Chapter 8-Campbell

This lecture is an amalgam of two different texts.

Live with it.

An Introduction to Metabolism

• Overview: The Energy of Life

• The living cell

– Is a miniature factory where thousands of reactions occur

– Converts energy in many ways

• Some organisms

– Convert energy to light, as in bioluminescence

• Concept 8.1: An organism’s metabolism transforms matter and energy, subject to the laws of thermodynamics

• Metabolism

– Is the totality of an organism’s __________ reactions

– Arises from interactions between molecules

Organization of the Chemistry of Life into Metabolic Pathways

• A metabolic pathway has many steps

– That begin with a specific molecule and end with a product

– That are each __________ by a specific enzyme

• Catabolic pathways

– Break down complex molecules into simpler compounds

– Release energy

• Anabolic pathways

– Build complicated molecules from simpler ones

– Consume energy

Forms of Energy

• Energy

– Is the capacity to cause change

– Exists in various forms, of which some can perform work

• Kinetic energy

– Is the energy associated with motion

• Potential energy

– Is stored in the location of matter

– Includes chemical energy stored in molecular structure

• Energy can be converted

– From one form to another

Figure 6.1 Energy Conversions and Work

The Laws of Energy Transformation

• Thermodynamics

– Is the study of energy transformations

The First Law of Thermodynamics

• According to the first law of thermodynamics

– Energy can be transferred and transformed

– Energy cannot be __________ or destroyed

• An example of energy conversion

The Second Law of Thermodynamics

• According to the second law of thermodynamics

– Spontaneous changes that do not require outside energy increase the entropy, or disorder, of the universe

Figure 6.2 The Laws of Thermodynamics

Biological Order and Disorder

• Living systems

– Increase the __________ of the universe

– Use energy to maintain order

• TANSTAAFL

• Concept 8.2: The free-energy change of a reaction tells us whether the reaction occurs spontaneously

Free-Energy Change, G

• A living system’s free energy

– Is energy that can do work under cellular conditions

• The change in free energy, ∆G during a biological process

– Is related directly to the enthalpy change (∆H) and the change in entropy

Free Energy, Stability, and Equilibrium

• Organisms live at the expense of free energy

• During a spontaneous change

– Free energy decreases and the stability of a system increases

• At maximum stability

– The system is at equilibrium

Exergonic and Endergonic Reactions in Metabolism

• An exergonic reaction

– Proceeds with a net release of free energy and is spontaneous

• An endergonic reaction

– Is one that absorbs free energy from its surroundings and is __________

Figure 6.3 Exergonic and Endergonic Reactions

Equilibrium and Metabolism

• Reactions in a closed system

– Eventually reach equilibrium

• Cells in our body

– Experience a constant flow of materials in and out, preventing metabolic pathways from reaching equilibrium

• An analogy for cellular respiration

• Concept 8.3: ATP powers cellular work by coupling exergonic reactions to endergonic reactions

• A cell does three main kinds of work

– Mechanical

– Transport

– Chemical

• Energy coupling

– Is a key feature in the way cells manage their energy resources to do this work

The Structure and Hydrolysis of ATP

• ATP (adenosine triphosphate)

– Is the cell’s energy shuttle

– Provides energy for cellular functions

• Energy is released from ATP

– When the terminal phosphate bond is broken

Figure 6.5 ATP (Part 1)

• ATP hydrolysis

– Can be __________ to other reactions

How ATP Performs Work

• ATP drives endergonic reactions

– By phosphorylation, transferring a phosphate to other molecules

• The three types of cellular work

– Are powered by the hydrolysis of ATP

The Regeneration of ATP

• Catabolic pathways

– Drive the regeneration of ATP from ADP and phosphate

Figure 6.7 Coupling ATP Hydrolysis to an Endergonic Reaction

• Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers

• A catalyst

– Is a chemical agent that speeds up a reaction without being consumed by the reaction

• An enzyme

– Is a catalytic protein

The Activation Barrier

• Every chemical reaction between molecules

– Involves both bond __________ and bond __________

• The hydrolysis

– Is an example of a chemical reaction

• The activation energy, EA

– Is the initial amount of energy needed to start a chemical reaction

– Is often supplied in the form of heat from the surroundings in a system

Figure 6.8 Activation Energy Initiates Reactions

Figure 6.9 Over the Energy Barrier

• The energy profile for an exergonic reaction

How Enzymes Lower the EA Barrier

• An enzyme catalyzes reactions

– By lowering the EA barrier

• The effect of enzymes on reaction rate

Substrate Specificity of Enzymes

• The substrate

– Is the __________ an enzyme acts on

• The enzyme

– Binds to its substrate, forming an enzyme-substrate complex

• The __________ site

– Is the region on the enzyme where the substrate binds

• Induced fit of a substrate

– Brings chemical groups of the active site into positions that enhance their ability to catalyze the chemical reaction

Figure 6.10 Enzyme and Substrate

Figure 6.12 Life at the Active Site

Catalysis in the Enzyme’s Active Site

• In an enzymatic reaction

– The substrate binds to the active site

• The catalytic cycle of an enzyme

• The active site can lower an EA barrier by

– Orienting substrates correctly

– Straining substrate bonds

– Providing a favorable microenvironment

– Covalently bonding to the substrate

Effects of Local Conditions on Enzyme Activity

• The activity of an enzyme

– Is affected by general environmental factors

Figure 6.16 Catalyzed Reactions Reach a Maximum Rate

Effects of Temperature and pH

• Each enzyme

– Has an __________ temperature in which it can function

– Has an __________ pH in which it can function

Cofactors

• Cofactors

– Are nonprotein enzyme helpers

• Coenzymes

– Are organic cofactors

Enzyme Inhibitors

• __________ inhibitors

– Bind to the active site of an enzyme, competing with the substrate

• __________ inhibitors

– Bind to another part of an enzyme, changing the function

• Concept 8.5: Regulation of enzyme activity helps control metabolism

• A cell’s metabolic pathways

– Must be tightly regulated

__________ Regulation of Enzymes

• __________ regulation

– Is the term used to describe any case in which a protein’s function at one site is affected by binding of a regulatory molecule at another site

__________ Activation and Inhibition

• Many enzymes are __________ regulated

Figure 6.17 Irreversible Inhibition

Figure 6.18 Reversible Inhibition (Part 1)

Figure 6.18 Reversible Inhibition (Part 2)

Figure 6.18 Reversible Inhibition (Part 3)

Figure 6.18 Reversible Inhibition (Part 4)

Figure 6.19 Allosteric Regulation of Enzymes

Figure 6.20 Allostery and Reaction Rate

Figure 6.21 Inhibition of Metabolic Pathways

– They change shape when regulatory molecules bind to specific sites, affecting function

• Cooperativity

– Is a form of allosteric regulation that can amplify enzyme activity

Feedback Inhibition

• In feedback inhibition

– The end product of a metabolic pathway shuts down the pathway

• Feedback inhibition

Specific Localization of Enzymes Within the Cell

• Within the cell, enzymes may be

– Grouped into complexes

– Incorporated into membranes

– Contained inside organelles

Animation 6.1 Enzyme Catalysis

Animation 6.2 Allosteric Regulation of Enzymes

Video 6.1 Lysozyme: A three-dimensional model

Video 6.2 Glyceraldehyde 3-phosphate dehydrogenase and coenzyme NAD