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Questions and Answers
What causes iodine to turn from brown to blue-black when mixed with starch?
What is the primary function of cellulose in plant cell walls?
Which enzyme breaks the α(1->4) glycosidic bonds in glycogen during hydrolysis?
How do cellulose chains establish strong cross-linking between each other?
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What is the role of glycogenin in glycogen structure?
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How do microfibrils contribute to plant cell walls?
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What type of bonds break upon hydrolysis of starch by amylase?
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What is the main respiratory substrate obtained from starch breakdown?
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What characteristic of amylose makes it ideal for storage?
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Why is amylopectin considered highly branched?
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What happens when debranching enzymes break α(1->6) glycosidic bonds in amylopectin?
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Why does starch not affect the osmotic concentration in cells?
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Study Notes
Structure and Property of Starch
- Composed of thousands of glucose linked by α(1→4) glycosidic bonds, storing large amounts of energy
- α(1→4) glycosidic bonds can be broken by amylase, hydrolysing starch into glucose for respiration
- Amylose chains are helical in shape, with six glucose per turn, maintained by intra-chain hydrogen bonding between hydroxyl groups of glucoses
- Amylopectin are highly branched due to branch points maintained by α(1→6) glycosidic bonds, compact and ideal for storage
- Debranching enzymes break α(1→6) glycosidic bonds, converting the branched structure of amylopectin into a more linear structure, increasing the accessibility of the remaining linear chains to amylase
- -OH groups are occupied in intra-chain hydrogen bonding, making starch insoluble and osmotically inactive, thus does not affect osmotic concentration in cells
Starch Test
- In the presence of starch, iodine forms a complex with starch molecules, resulting in a color change from brown to blue-black
- Iodine molecules fit into the helical structure of starch, changing the refractive index and causing the color change
Glycogen
- Branched chain polymer of α glucose, similar to amylopectin but larger and more highly branched
- Easily hydrolysed to α glucose by debranching enzymes and glycogen phosphorylase
- Functions as energy storage in animals, with a core protein of glycogenin surrounded by branches of glucose
Cellulose
- Comprises up to 50% of plant cell walls, providing strength, rigidity, and structural support to plant cells
- Protects plant cells and cytoplasm from damage and mechanical injuries
- Despite its strength, the cellulose cell wall is fully permeable to water and solutes, allowing for the functioning of plant cells
- Structure consists of unbranched polysaccharide of β glucose linked by β(1→4) glycosidic bonds, with each chain consisting of 1000 or more β glucose residues
- Formation of β(1→4) glycosidic bonds requires the 180º rotation of alternating glucose residues, resulting in straight chains of cellulose
- Hydroxyl groups (-OH) project outwards, allowing for the formation of hydrogen bonds between adjacent chains, establishing a rigid cross-linking between the chains
- Many unbranched linear chains run parallel to each other, forming microfibrils, macrofibrils, and fibers, contributing to the tensile strength of plant cell walls
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Description
Learn about the structure and significance of amylose, a polysaccharide composed of glucose molecules linked by α(1->4) glycosidic bonds. Discover how amylose stores energy, can be broken down by amylase into glucose for respiration, and its helical shape maintained by hydrogen bonding for compact storage.
