Chapter 8: Energy and Metabolism

Chapter 8: Energy and Metabolism
Why do organisms need energy? How do organisms manage their energy needs? Defining terms and issues: energy and thermodynamics metabolic reactions and energy transfers Harvesting and using energy ATP is the main energy currency in cells energy harvesting (redox reactions) Regulating reactions: Enzymes

Discuss energy conversions and the 1st and 2nd law of thermodynamics.
Be sure to use the terms work potential energy kinetic energy entropy What are Joules (J) and calories (cal)?

Energy and Thermodynamics
energy for work: change in state or motion of matter

energy for work: change in state or motion of matter expressed in Joules or calories 1 kcal = kJ

energy for work: change in state or motion of matter expressed in Joules or calories 1 kcal = kJ energy conversion: energy form change potential / kinetic

potential energy (capacity to do work)

potential energy (capacity to do work) kinetic energy (energy of motion, actively performing work) chemical bonds: potential energy work is required for the processes of life

Discuss energy conversions and the 1st and 2nd law of thermodynamics.
Be sure to use the terms work potential energy kinetic energy entropy What are Joules (J) and calories (cal)?

Laws of thermodynamics describe the constraints on energy usage…

The laws of thermodynamics are sometimes stated as:
In energy conversions, “You can’t win, and you can’t break even.” Explain.

Laws of Thermodynamics
First law: the total amount of energy (+ matter) in a closed system remains constant

First law: the total amount of energy (+ matter) in a closed system remains constant also called conservation of energy

First law: the total amount of energy (+ matter) in a closed system remains constant also called conservation of energy note: the universe is a closed system living things are open systems

First law: the total amount of energy (+ matter) in a closed system remains constant also called conservation of energy note: the universe is a closed system living things are open systems “You can’t win.”

Second law: in every energy conversion some energy is converted to heat energy heat energy is lost to the surroundings heat energy cannot be used for work

Second law: in every energy conversion some energy is converted to heat energy heat energy is lost to the surroundings heat energy cannot be used for work energy converted to heat in the surroundings increases entropy (spreading of energy)

Second law: in every energy conversion some energy is converted to heat energy heat energy is lost to the surroundings heat energy cannot be used for work energy converted to heat in the surroundings increases entropy (spreading of energy) thus, this law can also be stated as: Every energy conversion increases the entropy of the universe.

Second law: Upshot: no energy conversion is 100% efficient “You can’t break even.” Just to maintain their current state, organisms must get a constant influx of energy because of energy lost in conversions

The laws of thermodynamics are sometimes stated as:
In energy conversions, “You can’t win, and you can’t break even.” Explain.

Differentiate between:
anabolism and catabolism exergonic and endergonic reactions

Metabolism: anabolism + catabolism
metabolism divided into anabolism (anabolic reactions) anabolic reactions are processes that build complex molecules from simpler ones

Metabolism: anabolism + catabolism
metabolism divided into anabolism (anabolic reactions) anabolic reactions are processes that build complex molecules from simpler ones catabolism (catabolic reactions) catabolic reactions are processes the break down complex molecules into simpler ones

Differentiate between:
anabolism and catabolism exergonic and endergonic reactions

Chemical Reactions and Free Energy
Chemical reactions involve changes in chemical bonds

Chemical reactions involve changes in chemical bonds changes in substance concentrations

Chemical reactions involve changes in chemical bonds changes in substance concentrations changes in free energy free energy = energy available to do work in a chemical reaction (such as: create a chemical bond) free energy changes depend on bond energies and concentrations of reactants and products bond energy = energy required to break a bond; value depends on the bond

left undisturbed, reactions will reach dynamic equilibrium when the relative concentrations of reactants and products is correct forward and reverse reaction rates are equal; concentrations remain constant

left undisturbed, reactions will reach dynamic equilibrium when the relative concentrations of reactants and products is correct forward and reverse reaction rates are equal; concentrations remain constant cells manipulate relative concentrations in many ways so that equilibrium is rare

