MLT GlobeChemistry: Carbohydrates & diabetes
121 Chemistry MCQs on Carbohydrates & diabetes with answers and explanations.
Insulin is packed in β-cell secretory granules as hexamers. Which metal ion is needed for this crystalline storage?
Two Zn²⁺ ions coordinate histidine residues to form insulin hexamers, allowing dense storage; the hexamers dissociate after secretion.
Gram for gram, complete oxidation of which fuel releases the most energy?
Fat yields about 9 kcal/g because its carbons are highly reduced; carbohydrates and protein give about 4 kcal/g.
Inulin, used to measure glomerular filtration rate, differs from starch and cellulose in being a polymer of:
Inulin is a fructosan. Amylose, dextrin and cellulose are all polymers of glucose.
Glycogen breakdown in skeletal muscle cannot release free glucose into the blood because muscle lacks:
Only liver, kidney and intestine have glucose-6-phosphatase. Muscle uses its glucose-6-phosphate for its own glycolysis.
Which enzyme catalyses an irreversible step of glycolysis itself?
Pyruvate kinase converts phosphoenolpyruvate to pyruvate, generating ATP. Pyruvate carboxylase and glucose-6-phosphatase belong to gluconeogenesis.
A person regularly eats more carbohydrate than needed for energy and glycogen stores are full. The surplus glucose is mainly:
Once glycogen stores are saturated, excess glucose is oxidised to acetyl-CoA and used for lipogenesis. Essential amino acids cannot be synthesised, and normal glucose levels do not exceed the renal threshold.
In amylose, the unbranched component of starch, glucose units are joined by:
Amylose is a linear chain of α-1,4-linked glucose. α-1,6 bonds form branch points in amylopectin and glycogen; β-1,4 links occur in cellulose.
Which disaccharide is synthesised by the mammary gland and occurs naturally only in milk?
Lactose (galactose β-1,4 glucose) is made by lactose synthase in the lactating breast. Maltose comes from starch digestion, sucrose from plants, and trehalose from fungi and insects.
In aqueous solution, D-glucose exists predominantly as:
Over 99% of glucose in solution is cyclic glucopyranose (α and β anomers). The open-chain aldehyde is a tiny fraction, and the furanose form is minor for glucose.
In a red blood cell, which lacks mitochondria, what is the net ATP yield from converting one glucose to lactate?
Anaerobic glycolysis produces 4 ATP but uses 2, giving a net 2 ATP per glucose. About 30 ATP requires complete oxidation through mitochondria.
Glucose and galactose differ only in the configuration at carbon 4. Such a pair of sugars is called:
Epimers differ at one chiral carbon other than the anomeric carbon. Anomers differ only at the anomeric carbon (α/β); enantiomers are mirror images (D/L).
Honey is rich in invert sugar, a mixture of glucose and fructose produced by hydrolysis of:
Bee invertase splits sucrose into glucose and fructose. Lactose gives glucose and galactose, while maltose and starch give only glucose.
Which sugar is an aldopentose found in RNA?
Ribose has five carbons and an aldehyde group. Erythrulose is a ketotetrose, fructose a ketohexose, and glyceraldehyde an aldotriose.
Glycogen is best classified as a:
Glycogen contains only glucose, in α-1,4 chains with α-1,6 branches every 8–12 residues. Linear glucose polymers are amylose and cellulose; GAGs contain amino sugars and uronic acids.
After digestion of dietary starch and disaccharides, carbohydrate is used by body cells mainly in the form of:
Digestion yields monosaccharides; fructose and galactose are largely converted to glucose in the liver. Disaccharides are not absorbed intact and must be hydrolysed at the brush border.
Which sugar gives a negative Benedict's test because it has no free anomeric carbon?
In sucrose, the glycosidic bond joins the anomeric carbons of glucose and fructose, so it cannot reduce Cu2+. Lactose and maltose keep one free anomeric carbon and are reducing.
The α cells of the pancreatic islets secrete:
α cells secrete glucagon, β cells insulin, δ cells somatostatin and PP cells pancreatic polypeptide.
Under current ADA criteria, which fasting plasma glucose range is considered normal in an adult?
Normal fasting glucose is below 100 mg/dL (5.6 mmol/L). 100–125 mg/dL is impaired fasting glucose, ≥126 mg/dL on repeat testing indicates diabetes, and values below 70 suggest hypoglycaemia.
Humans cannot digest cellulose because its glucose units are joined by:
Human enzymes hydrolyse α-glycosidic bonds only; cellulose's β-1,4 bonds need cellulase from gut microbes. α-1,4 and α-1,6 bonds occur in starch and glycogen; α1–β2 in sucrose.
Which Krebs cycle intermediate is regenerated at the end of each turn to combine with a new acetyl-CoA?
Malate dehydrogenase regenerates oxaloacetate, which citrate synthase condenses with acetyl-CoA. Succinate, α-ketoglutarate and fumarate are intermediates within the cycle.