Module 6 Flashcards
Why is magnesium used in glycolysis?
it is used whenever an enzyme is transferring a phosphate group TO or FROM a molecule within the glycolysis cycle
the reason for its uses as a cofactor is to SHIELD the negative charges from the phosphate groups of ATP and to allow the enzyme to properly function
Outline the relationship b/w cancer and glycolysis
o Since glycolysis proceeds up to 10x faster in cancer cells, some chemotherapeutic agents available inhibit hexokinase (e.g. an agent like deoxyglucose)
o the high glycolytic turnover in cancer cells is also used for diagnosis by injecting isotopically labelled glucose followed by PET scanning
What did Otto Warburg propose?
He proposed that most cancer cells produce energy by anaerobic glycolysis rather than by oxidation of pyruvate in the mitochondria – this is known as the Warburg hypothesis
Where does gluconeogenesis happen?
in the LIVER
First irreversible step of GNG
Conversion of pyruvate back into PEP
mitochondrial pyruvate carboxylase converts pyruvate into oxaloacetate
(swinging arm activity)
cytosolic PEP carboxykinase converts oxaloacetate into PEP
GTP –> GDP, CO2 released
Why is GDP important?
it suppresses protein metabolism so it can be involved in NEGATIVE feedback
Second irreversible step of GNG
conversion of F-1,6-bisP to F-6-P
- catalyzed by CYTOSOLIC fructose-1,6-bisphosphatase
- hydrolyzes the bond b/w C1 and phosphate and releases the phosphate group (which gets replaced w hydroxyl group)
Third irreversible step of GNG
conversion of G-6-P to glucose
occurs in the ER lumen using glucose-6-phosphatase (which snips off the phosphate)
the free glucose that is produced would be exported out of the cell using the same transporter that brought it in the first place (usually G1)
this whole process happens in the ER of hepatocytes of the LIVER in the cortex of the KIDNEY
What are the 5 major fates of pyruvate?
- ethanol
- lactate
- acetyl-CoA –> mitochondrial matrix
- glucose (first, OAA) –> mitochondrial matrix
- amino acids like alanine
Explain the fermentation process from pyruvate to ethanol
o Pyruvate LOSES CO2 –> acetaldehyde (reduced) –> ethanol
o Pyruvate decarboxylase converts pyruvate to acetaldehyde
Involves TPP, Mg2+
CO2 lost
o Alcohol dehydrogenase converts acetaldehyde to ethanol
Oxidation of NADH + H+ –> NAD+
under anaerobic conditions, lactate dehydrogenase . . .
plays an important role in regenerating NAD+ for Step 6 of glycolysis – high amounts of lactic acid can produce acidosis
What is the Cori cycle?
o The process of transporting lactate from cells that are undergoing ANAEROBIC metabolism to the liver where it is used to provide glucose back to the cells
o An example of one of the critical roles of the liver in assuring an adequate supply of glucose in the body
Outline the steps of the Cori Cycle
o Muscle contraction is powered by glycolysis
o Glucose (from glycogen) goes through glycolysis –> pyruvate –> lactate
o Lactate is exported from the myocytes / muscle cells into the blood stream and taken to the liver
o When it reaches the liver, it is reconverted from lactate into pyruvate by lactate dehydrogenase, & then that pyruvate is taken through gluconeogenesis back to glucose
o that glucose from gluconeogenesis is then exported into the blood stream and taken back to the muscles & tissues to maintain homeostasis
Why is glycogen critical during fasting?
- because liver glycogen provides a source of glucose
- muscle glycogen cannot give rise to blood glucose, but can be used to power muscle contraction for long periods of time
What are the 4 enzymes involve din glycogenolysis?
o Glycogen phosphorylase
o Debranching enzyme (transferase)
o Debranching enzyme (glucosidase)
o Phosphoglucomutase