exergonic reactions – the products have less free energy than reactants the difference in energy is released and is available to do work

exergonic reactions – the products have less free energy than reactants the difference in energy is released and is available to do work exergonic reactions are thermodynamically favored; thus, they are spontaneous, but not necessarily fast (more on activation energy later)

catabolic reactions are usually exergonic ATP + H2O  ADP + Pi is highly exergonic

endergonic reactions – the products have more free energy than the reactants the difference in free energy must be supplied (stored in chemical bonds)

endergonic reactions – the products have more free energy than the reactants the difference in free energy must be supplied (stored in chemical bonds) endergonic reactions are not thermodynamically favored, so they are not spontaneous

How to get energy for an endergonic reaction?

How to get energy for an endergonic reaction? couple with an exergonic one!

How to get energy for an endergonic reaction? couple with an exergonic one! together, the coupled reactions must have a net exergonic nature

How to get energy for an endergonic reaction? couple with an exergonic one! together, the coupled reactions must have a net exergonic nature reaction coupling requires that the reactions share a common intermediate(s)

EXAMPLE: A  B (exergonic) C  D (endergonic)

EXAMPLE: A  B (exergonic) C  D (endergonic) Coupled: A + C  B + D (overall exergonic)

EXAMPLE: A  B (exergonic) C  D (endergonic) Coupled: A + C  B + D (overall exergonic) Actually: A + C  I  B + D

EXAMPLE: A  B (exergonic) C  D (endergonic) Coupled: A + C  B + D (overall exergonic) Actually: A + C  I  B + D typically, the exergonic reaction in the couple is ATP + H2O  ADP + Pi anabolic reactions are usually endergonic

EXAMPLE: A  B (exergonic) C  D (endergonic) Coupled: A + C  B + D (overall exergonic) Actually: A + C  I  B + D typically, the exergonic reaction in the couple is ATP + H2O  ADP + Pi anabolic reactions are usually endergonic This will be explored in more detail in an example in a bit, but first some more about ATP…

Why is ATP so darned important?
What is a phosphorylated intermediate? How much ATP is in a cell at any given time? Why must cells keep a high ATP/ADP ratio?

ATP is the main energy currency in cells
One way that organisms manage their energy needs is to use ATP as a ready energy source for many reactions.

ATP – nucleotide with adenine base, ribose sugar, and a chain of 3 phosphate groups

last two phosphate groups are joined to the chain by unstable bonds; breaking these bonds is relatively easy and releases energy; thus:

hydrolysis of ATP to ADP and inorganic phosphate (Pi) releases energy ATP + H2O  ADP + Pi

hydrolysis of ATP to ADP and inorganic phosphate (Pi) releases energy ATP + H2O  ADP + Pi the amount of energy released depends in part on concentrations of reactants and products is generally ~30 kJ/mol

Intermediates when ATP hydrolysis is coupled to a reaction to provide energy

Intermediates when ATP hydrolysis is coupled to a reaction to provide energy often phosphorylated compounds glucose glucose-6-phosphate

Intermediates when ATP hydrolysis is coupled to a reaction to provide energy often phosphorylated compounds the inorganic phosphate is transferred onto another compound rather than being immediately released glucose glucose-6-phosphate

Intermediates when ATP hydrolysis is coupled to a reaction to provide energy often phosphorylated compounds the inorganic phosphate is transferred onto another compound rather than being immediately released a phosphorylated compound is in a higher energy state glucose glucose-6-phosphate

EXAMPLE of a coupled reaction: glucose + fructose  sucrose + H2O (endergonic; requires ~27 kJ/mol) ATP + H2O  ADP + Pi (exergonic; provides ~30 kJ/mol) coupled: glucose + fructose + ATP + H2O  sucrose + H2O + ADP + Pi simplified: glucose + fructose + ATP  sucrose +ADP + Pi with intermediates: glucose + fructose + ATP + H2O  glucose-P + fructose + ADP  sucrose + H2O + ADP + Pi (net exergonic, releases ~3 kJ/mol)

