FOM 3.5.1 Flashcards
True or false: The activity of some enzymes simply relies on how much substrate is available.
True
True or false: If NADH is not regenerated to NAD+, then the TCA cycle quits working.
True
Under anaerobic conditions, NADH generated in the cytosol is regenerated to NAD+ via ___(enzyme)_________
Lactate Dehydrogenase
True or false: Aldolase cleaves fructose-2,6-bisphosphate into glyceraldehyde-3-phosphate and dihydroxyacetone phosphate. These two molecules are further metabolized in glycolysis.
False. Dat’s not tru
True or false: In the liver, fructose-2,6-bisphosphate acts as a feedforward allosteric activator of pyruvate kinase.
False
Pyruvate dehydrogenase kinase is __(activated/inhibited)__ by the metabolite ___________.
Inhibited, pyruvate
Dichloroacetate is an analogue of _______ and has the potential of reducing lactate concentrations by targeting __(enzyme)___.
pyruvate, pyruvate dehydrogenase kinase
True or false: Glycolysis and gluconeogenesis are activated by the same small molecules and inhibited by the same small molecules.
False
High levels of __(TCA cycle intermediate)___, indicate sufficient energy sources. Therefore, this small molecule is an allosteric activator of ___(enzyme)____ that controls the rate of fatty acid synthesis. This exemplifies regulatory crosstalk between different pathways.
Citrate, acetyl CoA carboxylase
True or false: Membranes do not play a role in metabolism.
False
One example of whole body metabolism is: ________
1) Ketone generation by the liver to feed brain and muscle 2) The Cori cycle 3) The glucose-alanine cycle
Provide a reason why our bodies can have multiple isozymes of the same enzyme, given that all isozymes catalyze the same reaction. _____________________________
Different isosymes often have unique regulatory responses that function within the needs of the tissue where that isozyme is expressed
True or false: Compared to glucokinase, hexokinase has a lower affinity for glucose. This lower affinity allows hexokinase to function in muscle even when glucose concentration is relatively low.
False
True or false: Compared to glucokinase, hexokinase has a lower affinity for glucose. This lower affinity allows hexokinase to function in muscle even when glucose concentration is relatively low.
False
True or false: When proteins are regulated by “covalent modification,” Covalent modification normally refers to phosphorylation.
False
One benefit of a regulatory _______ is that a very limited number of signaling molecule can influence the activities of a large number of enzyme molecules. In other words, the regulatory signaling gets amplified.
Cascade
When blood glucose is low, glucagon secretion goes __(up/down)__. This change in glucagon causes a/an __(increase/decrease)___ in cellular cAMP concentration. In the liver, phosphofructokinase activity ___(increases/decreases)_, consistent with the need to __(increase/decrease)__ hepatic glucose secretion.
up, increase, decreases, increases
True or false: Control of one enzymatic step in a metabolic pathway can control the flux through that pathway.
True, if the rate limiting step
True or false: Excessive alcohol consumption can cause hypoglycemia because the alcohol metabolism converts all available NAD+ to NADH. The cell’s attempt to regenerate NAD+ by transferring electrons to pyruvate can compete with the need to use pyruvate as a substrate for gluconeogenesis, thus causing hypoglycemia.
True
True or false: One of the arguments used to criticize the use of high fructose corn syrup is that fructose metabolism bypasses the regulatory steps in glycolysis at hexokinase/glucokinase and phosphofructokinase.
True
What is dichloroactetate structurally analagous to? How does that explain its function?
Pyruvate. That explains its inhibition of pyruvate dehydrogenase kinase
What are some mechanisms of regulation?
1) Substrate availability 2) Product buildup/Product inhibition 3) Regulation by specialty metabolite (allosteric) 4) Allosteric regulation by intermediate metabolites - Feed forward (not common) - Feed back inhibition - Coordination b/t pathways 5) Tissue specialization 6) Tissue specific isozyme expression 7) Covalent modifications 8) Change Enzyme [] 9) Regulatory cascade 10) Hormone regulation
As more substrate is available, what happens to Vo?
The Vo increases until enzyme has reached saturation
Why is there reduced activity of TCA cycle enzymes in hypoxic tissue?
NADH builds up inside the mito due to the loss of function of the ETC (lack of O2 as final e- acceptor)
What is an example of a specialty metabolite that allosterically regulates glycolysis?
Fru-2,6-BP, AMP
What catalyzes the formation of Fru-2,6-BP? And, degradation?
PFK-2, FBPase-2
What is another molecule that can be made when the pathway of glycolysis is diverted? (hint: it affects the affinity of oxygen binding in erythrocytes)
2,3-BPG (2,3-bisphosphoglycerate)
What is the only straightforward example of feed forward activation in glycolysis?
Fru-1,6-BP allosterically activates liver pyruvate kinase
Another example of feed forward activation comes when an inhibitor is inhibited. What is this example?
Pyruvate inhibits PDK, resulting in increased activity of pyruvate dehydrogenase
What molecule within the glycolysis pathway inhibits PFK? (Feedback inhibition)
PEP
Name some of the molecules involved in the coordination of pathways w/ Acetyl CoA carboxylase that forms Malonyl-CoA. Indicate if they activate or inhibit.
Insulin (+) Glucagon (-) Citrate from TCA (+) AcylCoA (-) Glutamate AA (+)
What does malonyl-CoA inhibit?
Caritine-Palmitoyltransferase-I
What are some examples of compartmentalization?
1) FA cata (beta oxi) v. anabolism (biosynthesis) 2) e- shuttling into mito
What are the two e- shuttling systems?
Malate-aspartate shuttle, Glycerophosphate shuttle
An example of tissue specialization is ketogenesis and ketogenolysis. Where do these occur?
genesis: Liver, lysis: Brain, Muscle can do both
The Cori cycle is used to recycle what? Explain how it works.
Lactate. Muscle turns glucose into lactate, then the liver turns the lactate back into glucose.
What is a product of the glucose-alanine cycle during gluconeogenesis in the liver?
Urea
What is a perfect example of isozymes used in glycolysis?
Hexokinase and glucokinase
What are some examples of covalent modifications? (2)
Phosphorylation and Acetylation
What are the purposes of an enzyme cascade?
Amplification of the original signal, faster response to stimuli
What is the second messenger used in the hormonal activation of glycogen phosphorylase?
cAMP
Give an example of when regulation is bypassed.
Alcohol metabolism
Alcohol metabolism results in the generation of what cofactor?
NADH
How does the body try to recycle some of the NADH produced during alcohol metabolism?
Lactate prod or Increased ETC usage
Describe the cascade that goes from low blood sugar to gluconeogenesis.
