplexProduct

Enzyme

EnzymesEnzymes

Enzymes are organic catalysts.

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EnzymesEnzymes

Catalysts are substances that speed up chemical reactions. Organic catalysts (contain carbon) are called enzymes.

Enzymes are specific for one particular reaction or group of related reactions.

Many reactions cannot occur without the correct enzyme present.

They are often named by adding "ase" to the name of the substrate. Example: Dehydrogenases are enzymes that remove hydrogen.

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Induced Fit TheoryInduced Fit Theory

An enzyme-substrate complex forms when the enzyme’s active site binds with the substrate like a key fitting a lock.

The substrate molecule does not fit exactly in the active site. This induces a change in the enzymes conformation (shape) to make a closer fit.

After the reaction, the products are released and the enzyme returns to its normal shape.

Only a small amount of enzyme is needed because they can be used repeatedly.

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Rate of ReactionRate of Reaction

Reactions with enzymes are up to 10 billion times faster than those without enzymes.

Enzymes typically react with between 1 and 10,000 molecules per second. Fast enzymes catalyze up to 500,000 molecules per second.

Substrate concentration, enzyme concentration, Temperature, and pH affect the rate of enzyme reactions.

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Substrate ConcentrationSubstrate Concentration

At lower concentrations, the active sites on most of the enzyme molecules are not filled because there is not much substrate. Higher concentrations cause more collisions between the molecules. With more molecules and collisions, enzymes are more likely to encounter molecules of reactant.

The maximum velocity of a reaction is reached when the active sites are almost continuously filled. Increased substrate concentration after this point will not increase the rate. Reaction rate therefore increases as substrate concentration is increased but it levels off.

Substrate Concentration

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Enzyme ConcentrationEnzyme Concentration

If there is insufficient enzyme present, the reaction will not proceed as fast as it otherwise would because there is not enough enzyme for all of the reactant molecules.

As the amount of enzyme is increased, the rate of reaction increases. If there are more enzyme molecules than are needed, adding additional enzyme will not increase the rate. Reaction rate therefore increases as enzyme concentration increases but then it levels off.

Enzyme Concentration

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Effect of Temperature on Enzyme Effect of Temperature on Enzyme ActivityActivity

30 40 50

Temperature

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30 40 50

Temperature

Increasing the temperature causes more collisions between substrate and enzyme molecules. The rate of reaction therefore increases as temperature increases.

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30 40 50

Temperature

Enzymes denature when the temperature gets too high. The rate of reaction decreases as the enzyme becomes nonfunctional.

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TemperatureTemperature

Higher temperature causes more collisions between the atoms, ions, molecules, etc. It therefore increases the rate of a reaction. More collisions increase the likelihood that substrate will collide with the active site of the enzyme.

Above a certain temperature, activity begins to decline because the enzyme begins to denature (unfold).

The rate of chemical reactions therefore increases with temperature but then decreases.

30 40 50

Temperature

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DenaturationDenaturation

If the hydrogen bonds within an enzyme are broken, the enzyme may unfold or take on a different shape. The enzyme is denatured.

A denatured enzyme will not function properly because the shape of the active site has changed.

If the denaturation is not severe, the enzyme may regain its original shape and become functional.

The following will cause denaturation:– Heat– Changes in pH– Heavy-metal ions (lead, arsenic, mercury)– Alcohol– UV radiation

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Effect of pH on Enzyme ActivityEffect of pH on Enzyme Activity

Each enzyme has its own optimum pH.

2 3 4 5 6 7 8 9

Pepsin Trypsin

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Each enzyme has an optimal pH. Pepsin, an enzyme found in the stomach, functions best at a low pH. Trypsin, found in the intestine, functions best at a neutral pH.

A change in pH can alter the ionization of the R groups of the amino acids. When the charges on the amino acids change, hydrogen bonding within the protein molecule change and the molecule changes shape. The new shape may not be effective.