EXAMPLE of a coupled reaction: glucose + fructose  sucrose + H2O (endergonic; requires ~27 kJ/mol) ATP + H2O  ADP + Pi (exergonic; provides ~30 kJ/mol)

EXAMPLE of a coupled reaction: glucose + fructose  sucrose + H2O (endergonic; requires ~27 kJ/mol) ATP + H2O  ADP + Pi (exergonic; provides ~30 kJ/mol) coupled: glucose + fructose + ATP + H2O  sucrose + H2O + ADP + Pi

EXAMPLE of a coupled reaction: glucose + fructose  sucrose + H2O (endergonic; requires ~27 kJ/mol) ATP + H2O  ADP + Pi (exergonic; provides ~30 kJ/mol) coupled: glucose + fructose + ATP + H2O  sucrose + H2O + ADP + Pi simplified: glucose + fructose + ATP  sucrose +ADP + Pi

EXAMPLE of a coupled reaction: glucose + fructose  sucrose + H2O (endergonic; requires ~27 kJ/mol) ATP + H2O  ADP + Pi (exergonic; provides ~30 kJ/mol) coupled: glucose + fructose + ATP + H2O  sucrose + H2O + ADP + Pi simplified: glucose + fructose + ATP  sucrose +ADP + Pi with intermediates: glucose + fructose + ATP + H2O  glucose-P + fructose + ADP  sucrose + H2O + ADP + Pi (net exergonic, releases ~3 kJ/mol)

Thus, energy transfer in cellular reactions is often accomplished through transfer of a phosphate group from ATP

Making ATP involves an endergonic condensation reaction reverse of an exergonic reaction is always endergonic ADP + Pi  ATP + H2O

Making ATP involves an endergonic condensation reaction reverse of an exergonic reaction is always endergonic ADP + Pi  ATP + H2O endergonic, usually requires more than ~30 kJ/mol

Making ATP involves an endergonic condensation reaction reverse of an exergonic reaction is always endergonic ADP + Pi  ATP + H2O endergonic, usually requires more than ~30 kJ/mol must be coupled with an exergonic reaction; typically from a catabolic pathway (more on that later)

Overall, ATP is typically created in catabolic reactions and used in anabolic reactions, linking those aspects of metabolism

Cells maintain high levels of ATP relative to ADP maximizes energy available from hydrolysis of ATP

Cells maintain high levels of ATP relative to ADP maximizes energy available from hydrolysis of ATP ratio typically greater than 10 ATP: 1 ADP

Overall concentration of ATP still very low supply typically only enough for a few seconds at best

Overall concentration of ATP still very low supply typically only enough for a few seconds at best instability prevents stockpiling

Overall concentration of ATP still very low supply typically only enough for a few seconds at best instability prevents stockpiling must be constantly produced in a typical cell, the rate of use and production of ATP is about 10 million molecules per second resting human has less than 1 g of ATP at any given time but uses about 45 kg per day

Why is ATP so darned important?
What is a phosphorylated intermediate? How much ATP is in a cell at any given time? Why must cells keep a high ATP/ADP ratio?

What are redox reactions used for in cells?
How (generally) can you tell which of two similar compounds is reduced and which is oxidized? Give some examples of compounds commonly used in redox reactions in cells.

Redox reactions are also used for energy transfer
Redox reactions are used to harvest energy from some chemicals. The acceptors of that energy typically cannot be used directly as energy currency.

