Ch. 8 Dynamic Study Module
Cells use ATP constantly, but ATP is considered a renewable resource. What process makes this possible?
*ATP can be regenerated by the addition of a phosphate group to ADP*
As ATP begins to build up in a cell, metabolism slows down. How does this happen?
*ATP acts as an allosteric inhibitor to many of the enzymes involved in metabolism, thus slowing their function* - ATP acts as an inhibitor, not an activator. - ATP is an allosteric inhibitor. It does not bind to the active site of the enzymes it regulates. - Excess ATP acts as an allosteric inhibitor. It deactivates enzymes by reversibly changing their shape.
What is the relationship between anabolic and catabolic pathways?
*Anabolic pathways synthesize more complex organic molecules using the energy derived from catabolic pathways* - CATABOLIC pathways = release energy by breaking down complex molecules to simpler compounds (breakdown pathways) ---eg. cellular respiration: in which the sugar glucose and other organic fuels are broken down in the presence of oxygen to carbon dioxide and water → Energy that was stored in the organic molecules becomes available to do the work of the cell, such as ciliary beating or membrane transport. - ANABOLIC pathways = consume energy to build complicated molecules from simpler ones(biosynthetic pathways) ---eg. the synthesis of an amino acid from simpler molecules and the synthesis of a protein from amino acids - Catabolic and anabolic pathways are the "downhill" and "uphill" avenues of the metabolic landscape. Energy released from the downhill reactions of catabolic pathways can be stored and then used to drive the uphill reactions of anabolic pathways.
How does ATP drive mechanical work in the cell?
*By binding to motor proteins* Chemical work is driven by ATP providing free energy to facilitate the formation of polymers from monomers. ATP adds a phosphate to a transport protein for this kind of work. A phosphate is not removed from the protein. Mechanical work is driven by ATP binding to motor proteins. ATP adds free energy to chemical reactions. It does not remove it.
What is the relevance of the first law of thermodynamics to biology?
*Energy can be freely transformed among different forms as long as the total energy is conserved*
If the entropy of a living organism is decreasing, what is most likely to be occurring simultaneously?
*Energy input into the organism must be occurring to drive the decrease in entropy* - A logical consequence of the loss of usable energy during energy transfer or transformation is that each such event makes the universe more disordered - Living systems increase the entropy of their surroundings
What is true regarding metabolic pathways?
*Metabolic pathways consist of a series of reactions, each catalyzed by a different enzyme*
What is changed by the presence of an enzyme in a reaction?
*The activation energy* - An enzyme catalyzes a reaction by lowering the activation energy (EA) barrier, enabling the reactant molecules to absorb enough energy to reach the transition state even at moderate temperatures. - An enzyme cannot change the ΔG for a reaction; it cannot make an endergonic reaction exergonic.
At low pH, a particular enzyme catalyzes a reaction at a high rate. At neutral pH, the enzyme is completely inactive. What explains the difference in how pH affects the function of this enzyme?
*The enzyme is adapted for low pH but is denatured at neutral pH, leaving it nonfunctional*
What is the role of ATP in cellular metabolism?
*The free energy released by ATP hydrolysis that may be coupled to an endergonic process via the formation of a phosphorylated intermediate*
The process of stabilizing the structure of an enzyme in its active form by the binding of a molecule is an example of __________.
*allosteric regulation* - Allosteric regulation: involves stabilizing the structure of an enzyme in its active form by the binding of a molecule; describes any case in which a protein's function at one site is affected by the binding of a regulatory molecule to a separate site -- may result in either inhibition or stimulation of an enzyme's activity -- The binding of an activator to a regulatory site stabilizes the shape that has functional active sites, whereas the binding of an inhibitor stabilizes the inactive form of the enzyme -- most enzymes known to be allosterically regulated are constructed from two or more subunits, each composed of a polypeptide chain with its own active site
what kind of reaction is glucose + fructose → sucrose?
*endergonic* Combining glucose and fructose to produce sucrose is an example of an energy storing endergonic reaction with the product more complex (lower entropy) than the reactants (glucose and fructose).
ATP allosterically inhibits enzymes in ATP-producing pathways. The result of this is called __________.
*feedback inhibition* - In feedback inhibition, a metabolic pathway is halted by the inhibitory binding of its end product to an enzyme that acts early in the pathway → preventing the cell from making more product than is necessary - Positive feedback is a type of feedback where the product facilitates, but does not inhibit, a process. - ATP is an allosteric inhibitor, not a competitive inhibitor. - Cooperativity is a mechanism that amplifies the response of enzymes to substrates. - Denaturing is the breakdown in structure of an enzyme, not an inhibition process.
Enzyme activity is affected by pH because __________.
