MODULE 9: Chapter 9.2 Flashcards
What is glycolysis?
The splitting of one molecule of glucose into two molecules of pyruvate.
What is the molecular formula of glucose?
C6H12O6
What type of sugar is glucose?
A polyhydroxyaldehyde.
What type of sugar is fructose?
A polyhydroxyketone.
What are the two forms of monosaccharides represented in Figure 9.5?
Fischer projections and Haworth perspectives.
What structural forms do monosaccharides exist in?
An equilibrium between linear and cyclic forms.
What conformations can glucose be represented by?
Chair or boat conformations.
What is the primary source of glucose for non-photosynthetic organisms?
Their environment.
What is the primary source of glucose for photosynthetic organisms?
Carbon fixation.
What is the sensation of sweetness attributed to?
Ligand activation of G protein–coupled receptor signaling in taste cells.
How much sweeter is fructose compared to glucose?
2.3 times sweeter.
What is sucralose and how sweet is it compared to sucrose?
A chlorinated sucrose molecule that is 600 times sweeter than sucrose.
What is aspartame?
A dipeptide derivative of aspartate and phenylalanine.
What distinguishes aldose sugars from ketose sugars?
Aldoses have the carbonyl carbon at the end of the carbon chain, while ketoses have it in the second position.
What is the smallest monosaccharide?
Glyceraldehyde.
What is a chiral center?
A carbon atom bonded to four different chemical groups.
What are enantiomers?
Mirror-image isomers that exist in nature.
What defines the D and L isomers of monosaccharides?
The position of the hydroxyl group in the Fischer projection.
What are epimers?
Monosaccharides that differ in the position of the hydroxyl group around one carbon atom.
What is the ratio of α-D-glucose to β-D-glucose in aqueous solution?
About 40:60.
What is the anomeric carbon?
The C-1 carbon of cyclic D-glucose.
What are the cyclic forms of glucose called?
α-D-glucopyranose and β-D-glucopyranose.
What are furanoses?
Cyclic structures of ketoses like fructose that contain five carbons.
What is the normal concentration of glucose in human blood?
~3.5 to 5.5 mM (60–100 mg/dL).
What are reducing sugars?
Sugars that can reduce Cu2+, such as glucose, galactose, and lactose.
What is Benedict’s test used for?
To measure the amount of glucose in a solution based on Cu2+ reduction.
What is a more accurate method for measuring blood glucose levels than Benedict’s test?
The glucose oxidase–peroxidase enzymatic reaction.
What happens to the color of solutions in Benedict’s test when reducing sugars are present?
The color changes from blue to red.
What is the implication of glucose concentrations above 7.2 mM in blood?
It is considered a diagnostic indicator of diabetes.
Fill in the blank: Monosaccharides can be categorized by the number of carbons, such as ______ for three carbons.
triose
Fill in the blank: When the carbonyl carbon is in the second position, the sugar is classified as a ______.
ketose
What is the qualitative color change of Cu2⁺ reduction by glucose?
Not very accurate and not sensitive enough to detect small changes in blood or urine glucose levels.
Which other reducing sugars can reduce Cu2⁺ besides glucose?
Galactose and lactose.
How can ketose sugars such as fructose be oxidized?
By conversion of the ketone in alkaline Benedict’s solution to an aldehyde through an enediol intermediate.
What enzyme is used in the improved blood glucose test?
Glucose oxidase.
What are the products of the reaction catalyzed by glucose oxidase?
Gluconate and hydrogen peroxide (H2O2).
What role does peroxidase play in the blood glucose test?
Catalyzes a redox reaction that changes a colorless reduced dye into a colored oxidized product.
What is the significance of the home-based glucose-monitoring device?
It allows diabetic patients to conveniently monitor their blood glucose levels.
What are disaccharides formed from?
A condensation reaction between two monosaccharides.
What type of bond connects monosaccharides in disaccharides?
O-glycosidic bond.
How is maltose represented in shorthand nomenclature?
Glc(α1→4)Glc.
What is the structure of lactose?
Gal(β1→4)Glc.
What is the structure of sucrose?
Glc(α1↔β2)Fru.
What is trehalose made of?
Glc(α1↔α1)Glc.
Why is lactose considered a reducing sugar?
It contains an anomeric carbon that can form an aldehyde group in the open-chain conformation.
What distinguishes nonreducing sugars like sucrose and trehalose?
Both C-1 anomeric carbons are covalently linked by the glycosidic bond.
What is the role of amylase in relation to maltose?
It hydrolyzes starch to release the two glucose units.
What is the biochemical explanation for aspartame’s sweetness compared to galactose?
Higher binding affinity and/or slower off-rate for gustatory receptors.
What is the millimolar equivalent of 200 mg/dL serum glucose?
Approximately 11.1 mM.
What is an aldose?
A monosaccharide that contains an aldehyde functional group.
What is a ketose?
A monosaccharide that contains a ketone functional group.
What is a chiral center?
The atom within a molecule that makes that molecule chiral.
What is an epimer?
One of a pair of monosaccharides that differ only in the position of a hydroxyl group around a single carbon atom.
What is a hemiacetal?
A molecule formed by the reaction of an alcohol and an aldehyde-containing compound.
What is a hemiketal?
A molecule formed by the reaction of an alcohol and a ketone-containing compound.
What is an anomeric carbon?
The carbon molecule in a cyclic monosaccharide derived from the carbonyl carbon of the linear form.
What is an anomer?
One of two stereoisomers that differ in configuration at the anomeric carbon.
What are pyranose and furanose?
Pyranose: cyclic hexose sugars; Furanose: cyclic sugar formed from a ketohexose or an aldopentose.
What is Benedict’s test used for?
Detecting the presence of reducing sugars in solution.
What is a reducing sugar?
A carbohydrate that reduces an oxidizing agent, such as cupric ion (Cu2⁺).
What is a nonreducing sugar?
A carbohydrate that is unable to reduce an oxidizing agent.
Fill in the blank: The covalent bond that links two monosaccharides together through oxygen is called an _______.
O-glycosidic bond.
