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# Energy and Metabolism - PowerPoint PPT Presentation

Energy and Metabolism. Chapter 6. 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. Flow of Energy.

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Chapter 6

• 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

• 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.)

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

• 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

• 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

• 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.

• 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

• 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)

• 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.

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

• Oxidation = loss of an electron

• Reduction = gain of an electron

• Oxidation

• A chemical reaction in which a molecule gives up electrons

• Oxidation releases energy

• The molecule loosing the electron is oxidized

79

• 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

80

• 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

• 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

• 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

• ATP= adenosine triphosphate

• the energy “currency” of cells

• ATP structure:

• ribose, a 5-carbon sugar

• three phosphates

• ATP - 1 PO4 = ADP (Adenosine Diphosphate)

• ADP - 1 PO4 = AMP (Adenosine Monophosphate)

• ADP + 1 PO4 = ATP

25

• 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

• 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

• When the bond between phosphates is broken:

ATP ADP + Pi

energy is released

• Pi = inorganic phosphate

• This reaction is reversible...

• When the bond between phosphates is formed:

ADP + Pi ATP

energy is consumed

• ATP - ADP Cycle

• It costs energy to build ATPs

(Adenosine Diphosphate +1 phosphate)

ATP

• 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.

• 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

38

• 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 activationrequired for a reaction to occur

• Are not changed or consumed by the reaction

• Cofactors, Coenzymes

40

• Enzymes catalyze cellular chemical reactions

• Metabolism - the chemical reactions in a cell:

• Two categories of cellular chemical reactions:

• 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

41

• 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

42

• 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.

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

44

• 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

46

• Enzyme/Substrate Complex:

E + S ES EP E + P

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

• The Enzyme/Substrate Complex is formed (ES)

• The Enzyme’s Substrate is changed to the Enzyme’s

• Product in the active site of the enzyme (EP)

• The Enzyme and Product Separate (E+P)

• The Enzyme is free to bind to another Substrate

48

• 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

51

• 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

52

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

55

• Reactions that break chemical bonds release their internal potential energy.

• Example: burning wood

• Oxidation reactions

• Organisms obtain energy through enzyme-catalyzed biochemical reactions.

• 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.

• ADase oxidizes alcohol

• Alcohol cannot be oxidized unless

• something else is reduced

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:

• Temperature

• pH

• Substrate concentration

• Regulatory molecules

59

• Temperature has two effects on enzymes:

• Changes the rate of molecular motion

• Increasing temperature increases molecular motion and increases turnover number

• 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.

• 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

63

• 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.

• Metabolic Pathwaysare 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

• 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

• 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:

• Enzymatic competition for substrate

• Gene regulation

• Enzyme inhibition

70

1. Enzymatic competition for substrate

• Enzymatic 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.

71

2. Gene regulation

• Enzymes 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.

73

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:

• Negative Feedback Inhibition

• Competitive Inhibition

• Noncompetitive Inhibition

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• 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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• 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

• Competitive inhibitors closely resemble the substrate.

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

• 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

• 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

82

• 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

84

• 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

• 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

C6H12O6 + 6 O2 6 H2O + 6 CO2 + Energy

-Now-

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