energy and metabolism

Energy and Metabolism

Chapter 6

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Flow of Energy

• Energy: the capacity to do work

-kinetic energy: the energy of motion

-potential energy: stored energy

• Energy can take many forms: chemical, mechanical, electric current, heat, light

Fig. 6.1

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Flow of Energy

• Most forms of energy can be converted to heat energy.

• Heat energy is measured in kilocalories.

• One calorie = the amount of heat required to raise the temp of water by 1oC

1 kilocalorie (kcal) = 1000 calories (Cal.)

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Laws of Thermodynamics

First Law of Thermodynamics – energy cannot be created or destroyed

-energy can only be converted from one form to another

For example:

sunlight energy chemical energy

photosynthesis

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Laws of Thermodynamics• Second Law of Thermodynamics: disorder is more likely than order

entropy: disorder in the universe

• The 2nd Law of Thermodynamics states that entropy is always increasing.

• Energy is required to keep order, to do work

- keep cells together and organized

- perform life processes

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Laws of Thermodynamics

• Enthalpy: All of the energy contained in a molecule’s chemical bonds

• Free energy: the energy available to do work, to reduce disorder (enthalpy)

- denoted by the symbol G (Gibb’s free energy)

• free energy = enthalpy – (entropy x temp.)

G = H - TS

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Laws of Thermodynamics• Chemical reactions can create changes in

free energy:

ΔG = ΔH - T ΔS

• When products of chemical reactions contain more free energy than reactants – ΔG is positive.

• When reactants contain more free energy than products – ΔG is negative.

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Laws of Thermodynamics

• Chemical reactions can be described by the transfer of energy that occurs:

• endergonic reaction: a reaction requiring an input of energy

•ΔG is positive

• exergonic reaction: a reaction that releases free energy

• ΔG is negative

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Laws of Thermodynamics

• Most reactions require some energy to get started - activation energy.

• activation energy: extra energy needed to get a reaction started

-destabilizes existing chemical bonds

-required even for exergonic reactions

• catalysts: substances that lower the activation energy of a reaction (enzymes)

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Flow of Energy

• Potential energy stored in chemical bonds can be transferred from one molecule to another by way of electrons.

oxidation: loss of electrons

reduction: gain of electrons

• Redox reactions are coupled to each other.

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Oxidation-Reduction Reactions

• A chemical reaction that transfers electrons from one atom to another

– Oxidation = loss of an electron– Reduction = gain of an electron

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Oxidation-Reduction Reactions

• Oxidation

–A chemical reaction in which a molecule gives up electrons

–Oxidation releases energy

–The molecule loosing the electron is oxidized

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Oxidation-Reduction Reactions

• Reduction–A chemical reaction in which a

molecule gains electrons and energy

–The molecule that accepts electrons is reduced

– The molecule being reduced receives energy

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Oxidation-Reduction Reactions

• LEO the lion says GER- If it Looses Electrons during the reaction, it’s Oxidized

- If it Gains Electrons during the reaction, it’s Reduced

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Redox Reactions

• Oxidation and Reduction reactions always occur in pairs– If an atom or molecule is reduced, another atom

or molecule must have been oxidized– If an atom or molecule is oxidized, another atom

or molecule must have been reduced

• For this reason Oxidation and Reduction Reactions are known as Redox Reactions

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ATP - Energy Currency of Cells• ATP is the molecule that cells use to store,

transfer, and provide energy• The energy from ATP is used to fuel

anabolic reactions– recall: for growth, repair, and reproduction

• ATP = Adenosine TriphosPhate– Adenosine (same molecule from DNA and

RNA)

+ – Three inorganic phosphates (functional group

PO4)21

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ATP - Energy Currency of Cells

• ATP = adenosine triphosphate- the energy “currency” of cells

• ATP structure:- ribose, a 5-carbon sugar

- adenine

- three phosphates

Photo Courtest of Dr. O’Steen

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ATP - Energy Currency of Cells

