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Questions and Answers
What is the primary structural role of cellulose in plants?
What is the primary structural role of cellulose in plants?
What is the main difference between cellulose and chitin at the molecular level?
What is the main difference between cellulose and chitin at the molecular level?
Which of these organisms primarily uses chitin for structural support?
Which of these organisms primarily uses chitin for structural support?
Which statement accurately describes cellulose?
Which statement accurately describes cellulose?
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What proportion of chitin is estimated to be produced annually in the biosphere?
What proportion of chitin is estimated to be produced annually in the biosphere?
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What distinguishes homopolysaccharides from heteropolysaccharides?
What distinguishes homopolysaccharides from heteropolysaccharides?
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Which of the following is a primary function of storage polysaccharides?
Which of the following is a primary function of storage polysaccharides?
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What is a characteristic of polysaccharides related to their synthesis?
What is a characteristic of polysaccharides related to their synthesis?
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Which statement accurately describes the role of heteropolysaccharides in animal tissues?
Which statement accurately describes the role of heteropolysaccharides in animal tissues?
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Which of the following polysaccharides serves a structural role in plant cell walls?
Which of the following polysaccharides serves a structural role in plant cell walls?
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What type of bonds often link monosaccharide units in polysaccharides?
What type of bonds often link monosaccharide units in polysaccharides?
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Why do starch and glycogen molecules attract water?
Why do starch and glycogen molecules attract water?
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Which type of polysaccharide provides extracellular support in bacteria?
Which type of polysaccharide provides extracellular support in bacteria?
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What type of glucose polymer is primarily found in starch?
What type of glucose polymer is primarily found in starch?
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What is the main distinction between glycogen and starch?
What is the main distinction between glycogen and starch?
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Which linkage types are involved in forming amylopectin?
Which linkage types are involved in forming amylopectin?
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Where is glycogen predominantly stored in mammals?
Where is glycogen predominantly stored in mammals?
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What are dextrans primarily composed of?
What are dextrans primarily composed of?
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What is a notable use of synthetic dextrans?
What is a notable use of synthetic dextrans?
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What kind of environment allows dextrans to form dental plaque?
What kind of environment allows dextrans to form dental plaque?
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How often do branch points occur in amylopectin molecules?
How often do branch points occur in amylopectin molecules?
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Study Notes
Polysaccharides
- Polysaccharides are polymers of medium to high molecular weight (greater than 20,000).
- Most carbohydrates in nature are polysaccharides.
- Polysaccharides differ in the repeating monosaccharide units, chain length, bond types, and branching degree.
- Glycans are another name for polysaccharides.
Types of Polysaccharides
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Homopolysaccharides: Contain a single monomeric species.
- Some serve as storage forms of monosaccharides.
- Starch: Found in plant cells.
- Glycogen: Found in animal cells.
- Others are structural elements in plant cell walls and animal exoskeletons.
- Cellulose: Forms plant cell walls.
- Chitin: Forms animal exoskeletons.
- Some serve as storage forms of monosaccharides.
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Heteropolysaccharides: Contain two or more different monomeric species.
- Provide extracellular support for organisms in all kingdoms.
Homopolysaccharides: Details
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Starch: Made of amylose and amylopectin.
- Amylose: Long, unbranched chains of D-glucose residues linked by α(1→4) linkages.
- Amylopectin: High molecular weight (up to 200 million Daltons) and highly branched.
- Branch points occur at every 24-30 residues and are linked by α(1→6) linkages.
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Glycogen:
- A polymer of α(1→4) linked glucose subunits.
- More extensively branched than starch (every 8-12 residues).
- More compact than starch.
- Found in the liver (7% of wet weight) and skeletal muscle.
- Occurs intracellularly in large granules (clusters of smaller, highly branched granules with average molecular weights in millions).
Heteropolysaccharides: Details
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Extracellular support: The rigid layer of the bacterial cell envelope is peptidoglycan, built from two alternating monosaccharides.
- In animal tissues, heteropolysaccharides occupy the extracellular space, forming a matrix that holds cells together.
- They contribute to the protection, shape, and support of cells, tissues, and organs.
Varying Lengths
- Polysaccharides do not have specific defining lengths or molecular weights.
- This is due to the mechanism of assembly, which is intrinsic to enzymes catalyzing the polymerization of monomer units.
- There is no template, and no specific stopping point in the synthesis process, leading to varied product lengths.
Storage Polysaccharides
- Starch and glycogen are the most important storage polysaccharides.
- They occur intracellularly as large clusters or granules.
- Starch and glycogen molecules are heavily hydrated due to exposed hydroxyl groups for hydrogen bonding with water.
- Plant cells form starch, particularly abundant in tubers (like potatoes) and seeds
Dextrans
- Bacterial and yeast polysaccharides made up of α(1→6)-linked poly-D-glucose.
- Some have α(1→3), α(1→2), or α(1→4) branches.
- Important component of dental plaque, allowing bacteria to adhere to teeth.
- Used in commercial products like Sephadex for protein fractionation via size-exclusion chromatography.
- Dextrans in these products are chemically cross-linked to form insoluble materials of various sizes.
Structural Polysaccharides
- Cellulose: A linear, unbranched homopolysaccharide composed of 10,000-15,000 D-glucose units linked by β(1→4) glycosidic bonds. This configuration leads to different macroscopic structures and physical properties compared to starch.
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Chitin: Another linear homopolysaccharide composed of N-acetylglucosamine residues linked by β(1→4) linkages. The only difference from cellulose is the replacement of the hydroxyl group at carbon 2 with an acetylated amino group.
- Forms extended fibers, similar to cellulose, not digestible by vertebrates.
- The major component in the hard exoskeletons of arthropods (insects, lobsters, etc.). Estimated at 1 billion tons produced annually in the biosphere.
Glycosaminoglycans
- Components of the extracellular matrix (ECM) in animals, not found in plants.
- Linear polymers composed of repeating disaccharide units.
- One of the two monosaccharides is either N-acetylglucosamine or N-acetylgalactosamine; the other is usually D-glucuronic acid or L-iduronic acid.
Examples of Heteropolysaccharides
- Hyaluronan: Forms highly viscous solutions that act as lubricants in synovial fluid of joints and the vitreous humor of the eye.
- Chondroitin sulfate: Provides tensile strength to cartilage, tendons, and ligaments.
- Keratan sulfates: Present in cornea, cartilage, bone, and other horny structures (hair, nails, claws).
- Heparan sulfate: A therapeutic agent used to inhibit coagulation.
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Description
Explore the world of polysaccharides with this quiz, covering their definition, types, and specific details about homopolysaccharides like starch and glycogen. Understand the differences between homopolysaccharides and heteropolysaccharides, as well as their roles in nature. Test your knowledge and learn more about these essential carbohydrates.