The diagram shows that pepsin functions best in an acid environment. This makes sense because pepsin is an enzyme that is normally found in the stomach where the pH is low due to the presence of hydrochloric acid. Trypsin is found in the duodenum (small intestine), and therefore, its optimum pH is in the neutral range to match the pH of the duodenum.

2 3 4 5 6 7 8 9

Pepsin Trypsin

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Metabolic PathwaysMetabolic Pathways

Metabolism refers to the chemical reactions that occur within cells.

Reactions occur in a sequence and a specific enzyme catalyzes each step.

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Metabolic PathwaysMetabolic Pathways

enzyme 1 enzyme 2 enzyme 3 enzyme 4

Fenzyme 5

A B C D E

Notice that C can produce either D or F. This substrate has two different enzymes that work on it.

Enzymes are very specific. In this case enzyme 1 will catalyze the conversion of A to B only.

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A Cyclic Metabolic PathwayA Cyclic Metabolic Pathway

A + F B

D F + E

In this pathway, substrate “A” enters the reaction. After several steps, product “E” is produced.

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Regulation of EnzymesRegulation of Enzymes

The next several slides illustrate how cells regulate enzymes. For example, it may be necessary to decrease the activity of certain enzymes if the cell no longer needs the product produced by the enzymes.

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Enzymes are proteins. Recall the central dogma:

DNA mRNA Proteins

Proteins can be regulated by making more or less of them as needed. The topic of regulating protein synthesis (manufacture) is deferred to a later chapter.

geneticregulation

regulation of enzymesalready produced

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geneticregulation

competitiveInhibition

(illustrated on the next slide)

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Competitive InhibitionCompetitive Inhibition

In competitive inhibition, a similar-shaped molecule competes with the substrate for active sites.

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Competitive InhibitionCompetitive Inhibition

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geneticregulation

competitiveinhibition

noncompetitiveInhibition

(see next slide)

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Noncompetitive InhibitionNoncompetitive Inhibition

Another form of inhibition involves an inhibitor that binds to an allosteric site of an enzyme. An allosteric site is a different location than the active site.

The binding of an inhibitor to the allosteric site alters the shape of the enzyme, resulting in a distorted active site that does not function properly.

Active site Inhibitor Altered active site

Enzyme

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Noncompetitive InhibitionNoncompetitive Inhibition

The binding of an inhibitor to an allosteric site is usually temporary. Poisons are inhibitors that bind irreversibly. For example, penicillin inhibits an enzyme needed by bacteria to build the cell wall. Bacteria growing (reproducing) without producing cell walls eventually rupture.

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geneticregulation

competitiveinhibition

noncompetitiveinhibition

feedbackinhibition

(next slide)

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Example of Feedback InhibitionExample of Feedback Inhibition

Cold Thermostat Heater Heat

inhibits

In this example of feedback inhibition, heat (the product) inhibits its production. This keeps the temperature constant.

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Enzyme regulation by negative feedback inhibition is similar to the thermostat example. As an enzyme's product accumulates, it turns off the enzyme just as heat causes a thermostat to turn off the production of heat.

Feedback InhibitionFeedback Inhibition

A B C Denzyme 1 enzyme 2 enzyme 3

The goal of this hypothetical metabolic pathway is to produce chemical D from A.

B and C are intermediates.

The next several slides will show how feedback inhibition regulates the amount of D produced.

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Enzyme 1 is structured in a way that causes it to interact with D. When the amount of D increases, the enzyme stops functioning.

The amount of B in the cell will decrease if enzyme 1 is inhibited.

C and D will decrease because B is needed to produce C and C is needed to produce D.

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When the amount of D drops, enzyme 1 will no longer be inhibited.

B, C, and D can now be synthesized.

X X XB C D

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As D begins to increase, it inhibits enzyme 1 again and the cycle repeats itself.

A B C Denzyme 1 enzyme 2 enzyme 3X

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RibozymesRibozymes

Ribozymes are molecules of RNA that function like enzymes, that is, they have an active site and increase the rate of specific chemical reactions.

