RQ/Final Questions Flashcards
Discuss the coordinate regulation of glycolysis and the TCA cycle. Include the bridging
reaction, important regulatory points, a comparison of allosteric effectors, and explain how
coordination is maintained.
The TCA Cycle is controlled by the metabolic demands of the body, specifically glycolytic needs. This is location and transport based. TCA happens in the mitochondria and glycolysis in cytosol. The main regulatory points of the TCA cycle are NADH and ATP which lowers TCA, AMP which activates, and acetyl COA which slows TCA cycle. Oxaloacetate bridges gluconeogenesis and TCA together. Pyruvate from glycolysis is converted to Acetyl COA via PDH.
Pyruvate carboxylase catalyzes a single reaction whose product has multiple fates. Specify
two possible fates, draw the structure of the product, and discuss the conditions under which
one fate would be preferred over the other. How would you expect exogenous addition of
this product to affect a suspension of respiring mitochondria (make a reasonable
assumption based on current knowledge; will cover more later in semester)?
Product is OAA. Two fates: TCA and gluconeogenesis. When glucose is high and energy low, TCA is preferred. When glucose is low and energy high, gluconeogenesis is preferred.
Anaplerotic reactions are catalyzed by an essential class of metabolic enzymes that include
pyruvate carboxylase and malic enzyme. You have extensively studied the pyruvate
carboxylase reaction. Malic enzyme utilizes the same pyruvate substrate to produce a
different TCA Cycle intermediate, by combining it with bicarbonate and reducing with
NADPH.
a) In one sentence, define anaplerotic reactions.
b) Draw the structures of the major substrate and product of the malic enzyme reaction.
c) Discuss the expected effect (direct or indirect) of a rise in NADH on this reaction.
d) Speculate briefly on the metabolic effect of over-producing this enzyme in the liver of
an Olympic athlete.
Anaplerotic rxns use metabolic enzymes to replace TCA intermediates.
Pyruvate to Malate
An increase in NADH will slow reaction because energy is high.
If you over produce this enzyme will increase the TCA cycle, acetyl COA, and glycolysis because pyruvate is being depleted.
Malonate is a potent competitive inhibitor of succinate dehydrogenase.
a) What reaction does this enzyme catalyze? In what two pathways does this enzyme
participate?
b) What effect would you expect this inhibitor to have on respiration?
c) Hans Krebs found that addition of oxaloacetate to a suspension of mitochondria treated
with malonate could reverse malonate’s effect on respiration and the enzyme succinate
dehydrogenase. Explain.
Succinate to Fumarate, fumarate is involved in TCA and ETC
Would increase respiration because inhibiting the ETC cycle which produces O_2.
The addition of OAA would allow for the increase of succinate. Higher levels of succinate would override the inhibitor.
Compare and contrast the chemical logic of b-oxidation and the tricarboxylic acid (TCA)
cycle with respect to the generation of NADH and FADH2. (Hint: Consider the enzymatic
steps in each pathway that generate either NADH or FADH2. Are there similarities?
differences?)
The metabolism of fatty acids via beta-oxidation is largely controlled by substrate
availability. Discuss the regulation of fatty acid release in adipocytes and its
ultimate transport into the mitochondria matrix. Include relevant sketches.
A prolonged dietary deficiency in vitamin B12 (cobalamin) may have dramatic
consequences. What metabolic pathway(s) might be affected by a lack of B12?
What metabolic intermediates might accumulate? What is the unique property of
vitamin B12 that allows it to be an effective cofactor?
Discuss the fates of acetyl-CoA. (Include relevant metabolic pathways, the
metabolic demands that would dictate a particular fate, the ultimate cellular and/or
subcellular location of acetyl-CoA product(s), etc.) (Hint: Revisit this question once
all lectures are over.)
Argininosuccinate lyase (ASL) catalyzes the breakdown of argininosuccinate to
arginine and fumarate. Deficiencies of this enzyme may result in life-threatening
hyperammonemia (elevated ammonia levels).
a) Why?
b) Patients with ASL deficiency that exhibit elevated ammonia levels are often
treated by (i) discontinuing oral protein intake and (ii) supplementing oral intake
with intravenous lipids, glucose, and intravenous insulin. Explain.
c) Long term management of ASL deficiency may require supplementation of
arginine in the diet. Explain.
- In a recent scientific paper, liver injury in non-alcoholic fatty liver disease correlated with
the following changes in protein expression:
- carbamoyl phosphate synthetase-1 (CPS1) expression was reduced
- ornithine transcarbamylase (OTC1) expression was reduced
- glutamine synthetase (GS) expression was increased
2
a) Indicate the normal biological function(s) of each of these three enzymes.
b) What are the expected consequences of a reduction in CPS1 and OTC1 protein levels?
Explain.
c) Speculate why GS protein levels are elevated. Explain your reasoning.
Atractyloside is an inhibitor of adenine nucleotide translocase, which is responsible for the
antiport of ATP out of the mitochondrial matrix and ADP in to the matrix. Antimycin A is a
potent inhibitor of Complex III.
a) Predict the effects of atractyloside and antimycin A on the electron transport chain and
ATP synthesis. Explain your reasoning.
b) Design an experiment using a chemical “uncoupler” that would allow you to distinguish
between these two inhibitors. For each case, sketch a graph showing how the
concentrations of relevant “reactants” would change over time. Indicate the points at
which the inhibitor (atractyloside or antimycin A) and subsequently the uncoupler, were
added.
When tissue is suddenly deprived of sufficient oxygen, a stress response to deal with
hypoxia is observed. Discuss the key metabolic adaptations in the oxygen-deprived cells.
Discuss the metabolic state of the liver during a prolonged fast. What would be the
immediate impacts on liver metabolism if the fast was broken by the consumption of a
carbohydrate-rich meal?
In your answer, provide the status of the metabolic pathways we have discussed (glycolysis,
gluconeogenesis, TCA cycle, urea cycle, beta-oxidation, oxidative phosphorylation).
Indicate how relative levels of critical intermediates regulate overall flux through a given
pathway.
Dichloroacetate is a chemical that activates the pyruvate dehydrogenase complex. Describe
the effects you would expect dichloroacetate treatment to have on overall flux through the major
metabolic pathways of the muscle we have now discussed. Draw a flow chart of the pathways that
illustrates their interrelatedness, focusing on the key regulatory enzymes, metabolites, and energy rich intermediates that control the outcomes. Be specific.
Discuss the fates of acetyl-CoA. (Include relevant metabolic pathways, the metabolic
demands that would dictate a particular fate, the ultimate cellular and/or subcellular location of acetyl CoA product(s), etc.)
