Biomolecules: Cellulose, Chitin, and Starch
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Questions and Answers

What is the primary structural component of cell walls that accounts for over half of the carbon in the biosphere?

  • Amylopectin
  • Chitin
  • Starch
  • Cellulose (correct)

    • Which type of glycosidic bond links the glucose residues in cellulose?

  • α(1→6)
  • β(1→4) (correct)
  • α(1→4)
  • β(1→6)

    • How does the structural arrangement of cellulose fibers contribute to their strength?

  • They are branched and irregularly shaped.
  • They are tightly packed with interchain hydrogen bonds. (correct)
  • They are made from a single unbranched chain.
  • They consist of randomized chains without hydrogen bonding.

    • Which biomolecule is second most abundant after cellulose and serves as a structural component in the exoskeletons of invertebrates?

    <p>Chitin</p> Signup and view all the answers

    What is the primary function of starch in plants?

    <p>Energy reserve</p> Signup and view all the answers

    Which statement accurately describes the arrangement of glucose units in cellulose?

    <p>Each unit is rotated 180 degrees with respect to neighboring units.</p> Signup and view all the answers

    What complicates the conversion of cellulose to biofuels?

    <p>The presence of lignin and other polysaccharides.</p> Signup and view all the answers

    What type of glycosidic bond links the N-acetyl-d-glucosamine residues in chitin?

    <p>β(1→4)</p> Signup and view all the answers

    How do cellulose and chitin compare in their structural properties according to X-ray analysis?

    <p>They have similar structures.</p> Signup and view all the answers

    What is the role of cellulases in the digestive tract of herbivores and termites?

    <p>To degrade cellulose.</p> Signup and view all the answers

    What type of glycosidic bond is present in lactose?

    <p>O-β-D-galactopyranosyl-(1→4)-D-glucopyranose</p> Signup and view all the answers

    Which of the following statements accurately describes cellulose?

    <p>Cellulose has a rigid structure, contributing to plant cell wall stability.</p> Signup and view all the answers

    What is a characteristic of aspartame as a sweetener?

    <p>It breaks down into aspartate, phenylalanine, and methanol upon ingestion.</p> Signup and view all the answers

    Which feature distinguishes sucrose from reducing sugars?

    <p>Both anomeric carbons of glucose and fructose participate in glycosidic bonds within sucrose.</p> Signup and view all the answers

    Which polysaccharide is primarily found in the exoskeletons of arthropods?

    <p>Chitin</p> Signup and view all the answers

    What is the main health risk associated with saccharin?

    <p>It is linked to cancer development in laboratory animals.</p> Signup and view all the answers

    Which type of polysaccharide consists of only one type of monosaccharide?

    <p>Homopolysaccharides</p> Signup and view all the answers

    What is one property of cellulose that contributes to its function in plants?

    <p>It provides structural integrity due to its rigid structure.</p> Signup and view all the answers

    Which of the following describes a characteristic of artificial sweeteners like aspartame?

    <p>They are generally safe for consumption in normal amounts.</p> Signup and view all the answers

    How are exo-glycosidases and endoglycosidases related to polysaccharides?

    <p>They hydrolyze monosaccharide units from polysaccharides.</p> Signup and view all the answers

    What type of glycosidic bond primarily links glucose residues in amylopectin?

    <p>α(1→4)</p> Signup and view all the answers

    Which enzyme initiates starch digestion in the mouth?

    <p>Amylase</p> Signup and view all the answers

    In what form does glycogen primarily exist within animal cells?

    <p>As cytoplasmic granules</p> Signup and view all the answers

    What is the average branching point interval for amylopectin's α(1→6) linkages?

    <p>Every 24 to 30 glucose residues</p> Signup and view all the answers

    What structural feature of glycogen allows for rapid mobilization of glucose?

    <p>Highly branched structure</p> Signup and view all the answers

    How does the structure of cellulose differ from that of amylose?

    <p>It has β-glycosidic linkages</p> Signup and view all the answers

    Which enzyme is responsible for cleaving α(1→4) bonds in glycogen degradation?

