Chapter 8 Biology An Introduction Into Metabolism

The action of competitive inhibitors may be reversible or irreversible

They consume energy to build up polymers from monomers.

energy cannot be created or destroyed but can be converted from one form to another,

Potential Chemical energy is a form of stored energy.

cellular respiration This is the name given to the process by which the body converts food energy to energy stored in ATP.

heat, carbon dioxide, and water

A molecule of glucose

dehydration

They consume energy to build up polymers from monomers

The entropy of the products is greater than the entropy of the reactans

The reaction proceeds with a net release of free energy.

The system can do no work

Ribose, 3 phosphorus, and nitrogenous base

Hydrolysis Hydrolysis involves breaking bonds with the addition of water.

They are exergonic and provide energy that can be used to produce ATP from ADP and i

It is lost to the environment.

ATP is a molecule that acts as an intermediary to store energy for cellular work.

Proteins

Enzymes work by reducing the energy of activation. reducing EA

is an organic catalyst Enzymes are proteins that behave as catalysts.

substrate

is unchanged

The compound is a competitive inhibitor. A competitive inhibitor slows down the enzyme by competing with the substrate for binding at the active site. Increasing substrate concentrations will reduce the effectiveness of a competitive inhibitor.

The catalyzed reaction will have the same G.

activation energy

by binding to an allosteric site, thus changing the shape of the active site of the enzyme

a substrate

an allosteric inhibitor

The final product of a metabolic pathway is usually the compound that regulates the pathway. It is quite common that the end product of the pathway controls the overall rate of the pathway.

by locally concentrating the reactants One of the ways enzymes work is to increase the concentrations of reactants at a single place.

Enzymes speed up the rate of the reaction without changing the DG for the reaction. Enzymes speed up reactions by lowering the activation energy barrier for the reaction. Enzymes cannot change the DG for the reaction.

The free-energy change (ΔG) of the hydrolysis of ATP to ADP and Pi may vary considerably with variations in pH, temperature, atmospheric pressure, and concentrations of reactants and products. The free-energy change (ΔG) of the hydrolysis of ATP to ADP and Pi is -7.3 kcal/mole under standard conditions. Standard conditions are defined as a temperature of 298 K (or 250C), 1 atm, pH 7, and equal 1M concentrations present of all reactants and products. In living cells, conditions do not conform to standard conditions, primarily because reactant and product concentrations differ from 1 M. For example, when ATP hydrolysis occurs under cellular conditions, the actual ΔG is about -13 kcal/mol, 78% greater than the energy released by ATP hydrolysis under standard conditions. Provide Feedback

In an endergonic reaction, in which order is increased, the change in entropy, symbolized by ΔS, is negative.

The speed of a reaction is determined by the activation energy barrier of the reaction and the temperature (which determines how many reactants have the energy to overcome the barrier).

The action of competitive inhibitors may be reversible or irreversible. Competitive inhibitors that bind covalently to the enzyme would be irreversible, and those that bind weakly would be reversible.

high-energy electrons "fall" to lower energy levels

allosteric activation

releasing free energy that can be coupled to other reactions With the help of specific enzymes, the cell can couple the energy of ATP hydrolysis directly to endergonic processes.

Competitive inhibitors compete physically and structurally with the substrate for an enzyme's active site; they can be outcompeted by adding extra substrate. Noncompetitive inhibitors do not compete for the active site, but inhibit the enzyme by binding elsewhere and changing the enzyme's shape. Irreversible inhibitors bind directly to the active site by covalent bonds, which change the structure of the enzyme and inactivate it permanently. Most medications are enzyme inhibitors of one kind or another.

The enzyme is inactive at this point. New enzyme must be added to regain enzyme activity. Because they bind directly to the active site by covalent bonds, irreversible inhibitors permanently render an enzyme inactive. Some drugs are irreversible inhibitors, including the antibiotic penicillin (which inhibits an enzyme involved in bacterial cell-wall synthesis) and aspirin (which inhibits cyclooxygenase-2, the enzyme involved in the inflammatory reaction).

Add more substrate; it will outcompete the inhibitor and increase the reaction rate. Competitive inhibition can be overcome by adding more substrate to outcompete the inhibitor. Many drugs used to treat different medical conditions, including hypertension, are competitive inhibitors. It is fairly easy to make a molecule that is similar in structure to a particular substrate because the known enzyme's shape can be used as a model of what the molecule needs to look like. It is more difficult to make a noncompetitive inhibitor because it is less obvious what the noncompetitive inhibitor's shape and structure should be.

The second law of thermodynamics states that every energy transformation makes the universe more disordered—carbon dioxide and water are more disordered than glucose.