Flashcards in Biochem - Metabolism (Glycolysis) Deck (24):
What is the first step of glycolysis? For what other process is this the first step, and where is this particular process located?
Phosphorylation of glucose to yield glucose-6-P serves as the 1st step of glycolysis (also serves as the 1st step of glycogen synthesis in the liver).
Again, what is the first step of glycolysis? What catalyzes this step, and on what does this generally depend?
Phosphorylation of glucose to yield glucose-6-P serves as the 1st step of glycolysis (also serves as the 1st step of glycogen synthesis in the liver); Reaction is catalyzed by either hexokinase or glucokinase, depending on the tissue.
What activity does hexokinase have at low glucose concentrations? What happens at high glucose concentrations?
At low glucose concentrations, hexokinase sequesters glucose in the tissue. At high glucose concentrations, excess glucose is stored in the liver.
What is the location of hexokinase versus glucokinase?
HEXOKINASE: Most tissues, but not liver nor Beta cells of pancreas; GLUCOKINASE: Liver, Beta cells of pancreas
What is the Km of hexokinase versus glucokinase?
HEXOKINASE: Lower (higher affinity); GLUCOKINASE: Higher (lower affinity)
What is the Vmax of hexokinase versus glucokinase?
HEXOKINASE: Lower (lower capacity); GLUCOKINASE: Higher (higher capacity)
Is hexokinase versus glucokinase induced by insulin?
HEXOKINASE: No; GLUCOKINASE: Yes
Is hexokinase versus glucokinase feedback-inhibited by glucose-6-P?
HEXOKINASE: Yes; GLUCOKINASE: No
Is hexokinase versus glucokinase gene mutation associated with maturity-onset diabetes of the young (MODY)?
HEXOKINASE: No; GLUCOKINASE: Yes
Where does glycolysis occur? What is its net equation? What is important to note about the equation?
Net glycolysis (cytoplasm): Glucose + 2 Pi + 2 ADP + 2 NAD+ => 2 pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2O; Equation not balanced chemically, and exact balanced equation depends on ionization state of reactants and products.
What are 2 key glycolysis enzymes that require ATP? What is important to remember about each of these enzymes?
(1) Hexokinase/Glucokinase (Glucokinase in liver and Beta cells of pancreas; Hexokinase in all other tissues) (2) Phoshofructokinase-1 (rate-limiting step)
What glycolysis reaction does hexokinase/glucokinase catalyze?
Glucose => Glucose-6-phosphate
What are the negative regulators of Hexokinase versus glucokinase?
HEXOKINASE: Glucose 6-P; GLUCOKINASE: Fructose-6-P
What glycolysis reaction does phosphofructokinase-1 catalyze?
Fructose 6-P => Fructose-1,6-BP (rate-limiting step)
What are the positive and negative regulators of Phosphofructokinase-1?
POSITIVE: AMP, Fructose-2,6-BP; NEGATIVE: ATP, citrate
What are 2 key glycolysis enzymes that produce ATP?
(1) Phosphoglycerate kinase (2) Pyruvate kinase
What glycolysis reaction does phosphoglycerate kinase catalyze?
1,3-BPG => 3-PG
What glycolysis reaction does pyruvate kinase catalyze?
Phosphoenolpyruvate => Pyruvate
What are the positive versus negative regulators of Pyruvate kinase?
POSITIVE: fructose-1,6-BP; NEGATIVE: ATP, alanine
What are 2 enzymes that allow regulation of gluconeogenesis/glycolysis by F2,6BP? Which is active in fasting versus fed states?
(1) Fructose bisphosphatase-2 (active in fasting state) (2) Phosphofructokinase-2 (active in fed state)
How do FBPase-2 and PFK-2 compare/contrast in terms of general structure/function?
FBPase-2 and PFK-2 are the same bifunctional enzyme whose function is reversed by phosphorylation by protein kinase A
What happens to glycolysis versus gluconeogenesis in the fasting state? Briefly detail the mechanism by which this occurs.
Fasting state: Increase glucagon => increase cAMP => increase protein kinase A => increase FBPase-2, decrease PFK-2, less glycolysis, more gluconeogenesis
What happens to glycolysis versus gluconeogenesis in the fed state? Briefly detail the mechanism by which this occurs.
Fed state: Increase insulin => decrease cAMP => decrease protein kinase A => decrease FBPase-2, increase PFK-2, more glycolysis, less gluconeogenesis