TBL-9+Discussion+of+Answers

Name: Biology TBL-9 a.  Endosymbiotic theory is the idea the mitochondria and chloroplasts were independent prokaryotic that were incorporated into eukaryotic cells b.  Both contain their own DNA that is different from that of the cell nucleus c.  They are surrounded by two or more membranes which are different in composition from the other membranes of the cell (the composition is like that of a prokaryotic cell membrane) d.  Each time the cell divides the mitochondria and chloroplasts must also divide. This happens through binary fission (prokaryotic division) e.  They have ribosomes that resemble prokaryotes f.  They can manufacture some of their own proteins which resemble bacteria (prokaryotic)
 * 1) Which of the following environments or actions affect(s) the rate of an enzyme reaction?
 * 2) heating the enzyme Increases kinetic energy and rate at which molecules collide
 * 3) cooling the enzyme Decreases kinetic energy and rate at which molecules collide
 * 4) substrate concentration Optimizes binding of substrate to active site of enzyme speeding the reaction
 * 5) pH Alters ionic interactions between substrate and amino acid chain at active site of enzyme
 * 6)  all of the above
 * 1) Enzyme activity is affected by pH because.
 * 2) most substrates don't function well at high or low pH  No. Although pH can affect the structure of the substrate, it is more likely to affect something else.
 * 3)  high or low pH may disrupt hydrogen bonding or ionic interactions and thus change the shape of the active site Each enzyme has an optimal pH at which it is most active, and variations in pH can alter the enzyme's structure, changing activity.
 * 4) low pH will denature all enzymes  No. Enzymes that function in the stomach function optimally at very low pH.
 * 5) changes in pH can cause loss of cofactors from the enzyme  No. Although pH changes can cause an enzyme to lose a cofactor, even enzymes without cofactors are affected by changes in pH.
 * 6) the binding of hydrogen ions to the enzyme absorbs energy and thus there may not be enough energy to overcome the activation energy barrier  No. Binding of hydrogen ions does not affect the energy that is available to overcome the activation energy barrier.
 * 1) Which of these statements about enzyme inhibitors is true?
 * 2) A competitive inhibitor binds to the enzyme at a place that is separate from the active site.  No. A competitive inhibitor competes with the substrate for binding at the active site.
 * 3)  The action of competitive inhibitors may be reversible or irreversible.  Correct. Competitive inhibitors that bind covalently to the enzyme would be irreversible, and those that bind weakly would be reversible.
 * 4) A noncompetitive inhibitor does not change the shape of the active site.  No. A noncompetitive inhibitor changes the shape of the enzyme and its active site by binding to a site different from the active site.
 * 5) When the product of an enzyme or an enzyme sequence acts as its inhibitor, this is known as positive feedback.  No. This is an example of negative feedback.
 * 6) Inhibition of enzyme function by compounds that are not substrates is something that only occurs under controlled conditions in the laboratory.  No. Almost all biological reactions or pathways are regulated by non-competitive or allosteric interactions.
 * 1) An exergonic (spontaneous) reaction is a chemical reaction that __.
 * 2) occurs only when an enzyme or other catalyst is present  No. Spontaneous reactions can occur in the absence of a catalyst.
 * 3) cannot occur outside of a living cell  No. The occurrence of spontaneous reactions is not limited to living systems.
 * 4)  releases energy when proceeding in the forward direction     Correct. Exergonic reactions proceed with a net release of free energy, and they occur spontaneously.
 * 5) is common in anabolic pathways  No. Anabolic pathways construct complex molecules out of simpler building blocks, and thus they require an input of energy (they are endergonic).
 * 6) leads to a decrease in the entropy of the universe  No. Spontaneous reactions must increase the entropy of the universe according to the second law of thermodynamics.
 * 1) Which of the following reactions would be endergonic?
 * 2) HCl → H+ + Cl-  No. This reaction results in less complex products (greater entropy).
 * 3) C6H12O6 + 6 O2 → 6 CO2 + 6 H2O  No. This represents the breakdown of glucose, a complex molecule, into less complex products (increasing entropy).
 * 4) ATP → ADP + Pi  No. Remember that the hydrolysis of ATP is the source of most of the immediate energy for metabolism.
 * 5)  ADP + Pi → ATP  Correct. In this case, the product is more complex (lower entropy) than the reactants, and like many anabolic reactions, this one requires an input of energy.
 * 6) all of the above  No. Only one of the choices is an endergonic reaction.
 * 1) Which part of the equation ΔG = ΔH - TΔS tells you if a process is spontaneous?
 * 2)  ΔG  Correct. In any spontaneous process, the free energy of a system decreases. The change in free energy equals the change in total energy minus the change in entropy times the temperature.
 * 3) ΔH  No. Although the change in enthalpy does contribute to the spontaneity of a reaction, other factors must also be taken into account.
 * 4) ΔS  No. Although the change in entropy does contribute to the spontaneity of a reaction, other factors must also be taken into account.
 * 5) TΔS  No. Although the change in entropy does contribute to the spontaneity of a reaction, other factors must also be taken into account.
 * 6) All of these values reveal the direction in which a reaction will go.  No. Only one of the above choices can determine definitively whether a reaction is spontaneous or not.
 * 1) Discuss endosymbiotic theory and explain the evidence used to justify the idea.