17 Questions
What is the characteristic of the cleavage products formed when starch is attacked internally by amylases?
The OH-group in the 1-position is in α-configuration.
What type of bonds are hydrolyzed by debranching enzymes at the branch points of starch molecules?
(1→6) glycosidic bonds
What is the product formed when phosphorylases cleave (1→4) bonds phosphorolytically?
Glucose 1-phosphate
What is the role of amylases in the degradation of transitory starch in chloroplasts?
Amylases cleave large starch molecules into smaller fragments.
Why are phosphorylases alone not capable of degrading large branched starch molecules?
Phosphorylases require smaller starch fragments produced by amylases to act on.
Describe the role of phosphoglucan water dikinase in the biosynthesis of starch.
Phosphoglucan water dikinase catalyzes the phosphorylation of glucose residues in starch molecules using ATP phosphate, contributing to starch biosynthesis.
Explain the difference between exoamylases and endoamylases in the context of starch hydrolysis.
Exoamylases, such as -amylase, hydrolyze starch at the end of the molecules, producing maltose, while endoamylases, like -amylase, hydrolyze starch in the interior of the glucan chain.
What is the function of limit dextrinase or pullulanase in starch degradation?
Limit dextrinase, also known as pullulanase, breaks down starch molecules by cleaving -glucosidic linkages, releasing linear glucan chains for further degradation.
How do exoamylases like -amylase contribute to the hydrolysis of starch?
Exoamylases, or -amylase, hydrolyze starch molecules at the ends, releasing the disaccharide maltose as the main reaction product.
What are the main steps involved in the transitory starch degradation process in plants?
Transitory starch degradation involves multiple steps, including phosphorylation (e.g., by phosphoglucan water dikinase), hydrolysis (by amylases), and phosphorolysis (by starch phosphorylase) to break down starch molecules into simple sugars.
How do debranching enzymes facilitate the degradation of starch molecules?
Debranching enzymes, such as limit dextrinase (pullulanase), help in starch degradation by cleaving -glucosidic linkages, releasing linear glucan chains and making them accessible for further hydrolysis or phosphorolysis.
What is the specific linkage that Debranching enzyme L hydrolyzes in amylopectin or branched dextrins?
a(1-6) glycosidic linkages
In which organelle does the synthesis of sucrose take place, and what is the role of uridine diphosphate (UDP) in this process?
Cytosol of the mesophyll cell; UDP activates glucose residue
What is the significance of phosphorylases in the degradation of transitory starch in chloroplasts?
They degrade small oligosaccharides, products of hydrolytic starch degradation, into glucose-1-phosphate
What is the difference between amylose and amylopectin in terms of their structure?
Amylose consists of unbranched chains of about 1,000 glucose molecules, whereas amylopectin has a larger molecule with branching points at every 20 to 25 glucose residues
What is the role of sucrose synthase in the degradation of sucrose for the synthesis of starch in storage tissues?
It breaks down sucrose to synthesize starch in amyloplasts of storage tissue such as potato tubers
What is the significance of the iodine test in the identification of starch molecules?
It forms blue- to violet-colored complexes with starch molecules, specifically amylose and amylopectin
Test your knowledge on enzymatic hydrolysis pathways involving cleavage products, debranching enzymes, phosphorylases, and formation of glucose 1-phosphate. Identify the enzymes and substrates involved in various reactions.
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