BIOCHEM Chp.9 Glycolysis, PDH, Glycogenesis, Glycogenolysis, Gluconeogenesis, & PPP Flashcards
What is Km?
the concentration of substrate when an enzyme is active at half of its maximum velocity. the lower the Km, the higher the enzyme affinity for the substrate
What is GLUT2?
a low-affinity, high Km transporter in hepatocytes and pancreatic cells that captures excess glucose for storage after a meal.
What are the glucose sensors for insulin release?
B-islet cells in the pancreas, GLUT2, and glucokinase
What is GLUT4?
a high affinity, low Km glucose transporter in adipose tissue and muscle that responds to [glucose] in peripheral blood
What is glucose stored in muscles and the liver?
muscle - glycogen
liver - FA
What is glycoslysis?
a pathway that converts glucose into 2 pyruvate molecules and 2 ATP. occurs in the cytoplasm and does not require oxygen
How do kinases operate?
they attach a phosphate group from ATP to their substrates
What is the function of Hexokinase?
glucose enters the cell by facilitated diffusion or active transport, then hexokinase phosphorylates the glucose to glucose 6-phosphate
What inhibits Hexokinase?
glucose 6-phosphate
What is the function of Glucokinase?
phosphorylates glucose to Glose-6-phosphate in the liver and pancreatic B-islet cells, works with GLUT2 as a glucose sensor
What induces Glucokinase?
insulin in the liver
What is the function of Phosphofrutokinase-1?
phosphorylates fructose 6-phosphate to fructose 1,6, biphosphate using ATP
What is the function of Phosphofrutokinase-2?
produces F2,6-BP that activates PFK-1
What inhibits and activates Phosphofrutokinase-2?
it is activated by insulin and inhibited by glucagon
What is the function of Glycaldhyde-3-phosphate dehydrogenase?
produced NADH to feed into the mitochondrial ETC when oxygen is present.
also phosphorylates Glyceraldehyde-3-phosphate to 1,3,-bisphosphoglycerate
What is the function of 3-phosphoglycerate kinase?
substrate-level phosphorylation transferring phosphate from 1,3, bisphosphoglycerate to ADP, forming ATP and 3-phosphoglycerate
What is the function of pyruvate kinase?
substrate-level phosphorylation transferring from Phosphoenolpyruvate to ADP forming ATP and pyruvate
What are the irreversible enzymes in glycolysis?
glucokinase or hexokinase, PFK-1, and pyruvate kinase
What inhibits and activates Phosphofrutokinase-1?
it is inhibited by ATP, citrate, and activated by AMP, F26BP
What activates and inhibits pyruvate kinase?
Fructose 1-6-Bisphosphatase activates, and acetyl-CoA inhibits pyruvate
How is NADH oxidized when oxygen or mitochondria are absent?
by cytoplasmic lactate dehydrogenase
Describe glycolysis in erythrocytes
1,3, BPG is converted to 2,3, BPG via BPG Mutase that the RBC can use to
What are the rate-limiting enzymes of carbohydrate metabolism?
Glycolysis: phosphofructokinase-1
Fermentation: lactase dehydrogenase
Glycogeneiss: glycogen synthase
Glycogenolysis: glycogen synthase phosphorylase
Gluconeogenesis: Fructose-1,6, biphosphatase
Pentose Phosphate Pathway: Glucose 6-phosphate dehydrogenase
What are the steps of glycolysis?
Glucose → Glucose 6-Phpspahte (G6P) via Hexokinase. Step is irreversible
G6P → Fructose 6-Pphopsate (F6P) via Isomerase
F6P → Fructose-1-6-Biphosphatase (F16BP) via phosphofructokinase 1 (PFK-1)
F-1-6-BP → DHA and GA3P via Aldose
GA-3P → 1-3-BPG via GA-3-PDH, facilitated with the reduction of NADH to NAD+ which can be used in the ETC or in Fermentation
1-3-BPG → 3PG via 3-PGK. The lost phosphate from 1-3 BPG is used to construct ATP
3-PG → 2-PG via Mutase
2PG → PEP via Enolase
PEP → Pyruvate via Pyruvate Kinase. Step is irreversible
What is the role of galactokinase?
to store of galactose in the cell
How is galactose converted to glucose-1-phosphate?
galactose is converted to glocose-1-phophate via galatcose-1-phosphate uridyltransferase and epimerase
What are the 3 fates of pyruvate made from glycolysis?
- converted to acetyl-CoA by pyruvate dehydrogenase to enter into the Citric Acid Cycle if ATP is needed
- FA synthesis i B-oxidation if sufficient ATP is present.