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Energy is transferred with electrons.Energy is transferred with electrons.

Oxidized atomElectron is donatedEnergy is donated

Reduced atomElectron is receivedEnergy is received

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This atom served as an energy carrier. It picked up an electron from the atom on the left and gave it to the one on the right.

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Oxidation and ReductionOxidation and Reduction

Oxidation is the loss of electrons or hydrogen atoms. Oxidation reactions release energy.

Reduction is gain of electrons or hydrogen atoms and is associated with a gain of energy.

Oxidation and reduction occur together. When a molecule is oxidized, another must be reduced.

These coupled reactions are called oxidation-reduction or redox reactions.

Food is highly reduced (has many hydrogens). The chemical pathways in cells that produce energy for the cell oxidize the food (remove hydrogens), producing ATP.

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CofactorsCofactors

Many enzymes require a cofactor to assist in the reaction. These "assistants" are nonprotein and may be metal ions such as magnesium (Mg++), potassium (K+), and calcium (Ca++).

The cofactors bind to the enzyme and participate in the reaction by removing electrons, protons , or chemical groups from the substrate.

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CoenzymesCoenzymes

Cofactors that are organic molecules are coenzymes.

In oxidation-reduction reactions, coenzymes often remove electrons from the substrate and pass them to different enzymes.

In this way, coenzymes serve to carry energy in the form of electrons (or hydrogen atoms) from one compound to another.

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CoenzymesCoenzymes

Coenzymes are cofactors that are not protein.

They bind to the enzyme and also participate in the reaction by carrying electrons or hydrogen atoms.

Enzyme Enzyme

Coenzyme

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Vitamins are CoenzymesVitamins are Coenzymes

Vitamin Coenzyme Name

Niacin NAD+

B2 (riboflavin) FAD

B1 (thiamine) Thiamine pyrophosphate

Pantothenic acid Coenzyme A (CoA)

B12 Cobamide coenzymes

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Electron CarriersElectron Carriers

Electron carriers function in photosynthesis and cellular respiration. Three major electron carriers are listed below.

Respiration– NAD+

– FAD

Photosynthesis– NADP+

NADNAD++ (Nicotinamide Adenine (Nicotinamide Adenine Dinucleotide)Dinucleotide)

OrganicMolecule + NAD+ NAD+

NAD+ + 2H NADH + H+

NAD+ functions in cellular respiration by carrying two electrons. With two electrons, it becomes NADH.

NAD+ oxidizes its substrate by removing two hydrogen atoms. One of the hydrogen atoms bonds to the NAD+. The electron from the other hydrogen atom remains with the NADH molecule but the proton (H+) is released.

NAD+ + 2H NADH + H+

NADH can donate two electrons (one of them is a hydrogen atom) to another molecule.

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NADNAD++ + 2H + 2H NADH + H NADH + H++

NADH + H+

Energy+

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FAD + 2H FAD + 2H FADH FADH22

Energy+

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FAD (flavin adenine dinucleotide)FAD (flavin adenine dinucleotide)

FAD is reduced to FADH2. It can transfer two electrons to another molecule.

FAD + 2H FADH2

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NADPNADP++ + 2H + 2H NADPH + H NADPH + H++

NADPH + H+

Energy+

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NADPNADP++ (Nicotinamide Adenine (Nicotinamide Adenine Dinucleotide Phosphate)Dinucleotide Phosphate)

NADP+ + 2H NADPH + H+

NADP+ is similar to NAD+ in that it can carry two electrons, one of them in a hydrogen atom, the other one comes from a hydrogen that is released as a hydrogen ion. (Click here to review NAD+.)

Electrons carried by NADPH in photosynthesis are ultimately used to reduce CO2 to carbohydrate.

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The EndThe End

Menu 1 Energy and Enzymes. Menu 2 Menu – Energy and Enzymes Instructions Instructions Energy Energy Chemical Bonds Chemical Bonds ATP ATP Catabolic.

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