CH. 8 WARM-UP

1. What are the 1st and 2nd laws of thermodynamics?

2. Give the definition and an example of:A. Catabolic reactionB. Anabolic reaction

CHAPTER 8

An Introduction to Metabolism

WHAT YOU NEED TO KNOW:

Examples of endergonic and exergonic reactions.

The key role of ATP in energy coupling. That enzymes work by lowering the energy

of activation. The catalytic cycle of an enzyme that results

in the production of a final product. The factors that influence enzyme activity.

Metabolism is the totality of an organism’s chemical reactionsManage the materials and energy

resources of a cell

METABOLIC PATHWAYSCatabolic pathways release energy

by breaking down complex molecules into simpler compoundsEg. digestive enzymes break down

food release energy

Anabolic pathways consume energy to build complex molecules from simpler onesEg. amino acids link to form muscle

protein

ENERGY = CAPACITY TO DO WORKKinetic energy (KE): energy associated

with motionHeat (thermal energy) is KE associated

with random movement of atoms or molecules

Potential energy (PE): stored energy as a result of its position or structureChemical energy is PE available for

release in a chemical reaction Energy can be convertedconverted from one form

to anotherEg. chemical mechanical electrical

A closedclosed system, such as liquid in a thermos, is isolated from its surroundings

In an openopen system, energy and matter can be transferred between the system and its surroundings

Organisms are open systemsOrganisms are open systems

THERMODYNAMICS IS THE STUDY OF ENERGY TRANSFORMATIONS THAT OCCUR IN NATURE

THE FIRST LAW OF THERMODYNAMICS

The energy of the universe is constantThe energy of the universe is constantEnergy can be transferred and

transformedEnergy cannot be created or destroyed

Also called the principle of Conservation of Energy

THE SECOND LAW OF THERMODYNAMICS

Every energy transfer or transformation Every energy transfer or transformation increases the entropy increases the entropy (disorder) of the universe(disorder) of the universe

During every energy transfer or transformation, some energy is unusable, often lost as heat

A cell does three main kinds of work:MechanicalTransportChemical

To do work, cells manage energy resources by energy coupling, the use of an:

exergonic (energy releasing) process to drive an endergonic (energy absorbing) one

ATP (adenosine triphosphate) is the cell’s main energy source in energy coupling

Modified nucleotide ATP = adenine + ribose + 3 phosphates

When the bonds between the phosphate groups are broken by hydrolysis hydrolysis energy is released

This release of energy comes from the chemical change to a state of lower free chemical change to a state of lower free energyenergy, not in the phosphate bonds themselves

HOW ATP PERFORMS WORK

Exergonic release of Pi is used to do the endergonic work of cell

When ATP is hydrolyzed, it becomes ADP (adenosine diphosphate)

LE 8-11

NH2

Glu

P i

P i

P i

P i

Glu NH3

P

P

P

ATPADP

Motor protein

Mechanical work: ATP phosphorylates motor proteins

Protein moved

Membraneprotein

Solute

Transport work: ATP phosphorylates transport proteins

Solute transported

Chemical work: ATP phosphorylates key reactants

Reactants: Glutamic acidand ammonia

Product (glutamine)made

+ +

+

CatalystCatalyst: substance that can change the rate of a reaction without being altered in the process; not consumed

EnzymeEnzyme = biological catalyst; highly specific; named for reaction they catalyze

Speeds up metabolic reactions by lowering the activation energyactivation energy (energy needed to start reaction)

SUBSTRATE SPECIFICITY OF ENZYMES

The reactant that an enzyme acts on is called the enzyme’s substrate substrate

The enzyme binds to its substrate, forming an enzyme-substrate complexenzyme-substrate complex

The active site active site is the region on the enzyme where the substrate binds

INDUCED FIT: ENZYME FITS SNUGLY AROUND SUBSTRATE, “CLASPING HANDSHAKE”

An enzyme’s activity can be affected by:temperaturepHSalinityEnzyme concSubstrate

concActivatorsInhibitors

ENZYME CONCENTRATION

ENZYME/SUBSTRATE CONCENTRATION

Enzyme ConcentrationAs ↑ enzyme = ↑ reaction rateReaction rate levels off when substrate

becomes limiting factor. Not all enzyme molecules can find substrate.

Substrate ConcentrationAs ↑ substrate = ↑ reaction rateReaction rate levels off when all

enzyme have active site engaged. Enzyme is saturated. Max rate of reaction

COFACTORS CofactorsCofactors are nonprotein enzyme helpers such

as minerals (eg. Zn, Fe, Cu) CoenzymesCoenzymes are organic cofactors (eg. vitamins)

Enzyme Inhibitors Competitive inhibitorsCompetitive inhibitors bind to the active site of

an enzyme, competing with the substrate Noncompetitive inhibitorsNoncompetitive inhibitors bind to another part

of an enzyme, causing the enzyme to change shape and making the active site nonfunctional

INHIBITION OF ENZYME ACTIVITY

REGULATION OF ENZYME ACTIVITY

To regulate metabolic pathways, the cell switches on/off the genes that encode specific enzymes

Allosteric regulation: protein’s function at one site is affected by binding of a regulatory molecule to a separate site (allosteric site)Activator – stabilizes active siteInhibitor – stabilizes inactive formCooperativity – one substrate triggers

shape change in other active sites increase catalytic activity

FEEDBACK INHIBITION End product of an metabolic pathway shuts

down pathway by binding to the allosteric site of an enzyme

Prevent wasting chemical resources, increase efficiency of cell

FEEDBACK INHIBITION