30 Questions
What is the most abundant monosaccharide in nature?
D-glucose
What type of carbohydrate is formed by the condensation of 3 to 10 monosaccharides?
Oligosaccharide
What is the bond formed between two monosaccharide units in a disaccharide?
Glycosidic bond
What determines whether a molecule is D- or L-?
The position of the -OH on the bottom-most chiral center
What type of carbohydrate is cellulose, a component of plant cell walls?
Polysaccharide
What is the relationship between D- and L- isomerism and optical rotation?
D- and L- isomerism have no relation to optical rotation
What is the characteristic of most natural sugars and amino acids?
Most natural sugars are D- and most natural amino acids are L- isomers
What happens when a beam of plane-polarized light is passed through a solution of an optical isomer?
It rotates either to the right, dextrorotatory (+), or to the left, levorotatory (–)
What is the term for the ring structure of an aldose?
Hemiacetal
What is the characteristic of epimers of glucose?
They are differing in configuration of the -OH and -H on carbon atoms 2, 3, and 4 of glucose
What is the basis for a simple chemical test for glucose in urine in poorly controlled diabetes mellitus?
Reduction of an alkaline copper solution
What is the term for the D- glucose solution that is also known as dextrose?
D- (+) glucose
What is the term for the process of forming a bond between the hydroxyl group of the anomeric carbon of a monosaccharide and a second compound?
Condensation
Which of the following is an example of a deoxy sugar?
Deoxyribose
What is the term for sugars composed of two monosaccharide residues linked by a glycoside bond?
Disaccharides
What is the function of D-glucuronate?
Glucuronide formation and in glycosaminoglycans
What is the term for the bond formed between an amine and a monosaccharide?
N-glycosidic bond
Which of the following antibiotics contains an amino sugar?
Erythromycin
Why is it beneficial to store low molecular weight metabolites in polymeric form?
To avoid high osmolarity that would result from storing them as individual monomers
What is the main function of the carbohydrate layer (glycocalyx) on the surface of eukaryotic cells?
To serve as an information-rich surface that the cell shows to its surroundings
What is the primary component of dietary fiber?
Cellulose
Why do mammals lack the ability to digest cellulose?
Because they lack the enzyme that hydrolyzes the β1 → 4 bonds
What is the purpose of determining the glycemic index of a starchy food?
To compare its digestibility to that of glucose or a reference food
What is the significance of inulin in the human body?
It has no nutritional value because it is not hydrolyzed by intestinal enzymes
What is the primary function of proteoglycans in the body?
To hold large quantities of water and cushion or lubricate other structures
What is the term for the carbohydrate-rich outer layer of the plasma membrane?
Glycocalyx
What is the primary function of glycosaminoglycans in the body?
To hold large quantities of water and cushion or lubricate other structures
What is the term for a protein that is covalently linked to a carbohydrate molecule?
Glycoprotein
What is the function of glycophorin in human erythrocytes?
To increase the flip-flop frequency of membrane phospholipids
What is the term for a carbohydrate molecule that is covalently linked to a lipid molecule?
Glycolipid
Study Notes
Classification of Carbohydrates
- Monosaccharides can be classified based on the number of carbon atoms (3-7) and whether they have an aldehyde or ketone group.
- The most abundant monosaccharide in nature is the six-carbon sugar D-glucose.
Disaccharides
- Disaccharides are sugars composed of two monosaccharide residues linked by a glycosidic bond.
- Examples of disaccharides include lactose (glucose + galactose), maltose (glucose + glucose), isomaltose (glucose + glucose), sucrose (glucose + fructose), and trehalose (glucose + glucose).
Oligosaccharides
- Oligosaccharides are condensation products of 3 to 10 monosaccharides.
- Most oligosaccharides are not digested by human enzymes and form the main component of dietary fiber.
Polysaccharides
- Polysaccharides are condensation products of more than 10 monosaccharide units.
- Examples of polysaccharides include glycogen (branched glucose polymers), starches, dextrins, cellulose (a glucose polymer), and inulin (a fructose polymer).
Representation of the Structure of D-Glucose
- D-glucose can be represented in three forms: Fischer projection (straight-chain form), Haworth projection, and chair form.
Isomerism of Sugars
- Isomerism occurs when two molecules have the same chemical formula but different structures.
- There are several types of isomerism, including D- and L- isomerism, optical isomerism, pyranose and furanose ring structures, alpha- and beta-anomers, epimers, and aldose-ketose isomerism.
Physiological Importance of Monosaccharides
- Derivatives of trioses, tetroses, and pentoses are formed as metabolic intermediates in glycolysis and the pentose phosphate pathway.
- Carboxylic acid derivatives of glucose, such as D-glucuronate, L-iduronate, and L-gulonate, are important in various biological processes.
Glycosides
- Glycosides are formed by condensation between the hydroxyl group of the anomeric carbon of a monosaccharide and a second compound.
- Examples of glycosides include cardiac glycosides, such as digoxin and ouabain, and antibiotics, such as streptomycin.
Deoxy Sugars
- Deoxy sugars are those in which one hydroxyl group has been replaced by hydrogen.
- An example of a deoxy sugar is deoxyribose in DNA.
Amino Sugars (Hexosamines)
- Amino sugars, such as D-glucosamine and D-galactosamine, are components of glycoproteins, gangliosides, and glycosaminoglycans.
Glycoconjugates: Proteoglycans, Glycoproteins, and Glycolipids
- Glycoconjugates are molecules composed of a carbohydrate chain attached to a protein or lipid.
- The carbohydrate chain is central to cell-cell recognition and adhesion, cell migration, blood clotting, and the immune response.
Glycosaminoglycans (GAGs)
- Glycosaminoglycans are complex carbohydrates containing amino sugars and uronic acids.
- They may be attached to a protein molecule to form a proteoglycan.
- Proteoglycans hold large quantities of water and occupy space, cushioning or lubricating other structures.
Learn about the classification of carbohydrates based on carbon number and functional groups, including monosaccharides and disaccharides.
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