- converted to oxaloacetate by pyruvate carboxylate and enters into gluconeogenesis
What physiological changes promote a right shift of the oxygen disassociation curve (Bohr Effect)?
high 2,3-BPG, low pH, high [H+] protons, high CO2, all of which occur during exercise
What is the role of mutases?
they move functional groups from one place in a molecular to another
What are the effects of 2,3-BPG on hemoglobin?
it binds allosterically to the B-chains of HbA and decreases its affinity for oxygen
What is glycogenesis?
the synthesis of glycogen using glycogen synthase and branching enzymes
What is the function of glycogen synthase?
it attached glucose molecules from UDP-glucose to the growing glycogen chain, forming a-1,4 glycosidic links b/w glucose molecules
What is the function of branching enzymes?
moves a block of oligoglucose from one branch and adds it to the growing glycogens in a new branch using a-1,6 glycosidic links
What stimulates and inhibits Glycogen synthase?
Insulin and ATP stimulate glycogen synthase, and Epinephrine, glucagon, and AMP inhibit it
What is gluconeogensis?
done in the cytoplasm and mitochondria of liver cells
What is glycogenolysis?
the breakdown of glycogen to glucose-1-phosphate using glycogen phosphorylase and debranching enzyme
What is the role of the debranching enzyme?
moves a block of oligosaccharides from one branch and connects it to the chain using a-1,4 glycosidic links. it also removes branching points connected via a-1,6 glycosidic links, freeing up glucose molecules
What is the function of Glycogen phosphorylase?
serves as the rate-limiting step in glycogenolysis. It removes glucose molecules from glycogen using phosphorylation, breaking the alpha-1-4 glycosidic linkages, and releasing glucose monomers but stops at branch points.
What inhibits and activates Glycogen phosphorylase?
Insulin and ATP inhibit glycogen phosphorylase
Epinephrine, glucagon, and AMP stimulate it (opposite of glycogen synthase)
Where do Glycolysis, the TCA, PPP/HMP shunt, and Oxidative phosphorylation occur?
Glycolysis occurs in the cytoplasm.
The citric acid cycle occurs in the mitochondrial matrix (Except succinate dehydrogenase, which is located in the inner membrane)
pentose phosphate pathway/hexone monophosphate shunt occurs in the cytoplasm
Oxidative phosphorylation occurs in the inner membrane.
What is the function of glucosidase?
it hydrolyzes the leftover alpha-1-6 linkages the debranching enzyme may not catch, releasing individual glucose molecules
What is the purpose of the pentose phosphate pathway/hexone monophosphate shunt?
ribose 5-phosphate and NADPH
What is the rate-limiting step of the Pentose Phosphate pathway/Hexone Monophosphate shunt?
glucose-6-phosphate dehydrogenase
What activates and inhibits Glucose-6-phosphate Dehydrogenase?
activated by NADP+ and insulin and inhibited by NADPH
What is the function of Pyruvate Carboxylate?
converts pyruvate into oxaloacetate in gluconeogenesis
What activates Pyruvate Carboxylate?
aCoA form B-oxidation
What is the function of Phosphoenolpyruvate Carboxykinase (PEPCK)?
converts Oxaloacetate to Phosphoenolpyruvate in gluconeogenesis
What activates Phosphoenolpyruvate Carboxykinase (PEPCK)?
glucagon and cortisol
What is the function of Fructose-1,6,-biphosphate?
Converts 1,6-biphosphate to fructose 6-phosphate bypassing phosphofructokinase-1
What activates and inhibites Fructose-1,6,-biphosphate?
ATP directly and glucagon indirectly (by decreasing levels of F-2,6-BP) activate, and AMP directly and insulin indirectly (bia increase levels of F-2,6-BP)
What is generated during fermentation?
coenzymes needed in glycolysis - no energy is generated
What is the function of fructokinase?
fructose is phosphorylated by fructokinase, trapping it in the cells
What does aldolase B produce?
dihydroxyacetone phosphate (DHAP) and glyceraldehyde (which can be phosphorylated to form glyceraldehyde 3-phosphate)
What are the reactants and products of the PDH complex?
Pyruvate, NAD+, and CoA are the reactants, and aCoA, NADH, and CO2 are the products.
What inhibits the PDH complex?
a build-up of the product, aCoA from either TCA or fatty acid b-oxidation signals the cell is energetically satisfied and the production of aCoA should be stopped
What is the function of NADPH?
antimicrobial resistance via bacterial destruction by bleach within lysosomes, and functional carriage of energy across organelle membranes for use within the mitochondria