*high or low pH may disrupt hydrogen bonding or ionic interactions and thus change the shape of the active site* - the optimal pH values for most enzymes fall in the range of pH 6-8, but there are exceptions - For example, pepsin, a digestive enzyme in the human stomach, works best at pH 2 - In contrast, trypsin, a digestive enzyme residing in the alkaline environment of the human intestine, has an optimal pH of 8 and would be denatured in the stomach
What would the value of ΔS be for a chemical reaction in which a molecule is broken down into smaller components? negative, neutral, zero, or positive?
*positive* ΔS is the change in a system's entropy. When entropy is increased, as in a reaction in which a molecule is broken down, the ΔS value is positive. ΔS would be zero only in a situation where a chemical reaction does not change the entropy of a system, which is unlikely. ΔS would be negative in a situation where a chemical reaction reduces the entropy of a system, such as when a molecule is formed from smaller components.
An exergonic (spontaneous) reaction is a chemical reaction that __________.
*releases energy when proceeding in the forward direction* Based on their free-energy changes, chemical reactions can be classified as either exergonic ("energy outward") or endergonic ("energy inward"). An exergonic reaction proceeds with a net release of free energy (ΔG < 0) --- ΔH must be negative (the system gives up enthalpy and H decreases) or TΔS must be positive (the system gives up order and S increases), or both --- every spontaneous process decreases the system's free energy, and processes that have a positive or zero ΔG are never spontaneous
In general, the hydrolysis of ATP drives cellular work by ________________
*releasing free energy that can be coupled to other reactions* - ATP is responsible for mediating most energy coupling in cells, and in most cases it acts as the immediate source of energy (NOT a catalyst) that powers cellular work - Byproducts such as heat are NOT effective energy sources for such work
Which of the following statements is correct regarding ATP? ATP cannot transfer energy to other molecules. a) The energy in an ATP molecule is released through hydrolysis of one of the phosphate groups b) The energy in an ATP molecule is released from the adenine group c) ATP molecules do not release free energy when hydrolyzed d) The energy in an ATP molecule is released from the ribose group e) ATP cannot transfer energy to other molecules
a) *The energy in an ATP molecule is released through hydrolysis of one of the phosphate groups* - The energy released from an ATP molecule is based on the hydrolysis of one of the phosphate groups, not the adenine nor the ribose. - The hydrolysis of ATP releases free energy. - ATP can transfer energy to other molecules through the transfer of one of the phosphate groups.
Which of these statements about enzyme inhibitors is true? a) A competitive inhibitor binds to the enzyme at a place that is separate from the active site. b) A noncompetitive inhibitor does not change the shape of the active site. c) Inhibition of enzyme function by compounds that are not substrates is something that only occurs under controlled conditions in the laboratory. d) The action of inhibitors may be reversible or irreversible. e) When the product of an enzyme or an enzyme sequence acts as its inhibitor, this is known as positive feedback.
d) *The action of inhibitors may be reversible or irreversible.*
Which statement correctly describes cofactors and coenzymes? a) Both cofactors and coenzymes act as allosteric inhibitors to various enzymes. b) Both are nonprotein enzyme helpers; but most coenzymes are metal ions, and most cofactors are organic molecules. c) Cofactors that are metal ions activate enzymes, but coenzymes deactivate them. d) Neither cofactors nor coenzymes assist enzyme function. e) Both are nonprotein enzyme helpers; but most cofactors are metal ions, and coenzymes are organic molecules that are a specific type of cofactor.
e) *Both are nonprotein enzyme helpers; but most cofactors are metal ions, and coenzymes are organic molecules that are a specific type of cofactor.* COFACTOR = nonprotein helpers for enzyme catalytic activity - may be bound tightly to the enzyme as permanent residents, or they may bind loosely and reversibly along with the substrate - the cofactors of some enzymes (such as the metal atoms zinc, iron, and copper in ionic form) are INORGANIC COENZYME = if the cofactor is an ORGANIC molecule - most vitamins are important in nutrition because they act as coenzymes or raw materials from which coenzymes are made
Which of the following statements is correct regarding competitive and noncompetitive enzyme inhibitors? a) Neither type of inhibitor affects enzyme function. b) Competitive inhibitors do not bind directly to the active site of an enzyme while noncompetitive inhibitors do. c) Only competitive inhibitors affect enzyme function. d) Inhibitors always bind irreversibly to an enzyme. e) Competitive inhibitors bind to the active site of an enzyme while noncompetitive inhibitors bind to an enzyme away from the active site.
e) *Competitive inhibitors bind to the active site of an enzyme while noncompetitive inhibitors bind to an enzyme away from the active site* - Competitive inhibitors bind to the active site of an enzyme (reducing the productivity of enzymes by blocking substrates from entering active sites) , and noncompetitive inhibitors bind to a site away from the active site (causing the enzyme molecule to change its shape in such a way that the active site becomes less effective at catalyzing the conversion of substrate to product) -Both types of inhibitors affect enzyme function. -Many inhibitors can bind reversibly to enzymes.
