M2c L16-18 Flashcards
Describe glucose metabolism in red blood cells and brain tissue cells
Red blood cells, anaerobic
GLUT1 transports glucose into cell, glucose –> lactate, leaves the cell
another pathway, pentose phosphate, makes other sugar molecules in RNA and DNA
Brain tissue cells, aerobic (must have O2 all the time)
GLUT3 glucose transporter, glucose–> 2CO2, 2 acetyl CoA through pyruvate dehydrogenase, Goes into TCA cycle, acetyl group –> CO2, reducing equivalents go into ETC to make ATP.
Describe gluconeogenesis and explain when it occurs
it is creating glucose out of non-carbohydrate compounds (lactate, glycerol, glucogenic amino acids, propionate), it happens after 24 hours of fasting and when the body is undergoing intense exercise, it happens in the liver and to a lesser extend the kidney cortex
Explain the metabolic importance of gluconeogenesis
some organs use glucose exclusively for ATP production
Describe the reactions of gluconeogenesis that bypass those of glycolysis
bypass 1: pyruvate carboxylase: pyruvate –> oxaloacetate, occurs in mitochondrion
PEP carboxykinase: oxaloacetate –> phosphoenolpyruvate, occurs in cytosol
Bypass 2 + 3:
Fructose-1,6-bisphosphatase –> Fructose-6-phosphate
Glucose-6-phosphatase –> Glucose
Describe the source of ATP for gluconeogenesis
ATP is used as a source of energy so that gluconeogenesis can happen. it comes from free fatty acids being oxidized to acetyl CoA
needs 6 ATP per glucose –> lactate
Outline the sources of precursors for gluconeogenesis
Lactate
red blood cells export lactate
skeletal muscle cells after strenuous exercise export lactate
Cori cycle
Amino acids from skeletal muscle cells
Glycerol from triacyl glycerides
Propionate from odd-chain fatty acid oxidation
from microorganisms in the rumen (ruminants)
Describe and explain the metabolic importance of the Cori cycle
Helps to recycle carbon for gluconeogenesis, Peripheral tissues must release lactate, Limits wastage of carbon
it is a metabolic pathway in which lactate, produced by anaerobic glycolysis in muscles, is transported to the liver and converted to pyruvate, then glucose is produced by gluconeogenesis, which then returns to the muscles and is metabolized back to lactate
Describe and explain the reciprocal regulation (allosteric) of gluconeogenesis and glycolysis using metabolic logic
Hexokinase is inhibited by G6P
Glucose-6-phosphatase is activated by G6P
High level of G6P means high level of glucose
PFK is activated by AMP and ADP, inhibited by ATP
FBPase is inhibited by AMP
Pyruvate kinase is inhibited by Acetyl-CoA and ATP
Pyruvate carboxylase + PEPCK is activated by Acetyl-CoA
1st step in gluconeogenesis PEPCK decarboxylates and phosphorylates oxaloacetate (OAA) for its conversion to PEP, when GTP is present.
Describe glucose metabolism in muscle and heart tissue
Muscle and heart tissue cells
GLUT4 glucose transporter
glucose –> glucose-6-phosphate–> 2 pyruvate through glycolysis
Pentose phosphate pathway for sugar molecules for RNA and DNA
Muscle (anaerobic)
2 pyruvate into 2 lactate, reducing equivalents are put onto pyruvate to regenerate NAD+ so glycolysis can continue, lactate + 2 protons–> outside the cell, into blood stream
Muscle & heart tissue (aerobic)
Pyruvate is converted into 2CO2 and 2 acetyl CoA through pyruvate dehydrogenase, goes into TCA cycle, 4CO2, Fatty acid oxidation from 2 acetyl CoA as a source of energy
Describe glucose metabolism in liver parenchymal cells
Liver parenchymal cells Anaerobic or aerobic
GLUT2 (low affinity to glucose)
glucose into glucose-6-phosphate into 2 pyruvate and pyruvate into 2CO2 and 2 acetyl CoA through pyruvate dehydrogenase, goes into TCA cycle, 4CO2, Glucose-6-phosphate into glycogen and vice versa to store it, glycogen used to maintain blood glucose, Pentose phosphate pathways to make sugar molecules, lots of metabolism, Acetyl CoA –> fat, –> VLDL goes outside the cell, Liver can take up the lactate with 2 protons , Liver does gluconeogenesis, to get glucose to maintain glucose blood levels as it is essential , Only liver cells have a glucose-6-phosphatase to remove the phosphate from glucose-6-phosphate to make glucose so it can go into the bloodstream
explain how glucogenesis is not glycolysis in reverse
Gluconeogenesis Is More Specific. and the steps are different there are also 3 irreversible steps in glycolysis, bc they require different enzymes and have large negative delta G. gluconeogenesis is thermodynamically favorable
explain why fatty acids cannot be used to make glucose in animals
Fatty acids are converted into acetyl-CoA, which cannot be reverted into pyruvate because humans do not have the enzyme required
can glucose be synthesized from fatty acids?
yes if they have an odd number of carbons, normally fatty acids are chopped into molecules with 2 carbon atoms, Odd chain fatty acids are oxidized to acetyl CoA and propionyl CoA, Propionyl CoA –> Succinyl-CoA –> oxaloacetate, it can now enter gluconeogenesis
describe the regulation of glycolysis and gluconeogenesis
Hexokinase is inhibited by G6P
Glucose-6-phosphatase is activated by G6P
High level of G6P means high level of glucose
PFK is activated by AMP and ADP, inhibited by ATP
FBPase is inhibited by AMP
Pyruvate kinase is inhibited by Acetyl-CoA and ATP
Pyruvate carboxylase + PEPCK is activated by Acetyl-CoA
