30 Questions
What is the main role of transketolase in the pentose phosphate pathway?
To transfer a two-carbon unit onto an aldose sugar
What are the cofactors required for the transketolase reaction?
Mg2+ and thiamin diphosphate (vitamin B1)
What is the purpose of the reversal of glycolysis and the gluconeogenic enzyme fructose 1,6-bisphosphatase in the pentose phosphate pathway?
To convert glyceraldehyde-3-phosphate to glucose-6-phosphate
Which tissues have a high activity of the pentose phosphate pathway?
Liver, adipose tissue, adrenal cortex, thyroid, erythrocytes, testis, and lactating mammary gland
What is the main purpose of the pentose phosphate pathway in tissues where it is active?
To produce NADPH for reductive biosynthesis
How is the synthesis of glucose-6-phosphate dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase regulated?
They are induced by insulin in the fed state when lipogenesis increases
What is the fate of much of the fructose metabolized in the liver?
Substrates for gluconeogenesis
What is the result of excessive glucose-6-phosphate production from fructose ingestion?
Increased uric acid production and gout
What does the enzyme galactokinase catalyze?
Phosphorylation of galactose
What is the result of increased fatty acid and triglyceride synthesis from fructose ingestion?
Increased LDL cholesterol levels
What enzyme catalyzes the conversion of UDPGal to UDPGlc?
UDPGal 4-epimerase
What is the fate of the two triose phosphates, dihydroxyacetone phosphate, and glyceraldehyde-3-phosphate, formed from fructose metabolism?
They are either degraded by glycolysis or are substrates for gluconeogenesis
Which enzyme is responsible for the conversion of glucose to sorbitol?
Aldose reductase
What is the primary reason for the accumulation of sorbitol in the lens, peripheral nerves, and renal glomeruli in diabetic patients?
Slow activity of sorbitol dehydrogenase
What is the primary consequence of the accumulation of sorbitol in the lens, peripheral nerves, and renal glomeruli?
All of the above
Why is the polyol (sorbitol) pathway not found in the liver?
The liver has high sorbitol dehydrogenase activity
What is the role of NAD+ in the polyol pathway?
It is required for the conversion of sorbitol to fructose
Which of the following tissues is not affected by the accumulation of sorbitol in diabetic patients?
Liver
What is the primary function of the uronic acid pathway in the liver?
To convert glucose to glucuronic acid, ascorbic acid, and pentoses
Which enzyme catalyzes the isomerization of glucose-6-P to glucose-1-P in the uronic acid pathway?
Phosphoglucomutase
What is the final product of the oxidation of UDPGlc by UDPGlc dehydrogenase in the uronic acid pathway?
UDP-glucuronate
What is the primary fate of UDP-glucuronate in the uronic acid pathway?
It is incorporated into proteoglycans or conjugated with steroid hormones, bilirubin, and drugs
What happens when large quantities of fructose are ingested?
Fructose is not phosphorylated in extrahepatic tissues due to inhibition by glucose
Which of the following pathways is an alternative oxidative pathway for glucose that does not lead to ATP formation?
Uronic acid pathway
What is the key reason that fructose undergoes more rapid glycolysis in the liver compared to glucose?
Fructose bypasses the regulatory step catalyzed by phosphofructokinase-1
Which enzyme is responsible for the phosphorylation of fructose in the liver, kidney, and intestine?
Fructokinase
What is the product formed after fructose-1-phosphate is cleaved by aldolase B in the liver?
D-glyceraldehyde and dihydroxyacetone phosphate
How is fructose metabolism affected by insulin and glucagon levels, compared to glucose metabolism?
Fructose metabolism is not affected by insulin or glucagon levels
What is a potential consequence of increased fructose metabolism in the liver?
Increased fatty acid synthesis and triglyceride production
How does fructose clearance from the blood compare between diabetic and non-diabetic individuals?
Fructose is cleared at a normal rate in diabetic patients
Test your knowledge on transketolase enzyme, its role in the production of 3 and 7 carbon-sugars, and the significance of measurement of erythrocyte transketolase in assessing vitamin B1 nutritional status. Also, explore questions related to the pentose phosphate pathway enzymes for complete oxidation of glucose.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
