MLT GlobeChemistry: Carbohydrates & diabetes – page 3
121 Chemistry MCQs on Carbohydrates & diabetes with answers and explanations.
The formation of glucose from non-carbohydrate sources such as lactate, glycerol and amino acids is called:
Gluconeogenesis makes new glucose from non-carbohydrate precursors, mainly in the liver. Glycogenolysis is the breakdown of stored glycogen to glucose.
For an accurate blood lactate result, which collection practice is correct?
Muscle activity and venous stasis raise lactate, and red cells keep producing lactate by glycolysis after collection. Cooling or fluoride and quick analysis prevent false increases.
For most non-pregnant adults with diabetes, the ADA recommends an HbA1c goal of less than:
The general ADA target is below 7% (53 mmol/mol), made stricter or looser for individual patients. 6.5% is the diagnostic cut-off, not the treatment goal.
Mature red blood cells lack mitochondria. Their glycolysis therefore ends with the formation of:
Without mitochondria, pyruvate cannot enter the citric acid cycle, so red cells reduce it to lactate to regenerate NAD+. Acetyl-CoA formation needs mitochondrial pyruvate dehydrogenase.
Before a fasting plasma glucose test, an adult should have had no caloric intake for at least how long?
ADA defines fasting as no caloric intake for at least 8 hours. Shorter fasts can give falsely high results, and a 24-hour fast is not required.
Type 1 diabetes mellitus is mainly caused by:
Type 1 diabetes results from autoimmune destruction of insulin-producing beta cells, causing absolute insulin deficiency. Insulin resistance is the main feature of type 2 diabetes.
Lactose, the sugar in milk, is made of which two monosaccharides?
Lactose is a disaccharide of glucose and galactose. Glucose plus fructose forms sucrose, and two glucose units form maltose.
Which specimen is used to measure HbA1c?
HbA1c is measured in red cells, so anticoagulated whole blood (usually EDTA) is used. Serum and separated plasma contain no red cells.
The breakdown of glycogen to release glucose is called:
Glycogenolysis is the breakdown of glycogen. Glycogenesis is glycogen synthesis, gluconeogenesis makes new glucose from non-carbohydrate sources, and glycolysis breaks glucose down to pyruvate.
In diabetic ketoacidosis, which ketone body is present in the blood in the highest concentration?
Beta-hydroxybutyrate is the predominant ketone body in DKA. It is not detected by the nitroprusside reaction, which reacts mainly with acetoacetate. Lactate is not a ketone body.
Polyuria in uncontrolled diabetes mellitus is mainly due to:
When plasma glucose exceeds the renal threshold, filtered glucose stays in the tubule and draws water with it (osmotic diuresis), producing large urine volumes.
In poorly controlled diabetes, lens cataract is partly caused by aldose reductase converting glucose into which osmotically active compound?
In the lens, excess glucose is reduced to sorbitol, which is trapped, draws in water and makes the lens opaque. This is the polyol pathway.
If sucrose is injected intravenously, what happens to it?
Sucrase exists only on the intestinal brush border, so circulating sucrose is not hydrolysed and is filtered by the kidneys unchanged.
When fructose closes into a five-membered (furanose) ring, which carbon becomes the anomeric hemiketal carbon?
Fructose is a ketose with its carbonyl at C-2; ring closure with the C-5 hydroxyl makes C-2 the anomeric carbon. C-1 is anomeric only in aldoses such as glucose.
Which monosaccharide has no chiral carbon and therefore cannot exist as D and L forms?
Dihydroxyacetone is a symmetrical ketotriose with no asymmetric carbon. Glyceraldehyde, the other triose, has one chiral centre and is the reference compound for D/L notation.
Which structural feature is shared by glycosaminoglycans such as hyaluronate and chondroitin sulfate?
GAGs are long linear polymers of repeating disaccharides (amino sugar plus uronic acid). Carboxyl and sulfate groups make them strongly negative, not positive.
Glucose-6-phosphate is converted to fructose-1,6-bisphosphate in two steps. Which pair of enzymes is involved?
Phosphoglucose isomerase forms fructose-6-phosphate, which PFK-1 phosphorylates. Phosphoglucomutase interconverts glucose-6- and glucose-1-phosphate; aldolase acts after fructose-1,6-bisphosphate is formed.
Glucose is taken up by intestinal cells against its concentration gradient, coupled to sodium entry via SGLT1. This process is:
SGLT1 uses the Na+ gradient created by Na+/K+-ATPase to move glucose uphill. Diffusion, simple or facilitated, only moves solutes down their gradient.
Which monosaccharide shares the SGLT1 transporter with glucose and is absorbed by active transport in the small intestine?
SGLT1 co-transports glucose and galactose with sodium. Fructose is absorbed by facilitated diffusion through GLUT5.
A patient has glucose in the urine, yet fasting and post-load plasma glucose are normal. The most likely explanation is:
In renal glycosuria, defective tubular reabsorption (e.g. SGLT2 variants) lets glucose spill at normal plasma levels. Diabetes and alimentary glycosuria involve raised plasma glucose; insulinoma causes hypoglycaemia.