Redox reactions are used to harvest energy from some chemicals. The acceptors of that energy typically cannot be used directly as energy currency. Electrons can also be used for energy transfer

Redox reactions are used to harvest energy from some chemicals. The acceptors of that energy typically cannot be used directly as energy currency. Electrons can also be used for energy transfer Redox reactions: recall reduction, gain electrons; oxidation, lose electrons; both occur simultaneously in cells (generally no free electrons in cells)

Redox reactions are used to harvest energy from some chemicals. The acceptors of that energy typically cannot be used directly as energy currency. Electrons can also be used for energy transfer Redox reactions: recall reduction, gain electrons; oxidation, lose electrons; both occur simultaneously in cells (generally no free electrons in cells) Typically, the oxidized substance gives up energy with the electron, the reduced substance gains energy with the electron

Loss of electron (oxidation)
08.04 Redox Reactions Slide number: 6 Loss of electron (oxidation) A* + A B o + B* _ Gain of electron (reduction) e– B A Low energy High energy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

chain of redox reactions / electron transfers common more on electron transport chains later

chain of redox reactions / electron transfers common more on electron transport chains later each electron transfer releases free energy free energy can be used for other chemical reactions

chain of redox reactions / electron transfers common more on electron transport chains later each electron transfer releases free energy free energy can be used for other chemical reactions proton often removed as well if so, equivalent of a hydrogen atom is transferred

Catabolism typically involves: removal of hydrogen atoms from nutrients (such as carbohydrates) transfer of the protons and electrons to intermediate electron acceptors

intermediate acceptor example: nicotinamide adenine dinucleotide (NAD+)

intermediate acceptor example: nicotinamide adenine dinucleotide (NAD+) Use XH2 to represent a nutrient molecule: XH2 + NAD+  X + NADH + H+

intermediate acceptor example: nicotinamide adenine dinucleotide (NAD+) Use XH2 to represent a nutrient molecule: XH2 + NAD+  X + NADH + H+ Often, the reduced form is just called NADH

Reduced state stores energy, which is partially released as free energy when NADH is oxidized

Reduced state stores energy, which is partially released as free energy when NADH is oxidized The free energy usually winds up being used to make ATP

Other commonly used acceptors are NADP+, FAD, and cytochromes NADP+/NADPH – important in photosynthesis FAD/FADH2 – flavin adenine dinucleotide Cytochromes – small iron-containing proteins; iron serves as electron acceptor

What are redox reactions used for in cells?
How (generally) can you tell which of two similar compounds is reduced and which is oxidized? Give some examples of compounds commonly used in redox reactions in cells.

What do enzymes do for cells, and how do they do it?
Be sure to use the following terms: catalyst (or catalyze) activation energy enzyme-substrate complex active site induced fit

Enzymes Manipulation of reactions is essential to and largely defining of life.

Enzymes Manipulation of reactions is essential to and largely defining of life. Organisms use enzymes to manipulate the speed of reactions.

Enzymes Manipulation of reactions is essential to and largely defining of life. Organisms use enzymes to manipulate the speed of reactions. Understanding life requires understanding how enzymes work.

Enzymes Enzymes regulate chemical reactions in living organisms
An enzyme is an organic molecule (typically a protein) that acts as a catalyst

An enzyme is an organic molecule (typically a protein) that acts as a catalyst catalyst –increases the rate of a chemical reaction without being consumed in the reaction (the catalyst recycles back to its original state)

An enzyme is an organic molecule (typically a protein) that acts as a catalyst catalyst –increases the rate of a chemical reaction without being consumed in the reaction (the catalyst recycles back to its original state) enzymes (catalysts) only alter reaction rate; thermodynamics still governs whether the reaction can occur

substrate complex. Products are Enzyme The substrate,
Fig. 8.9 (TEArt) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The substrate, sucrose, consists of glucose and fructose bonded together. 1 2 The substrate binds to the enzyme, forming an enzyme- substrate complex. Glucose Fructose Bond 4 Products are released, and the enzyme is free to bind other substrates. H2O Active site 3 The binding of the substrate and enzyme places stress on the glucose- fructose bond, and the bond breaks. Enzyme

