Starch Isolation and Hydrolysis Overview

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Questions and Answers

What color change is expected when iodine is added to the starch solution?

Yellow

Blue-black (correct)

Red

Colorless

What role does NaCl play in the iodine test with glycogen?

It dilutes the sample

It breaks down the glycogen

It enhances color reaction (correct)

It neutralizes the iodine

Which of the following is a feature of salivary amylase in starch hydrolysis?

It requires high temperatures to function

It chemically alters starch structure completely

It is a catalyst that slows down reactions

It breaks starch into maltose and dextrin (correct)

What happens when starch is mixed with 10% NaOH in Tube 2B?

The blue-black color disappears Signup and view all the answers

Which result should be observed in test tube 1 that contains only water during the iodine test?

Clear solution Signup and view all the answers

What is the main mechanism through which salivary amylase acts on starch?

Hydrolysis of glycosidic bonds Signup and view all the answers

How does the presence of amylose versus amylopectin influence iodine's color reaction?

Amylopectin produces a stronger blue-black coloration Signup and view all the answers

What occurs during the hydrolysis of starch when the iodine reaction indicates a decrease in starch presence?

Starch is converted to glucose Signup and view all the answers

What is the color of the complex formed when starch reacts with iodine?

Intense blue Signup and view all the answers

Which polysaccharide gives a pale reddish brown color when treated with iodine?

Glycogen Signup and view all the answers

What effect does excessive heating have on the amylose-iodine complex?

Displaces iodine from the helical structure Signup and view all the answers

Which solution pH is necessary for optimal interaction between starch and iodine?

Neutral to slightly acidic Signup and view all the answers

What is the result of adding sodium thiosulfate to the iodine-starch complex?

Causes disappearance of the blue-black color Signup and view all the answers

Which type of polysaccharide does dextrin resemble in terms of iodine reaction color?

Glycogen Signup and view all the answers

What role does salivary amylase play in the reaction with starch?

It hydrolyzes starch into simpler sugars Signup and view all the answers

Which of the following statements is true regarding the helical structure of amylose?

Amylose exists as a left-handed helix containing 6 glucosyl residues per turn Signup and view all the answers

Which structural feature distinguishes amylopectin from amylose?

Presence of α(1-6) linkages Signup and view all the answers

What is the optimal pH range for the activity of α-amylase in hydrolyzing starch?

6-7 Signup and view all the answers

What type of polysaccharide is primarily found in animal cells?

Glycogen Signup and view all the answers

Which bond types can α-amylase hydrolyze?

α(1-4) bonds only Signup and view all the answers

What forms when iodine interacts with amylose in a neutral solution?

Absorption complexes Signup and view all the answers

How does β-amylase differ from α-amylase in its function?

Hydrolyzes maltose stepwise from the non-reducing end Signup and view all the answers

Why is hydration important for the digestion of starch?

It allows exposure of hydroxyl groups for bonding Signup and view all the answers

What type of bonds connect the glucose units in branched regions of glycogen?

α(1-6) Signup and view all the answers

Study Notes

Starch Isolation and Hydrolysis

Starch is a plant storage polysaccharide composed of amylose and amylopectin.
- Amylose is a linear chain of glucose units linked by α(1→4) glycosidic bonds.
- Amylopectin has α(1→4) linkages and branches every 24 to 30 residues, formed by α(1→6) glycosidic bonds.
Glycogen is an animal storage polysaccharide structurally similar to amylopectin but with more frequent branches (every 8 to 12 residues).
α-Amylase, found in saliva and pancreatic juice, hydrolyzes internal α(1→4) bonds in starch and glycogen.
- Produces maltose, maltotriose, and α-limit dextrins (average 8 glucose units with α(1→6) bonds).
- Cannot break α(1→6) bonds or α(1→4) bonds at branch points.
β-Amylase, found in plants, removes maltose units from the non-reducing end of starch.
- An exoenzyme that produces β-maltose and β-limit dextrins.
- Cannot pass α(1→6) branch points.
Iodine forms complexes with starch, amylopectin, glycogen, and dextrins.
- Starch forms an intense blue complex due to the interaction of iodine with amylose's helical structure.
- Amylopectin and glycogen form less intense reddish-brown complexes due to their branched structures.
- Dextrin forms a pale color similar to glycogen.
- Maltose and glucose do not form complexes with iodine.
NaCl addition intensifies the color reaction with glycogen and dextrin due to its role in α-amylase activity.
Factors affecting the iodine-starch reaction:
- Excessive heating denatures amylose's helical structure, reducing the blue color.
- Extreme acidity or alkalinity reduces the interaction between iodine and starch.
- Sodium thiosulfate reacts with iodine, causing the blue-black color to disappear.

Starch Isolation Procedure

Potato is ground and strained through cheesecloth to obtain a suspension of starch granules.
The starch suspension is washed repeatedly with water to remove impurities.
The washed starch is suspended in water and boiled to dissolve it.

Iodine Test

Water (negative control), starch solution, and glycogen solution are tested with iodine.
Starch solution forms a blue-black color, while glycogen solution forms a pale reddish-brown color.
NaCl intensifies the color reaction with glycogen.
Heating, adding NaOH, or adding thiosulfate solution alters the iodine reaction based on the factors mentioned above.

Starch Hydrolysis by Salivary Amylase

Salivary amylase hydrolyzes starch, and the products can be tracked using iodine and Benedict's reagent.
Iodine reaction provides information about starch degradation, with different colors indicating the presence of various starch products.
Benedict's reagent detects the presence of reducing sugars produced during starch breakdown.

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Description

This quiz explores the composition and structure of starch and glycogen, including the roles of α-amylase and β-amylase in their hydrolysis. Understand the key differences between amylose and amylopectin and how iodine interacts with these polysaccharides. Test your knowledge on the enzymatic processes involved in starch breakdown.