MetabolismChapter

06

Metabolism 2Outline

Forms of EnergyLaws of Thermodynamics

Metabolic ReactionsATP

Metabolic PathwaysEnergy of ActivationEnzymes

Metabolism 3

Forms of EnergyKinetic:

Energy of motion

Mechanical

Potential:

Stored energy

Chemical

Metabolism 4

Energy•Energy is capacity to do work; cells must continually use energy to do biological work.Kinetic energy is energy of motion; all moving objects have kinetic energy.Potential energy is stored energy.­Ex. Water behind a dam has potential energy that can be converted to kinetic energy.

5Flow of Energy

Metabolism 6

Laws of ThermodynamicsFirst Law:

Law of conservation of energyEnergy cannot be created or destroyed, butEnergy CAN be changed from one form to another

Second Law:Law of ENTROPYWhen energy is changed from one form to another, there is a loss of usable energy

Waste energy goes to increase disorder

Metabolism 7

Laws of Thermodynamics

Second law: (Law of ENTROPY)Energy conversions result in heat and therefore the entropy of the universe is always increasing.It takes a constant input of usable energy from the food you eat to keep you organized.

8Carbohydrate Synthesis

9Carbohydrate Metabolism

10

Cells &

Energy

Metabolism 11

Metabolism:Sum of cellular chemical reactions in cellReactants participate in reactionProducts form as result of reaction

Free energy is the amount of energy available to perform workExergonic Reactions - Products have less free energy than reactants

Endergonic Reactions - Products have more free energy than reactants

Metabolic Reactions andEnergy Transformations

Animation

Living systems require free energy and matter to maintain order, grow and

reproduce.

Gibbs Free Energy (G)

• “Available energy”• Energy that can do work

under cellular conditions

• Concept from Thermodynamics

Life requires a highly ordered system.

Order is maintained by constant input of free energy into the system.

Loss of order or free energy flow results in death.

An organism’s metabolism transforms matter and energy, subject to the laws of

thermodynamics.

Thermodynamics: the laws of energy transformations.

The First Law of Thermodynamics

According to the first law of thermodynamics:– Energy cannot be created or destroyed– Energy can be transferred and transformed

The Second Law of Thermodynamics: spontaneous changes that do not

require outside energy increase the entropy, or disorder, of the universe.

Increased disorder and entropy are offset by biological processes that maintain or increase

order.

Metabolism 23Metabolic Reactions andEnergy Transformations

Catabolic pathwaysrelease energy by breaking down complex molecules to simpler compounds.

Ex: Cellular respiration - degrades glucose to carbon dioxide & water; provides energy for cellular work.

Anabolic pathwaysconsume energy to build complicated molecules from simpler ones.

Ex: Photosynthesis - synthesizes glucose from carbon dioxide & water

Catabolic pathways break down complex molecules into simpler compounds.

Catabolic pathways are spontaneous ( G < 0) and release energy: exergonic.

Exergonic Reactions

Anabolic pathways build complicated molecules from simpler ones and

consume energy.

Anabolic pathways are nonspontaneous ( G > 0) and consume energy:

endergonic.

Endergonic Reactions

MetabolismCatabolic & Anabolic Reactions

Cells need both types of reactions; both require enzymes

Anna – builds things

Cats – break things

29The ATP Cycle*High energy compound used to drive metabolic reactions*Constantly being generated from adenosine diphosphate (ADP)

30The ATP CycleATP Composed of:Adenine and ribose

(together = adenosine), and

3 phosphate groups

31The ATP CycleCoupled reactions

•Energy released by an exergonic reaction captured in ATP•That ATP used to drive an endergonic reaction

32

Figure­6.4

Coupled Reactions

Metabolism 33Work-Related Functionsof ATP

ATP - needed to perform cellular workChemical Work - Energy needed to synthesize macromolecules

Transport Work - Energy needed to pump substances across plasma membrane

Mechanical Work - Energy needed to contract muscles, beat flagella, etc

Metabolism 34

Enzymes

EnzymesProtein molecules that function as catalystsThe reactants of an enzymatically accelerated reaction are called substrates

See Biochemical Pathway Animation

Metabolism 35Enzymes:Energy of Activation

Reactants often “reluctant” to participate in reactionEnergy must be added to at least one reactant to initiate the reaction

Energy of activationEnzyme Operation:

Enzymes operate by lowering the energy of activation

Accomplished by bringing the substrates into contact with one another

Metabolism

MetabolismEnergy of Activation

Energy of activation (Ea) is energy that must be added to cause molecules to react.