• ATP - 1 PO4 = ADP (Adenosine Diphosphate)

• ADP - 1 PO4 = AMP (Adenosine Monophosphate)

• ADP + 1 PO4 = ATP 25

Figure 5_12

ATP• ATP is a molecule that is used as an

Energy Currency in cells

– ATP’s can be broken down to provide energy for endergonic reactions

– Cells use energy to build ATP’s– Enzymes of allow cells to efficiently build

ATP’s - Cells can make ATP’s for less energy than ATP’s can provide

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ATP - Energy Currency of Cells

• ATP stores energy in the covalent bonds between phosphates:

– Phosphates are highly negative, therefore:• the phosphates repel each other• much energy is required to keep the phosphates

bound to each other

• Energy is released when the bond between two phosphates is broken

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Energy Currency of Cells

• When the bond between phosphates is broken:

ATP ADP + Pi

energy is released

• ADP = adenosine diphosphate

• Pi = inorganic phosphate

• This reaction is reversible...

Text art 5_06

ATP/ADP Cycling

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Energy Currency of Cells

• When the bond between phosphates is formed:

ADP + Pi ATP energy is consumed

• ATP - ADP Cycle

Text art 5_07

ATP/ADP Cycling

Energy Currency of Cells

• It costs energy to build ATPs

ADP + 1P ATP(Adenosine Diphosphate +1 phosphate)

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ATP/ADP Cycling

ATP

ADP

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Energy Currency of Cells

• The energy released when ATP is broken down to ADP can be used to fuel endergonic reactions.

• The energy released from an exergonic reaction can be used to fuel the production of ATP from ADP + Pi.

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Other Functions of ATP

ATP regulates enzyme activity

Phosphorylation and dephosphorylation - process of adding or removing phosphate groups - can activate or deactivate enzymes

ATP serves as a source of phosphate groups

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ATP/ADP Cycling

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Enzymes

• Enzymes: molecules that catalyze - speed up - biochemical reactions in living cells

• Three rules to be considered an enzyme– Most are proteins (some RNA enzymes)– Lower the energy of activation required for

a reaction to occur– Are not changed or consumed by the reaction

• Cofactors, Coenzymes 40

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Metabolism

Enzymes catalyze cellular chemical reactions Metabolism - the chemical reactions in a cell: Two categories of cellular chemical reactions:

1.Anabolic Reactions Build larger molecules for growth, repair, reproduction Dehydration Synthesis Reactions require energy and nutrients

– Catabolic Reactions Breakdown larger molecules Hydrolysis Reactions mobilize nutrients for energy making it available to the cell

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Metabolism

Metabolism is the sum total of all anabolic and catabolic reactions that occur in the cell

The metabolism of cells is carried out and controlled by the enzymes– There are catabolic enzymes – those that cleave

larger molecules into smaller ones Ex. Hydrolysis Reactions

– There are also anabolic enzymes – those that assemble smaller molecules into larger ones

Ex. Dehydration Reactions

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Enzymes

• Enzymes interact with substrates.

• substrate: molecule that will undergo a reaction

• active site: region of the enzyme that binds to the substrate

• Binding of an enzyme to a substrate causes the enzyme to change shape, producing a better induced fit between the molecules.

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Enzymes

Enzymes interact with substrates

Substrates: molecules that will undergo a reaction when bound to the enzyme

– lactose, hydrogen peroxide (H2O2)

On the Enzymes:– Active site: region of the enzyme that binds to the

substrate– Allosteric site: region of the enzyme that binds

substances other that the substrate

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Figure 5_02

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Enzymes

Enzymes are very specific:– Enzymes will only interact with a specific substrates– The substrate fits into the active site like a key fits

into a lock (Lock and Key Hypothesis)– Substrate binding causes the enzyme to change

shape, producing a better induced fit between the molecules (Induced Fit Hypothesis)