08.09 Enzyme Catalytic Cycle
Slide number: 2 1 The substrate, sucrose, consists of glucose and fructose bonded together. Bond Enzyme Active site Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Slide number: 3 1 The substrate, sucrose, consists of glucose and fructose bonded together. Bond Enzyme Active site Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Slide number: 4 1 The substrate, sucrose, consists of glucose and fructose bonded together. Bond Enzyme Active site The substrate binds to the enzyme, forming an enzyme-substrate complex. 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Slide number: 5 1 The substrate, sucrose, consists of glucose and fructose bonded together. Bond Enzyme Active site The substrate binds to the enzyme, forming an enzyme-substrate complex. 2 H2O The binding of the substrate and enzyme places stress on the glucose-fructose bond, and the bond breaks. 3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Slide number: 6 1 The substrate, sucrose, consists of glucose and fructose bonded together. Bond Enzyme Active site Glucose Fructose Products are released, and the enzyme is free to bind other substrates. 4 The substrate binds to the enzyme, forming an enzyme-substrate complex. 2 H2O The binding of the substrate and enzyme places stress on the glucose-fructose bond, and the bond breaks. 3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Enzymes work by lowering activation energy of a reaction
all reactions have a required energy of activation

all reactions have a required energy of activation energy required to break existing bonds and bring reactants together

all reactions have a required energy of activation energy required to break existing bonds and bring reactants together must be supplied in some way before the reaction can proceed

Enzymes activation energy
catalysts greatly reduce the activation energy requirement, making it easier for a reaction to occur

Enzymes Enzymes lower activation energy by forming a complex with the substrate(s) the ability to form an enzyme-substrate complex is highly dependent on the shape of the enzyme

Enzymes Enzymes lower activation energy by forming a complex with the substrate(s) the ability to form an enzyme-substrate complex is highly dependent on the shape of the enzyme the site where the substrate(s) binds to the enzyme is called the active site

Enzymes Enzymes lower activation energy by forming a complex with the substrate(s) the ability to form an enzyme-substrate complex is highly dependent on the shape of the enzyme the site where the substrate(s) binds to the enzyme is called the active site when the enzyme-substrate complex forms, there are typically shape changes in the enzyme and substrate(s) – called induced fit

Enzymes ES complex typically very unstable

Enzymes ES complex typically very unstable short-lived

Enzymes ES complex typically very unstable short-lived
breaks down into released product(s) and a free enzyme that is ready to be reused

Enzymes ES complex typically very unstable overall: short-lived
breaks down into released product(s) and a free enzyme that is ready to be reused overall: enzyme + substrate(s)  ES complex  enzyme + product(s)

What do enzymes do for cells, and how do they do it?
Be sure to use the following terms: catalyst (or catalyze) activation energy enzyme-substrate complex active site induced fit

What are the four main things that enzymes do to lower activation energy?

Enzymes reduction in activation energy is due primarily to four things:

Enzymes reduction in activation energy is due primarily to four things: an enzyme holds reactants (substrates) close together in the right orientation for the reaction, which reduces the reliance on random collisions

Enzymes reduction in activation energy is due primarily to four things: an enzyme holds reactants (substrates) close together in the right orientation for the reaction, which reduces the reliance on random collisions an enzyme may put a “strain” on existing bonds, making them easier to break

Enzymes reduction in activation energy is due primarily to four things: an enzyme holds reactants (substrates) close together in the right orientation for the reaction, which reduces the reliance on random collisions an enzyme may put a “strain” on existing bonds, making them easier to break an enzyme provides a “microenvironment” that is more chemically suited to the reaction

Enzymes reduction in activation energy is due primarily to four things: an enzyme holds reactants (substrates) close together in the right orientation for the reaction, which reduces the reliance on random collisions an enzyme may put a “strain” on existing bonds, making them easier to break an enzyme provides a “microenvironment” that is more chemically suited to the reaction sometimes the active site of the enzyme itself is directly involved in the reaction during the transition states

Enzymes enzyme + substrate(s)  ES complex  enzyme + product(s)

What are the four main things that enzymes do to lower activation energy?

How are enzymes named (what suffixes indicate an enzyme)?

