Chapter 8 Introduction to Metabolism

Chapter 8Introduction to Metabolism

Think Tank Question…

Using the concepts of energy, entropy, and metabolism answer the following:

Does the concept of evolution violate the 2nd law of thermodynamics? Explain.

Metabolism Metabolism is the sum of all of the chemical reactions

in a biological organism A metabolic pathway is a series of defined steps

resulting in a certain product, each step catalyzed by an enzyme

Catabolic pathway – release energy by breaking down complex molecules into simpler compounds; energetically “downhill”; example – cellular respiration

Anabolic pathway – consume energy to build complicated molecules from simple ones; energetically “uphill”; example - photosynthesis

The energy released from a catabolic pathway is stored and used to complete an anabolic pathway

Energy Energy – the capacity

to cause change or do work

Kinetic energy – energy of motion

Potential energy – stored energy, the energy in an object currently not moving

Thermodynamics Thermodynamics – the study of energy

transformations that occur in a collection of matter

1st law – energy can be transferred and transformed, but cannot be created or destroyed

2nd law – every energy transfer or transformation increases the entropy of the universe Entropy is a measure of randomness or disorder in

the universe Disorder = randomness caused by the thermal motion of

particles; the energy is so dispersed it is unusable.

Back to the tank…

Does evolution violate the 2nd law???

NOPE.① The construction of complex molecules

(metabolism) generates disorder.② Life requires as constant input of energy to

maintain order.

The Laws of Thermodynamics

Free Energy Free energy – the energy available to do work ΔG = ΔH - T ΔS ; the Gibbs-Helmholtz equation

ΔG = the change in free energy, the maximum amount of usable energy that can be harvested

ΔH = enthalpy or total energy in biological systems T = temperature in Kelvin ΔS = change in entropy

Significance Indicates the maximum energy available to do work Indicates whether a reaction will occur spontaneously

or not At equilibrium ΔG = 0

Reaction typesExergonic

Chemical products have less free energy than the reactants

Energetically downhill Spontaneous Loses free energy ΔG is negative - ΔG is the max amount of work the reaction can perform

Endergonic Products have more free energy than reactants Energetically uphill Non-spontaneous Requires energy ΔG is positive + ΔG is the minimum amount of work required to drive

the reaction

Applying Concepts…REACTION REACTANTS PRODUCTS ΔG

Hydrolysis of sucrose Sucrose + H2O Glucose + Fructose 7.0

Triglyceride attachment Glycerol + fatty acid Monoglyceride 3.5

Photosynthesis 6CO2 + 6H2O Glucose + 6O2 686

The table shows some reactions and the absolute values of their associated free energy changes (ΔG).1. For each reaction, would you expect ΔG to

be positive or negative?2. Which reactions will be spontaneous?

Explain your answers.

Cellular Work ATP powers cellular work by coupling exergonic

and endergonic reactions Cell conducts 3 main types of work: mechanical,

transport, and chemical ATP – Adenosine triphosphate

ATP Hydrolysis Breaking of the bonds between phosphate groups ATP + H2O ADP + Pi ΔG = -7.3 kcal/mol or -30.5 kJ/mol (under standard

conditions

Energy Coupling Example

How ATP Performs Work

Regeneration of ATP Organisms at work are constantly using ATP, but

ATP can be regenerated with the addition of a phosphate to ADP

Requires energy; ΔG = +7.3 kcal/mol or +30.5 kJ/mol

Enzymes Enzyme – biological catalysts or catalytic protein (a

chemical agent that speeds up a reaction without being consumed by the reaction) All reactions require an initial investment of energy for starting a

reaction called the activation energy (EA) Enzymes reduce this activation energy

How Enzymes Work

Induced Fit Model Substrate – enzyme reactant Active site – pocket or groove on enzyme that

binds to substrate Enzyme substrate complex – enzyme flexes

and molds to the shape of the substrate

Induced Fit Model

Enzyme Specificity Enzymes function in a

very specific range of environmental conditions including temperature and pH

Some enzymes require ions or other molecule partners: Cofactors – inorganic

nonprotein helpers, ex: zinc, iron, copper

Coenzymes – organic cofactors, ex: vitamins

Enzyme Inhibitors

Competitive inhibitors – block active site, direct competition with substrate

Noncompetitive inhibitors – bind away from the active site, not in direct competition with substrate

Allosteric Regulation

Allosteric regulation can be described as any case in which a protein’s function at one site is affected by the binding of a regulatory molecule to a separate site

Activation, inhibition, and cooperativity

Feedback Inhibition

In feedback inhibition a metabolic pathway is switched off by the binding of its end product to an enzyme that acts early in the pathway

Applying Concepts…

The Scenario: In the boy’s locker room a bacteria is found

growing on some old socks made of a synthetic polymer.

You make a protein extract from the bacteria and isolate the probable enzyme that can cleave the monomers from the polymer.

You also synthesize a dipeptide glycine-glycine to test as a possible inhibitor of the enzyme.

Applying Concepts…

EXPERIMENT CONDITION RATE OF POLYMER CLEAVAGE

1 No enzyme 0.505

2 Enzyme 825.0

3 Enzyme pre-boiled at 100 C 0.520

4 Enzyme + RNA 799.0

5 Enzyme + dipeptide 0.495

1. Explain the results of each experiment.2. How do you think the dipeptide works? How

would you test your hypothesis?