MetabolismLower Ea

39Energy of Activation

Metabolism 40

Enzyme-Substrate Complex

Induced fit model •The active site complexes with the substrates

•Causes active site to change shape•Shape change forces substrates together or apart… initiating or breaking bonds

Enzymes Animation

41Induced Fit Model

43

Synthesis Reaction

44

Degradation or Decomposition

reaction

Metabolism 45

Factors Affecting Enzyme Activity

Substrate concentrationEnzyme activity increases with substrate concentration

More collisions between substrate molecules and the enzyme

TemperatureEnzyme activity increases with temperatureWarmer temperatures cause more effective collisions between enzyme and substrate

However, hot temperatures destroy enzymepH

Most enzymes are optimized for a particular pH

46Factors Affecting Enzyme Activity:Temperature

Normal protein Denatured protein

Denaturation

• Denaturation is when a protein unravels and loses its normal structure and function

• Generally irreversible

48Factors Affecting Enzyme Activity:pH

Metabolism 49

Factors Affecting Enzyme Activity

Cells can affect presence/absence of enzyme

Cells can affect concentration of enzyme

Cells can activate or deactivate enzyme

Enzyme Cofactors - Non-protein molecules that assist enzymes. (often metal ions, Fe2+)

Coenzymes are organic cofactors, like some vitamins

Phosphorylation – some require addition of a phosphate

Enzyme Cofactors (& Coenzymes)

GrooveGroove

• Some enzymes need cofactors to work; these are non-protein groups that attach to the enzyme. Ex. Minerals such as zinc or Mg

• Many vitamins (because they are organic are important because they are called coenzymes

This enzyme is DNA polymerase. It makes copies of

DNA. The purple things are magnesium (Mg), a mineral. Mg

is a cofactor for DNA polymerase. This is why you need some Mg in your diet.

51Factors Affecting Enzyme Activity:Activation by Phosphorylation

Metabolism 52Factors Affecting Enzyme Activity

Reversible enzyme inhibitionWhen a substance known as an inhibitor binds to an enzyme and decreases its activity­Competitive inhibition – substrate and the inhibitor are both able to bind to active site­Noncompetitive inhibition – the inhibitor binds not at the active site, but at the allosteric site

Feedback inhibition – The end product of a pathway inhibits the pathway’s first enzyme

Metabolism 53Competitive Inhibition

In competitive inhibition, another molecule is similar to enzymes substrate, competes with true substrate for enzyme’s active site, resulting in decreased product formation.

Metabolism 54Noncompetitive Inhibition

In noncompetitive inhibition, a molecule binds to allosteric site, a site other than active site, hereby changing the three-dimensional structure of enzyme and ability to bind to its substrate.

Metabolism 55

Allosteric EnzymesAllosteric Enzymes- 2 binding sites1. Active Site – substrate binds to2. Allosteric Site – allosteric affector binds

• Allosteric Activator – molecule binds to allosteric site and ACTIVATES enzyme.­ Creates active form of enzyme.

• Allosteric Inhibitor - molecule binds to allosteric site and INHIBITS enzyme.­ Creates inactive form of enzyme.

56Factors Affecting Enzyme Activity:Feedback Inhibition

See Feedback Inhibition Animation

Metabolism 57

EnzymesEach reaction in a metabolic pathway requires a unique and specific enzymeEnd product will not appear unless ALL enzymes present and functional

E1 E2 E3 E4 E5 E6AB C D E F G

See Biochemical Pathway Animation

Metabolism 58

Metabolic PathwaysReactions are usually occur in a sequenceSuch linked reactions form a metabolic pathway

­Begins with a particular reactant,

­Proceeds through several intermediates, and

­Terminates with a particular end productAB C D E FG

“A” is InitialReactant

“G” is EndProductIntermediates

Enzyme Inhibitors

Groove

• Inhibition is when the wrong molecule (an inhibitor) binds, blocking the active site;

substrate can’t bind

• Many poisons are inhibitors of essential enzymes (e.g. death cap mushroom, arsenic,

cadmium)

active site

amanitin (mushroom toxin)

This enzyme is RNA polymerase. It

reads the information in the

genetic code in DNA.

Metabolism 60

Irreversible InhibitionMaterials that irreversibly inhibit an enzyme are known as poisonsCyanides inhibit enzymes resulting in all ATP production

Penicillin inhibits an enzyme unique to certain bacteria

Heavy metals irreversibly bind with many enzymes

Nerve gas irreversibly inhibits enzymes required by nervous system