Lessons 9, 10, and 11 - glycolysis and gluconeogenesis Flashcards
describe stage 1 of glycolysis
stage 1 is the trapping and preparation phase. no ATP is generated. it begins with conversion of glucose into fructose 1,6 - biphosphate
what is the strategy of the initial steps of glycolysis
to trap the glucose in the cell and form a compound that can be readily cleaved into phosphorylated three-carbon units.
when is stage 1 completed
with the cleavage of fructose 1,6-biphosphate
what is a reversible reaction
in a reversible reaction all reagents and products are always the same
what is an irreversible reaction
some (but not all) of the products may still be converted into reagents through an alternative path
what are committed steps
they’re irreversible reactions in which none of the products may be converted to reagents
what is the importance of metabolically irreversible reactions
these reactions are always points of regulation in all metabolic pathways. since they are irreversible, blocking or activating them only affects a pathway in one direction, leaving the opposing pathway unaffected
what does glycolysis do
it converts 1 glucose into 2 pyruvate molecules. pyruvate can be further metabolized to: lactate or ethanol (anaerobic) or acetyl CoA (aerobic). acetyl CoA is further oxidized to CO2 and H2O via the citric acid cycle
what is the net reaction of glycolysis
2 ATP are produced and 2 NAD+ are reduced to NADH
what doe hexokinase do in glycolysis
it phosphorylates glucose to make glucose 6-phosphate
what does phosphoglucose isomerase do in glycolysis
isomerizes glucose 6-phosphate into fructose 6-phosphate
what does phosphofructokinase do in glycolysis
phosphorylates fructose 6-phosphate to form fructose 1,6-biphosphate
what does aldolase do
transforms fructose 1,6 biphosphate into glyceraldehyde 3-phosphate.
what does triose phosphate isomerase do
isomerizes between dihydroxyacetone phosphate and glyceraldehyde 3-phosphate as dihydroxyacetone phosphate isn’t on the main glycolysis pathway
what does glyceraldehyde 3-phosphate dehydrogenase do
converts glyceraldehye 3-phosphate into 1,3 biphosphoglycerate while reducing NAD+ to NADH
what does phosphoglycerate kinase do
converts 1,3 -biphosphoglycerate into 3-phosphoglycerate and creates 1 ATP
what does phosphoglycerate mutase do
converts 3-phosphoglycerate into 2-phosphoglycerate
what does enolase do
converts 2-phosphoglycerate into phosphoenolpyruvate and discards an H2O
what does pyruvate kinase do
converts phosphoenolpyruvate into pyruvate and creates 1 ATP
what happens when pyruvate is metabolized into lactate
NADH is oxidized to NAD+
what happens when pyruvate is metabolized to acetyl CoA
CO2 is created and Acetyl CoA goes onto further oxidation
what happens when pyruvate is metabolized to acetalaldehyde
CO2 is produced and the NADH is oxidized to NAD+ to form ethanol
what does pyruvate decarboxylase do
converts pyruvate to acetaldehyde (producing CO2)
what does alcohol dehydrogenase do
converts acetalaldehyde to ethanol (oxidizing NADH)
what does lactate dehydrogenase do
converts pyruvate to lactate (oxidizing NADH)
in anaerobic metabolism where is the NADH obtained to keep on converting pyruvate into lactate
from the conversion of glyceraldehyde phosphate into 1,3 biphosphoglycerate
describe fructose being converted into the usable glyceraldehyde 3-phosphate
fructokinase turns fructose into fructose 1-phosphate, then fructose 1-phosphate aldolase converts it into glyceraldehyde + dihydroxyacetone phosphate. the glyceraldehyde is turned into glyceraldehyde 3-phosphate by triose kinase
what does galactokinase do
converts galactose into galactose 1-phosphate
describe process of going from galactose 1-phosphate to glucose 1-phosphate
galactose 1-phosphate uridyl transferase adds a uridine group to it, this allows glucose 1-phosphate to be formed. the leftover UDP-galactose is catalyzed by UDP-galactose 4-epimerase to create a UDP-glucose which is what originally provided the uridine group to galactose 1-phosphate
what does lactase do
splits lactose into galactose and glucose
what does aldose reductase do
converts galactose to galacitol by oxidizing NADPH to NADP+
how does PFK regulate glycolysis
at rest there are high levels of ATP. ATP inhibits phosphofructokinase and pyruvate kinase, while glucose 6-phosphate inhibits hexokinase. glucose 6-phosphate is then converted into glycogen. during exercise the decrease in ATP/AMP ratio resulting from muscle contractions activates PFK and hence glycolysis.
how is PFK-1 in liver additionally regulated
fructose 2,6 BP produced by PFK-2 activates PFK, once PFK is activated glycolysis is stimulated and more ATP is produced (and less fructose 6-phosphate)
describe glucokinase vs. hexokinase
Km for glucose in glucokinase = 10mM. Km for glucose in hexokinase = 10mM physiological [glucose] = 5mM
describe control of catalytic activity of pyruvate kinase
pyruvate kinase is regulated by allosteric effectors and covalent modification. fructose 1,6 bp allosterically stimulates the enzyme, while ATP and alanine (in liver) are allosteric inhibitors. Glucagon, secreted inresponse to low blood glucose, promotes phosphorylation and inhibition of the enzyme. when blood-glucose levels are adequate, the enzyme is dephosphorylated and activated
describe gluconeogenesis
happens mostly in liver and also in kidney. the substrates are glycerol, pyruvate, lactate and amino acids. it happens in prolonged fasting and starvation. stimulated by PKA (epinephrine/glucagon) and glucocorticoids
what does pyruvate carboxylase do
converts pyruvate into oxaloacetate (using 1 ATP) during gluconeogenesis
what does phosphoenolpyruvate carboxykinase do
converts oxaloacetate into phosphenolpyruvate (using 1 GTP)
where are the enzymes for gluconeogeneis found
all are found in the cytoplasm except for pyruvate carboxylase (in the mitochondria) and glucose 6-phosphatase (membrane bound in the endoplasmic reticulum)
where does glycerol enter gluconeogenesis
it becomes dihidroxyacetone phosphate
where do lactate and amino acids enter gluconeogenesis
lactate and some amino acids enter by becoming pyruvate while some other amino acids enter by becoming oxaloacetate
what does fructose 1,6 biphosphatase do
converts fructose 1,6 bp into fructose 6-phosphate
what does glucose 6-phosphatase do
converts glucose 6-phosphate into glucose
what stimulates and what inhibits PFK
fructose 2,6 bp and AMP stimulate while ATP, Citrate, and H+ inhibit
what stimulates and inhibits pyruvate kinase
fructose 1,6 bp stimulates while ATP and alanine inhibit
what stimulates and inhibits fructose 1,6 biphosphatase
citrate stimulates while AMP and fructose 2,6 bp inhibit
what stimulates and inhibits pyruvate carboxylase
acetyl CoA stimulates while ADP inhibits.
what inhibits phosphoenolpyruvate carboxykinase
ADP inhibits it