Enzymes Enzyme names many names give some indication of substrate

Enzymes Enzyme names many names give some indication of substrate
most enzyme names end in –ase (example: sucrase)

most enzyme names end in –ase (example: sucrase) some end in –zyme (example: lysozyme)

most enzyme names end in –ase (example: sucrase) some end in –zyme (example: lysozyme) some traditional names are less indicative of enzyme function (examples: pepsin, trypsin)

Enzymes Enzymes are generally highly specific
overall shape as well as spatial arrangements in the active site limit what enzyme-substrate complexes can readily form

Enzymes the amount of specificity depends on the particular enzyme
example of high specificity: sucrase splits sucrose, not other disaccharides

Enzymes the amount of specificity depends on the particular enzyme
example of high specificity: sucrase splits sucrose, not other disaccharides example of low specificity: lipase splits variety of fatty acids from glycerol

Enzymes enzymes are classified by the kind of reaction they catalyze
The International Union of Biochemistry and Molecular Biology has developed a nomenclature for enzymes; the top-level classification is Oxidoreductases: catalyze oxidation/reduction reactions Transferases: transfer a functional group (e.g. a methyl or phosphate group) Hydrolases: catalyze the hydrolysis of various bonds Lyases: cleave various bonds by means other than hydrolysis and oxidation Isomerases: catalyze isomerization changes within a single molecule Ligases: join two molecules with covalent bonds The complete nomenclature can be browsed at

How are enzymes named (what suffixes indicate an enzyme)?

Explain the terms cofactor, apoenzyme, and coenzyme.

Enzymes Many enzymes require additional chemical components (cofactors) to function

Enzymes Many enzymes require additional chemical components (cofactors) to function apoenzyme + cofactor  active enzyme (bound together)

Enzymes Many enzymes require additional chemical components (cofactors) to function apoenzyme + cofactor  active enzyme (bound together) alone, an apoenzyme or a cofactor has little if any catalytic activity

Enzymes Many enzymes require additional chemical components (cofactors) to function apoenzyme + cofactor  active enzyme (bound together) alone, an apoenzyme or a cofactor has little if any catalytic activity cofactors may or may not be changed by the reaction

Enzymes cofactors can be organic or inorganic
organic examples (coenzymes): ADP, NAD+, NADP+, FAD typically changed by the catalyzed reaction

organic examples (coenzymes): ADP, NAD+, NADP+, FAD typically changed by the catalyzed reaction inorganic examples: metal ions like Ca2+, Mg2+, Fe3+, etc. typically not changed by the catalyzed reaction

organic examples (coenzymes): ADP, NAD+, NADP+, FAD typically changed by the catalyzed reaction inorganic examples: metal ions like Ca2+, Mg2+, Fe3+, etc. typically not changed by the catalyzed reaction most vitamins are coenzymes or part of coenzymes, or are used for making coenzymes

Energy-rich molecule Enzyme H H NAD+ H Product NAD+ NAD+ NAD H NAD H
Fig. 8.3 (TEArt) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Energy-rich molecule Enzyme H H NAD+ H Product NAD+ NAD+ NAD H 1. Enzymes that harvest hydrogen atoms have a binding site for NAD+ located near another binding site. NAD+ and an energy-rich molecule bind to the enzyme. 2. In an oxidation- reduction reaction, a hydrogen atom is transferred to NAD+, forming NADH. NAD H 3. NADH then diffuses away and is available to other molecules.

Fig. 8.A

Explain the terms cofactor, apoenzyme, and coenzyme.

Discuss the effects of temperature and pH on enzyme activity.

Enzymes are most active under optimal conditions
each enzyme has an optimal temperature most effective as a catalyst at the optimal temperature

each enzyme has an optimal temperature most effective as a catalyst at the optimal temperature rate of drop-off in effectiveness away from optimal temperature depends on the enzyme

each enzyme has an optimal temperature most effective as a catalyst at the optimal temperature rate of drop-off in effectiveness away from optimal temperature depends on the enzyme high temperatures tend to denature enzymes

each enzyme has an optimal temperature most effective as a catalyst at the optimal temperature rate of drop-off in effectiveness away from optimal temperature depends on the enzyme high temperatures tend to denature enzymes human enzymes have temperature optima near human body temperature (37°C)

each enzyme has an optimal pH again, most effective at the optimum; drop-off varies

each enzyme has an optimal pH again, most effective at the optimum; drop-off varies extremes of pH tend to denature enzymes

each enzyme has an optimal pH again, most effective at the optimum; drop-off varies extremes of pH tend to denature enzymes a particular organism shows more variety in enzyme pH optima than in temperature optima, but most of its enzymes will still be optimal at the pH normally found in the cytosol of its cells

Discuss the effects of temperature and pH on enzyme activity.