Changing the shape of an enzyme affects its ability to function

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Enzymes

Enzyme/Substrate Complex:

E + S ES EP E + P

1. The Enzyme and the Substrate come together (E+S)

2. The Enzyme/Substrate Complex is formed (ES)

3. The Enzyme’s Substrate is changed to the Enzyme’s- Product in the active site of the enzyme (EP)

4. The Enzyme and Product Separate (E+P)• The Enzyme is free to bind to another Substrate

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Figure 5_03b

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Enzyme Naming Convention

Because enzymes catalyze specific reactions each enzyme has a unique name:– The first part of an enzyme’s name usually describes

the substrate– The second part of an enzyme’s usually indicates the

type of reaction it will catalyze Most enzyme names end in the suffix -ase Examples of enzymes:

– DNA polymerase– Glycogen synthetase– Lactase – Catalase

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How Enzymes Work

Enzymes lower the activation energy of biochemical reactions.

Enzymes make it easier for chemical reactions to occur:– by destabilizing the bonds in the substrate– by bringing substrates together so they react– by decreasing entropy - disorder - in the

system Enzymes make the chemical reactions

possible in the cell’s environment Enzymes make cells very efficient

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How Enzymes Work

Enzymes make cells very efficient

Through enzymes, cells can carry out anabolic and catabolic reactions and end up with a net profit of energy

Cellular respiration is the process of breaking down glucose and storing the excess energy from the molecule into a form of energy that is available and useful to the cell

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Cells Use Enzymes to Process Energy and Matter

Reactions that break chemical bonds release their internal potential energy.– Example: burning

wood– Oxidation reactions

• Organisms obtain energy through enzyme-catalyzed biochemical reactions.

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Coenzymes and Cofactors

Many enzymes require special molecules to help them function correctly: – Cofactors

• inorganic molecules ions, such as zinc or iron

– Coenzymes• organic molecules

Vitamins are the precursors for many coenzymes.

Vitamins must be acquired from the diet, cells cannot make them.

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The Role of Coenzymes

• ADase oxidizes alcohol- Alcohol cannot be oxidized unless something else is reduced- NAD+ is reduced to NADH

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The Environment Affects Enzyme Function

The rate at which an enzyme can bind to a substrate is called the turnover number.

The turnover number is maximized under the ideal conditions for that enzyme.

Conditions that can change an enzyme’s 3-dimensional shape can change its function

Each enzyme has ideal conditions that include:1.Temperature2.pH3.Substrate concentration– Regulatory molecules

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1. Temperature Temperature has two effects on enzymes:

• Changes the rate of molecular motion1. Increasing temperature increases molecular motion and increases

turnover number2. Decreasing temperature decreases molecular movement and

decreases turnover number

• Causes changes in the shape of an enzyme Temperature changes above optimum will denature the enzyme. This changes its shape, and it can no longer bind substrate and

catalyze the reaction.

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2. pH

Enzymes are composed of amino acids– In a basic environment

The acidic side chains (R groups) could donate protons which affects the charge of the side chain

A neutral side chain that donates protons would become negatively charged

– In an acidic environment The basic side chains (R groups) could accept protons

which affects the charge of the side chain A neutral side chain that accepts protons would become

positively charged

Both of these events can change the enzyme’s shape

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Enzymes

• Enzymes work together in chains of reactions known as biochemical or metabolic pathways

• Biochemical pathways are a series of reactions in which the product of one reaction becomes the substrate for the next reaction.

• Examples: photosynthesis, cellular respiration, protein synthesis, etc.

