Generation of Biochemical Energy and Krebs cycle:
1. . Distinguish between cyclic vs spiral metabolic pathways?
A metabolic pathway in which a molecule is progressively built up/broken by repeated
interaction with the same set of enzymes is a spiral pathway.
A metabolic pathway in which a series of steps, each using different enzymes,
regenerates one of the early reactants, is a cyclic pathway.
2. Which sequence illustrates the order of the steps from food to biochemically useful
energy?
A) digestion, citric acid cycle, ATP production, acetyl-ScoA production
B) digestion, citric acid cycle, acetyl-ScoA production, ATP production
C) citric acid cycle, digestion, acetyl-ScoA production, ATP production
D) digestion, acetyl-ScoA production, citric acid cycle, ATP production
E) digestion, acetyl-ScoA production, ATP production, citric acid cycle
3. List and discuss the reasons that ATP is so useful as a biochemical energy transport
molecule.
The text is not real explicit on this, but it is the one molecule that can be used by all
cells in the body. Other texts use the term "universal energy currency " for cells.
ATP is only hydrolyzed slowly in the absence of the correct enzymes. This means it is a
stable energy storage molecule and the release of its energy can be carefully
controlled.
4. The reaction in which ATP is converted to ADP with release of 7.3 kcal is a(an)
Hydrolysis reaction. Exergonic.
5. Below are two sets of molecules? Circle the one that has higher energy.
ADP, CO2, NAD+, FAD
ATP, acetyl-SCoA, NADH, FADH2
6. In the Krebs cycle, which enzyme catalyzes a hydration reaction? Fumarase
7. How many ATP molecules are generated per turn of the Krebs cycle? What other type
of energy molecules and chemical waste are also generated?
One mlecule of ATP per turn
Reduced Coenzymes
CO2
8. Match the left and the right hand side:
Catabolism (D)
anabolism (B)
ADP(A)
Digestion (C)
ATP (E)
citric acid cycle (H)
acetyl-ScoA(G)
A) a molecule which can be phosphorylated as
a means of temporarily storing energy
B) metabolic processes which consume
energy in order to build molecules
C) the stage of catabolism in which complex
food molecules are broken down into
simpler substances for transport and/or
further reaction
D) metabolic processes that break down large
molecules, thereby releasing energy
E) the universal energy currency of the cell; a
molecule used to transfer energy
F) the stage of catabolism in which the energy
stored in reduced coenzymes is converted
to ATP
G) the molecule produced from digestion
products in the second stage of catabolism
H) the stage of catabolism in which acetyleSCoA is oxidized to produce ATP, reduced
coenzymes, and CO2
electron transport chain (F)
9. State the reactants and the products for the citric acid cycle
The reactants for the citric acid cycle for 1 acetyl group, 3 NAD+, 1 FAD, 1 ADP, and 1
Pi (inorganic phosphates). Products are HS-CoA, 3 NADH, 1FADH2, 1 ATP.
Because two acetyl-CoA molecules are produced from each glucose molecule, two
cycles are required per glucose molecule. Therefore, at the end of all cycles, the
products are: two GTP (ATP) , six NADH, two FADH2, and four CO2
10. State the total number of NADH and FADH2 produced for each acetyl-CoA that
enters the citric acid cycle.
Products of the first turn of the cycle are: one GTP (or ATP), three NADH, one FADH2.
11. The only reaction in the citric-acid cycle in which a carbon-carbon bond is formed is
catalyzed by: citrate synthase (Lyase’s)
Glycolysis:
1. What are the reactants and products of Glycolysis?
The reactants in glycolysis are glucose (a 6 carbon sugar), 2 NAD+, 2 ADP, and 2
inorganic phosphates (also written as 2Pi).
The products in glycolysis are 2 pyruvate (a 3 carbon molecule), 2 NADH, 2 H+, and 2
net ATP. 2H2O also produced.
2. Which molecule/s is most likely to be used in a reaction coupled with the reaction
shown below?
glucose  glucose-6-phosphate
ATP
3. What is the total number and the net number of ATP produced by substrate-level
phosphorylation during glycolysis.?
A total of 4 ATP are produced by substrate-level phosphorylation during glycolysis,
but since 2 ATP were used in endergonic steps 1 and 3, the net total is 2 ATP.
(Challenge question)
4. The proper sequence of stages in glycolysis is
A)
glucose priming, cleavage and rearrangement, oxidation, ATP generation
B)
cleavage and rearrangement, glucose priming, ATP generation, oxidation
C)
glucose priming, oxidation, cleavage and rearrangement, ATP generation
D)
ATP generation, oxidation, glucose priming, cleavage and rearrangement
E)
oxidation, cleavage and rearrangement, ATP generation, glucose priming
5. Why is Glycolysis considered a catabolic pathway?
6. Conversion of dihydroxyacetone phosphate to D-glyceraldehyde 3-phosphate is a(n)
isomerization reaction
Fatty Acid Metabolism:
1. What is a beta-oxidation?
the catabolic reaction in which fatty acids are broken down two carbons at a time
2. What are the products of a first chemical breakdown of a triacylglycerol?
Fatty acids and glycerol
3. Where in the cell does beta-oxidation of fatty acids occur? MitoChondria
4. How many turns of the b-oxidation pathway is needed for a complete breakdown of
Stearic Acid (18 carbon atoms)? How many molecules of Acetyl-ScoA are produced at
the end? 8 and 9
5. What conversion occurs for the activation of fatty acids before breakdown?
Conversion of Fatty Acid to Fatty Acid-Acyl-Co-A (esterification of an acid)
6. Challenge question:
What is the correct order for these three processes leading from a fatty acid molecule in
a cell needing energy to high energy molecules capable of meeting the energy need is
I. activation by reaction with coenzyme A
II. oxidation to acetyl-SCoA and reduced coenzymes
III. transport from cytosol into mitochondrial matrix
I, III, II
7. Which has greater "energy density," carbohydrates or fats. Explain your answer in
terms of molecular structure and net energy production.
Fats have a greater energy density than carbohydrates. Fats provide nine Calories
energy per gram, and carbohydrates only four Calories per gram. One reason for this
is that one gram of fat contains more molecules of fat than a gram of carbohydrates
because the molecules fit together more closely and because the carbohydrates are
hydrophilic and may include some water in their overall structure. In addition, in
considering a carbohydrate and a fat of similar molecular mass, the fat contains more
carbon atoms and those carbon atoms are more highly reduced (and therefore of
higher energy) than the carbon atoms in the carbohydrate.
7. Calculate the energy released for oxidation of Lauric acid (12 Carbon acid)?
[Assume each NADH produces app 2.5 ATP’s and each FADH2 produces 1.5 ATP, Assume
2 ATP’s needed for the first activation step]
A. First, calculate the number of acetyl-Sco-A that can be produced from Lauric Acid.
(We do this by taking the number of carbon atoms in the acid and divide by 2.)
This is 6 Acetyl-Sco-A’s
B. Then each Acetyl-Sco-A will produce 1 ATP, 3NADH, and 1 FADH2 (Citirc A. cycle)
Using the info provided this is 10 ATP’s from 1 Acetyl Sco-A
So total number of ATP’ s now is 60 (from 6 acetyl-sco-A)
C. Then, recall that for Lauric Acid there are 5 turns of beta-oxdn. This is 20 ATP’s.
D. Total: [60 ATP + 20 ATP] produced – 2 ATP (used in first step of activation) = 78
ATP’s NET