• Chapter 8~ An Introduction to Metabolism

MetabolismMetabolism

• Metabolism: The totality of an organism’s chemical processes; managing the material and energy resources of the cell

• Catabolic pathways: degradative (break down) process such as cellular respiration; net release of energy from molecules

• Anabolic pathways: building process such as protein synthesis; photosynthesis; net gain of energy in molecules

Energy can be convertedEnergy can be converted

• From one form to another

On the platform, a diver has more potential energy.

Diving converts potential energy to kinetic energy.

Climbing up converts kineticenergy of muscle movement to potential energy.

In the water, a diver has less potential energy.

ThermodynamicsThermodynamics• Energy (E)~ capacity to do work;

– Kinetic energy~ energy of motion – Potential energy~ stored energy

• Chemical energy~ potential energy of molecules• Thermodynamics~ study of E transformations• 1st Law: conservation of energy; E transferred/transformed, not

created/destroyed

• 2nd Law: transformations increase entropy (disorder, randomness)

An example of energy conversionAn example of energy conversion

First law of thermodynamics: Energy can be transferred or transformed but neither created nor destroyed. For example, the chemical (potential) energy in food will be converted to the kinetic energy of the cheetah’s movement in (b).

(a)

Chemicalenergy

The Second Law of ThermodynamicsThe Second Law of Thermodynamics

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

Second law of thermodynamics: Every energy transfer or transformation increases the disorder (entropy) of the universe. For example, disorder is added to the cheetah’s surroundings in the form of heat and the small molecules that are the by-products of metabolism.

(b)

Heat

co2

H2O+

Energy ChangesEnergy Changes

• Free energy: portion of system’s E that can perform work

• Exergonic reaction: net release of free E to surroundings

• Endergonic reaction: absorbs free E from surroundings

The Structure and Hydrolysis of ATPThe Structure and Hydrolysis of ATP

• ATP (adenosine triphosphate)– Is the cell’s energy shuttle– Provides energy for cellular functions

O O O O CH2

H

OH OH

H

N

H H

ON C

HC

N CC

N

NH2

Adenine

Ribose

Phosphate groups

O

O O

O

O

O

-

- - -

CH

Energy is released from ATPEnergy is released from ATP

• When the terminal phosphate bond is broken

P

Adenosine triphosphate (ATP)

H2O

+ Energy

Inorganic phosphate

Adenosine diphosphate (ADP)

PP

P PP i

How ATP Performs WorkHow ATP Performs Work

• ATP drives endergonic reactions– By phosphorylation, transferring a phosphate

to other molecules

The three types of cellular workThe three types of cellular work

(c) Chemical work: ATP phosphorylates key reactants

P

Membraneprotein

Motor protein

P i

Protein moved

(a) Mechanical work: ATP phosphorylates motor proteins

ATP

(b) Transport work: ATP phosphorylates transport proteinsSolute

P P i

transportedSolute

GluGlu

NH3

NH2

P i

P i

+ +

Reactants: Glutamic acid and ammonia

Product (glutamine)made

ADP+

P

Energy & ATPEnergy & ATP

• Exergonic processes drive endergonic ones (ATP)

• Adenosine triphosphate• ATP tail: high negative

charge• ATP hydrolysis: release

of free E• Phosphorylation-

phosphate group transferred to a molecule

ATP

ADP + P i

Energy for cellular work (endergonic, energy-consuming processes)

Energy from catabolism (exergonic, energy yielding processes)

ATP/ADP cycleATP/ADP cycle

• Catabolic pathways– Drive the regeneration of ATP from ADP and

phosphate

ATP synthesis from ADP + P i requires energy

ATP hydrolysis to ADP + P i yields energy

Directional chemical reactionsDirectional chemical reactions

• Chemical reactions start with reactants and end with products.– Most reactions can proceed in both directions

A + B C

(starting) (product)

Equilibrium is met when the reaction proceeds equally in either direction

Chemistry of Life during Metabolic ActivityChemistry of Life during Metabolic Activity

• A metabolic pathway has many steps– That begin with a specific molecule and end

with a product– That are each catalyzed by a specific enzyme

Enzyme 1 Enzyme 2 Enzyme 3

A B C DReaction 1 Reaction 2 Reaction 3

Startingmolecule

Product

• Catabolic pathways (degradative)– Break down complex molecules into simpler

compounds– Release energy

• Anabolic pathways (biosynthetic)– Build complicated molecules from simpler ones– Consume energy

Chemistry of Life during Metabolic ActivityChemistry of Life during Metabolic Activity

EnzymesEnzymes

• Catalytic proteins: speed up the rate of reactions w/o being consumed

• Activation Energy: the E required to break or form bonds

• Substrate: enzyme reactant• Active site: pocket or groove

on enzyme that binds to substrate

• Induced fit model- strained reactants more readily react

The active siteThe active site

• Is the region on the enzyme where the substrate binds

Substrate

Active site

Enzyme

Induced fit of a substrateInduced fit of a substrate

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

Enzyme- substratecomplex

How Enzymes WorkHow Enzymes Work

Progress of the reaction

Products

Reactants

Course of reaction with enzyme

Course of reaction without enzyme

EA

withoutenzyme

EA with enzymeis lower

∆G is unaffected by enzyme

Fre

e e

nerg

y

How Enzymes WorkHow Enzymes Work

1. Enzyme attaches to the substrate during the chemical reaction and slightly changes its shape so the substrate fits tightly

2. At the active site, the activation energy is reduced making the substrate more likely to react

3. When the reaction is complete, products leave the enzyme and it can catalyze other reactions

Effects of Local Conditions on Enzyme ActivityEffects of Local Conditions on Enzyme Activity

• The activity of an enzyme– Is affected by general environmental factors

Effects on Enzyme ActivityEffects on Enzyme Activity

• Temperature• pH• Allosteric control-

substances can bind and affect enzymes.

• Cofactors: – inorganic, nonprotein helpers;

ex.: zinc, iron, copper

• Coenzymes:– organic helpers; ex.: vitamins