    <p>Glycogen phosphorylase</p> Signup and view all the answers

    Which statement correctly describes the reducing ends of starch?

    <p>Starch has one reducing end without a glycosidic bond</p> Signup and view all the answers

    What role does α-glucosidase play in starch digestion?

    <p>Removes one glucose residue at a time</p> Signup and view all the answers

    What distinguishes glycogen's branching from amylopectin's?

    <p>Glycogen has more frequent branches</p> Signup and view all the answers

    Study Notes

    Cellulose

    • Primary structural component of plant cell walls.
    • Accounts for over half of the carbon in the biosphere.
    • Linear polymer of up to 15,000 D-glucose residues linked by β(1→4) glycosidic bonds.
    • Fibers consist of ~40 parallel, extended glycan chains.
    • Tightly packed, fully extended conformation due to β(1→4) linkages and interchain hydrogen bonds.
    • Exceptional strength and water insolubility despite hydrophilicity.
    • Linked with other polysaccharides and lignin, hindering biofuel conversion.
    • Hydrolyzed by cellulases in herbivores and termites.

    Chitin

    • Structural component of invertebrate exoskeletons and fungal cell walls.
    • Second most abundant biomolecule after cellulose.
    • Homopolymer of β(1→4) linked N-acetyl-d-glucosamine residues.
    • Differs from cellulose by an acetamido group replacing each C2-OH group.
    • Similar structure to cellulose based on X-ray analysis.

    Starch

    • Plant's principal energy reserve.
    • Mixture of α-amylose and amylopectin.
    • Deposited in chloroplasts as insoluble granules.

    α-Amylose

    • Linear polymer of several thousand glucose residues linked by α(1→4) bonds.
    • Irregularly aggregating helical coiled (left-handed helix) conformation due to α-glycosidic bonds.

    Amylopectin

    • Primarily α(1→4) linked glucose residues with α(1→6) branch points every 24-30 residues.
    • Contains up to 106 glucose residues.
    • Large molecules.

    Starch Digestion

    • Reducing sugar with one reducing end.
    • Digestion begins in the mouth with salivary amylase.
    • Pancreatic amylase degrades starch to oligosaccharides in the small intestine.
    • α-glucosidase and debranching enzyme further hydrolyze to monosaccharides for absorption.

    Glycogen

    • Animal storage polysaccharide.
    • Most prevalent in skeletal muscle and liver as cytoplasmic granules.
    • Structure resembles amylopectin but is more branched (every 8-14 glucose residues).
    • Degraded by glycogen phosphorylase (cleaves α(1→4) bonds).
    • Highly branched structure allows rapid glucose mobilization.
    • α(1→6) branches cleaved by glycogen debranching enzyme.

    Polysaccharides (Glycans)

    • Monosaccharides linked by glycosidic bonds.
    • Homopolysaccharides: one type of monosaccharide.
    • Heteropolysaccharides: more than one type of monosaccharide.
    • Form branched and linear polymers.
    • Hydrolyzed by exo- and endoglycosidases.

    Lactose

    • Reducing disaccharide found naturally only in milk.
    • Composed of galactose and glucose (O-β-D-galactopyranosyl-(1→4)-D-glucopyranose).
    • Free anomeric carbon on glucose.

    Sucrose

    • Most abundant disaccharide.
    • Major carbohydrate transport form in plants.
    • Composed of glucose and fructose (O-α-D-glucopyranosyl-(1→2)-β-D-fructofuranoside).
    • Non-reducing sugar due to participation of both anomeric carbons in glycosidic bond.

    Artificial Sweeteners

    • Added to foods and beverages for sweetness without calories.
    • Examples: saccharin, aspartame, acesulfame.
    • Varying levels of sweetness relative to sucrose.
    • Potential health concerns and limitations (e.g., saccharin, aspartame).

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    Description

    This quiz covers the structural and functional aspects of cellulose, chitin, and starch. Explore the primary components of plant walls, invertebrate exoskeletons, and the energy reserves of plants. Test your knowledge on their compositions and significance in the biosphere.

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