Oxidative Phosphorylation and Gluconeogenesis Flashcards
What are Km and Vmax?
Vmax is the maximum speed at which an enzyme can catalyze a reaction, and Km is half that.
There are two ways that an enzyme can be chemically modified to regulate its production: ___________.
allosteric (non-covalent) and convalent
What intracellular mechanism is common in the effects of fed-state hormones?
Insulin (the most common fed-state hormone) works by dephosphorylating enzymes.
The counterregulatory hormones tend to work by _________.
phosphorylation
What two glucose transporters do we need to know? What do they do?
Glut-4: insulin sensitive
Glut-2: not insulin-sensitive (it’s always there)
What two enzymes catalyze the glucose to glucose-6-phosphate reaction?
Hexokinase (all other tissues)
Glucokinase (liver and beta-cell)
Why is it important to have glucokinase in the liver?
Because the liver can respond to increases in glucose by increasing gluconeogenesis (which needs glucose-6-phosphate)
What enzyme catalyzes the fructose-6-phosphate to fructose-1,6-bis-phosphate reaction?
Phosphofructokinase
What things negatively and positively regulate the activity of phosphofructokinase?
Negative: ATP, citrate
Positive: AMP, fructose-2,6-bis-phosphate
What is the enzyme that catalyzes the phosphoenolpyruvate to pyruvate reaction?
Pyruvate kinase
The energetics of lactate dehydrogenase is such that __________.
it goes both ways equally (converting pyruvate to lactate)
What molecular product of glycolysis gets pumped into the mitochondria?
Pyruvate
What negatively regulates the enzyme pyruvate dehydrogenase?
Acetyl co-a
ATP
NADH
True or false: the rate-limiting step in the TCA cycle is the conversion of fumarate to malate.
False. There is no rate-limiting step in the TCA cycle.
The electron transport chain is linked to the TCA at _______________.
the succinate to fumarate reaction (catalyzed by succinate dehydrogenase)
Protons come from the __________ space to the ___________ space.
mitochondrial matrix, intermembrane
NADH delivers its electron to ______________ and becomes NAD+.
complex I
______________ acts as an electron shuttle that brings electrons from complex I to complex III.
Coenzyme Q
The movement of electrons through the electron transport chain stimulates _____________.
proton movement into the intermembrane space
______________ accounts for a major portion of the oxygen consumption at rest –the basal metabolic rate.
Inherent proton leak
This can also generate heat. Brown adipose tissue utilizes this to generate heat.
___________ accelerates electron flow.
ATP demand
In a setting with a lot of ___________, gluconeogenesis can occur.
lactate (which can convert to pyruvate)
Pyruvate, in order to start gluconeogenesis, gets converted to _______________.
oxaloacetate, then malate –which gets moved out of the mitochondria –then converted back to oxaloacetate and then phosphoenolpyruvate
The enzyme ______________ is only present in the liver and kidneys. What does it do?
glucose-6-phosphatase; it removes the phosphate from glucose-6-phosphate, allowing the gluconeogenesis to send glucose into the circulation
The only energy source for RBCs is _____________.
glycolysis
RBCs send out their metabolic product as ______________.
lactate
_____________ catalyzes the conversion of pyruvate to oxaloacetate.
Pyruvate carboxylase (uses 2 ATP –one per pyruvate); this works by charging a molecule of CO2 to a biotin prosthetic group and then transferring that CO2 to pyruvate to generate oxaloacetate.
_____________ converts oxaloacetate to phosphoenolpyruvate.
Phosphoenolpyruvate carboxykinase (PEP CK) (uses 2 GTP –one per oxaloacetate)
_____________ converts the conversion of fructose 1,6-bisphosphate to fructose 6-phosphate.
Fructose 1,6-bisphosphatase
Those without ______________ will become extremely hypoglycemic after three or four hours without food.
glucose-6-phosphatase
List the pathway for glycogen synthesis.
Glucose Glucose 6-phosphate Glucose 1-phosphate UDP-glucose (Glycogen synthase) *** key regulating enzyme Glycogen
List the breakdown pathway for glycogen.
Glycogen (Glycogen phosphorylase) Glucose 1-phosphate Glucose 6-phosphate (Glucose 6-phosphatase) Glucose
Glycogen branching is accomplished by ____________.
4,6-transferase
____________ strongly stimulates glycogen phosphorylase.
Calcium (because it signals use)
The proton gradient is generated by complexes __________.
I, III, and IV
ATP synthase is also known as ____________.
complex V
ATP synthesis is inhibited by the drug ______________.
oligomycin
ATP synthase accounts for about ________ of the 36 molecules of ATP made by the oxidation of one molecule of glucose.
30
One NADH can yield _____ ATP from the ETC, while one FADH2 can only yield _______ molecules of ATP.
2.5; 1.5
True or false: glycerol enters gluconeogenesis in the TCA cycle.
False. It enters it “halfway up” gluconeogenesis (above PEP)
Oxidation of fatty acids provides ________________.
ATP that can be used in gluconeogenesis
What are the three key reactions in gluconeogenesis?
Pyruvate to PEP
(Pyruvate carboxylase and then phosphoenolpyruvate carboxykinase)
Fructose 1,6-bisphosphate to fructose 6-phosphate
(Fructose 1,6-bisphosphatase)
Glucose 6-phosphate to glucose
(Glucose 6-phosphatase)
Oxaloacetate must be converted to ___________ in order to exit the mitochondrion.
malate by malate dehydrogenase (it gets converted back to oxaloacetate in the cytosol so that PEP CK can convert it to PEP)
The key regulator of fructose 1,6-bisphosphatase is _____________.
fructose 2,6-bisphosphate (the same molecule that regulates PFK-1 in glycolysis)
Autosomal recessive defects in _____________ (called Von Gierke’s disease) result in enlarged kidneys and liver along with hypoglycemia during fasting.
glucose 6-phosphatase
True or false: 4 ATP molecules are needed to convert 2 pyruvates to 2 PEPs.
False. Two GTPs are needed (one per molecule) and two ATPs.
Increased levels of ___________ in the liver stimulate pyruvate carboxylase to initiate gluconeogenesis.
acetyl co-a
What is the regulated enzyme in glycogen breakdown?
Glycogen phosphorylase (inhibited by G6P, glucose, and ATP; stimulated by AMP and Ca in muscle –both signs of increased energy use)
Glycogen phosphorylase is ___________ when phosphorylated.
activated (think about it –you want this on when glucagon is present)
Glycogen phosphorylase kinase is ____________ when phosphorylated.
activated (again, you want this on when glucagon has stimulated the cell)
Glycogen synthase is active when _____________.
dephosphorylated