What is a metabolic pathway?

Enzymes Metabolic pathways use organized “teams” of enzymes
the products of one reaction often serve as substrates for the next reaction

the products of one reaction often serve as substrates for the next reaction removing products (by having them participate the “next reaction”) improves reaction rate (avoids equilibrium)

the products of one reaction often serve as substrates for the next reaction removing products (by having them participate the “next reaction”) improves reaction rate (avoids equilibrium) multiple metabolic pathways exit in cells, overlapping in some areas and diverging in others

Fig. 8.15

What is a metabolic pathway?

How do cells regulate enzyme activity?
Include the terms: inhibitors activators allosteric site feedback inhibition Also, differentiate between: irreversible and reversible inhibition competitive and noncompetitive inhibition

Enzymes Cells can regulate enzyme activity to control reactions
increase substrate amount  increase reaction rate (up to saturation of available enzyme molecules)

increase substrate amount  increase reaction rate (up to saturation of available enzyme molecules) increase enzyme amount  increase reaction rate (as long as substrate amount > enzyme amount)

increase substrate amount  increase reaction rate (up to saturation of available enzyme molecules) increase enzyme amount  increase reaction rate (as long as substrate amount > enzyme amount) compartmentation of the enzyme, substrate, and products can help control reaction rate

Substrate concentration
When substrate concentration >> enzyme concentration…. Rate of reaction Rate of reaction Enzyme concentration Substrate concentration (a) (b)

Cells can regulate enzyme activity to control reactions
inhibitors and activators of enzymes activators allow or enhance catalytic activity

inhibitors and activators of enzymes activators allow or enhance catalytic activity inhibitors reduce or eliminate catalytic activity

inhibitors and activators of enzymes activators allow or enhance catalytic activity inhibitors reduce or eliminate catalytic activity sometime, this uses an allosteric site – a receptor site on an enzyme where an inhibitor or activator can bind

a common example of allosteric control is feedback inhibition the last product in a metabolic pathway binds to an allosteric site of an enzyme in an early step of the pathway (often the first) this product inhibits activity of the enzyme

-Aceto--hydroxybutyrate
Threonine Enzyme #1 (Threonine deaminase) -Ketobutyrate Enzyme #2 -Aceto--hydroxybutyrate Enzyme #3 Feedback inhibition (Isoleucine inhibits enzyme #1) ,b-Dihydroxy-b-methylvalerate Enzyme #4 -Keto-b-methylvalerate Enzyme #5 Isoleucine

Fig. 9.20

irreversible inhibition – enzyme is permanently inactivated or destroyed; includes many drugs and toxins

irreversible inhibition – enzyme is permanently inactivated or destroyed; includes many drugs and toxins reversible inhibition – if inhibitor is removed, the enzyme activity can be recovered

reversible inhibition – if inhibitor is removed, the enzyme activity can be recovered competitive inhibition – inhibitor is similar in structure to a substrate; competes with substrate for binding to the active site

reversible inhibition – if inhibitor is removed, the enzyme activity can be recovered competitive inhibition – inhibitor is similar in structure to a substrate; competes with substrate for binding to the active site noncompetitive inhibition – binds at allosteric site, alters enzyme shape to make active site unavailable

How do cells regulate enzyme activity?
Include the terms: inhibitors activators allosteric site feedback inhibition Also, differentiate between: irreversible and reversible inhibition competitive and noncompetitive inhibition

Chapter 8: Energy and Metabolism

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