Enzyme and Bioenergetics True or False

What is the second law of thermodynamics

Everything tends toward disorder

ADP has more free energy than AMP because it is a more stable molecule

FALSE. ADP is less stable (negatively charged, phosphates repel each other), than AMP. Instability is the tendency to change. Stability is a low free energy state.

Enzymes act to lower the free energy of the products of chemical reactions

FALSE. Enzymes lower the energy of activation - the "hump" over which the reactants must pass before reacting exergonically. The energy needed for activation can be thought of for two reactants as energy needed to bring the molecules together in the right orientation and with enough force that bonds will break/reform. An enzyme that can bind two reactants in the right conformation and through induced fit can stress bonds can lower the activation energy and make the reaction more likely to occur.

ATP stands for apipide tetra phosphorous

FALSE. In biology ATP stands for adenosine triphosphate

ATP hydrolysis is endergonic

FALSE. The breakdown of ATP (loss of phosphate) to yield to ADP is exergonic. The products are more stable than the starting materials. The energy that is released as ATP breaks down is used to drive cellular reactions

The dG for a spontaneous chemical reaction is always positive

FALSE. The dG for a spontaneous chemical reaction is negative. The starting materials have more free energy than do the products. The reaction is energetically downhill and follows the second law of thermodynamics.

The shape of an enzyme changes irreversibly once it binds to its substrate.

FALSE. The shape change caused when substrates bind to the active site of the enzyme is called induced fit and it is temporary. Like handshake the fit tightens then relaxes back to the starting conformation when the product is released.

The terms "reactants" and "substrates" are synonymous

TRUE TRUE TRUE

All enzymes are proteins but not all catalytic units are proteins.

TRUE. All enzymes are proteins but there are inorganic catalysts and other organic catalysts such as catalytic RNAs (ribozymes)

An enzyme inhibitor may bind to the enzyme's active site or its allosteric site.

TRUE. An inhibitor may directly block the active site or may change the shape of the active site by binding elsewhere.

A new medicine that inhibits an enzyme is tested in the lab. Data show that an increase in the substrate concentration, in the presence of constant enzyme and inhibitor concentrations, causes an increase in reaction rate of the enzyme. The inhibitor should be classified as competitive.

TRUE. In competitive inhibition both substrate and inhibitor can bind to the active site. The more substrate there is the more often it will reach the active site before the inhibitor does. Think about all the Cavs playing basketball against one of the Lakers. Chances are the Cavs will make more baskets

The amino acids that form the active site of a sucrase enzyme would likely be hydrophilic.

TRUE. Sucrose, the substrate or reactant, is a carbohydrate. It is hydrophilic. It will "dissolve" or bind to a site that has hydrophilic side chains with which it can hydrogen bond. It will not bind well to a hydrophobic site.

An example of the second law of thermodynamics is the fact that as a wax candle burns the wax is broken down into carbon dioxide and heat and light are released.

TRUE. There is less free energy in the carbon dioxide (completely oxidized), heat and light than there was in the wax (a lipid, highly reduced form of carbon.)