BIOL275 Exam 3|Graded A+
Highly exothermic redox reactions lead to high levels of released energy. This wouldn't be compatible with life if too much energy is released at once, because this would be wasteful and potentially damaging to the cell.
If the cartoon above represents a molecular reactio...
BIOL275 Exam 3|Graded A+
Highly exothermic redox reactions lead to high levels of released energy. This wouldn't be compatible
with life if too much energy is released at once, because this would be wasteful and potentially
damaging to the cell.
If the cartoon above represents a molecular reaction taking place between common biological
molecules in a living cell, why would we expect that the change in energy level of electrons would NOT
be highly exothermic?
Living functions in the cell depend on the ability to assemble and disassemble biological molecules.
Metastable means the molecule can stay intact indefinitely by itself, but can be broken down by
reactions with other molecules. Life would not work if it depended on molecules that fell apart by
themselves (unstable) or could not be broken down in chemical reactions (overly stable).
Why is it significant that life evolved to use biological molecules that are metastable? What is the
meaning of that word? Contrast this to what would happen if cells depended on molecules that
are unstable or overly stable. (Hint: think of the ball on the hill).
Each step between molecules in the picture represents a redox reaction where electrons have
rearranged to form lower energy bonds compared to the previous arrangement. Therefore energy is
being released at each step, and the resulting new molecule represents a lower energy molecule than
the one before it.
Why is there "Diminishing availability of energy" as you go from a more reduced state to a more
oxidized state in the above figure?
The 686 kcal / mol is how much energy is represented by a mol of glucose. On the left side the glucose is
being broken down to release the energy, and thus it is a negative change in G, whereas on the right
side the energy of the sun is used to assemble the CO2 and H20 into a glucose molecule, and therefore it
is (+) delta G.
Explain where the 686 kcal / mol of energy comes from on the left and right sides of the above figure,
and what is meant by one side being ( - ) delta G and the other side ( + ) delta G.
The generation of heat is a byproduct of energy released in chemical reactions, and is therefore not a
direct purpose of breaking chemical bonds.
Of the six different categories of energy functions in a living cell that we discussed in lecture, which one
is not considered a direct use of energy, but rather a very important byproduct?
Because biological molecules are metastable, that means their chemical bonds won't simply break on
their own and must require the input of some energy to disrupt them. That amount of energy is
represented by the transition state. A molecular catalyst would lower the height of the transition state
(lower the energy of activation) thereby making the reaction proceed faster because less energy is
required to initiate it.
, The above figure depicts the change in G going from ATP to ADP. Explain why in any biochemical
reaction there is a "hump" or Transition State involved? How does the presence of a molecular catalyst
impact the shape of this curve? (Hint: think again about biological molecules being metastable)
Catalase enzyme binds to iron and to hydrogen peroxide, thereby bringing the two together. The
association of iron with the peroxide greatly encourages the bonds of the peroxide to break, so the
presence of the catalase speeds up the reaction dramatically. Our cells need to catalyze this reaction
because peroxide is damaging to the cell, so the cell cannot afford to wait for the peroxide to fall apart
on its own.
Explain how the presence of a catalase enzyme speeds up the dissociation of hydrogen peroxide in our
cells? Why do our cells need an enzyme like this rather than letting peroxide break down by itself? (Hint:
for full credit mention the role of iron and what that has to do with the catalytic reaction)
Although the red regions are far apart in the linear polypeptide chain, once the protein folds up into its
normal tertiary structure these regions are brought together to form the 3D active site of the protein.
The R group side chains of the specific amino acids labeled above are the ones that are most important
for the proper shape of the active site where a substrate will fit. If the active site is not shaped correctly,
the enzyme may not bind substrate.
The polypeptide chain shown above is that of an enzyme (like the catalase discussed in Question 7).
Explain how in the functional enzyme the five different red sites could be involved in binding one single
substrate molecule if they are so far apart in the peptide chain? Why do you think the amino acids that
are identified by name are the most critical ones that MUST be correct in the sequence in order for the
enzyme to work?
The big brown blob is actually a polypeptide chain that is folded up into a specific 3D shape determined
by all of the amino acid side chains finding energetically favorable positions. If there is a disruption to
one side of the protein, there is a ripple effect throughout the protein as the side chains shift around to
find a new low energy position. Thus the ability of the substrate binding site to assume the correct
shape will change depending on whether an allosteric activator or inhibitor binds the enzyme.
The above image depicts allosteric activation and inhibition of an enzyme. Explain how the binding of
the little square activator molecule or little triangular inhibitor molecule results in a change in the
substrate binding site of the protein? (Hint: the cartoon shows the protein as a big brown blob, but what
is it really, and how could something interacting on one side of the blob cause the other side to change?)
In the equation E = enzyme, S = substrate, ES = the intermediate transition state, and P = product(s). The
reason the arrows go in both directions is that in this case the enzyme can catalyze both the breaking OR
assembly of the bonds between the molecular components (in other words, in reverse the products can
be considered the substrates that get joined together).
The above image depicts a biological chemical reaction that is catalyzed by an enzyme. Explain what "E",
"S", "ES", and "P" stand for, and why the three steps of the equation are written this way. Why do the
arrows point in both directions?
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