18 Questions
Why do polysaccharides differ from each other?
In the identity of their recurring monosaccharide units
What distinguishes homopolysaccharides from heteropolysaccharides?
Whether they contain only a single monomeric species or multiple different kinds
What is the main function of homopolysaccharides like starch and glycogen?
Serve as storage forms of monosaccharides used as fuels
Where is glycogen notably abundant in the body?
In the liver
What is a key characteristic of glycogen granules found in hepatocytes?
They are clusters of smaller granules with highly branched glycogen molecules
Why is glucose not stored in its monomeric form like polysaccharides?
Monomeric glucose does not provide long-term energy storage
Which process can hydrolyze disaccharides to yield their free monosaccharide components?
Boiling with dilute acid
What type of bond joins the anomeric carbon of a sugar to a nitrogen atom in glycoproteins and nucleotides?
N-glycosyl bond
Why is lactose considered a reducing disaccharide?
It has a free anomeric carbon available for oxidation
Which disaccharide yields D-galactose and D-glucose upon hydrolysis, and is naturally found in milk?
Lactose
What characteristic makes sucrose a suitable molecule for the storage and transport of energy in plants?
Its stability towards oxidation
What distinguishes sucrose from maltose and lactose in terms of the anomeric carbons?
Both anomeric carbons in sucrose are involved in the glycosidic bond
What is the defining feature of disaccharides?
They contain a glycosidic bond
Which of the following is a hexose derivative with an amino group replacing a hydroxyl group?
Glucosamine
In the context of polysaccharides, what does a glycosidic bond connect?
Two monosaccharides
Which type of bond is readily hydrolyzed by acid but resists cleavage by base?
Glycosidic bond
What is the function of glucosamine in many structural polymers?
It maintains cell shape
Which sugar derivative contains an oxidized carbon atom resulting in a carboxyl group?
Sucrose
Study Notes
Disaccharides
- Disaccharides can be hydrolyzed to yield their free monosaccharide components by boiling with dilute acid.
- N-glycosyl bonds join the anomeric carbon of a sugar to a nitrogen atom in glycoproteins and nucleotides.
- Lactose, a disaccharide of D-galactose and D-glucose, occurs naturally in milk and is a reducing disaccharide.
- Sucrose, a disaccharide of glucose and fructose, is formed by plants but not by animals and is a nonreducing sugar.
- Trehalose, a disaccharide of D-glucose, is a nonreducing sugar and a major constituent of the circulating fluid of insects, serving as an energy-storage compound.
Polysaccharides
- Polysaccharides are polymers of medium to high molecular weight and differ from each other in the identity of their recurring monosaccharide units, chain length, bond types, and degree of branching.
- Homopolysaccharides contain only a single monomeric species, while heteropolysaccharides contain two or more different kinds.
- Homopolysaccharides serve as storage forms of monosaccharides that are used as fuels, such as starch and glycogen.
- Other homopolysaccharides, such as cellulose and chitin, serve as structural elements in plant cell walls and animal exoskeletons.
- Heteropolysaccharides provide extracellular support for organisms of all kingdoms, such as the peptidoglycan in bacterial cell envelopes.
Glycogen
- Glycogen is a homopolysaccharide of glucose, especially abundant in the liver, where it may constitute up to 7% of the wet weight.
- Glycogen is also present in skeletal muscle and is found in large granules, which are themselves clusters of smaller granules composed of single, highly branched glycogen molecules.
- Glycogen granules also contain, in tightly bound form, the enzymes responsible for the synthesis and degradation of glycogen.
Hexose Derivatives
- Organisms contain a variety of hexose derivatives, including sugar derivatives with a hydroxyl group replaced with another substituent or a carbon atom oxidized to a carboxyl group.
- Examples of hexose derivatives include glucosamine, galactosamine, and mannosamine, which are part of many structural polymers, including those of the bacterial cell wall.
Test your knowledge on the hydrolysis of disaccharides to yield free monosaccharide components, N-glycosyl bonds, and characteristics of specific disaccharides like lactose and sucrose.
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