Chapter 8 Metabolism and Enzymes
Which of the following shows the correct changes in thermodynamic properties for a chemical reaction in which amino acids are linked to form a protein? a. +△H, +△S, +△G b. +△H, -△S, -△G c. +△H, -△S, +△G d. -△H, -△S, +△G e. -△H, +△S, +△G
+△H, -△S, +△G
During a laboratory experiment, you discover that an enzyme-catalyzed reaction has a ∆G of -20 kcal/mol. If you double the amount of enzyme in the reaction, what will be the ∆G for the new reaction?
-20 kcal/mol (does not change amount of free energy)
Look at graphs 2 & 3. Which temperature and pH profile curves on the graphs were most likely generated from analysis of an enzyme from a human stomach where conditions are strongly acid?
1 and 4
Look at graphs 2 & 3. Which curve(s) on the graphs may represent the temperature and pH profiles of an enzyme taken from a bacterium that lives in a mildly alkaline hot springs at temperatures of 70°C or higher?
3 and 5 (higher temp higher pH)
What are co-factors?
A non-protein substance such as zinc, iron, aluminum, and magnesium that helps enzymes convert substrate to product and help make catalytic processes more efficient
What does the first law of thermodynamics state?
Energy cannot be created or destroyed
Which of the following statements regarding enzymes if true? a. Enzymes increase the rate of a reaction by making the reaction more exergonic b. Enzymes increase the rate of a reaction by lowering the activation energy barrier c. Enzymes increase the rate of the reaction by reducing the rate of reverse reactions d. Enzymes change the equilibrium point of the reactions they catalyze e. Enzymes make the rate of a reaction independent of substrate concentrations
Enzymes increase the rate of a reaction by lowering the activation energy barrier
Why is ATP an important molecule in metabolism?
It provides energy coupling between exergonic and endergonic reactions
What are competitive inhibitors?
Molecules that bind to the active site of an enzyme and inhibit the ability of the substrate to bind
Assume that the reaction has a △G of -5.6 kcal/mol. Which of the following would be true? A) The reaction could be coupled to power an endergonic reaction with a △G of +6.2 kcal/mol. B) The reaction could be coupled to power an exergonic reaction with a △G of +8.8 kcal/mol. C) The reaction would result in a decrease in entropy (S) and an increase in the total energy content (H) of the system. D) The reaction would result in an increase in entropy (S) and a decrease in the total energy content (H) of the system. E) The reaction would result in products (C + D) with a greater free-energy content than in the initial reactants (A + B).
The reaction would result in an increase in entropy (S) and a decrease in the total energy content (H) of the system
What represents the activation energy needed for the enzyme-catalyzed reverse reaction C+D -> A+B, in Figure 8.1?
a
What is an enzyme?
a biological catalyst
What is entropy?
a measure of disorder or randomness.
What is a spontaneous reaction?
a reaction that occurs by itself without the input of energy
A series of enzymes catalyze the reaction X → Y → Z → A. Product A binds to the enzyme that converts X to Y at a position remote from its active site. This binding decreases the activity of the enzyme. What is substance X? With respect to the enzyme that converts X to Y, substance A functions as...
a substrate, an allosteric inhibitor
What is an endergonic reaction? How is the change in the system's enthalpy represented?
absorbs free energy from its surroundings, △H is positive, not spontaneous
Reactants capable of interacting to form products in a chemical reaction must first overcome a thermodynamic barrier known as the reaction's
activation energy
Allosteric molecules can be _____________ or _______________. What do they do overall?
activators, inhibitors, regulates metabolism
What is primarily involved in the ESC?
active site, substrate, enzyme
What does the second law of thermodynamics state?
all reactions that are spontaneous will increase the entropy of the reaction
What is bioenergetics?
all the metabolic processes in a living system
What is a type of non-competitive inhibitor? Ex?
allosteric inhibitors, DDT (pesticides that inhibit enzymes of the nervous system)
Which of the following types of reactions would decrease the entropy within a cell?
anabolic reactions
Living organisms increase in complexity as they grow, resulting in a decrease in the entropy of an organism. How does this relate to the second law of thermodynamics?
as a consequence of growing, organisms cause a greater increase in entropy in their environment than the decrease in entropy associated with their growth (amino acids linking together decreases entropy)
Describe the factor of temperature concerning enzymes.
as temp increases, reaction rates increase until the optimal temperature which is for most enzymes around 30-40 degrees C, when temp exceeds it the bonds of the enzyme are broken causing it to denature (lose its shape and limit its function)
What represents the activation energy required for the enzyme-catalyzed reaction in Figure 8.1?
b
What is catabolism?
breaking down larger molecules into smaller ones, hydrolysis happens here
How do cells combate competitive inhibitors?
by adding more substrates
How does a noncompetitive inhibitor decrease the rate of an enzyme reaction?
by changing the shape of the enzyme's active site
What represents the activation energy required for a non catalyzed reaction in Figure 8.1?
c
A system at equilibrium ...
can do no work
Which term most precisely describes the cellular process of breaking down large molecules into smaller ones?
catabolism
What is an example of a catabolic reaction? What is this?
cellular respiration, when glucose and other organic fuels are broken down in the presence of oxygen into carbon dioxide and water
Increasing the substrate concentration in an enzymatic reaction could overcome which of the following? a. denaturation of the enzyme b. allosteric inhibition c. competitive inhibition d. saturation of the enzyme activity e. insufficient cofactors
competitive inhibition
What represents the different between the free-energy content of the reactants and the free-energy content of the products in Figure 8.1?
