1 A What is an anabolic metabolic pathway? Does it involve more than one reaction? If
so are these reactions endergonic or exergonic? Explain.
An anabolic metabolic pathway is a controlled series of reactions in which smaller, lower
energy, less complex molecules are built up into larger, higher energy, and more complex
molecules. This requires a net input of energy. Anabolic pathways can consist of both
exergonic and endergonic reactions, but the net input of energy will always exceed the
net output.
B What is a catabolic metabolic pathway? Does it involve more than one reaction? If so
are these reactions endergonic or exergonic? Explain.
A catabolic metabolic pathway is a controlled series of reactions in which larger, higher
energy, and more complex molecules are broken down into smaller, lower energy, less
complex molecules. This results in a net release of energy. Catabolic pathways can
consist of both exergonic and endergonic reactions, but the net input of energy will
always be less than the net output.
2 Define the following:
• Enzyme – a molecule that catalyzes (speeds up) a reaction
• Catalyst – any agent that speeds up the rate of a reaction
• Energy of activation – the amount of energy required for a reaction to proceed
• Active site – the part of an enzyme that conforms to the substrate
• Substrate – the reactant(s) of the reaction catalyzed by an enzyme
3 Explain the concept of "induced fit" with respect to how an enzyme functions.
Induced fit refers to the process by which an enzyme’s active site conforms to the shape
of the substrate thereby forming the enzyme-substrate complex. This is the least stable
configuration but also is the most favorable to promote the reaction.
4 Write the basic equation for photosynthesis/respiration and indicate a) the direction for
each process b) whether that process is catabolic or anabolic and c) the form of any
energy that is produced of consumed.
A
B
C6H12O6 + 6O2 ↔ 6CO2 + 6H2O + Energy
Direction A to B = aerobic respiration, catabolic, energy = ATP
Direction B to A = photosynthesis, anabolic, energy = sunlight
5 In which phase of aerobic respiration would you find electron carriers? Electron
transport systems? What is the final electron acceptor for aerobic respiration?
Electron carriers are found in all phases of aerobic respiration. They are reduced (receive
high energy electrons) in both Glycolysis and the Krebs cycle (where the majority are
reduced) and oxidized during the Electron Transport Chain. Electron transport systems
are found in the final phase of aerobic respiration (Electron Transport Chain). Oxygen
serves as the final electron acceptor at the end of the electron transport chain.
6 Why is visible light suitable for photosynthesis? Why isn’t ultra-violet light suitable?
What about microwave radiation?
Visible light has the right wavelength to excite electrons to higher energy levels where
they can be tapped to produce chemical energy. The wavelengths of UV light are too
short and powerful and will break chemical bonds while those of infra-red are too long
and weak and will simply rotate whole molecules.
7 What is the role of photosystem II and photosystem I in the light dependent reaction.
Where do replacement electrons for each photosystem come from?
Photosystem II is responsible to provide high energy electrons with which to produce
ATP to be used in the Calvin Cycle, while Photosystem I is responsible for providing
high energy electrons with which to reduce NADP+ to produce NADPH to be used in the
Calvin Cycle.
8 Describe in broad terms what happens during the Calvin cycle (ie where does it happen,
what goes in, what comes out). Why is called a cycle?
The calvin cycle occurs in the stroma of the chloroplast. Basically carbon dioxide, ATP
and NADPH are used to produce sugar. It is called a cycle because material enters and
exits during the cycle but at the end of each turn, the molecules in the cycle revert back to
their original state.
9 Which phase of photosynthesis is most similar to the electron transport chain phase of
aerobic respiration and why? How do these two differ?
The light dependent reaction is most similar because it involves electron transport
systems and electron carriers it occurs in membrane bound complexes, and it produces
ATP. It differs in that the process is driven by sunlight and is used to build up molecules
rather than break them down.
10 Which phase of aerobic respiration is most similar to the Calvin cycle of
photosynthesis and why? How do these two differ?
The krebs cycle is most similar to the calvin cycle as it occurs in the cytoplasm like
medium inside the mitochondrion (just like the calvin cycle occurs in the cytoplasm like
stroma of the chloroplast), and it involves a cycle in which material combines with
intermediates and then is extracted as the cycle returns to its original state. It differs in
that it produces energy and reduced electron carriers while the calvin cycle requires
energy and oxidizes electron carriers.