What happens to Cu2+ in Fehling's solution with oses in alkaline solution?
Cu2+ is reduced to brick-red Cu2O.
What does reduction of an ose carbonyl group produce?
It produces a polyol by converting the aldehyde or ketone into an alcohol.
What do hydroxyl functions of oses react with to form esters?
Acids
Which enzymes phosphorylate D-glucose in the first glycolysis step?
Hexokinase or glucokinase
What is an osamine?
An ose with the C2 hydroxyl replaced by an NH2 group
What is glycation in biochemical terms?
The association of a reducing sugar with a primary amine forming an imine via Maillard reaction.
Which reaction forms an imine between a sugar and an amino acid in glycation?
The Maillard reaction.
What defines an oside in terms of hydrolysis products?
It releases one or more oses upon hydrolysis.
How is an O-glycosidic bond formed between two oses?
By condensation between their hydroxyl groups with water elimination.
What distinguishes an ose–oside bond regarding reducing functions?
It leaves one reducing function free.
What distinguishes an oside–oside bond regarding reducing functions?
It leaves no reducing function free.
What does acid hydrolysis with concentrated HCl do to osides?
It breaks glycosidic bonds and releases constituent oses.
Which methods separate and identify simple oses after hydrolysis?
Thin-layer chromatography, gas chromatography, and high-performance liquid chromatography.
What does a positive Fehling test indicate about an ose–oside linkage?
It indicates a free reducing function is present.
What does Haworth methylation reveal about glycosidic bonding positions?
Non-methylated hydroxyl groups identify glycosidic bonding positions.
What specificity does an osidase enzyme have?
It hydrolyzes glycosidic bonds according to the anomeric conformation and hemiacetal function participation.
What is the chemical name of sucrose?
α-D-glucopyranosyl (1-2) β-D-fructofuranoside.
What type of bond does sucrose contain?
An oside–oside bond.
Is sucrose a reducing sugar?
No, it is non-reducing.
Which enzymes hydrolyze sucrose?
α-glucosidase and β-fructosidase.
What is the chemical name of maltose?
α-D-glucopyranosyl (1-4) D-glucopyranose.
Is maltose a reducing sugar?
Yes, it is reducing.
Which enzyme hydrolyzes maltose?
α-glucosidase.
What is the chemical name of lactose?
β-D-galactopyranosyl (1-4) D-glucopyranose.
What is a polyoside composed of exclusively?
Ose units only.
What differentiates homopolyosides from heteropolyosides?
Homopolyosides contain one type of ose; heteropolyosides contain several types.
What are the two main components of starch and their proportions?
20–30% amylose and 70–80% amylopectin.
What type of bonds branch amylopectin and how often?
α(1-6) bonds every 25–30 glucose units.
Which enzymes cleave starch α(1-4) bonds during digestion?
Salivary and pancreatic α-amylase.
How does glycogen structure compare to amylopectin?
It is more highly branched but analogous in structure.
When is glycogenesis activated in the body?
When blood glucose is high.
What two parts compose a heteroside molecule?
A carbohydrate part called glycone and a non-carbohydrate part called aglycone.
What does an N-glycosidic bond connect in a molecule?
The hemiacetal function of an ose to a primary amine function of a non-carbohydrate molecule.
Where does N-glycosylation occur during protein maturation?
At the endoplasmic-reticulum membrane.
Which amino acid cannot be X in the Asn–X–Ser/Thr motif for N-glycosylation?
Proline.
Where does O-glycosylation mainly occur in the cell?
In the Golgi apparatus.
What is the function of glycosylphosphatidylinositol in membranes?
To anchor proteins lacking a hydrophobic domain in the membrane.
What is Fehling's solution used to assay?
Reducing sugars.
What modification forms N-acetyl-osamines from osamines?
Acetylation of the NH2 group
What does glycation of hemoglobin produce?
HbA1c.
What clinical use does HbA1c have?
To distinguish healthy and diabetic conditions.
What suffix does a residue with an internal hemiacetal glycosidic bond take?
The suffix -osyl.
What suffix does a terminal residue with a hemiacetal glycosidic bond take?
The suffix -oside.
What suffix does a residue with a free hemiacetal function take?
The suffix -ose.
How does thin-layer chromatography separate molecules?
By their different affinities for stationary and mobile phases.
What is the stationary phase in thin-layer chromatography?
Silica gel, which is polar.
What is the mobile phase in thin-layer chromatography?
An organic solvent, which is nonpolar.
What is the role of starch in plants?
It serves as the carbohydrate energy reserve.
How is adenine linked to β-D-ribofuranose in ATP?
By an N-glycosidic bond.
What roles do proteoglycans play in cells?
Cell signaling, cell–cell adhesion, growth-factor presentation, extracellular-matrix organization, and cell–matrix adhesion.
Test your knowledge with 25 questions on Carbohydrates: Oses and Osides.
1. What occurs when the free pseudoaldehydic or pseudoketonic function of an ose reacts with Fehling’s solution in alkaline conditions?
2. What product results when an ose carbonyl group undergoes chemical reduction?
Review the complete course in the study sheet for Carbohydrates: Oses and Osides.
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