Podcast
Questions and Answers
What causes iodine to turn from brown to blue-black when mixed with starch?
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?
What is the primary function of cellulose in plant cell walls?
Which enzyme breaks the α(1->4) glycosidic bonds in glycogen during hydrolysis?
Which enzyme breaks the α(1->4) glycosidic bonds in glycogen during hydrolysis?
How do cellulose chains establish strong cross-linking between each other?
How do cellulose chains establish strong cross-linking between each other?
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What is the role of glycogenin in glycogen structure?
What is the role of glycogenin in glycogen structure?
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How do microfibrils contribute to plant cell walls?
How do microfibrils contribute to plant cell walls?
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What type of bonds break upon hydrolysis of starch by amylase?
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?
What is the main respiratory substrate obtained from starch breakdown?
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What characteristic of amylose makes it ideal for storage?
What characteristic of amylose makes it ideal for storage?
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Why is amylopectin considered highly branched?
Why is amylopectin considered highly branched?
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What happens when debranching enzymes break α(1->6) glycosidic bonds in amylopectin?
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?
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.