d
What represents the △G of the reaction in Figure 8.1?
d
Which in Figure 8.1 would be the same in either an enzyme-catalyzed or non catalyzed reaction?
d
Look at the graph 1. For the enzyme-catalyzed reaction shown in the figure, which of these treatments will cause the greatest increase in the rate of the reaction, if the initial reactant concentration is 1.0 micromolar?
doubling the enzyme concentration
What represents the activation energy needed for the non catalyzed reverse reaction, C+D -> A+B, in Figure 8.1?
e
A chemical reaction that has a positive △G is best described as
endergonic
What is kinetic energy? Ex?
energy associated with the motion of objects, ex. water gushing through a dam turns turbines/contraction of leg muscles pushes bike pedals
What does a change in "free energy" mean?
energy available in a system to accomplish work
What is activation energy?
energy needed to start a reaction and break the bonds of the reactant
What happens in the ESC/enzyme substrate complex?
enzyme attaches to substrate at the active site, held together by hydrogen and ionic bonds, R chains from the enzyme are what break down the substrate and send the message for product release
Which of the following terms best describes the forward reaction in Figure 8.1? a. endergonic, △G > 0 b. exergonic, △G < 0 c. endergonic, △G < 0 d. exergonic, △G > 0 e. chemical equilibrium, △G = 0
exergonic, △G < 0
The mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway is most precisely described as
feedback inhibition (more specifically allosteric inhibition)
What is an exergonic reaction? How is the change in the system's enthalpy represented?
has a net release of free energy, △H is negative, spontaneous
What are some basic characteristics of enzymes?
highly specific, have finite lives (become labile), do not fit like a lock and key with its substrate more like a hand and glove
What does a positive △S mean? What is an example?
increasing entropy, becoming more disordered, ex. hydrolysis
The active site of an enzyme is the region that
is involved in the catalytic reaction of the enzyme
When chemical, transport, or mechanical work is done by an organism, what happens to the heat generated?
it is lost to the environment
Endergonic reactions. Reactants vs. Products.
less reactant more product
Enzymes _____ activation energy
lower
What are non-competitive inhibitors?
molecules that bind at a location other than the active site, which results in a change of shape in the enzyme so that the enzyme cannot bind to the substrate and cannot function
Exergonic reactions. Reactants vs. Products.
more reactant less product
Look at the graph 1. In the figure, why does the reaction rate plateau at higher reactant concentrations?
most enzyme molecules are occupied by substrate at high reactant concentrations
What is potential energy? Ex?
non-kinetic energy, energy that matter possesses because of its location or structure, ex. water behind a dam possesses energy because of its height
Describe the factor of pH concerning enzymes.
optimal is 6-8 (except for the stomach where it is 1-2), higher or lower pHs will cause enzyme to denature
What are coenzymes?
organic molecules derived from vitamins
Enzymes are ____________ but not ______________.
reusable, infinite
What are 3 factors that affect an enzymes ability to work optimally?
temperature, pH, salinity
What happens during the ATP cycle?
terminate phosphate bond is broken by the addition of a water molecule causing a molecule of inorganic phosphate leaves the ATP and releases energy
Why is chemical equilibrium not a good thing for living organisms?
the cell must constantly maintain metabolic disequilibrium in order to remain alive, this would stop the flow of materials in and out of the cell and would kill the cell
What is △G?
the change in free energy
What is △H?
the change in the system's enthalpy (heat content)
What is △S?
the change in the system's entropy
What happens to the concentration of something as entropy increases?
the concentration increases
What is not different whether the reaction is catalyzed or not?
the energy of the products
Describe the factor of salinity concerning enzymes.
the higher the salinity the more likely to denature the enzyme
For living organisms, which of the following is an important consequence of the first law of thermodynamics?
the organism ultimately must obtain all of the necessary energy for life from its environment
Which of the following is true for all exergonic reactions? a. the products have more total energy than the reactants b. the reaction proceeds with a net release of free energy c. the reaction goes only in a forward direction: all reactants will be converted to products, but no products will be converted into reactants d. a new input of energy from the surroundings is required for the reactions to proceed e. the reactions are rapid
the reaction proceeds with a net release of free energy
What is the active site?
the region on the enzyme where the substrate binds
What is the substrate?
the substance on which an enzyme acts that is broken down
What is metabolism?
the sum of an organism's chemical reactions
What is an example of an anabolic reaction?
the synthesis of a protein from amino acids
What is anabolism?
the synthesis of complex molecules from simpler ones, condensation reaction happens here
What does it mean if △G = 0?
the system is at equilibrium which means death
Some bacteria are metabolically active in hot springs because
their enzymes have high optimal temperatures
Which of the following statements is true concerning catabolic pathways? a. They combine molecules into more energy rich molecules. b. They supply energy, primarily in the form of ATP, for the cell's work. c. They are endergonic. d. They are spontaneous and do not need enzyme catalysis. e. They build up complex molecules such as proteins from simpler compounds.
they supply energy, primarily in the form of ATP, for the cells work
What is an example of a hormone that affects metabolism?
thyroxin is a hormone that increases metabolism, more thyroxin more metablishm, hypothyroidism (lethargic, get fat, not enough metabolism), hyperthyroidism (produce too much thyroxin, have too high metabolism)
What is an example of a feedback inhibition made up of allosteric inhibitors? What is a specific example?
triptophan
What is the activated complex?
when the bonds are rearranged
How do you calculate free energy (△G) ?
△G = △H-T△S