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Metabolic Pathways

• Metabolic Pathways are series of chemical reactions carried out by separate enzymes

• It is a sequence of chemical reactions where each reaction is controlled by a separate enzyme

• The product of one enzyme serves as the substrate for the enzyme of subsequent reaction in the metabolic pathway

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Enzymes

• These biochemical pathways offer certain advantages:

1.The product of one reaction can be directly delivered to the next enzyme

2.The possibility of unwanted side reactions is eliminated

3. All of the reactions can be regulated

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Regulation of Biochemical Pathways

Metabolism is tightly regulated

There is a delicate balance between all of the reactions that take place in the cell

Metabolism is commonly regulated 3 ways:1.Enzymatic competition for substrate2.Gene regulation3.Enzyme inhibition

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Enzyme Regulation

1. Enzymatic competition for substrateEnzymatic competition occurs when more than one enzyme interacts with the same substrate

Each enzyme converts the substrate to a different product.

The enzyme that “wins” is the one that is the most abundant at the time.

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Figure 5_07

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Enzyme Regulation

2. Gene regulationEnzymes are proteins.Protein production is controlled by genes.Certain chemicals in the cell turn particular enzyme-producing genes on or off depending on the situation.

– Called gene-regulator proteins Those that decrease the amount of an enzyme made are

called gene-repressor proteins. Those that increase the amount of an enzyme made are

called gene-activator proteins.

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Enzyme Regulation

3. Enzyme inhibition

•Inhibitors are molecules that attach to enzymes and make them unable to bind to substrate.

•Many drugs, pesticides and herbicides target enzymes.

•Three types of inhibition:A. Negative Feedback InhibitionB. Competitive Inhibition– Noncompetitive Inhibition

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A. Negative-Feedback Inhibition

The end-product of the metabolic pathways accumulate– Those molecules feedback and bind to an

enzyme early in the sequence.– They inhibit that enzyme, and stop the sequence.– This decreases the amount of end-product made.

This functions to keep levels of the end-product within a certain range.

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Feedback Inhibition

Text art 5_05

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Enzyme Regulation

• Inhibitors are molecules that bind to an enzyme to decrease enzyme activity.

- competitive inhibitors compete with the substrate for binding to the same active site

- noncompetitive inhibitors bind to sites other than the enzyme’s active site

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B. Competitive Inhibition

Competitive inhibitors closely resemble the substrate.

– they bind to the active site of the enzyme and block the substrate from binding.

Figure 5_09

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Enzyme Regulation

• Allosteric enzymes exist in either an active or inactive state.

- possess an allosteric site where molecules other than the substrate bind

- allosteric inhibitors bind to the allosteric site to inactivate the enzyme

- allosteric activators bind to the allosteric site to activate the enzyme

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C. Noncompetitive Inhibition

Noncompetitive inhibitors bind to sites other than the enzyme’s active site - allosteric sites

“allo” = other; “steric” = shape– binding to an allosteric site changes the shape of the

enzyme and affects its function

Noncompetitive because the noncompetitive inhibitor does not compete with the substrate to bind to the active site

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Cellular Respiration

Cellular Respiration is a metabolic pathway that breaks down glucose and extracts the energy to produce energy

C6H12O6 + 6O2 6H2O + 6CO2 + Energy Glucose Oxygen Water Carbon Dioxide

The Energy is in the form of ATP

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Metabolism

• The metabolism of cells is carried out and controlled by ENZYMES

• There are catabolic enzymes – those that cleave larger molecules into smaller ones– Ex. Hydrolysis Reactions

• There are also anabolic enzymes – those that assemble smaller molecules into larger ones– Ex. Dehydration Reactions

Cellular Respiration• Glucose contains energy that can be

extracted• Cellular Respiration is a metabolic

pathway that breaks down glucose and extracts the energy to produce ATP

• Recall:C6H12O6 + 6 O2 6 H2O + 6 CO2 + Energy

Glucose Oxygen Water Carbon Dioxide

• The Energy is in the form of ATP

Cellular Respiration

C6H12O6 + 6 O2 6 H2O + 6 CO2 + Energy

-Now-

C6H12O6 + 6O2 + 38 ADP + 38 P 6 H2O + 6CO2 + 38 ATP