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Questions and Answers
Which of the following sugars is considered a reducing sugar?
Which of the following sugars is considered a reducing sugar?
Sucrose contains free anomeric carbon atoms and is therefore classified as a reducing sugar.
Sucrose contains free anomeric carbon atoms and is therefore classified as a reducing sugar.
False
What are the two monosaccharides that compose lactose?
What are the two monosaccharides that compose lactose?
Galactose and Glucose
Cellobiose is produced by the hydrolysis of __________.
Cellobiose is produced by the hydrolysis of __________.
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Match the following disaccharides with their characteristics:
Match the following disaccharides with their characteristics:
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Which reaction is necessary for the metabolic breakdown of monosaccharides?
Which reaction is necessary for the metabolic breakdown of monosaccharides?
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All monosaccharides are considered reducing sugars.
All monosaccharides are considered reducing sugars.
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What is the product formed when glucose is oxidized using the Fehling reagent?
What is the product formed when glucose is oxidized using the Fehling reagent?
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The formation of a glycoside involves the linkage of __________ to form oligo- and polysaccharides.
The formation of a glycoside involves the linkage of __________ to form oligo- and polysaccharides.
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Match the carbohydrate reaction type with its description:
Match the carbohydrate reaction type with its description:
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Which of the following is a non-reducing sugar?
Which of the following is a non-reducing sugar?
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Ketones have reducing properties similar to aldehydes.
Ketones have reducing properties similar to aldehydes.
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What defines a sugar as non-reducing?
What defines a sugar as non-reducing?
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What type of bond do N-linked oligosaccharides involve?
What type of bond do N-linked oligosaccharides involve?
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Maltose is a non-reducing sugar.
Maltose is a non-reducing sugar.
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What is the primary sugar component in maltose?
What is the primary sugar component in maltose?
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Glycosidic bonds can be hydrolyzed by _____ but resist cleavage by base.
Glycosidic bonds can be hydrolyzed by _____ but resist cleavage by base.
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Match the following sugars with their classification:
Match the following sugars with their classification:
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Which of the following is a characteristic of reducing sugars?
Which of the following is a characteristic of reducing sugars?
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The reaction between blood glucose and the N-terminal of hemoglobin forms a _____ base.
The reaction between blood glucose and the N-terminal of hemoglobin forms a _____ base.
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Name a type of sugar acid mentioned in the content.
Name a type of sugar acid mentioned in the content.
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Study Notes
Carbohydrates (Cont.)
- Simple sugars undergo various reactions, including oxidation-reduction for breakdown, esterification/phosphorylation, amino derivatives for structural components, and glycoside formation to create oligo- and polysaccharides.
Reducing vs Non-reducing Sugars
- The hemiacetal linkage in sugars can be easily dissociated, enabling the carbonyl group to reduce mild oxidizing agents (like ferric or cupric ions).
- This oxidation converts the carbonyl carbon to a carboxyl group.
- Monosaccharides with a hemiacetal are reducing sugars because their open-chain form contains an aldehyde or ketone.
- All monosaccharides are reducing sugars.
- Converting all hemiacetals/hemiketals to acetals/ketals removes reducing ability, creating a non-reducing sugar.
- Sucrose is a non-reducing sugar.
Oxidation of Aldoses (Using Fehling Reagent)
- Ketones lack the aldehyde group's reducing properties and are not oxidized under similar conditions.
- Fructose, despite having a ketone group, can reduce Fehling reagent due to isomerization into aldoses under basic conditions.
Esterification
- Phosphate esters are crucial biological esters of carbohydrates.
- Phosphorylation adds a phosphate group from ATP to a sugar molecule, often catalyzed by kinases.
- This phosphorylation adds a negative charge, preventing the sugar from spontaneously leaving the cell.
Amino Derivatives
- Amino sugars are formed by replacing a hydroxyl group on a carbohydrate with an amino group..
- Amino sugars are components of bacterial cell walls, chitin, chondroitin sulfate, glycoproteins, and glycolipids.
- N-acetylneuraminate (sialic acid) is a terminal residue in glycoproteins, carrying a negative charge due to its carboxyl group dissociation.
Glycoside Formation
- Glycosidic bonds form between the anomeric carbon of a carbohydrate and another compound's oxygen, nitrogen, or phosphorus.
- The anomeric carbon involved in bond formation is stabilized and converted to either an acetal or ketal.
- This stabilization prevents potential free aldehyde or ketone groups.
Glycosylation Reaction
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Sugars are typically attached to other molecules during glycosylation.
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N-glycosylation attaches sugars to nitrogen (often asparagine).
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O-glycosylation attaches sugars to oxygen (often serine, threonine, or other amino acids).
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Glypiation involves a glycosyl phosphatidylinositol anchor to localize proteins to cell membranes.
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C-glycosylation attaches sugars directly to carbon.
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P-glycosylation attaches sugars to phosphorus.
N-linked Glycosylation
- N-linked oligosaccharides are typically complex and branched.
- The process starts with attaching an N-acetylglucosamine to an asparagine residue in a specific sequence.
- Additional monosaccharides are added and modified, leading to the characteristic branched structure.
O-linked Glycosylation
- O-linked oligosaccharides bind to serine or threonine via an O-glycosidic bond.
- These linkages can form linear or branched chains.
- Cellular proteins, including factors, are regulated by reversible GlcNAc attachment.
O-linked vs N-linked Glycosidic Bond
- O-linked bonds connect to hydroxyl groups of serine or threonine.
- N-linked bonds connect to amide nitrogen of asparagine.
Glucose in the Blood and Glycated Hemoglobin
- Blood glucose reacts non-enzymatically with hemoglobin's N-terminal beta chain.
- This forms a Schiff base, which converts to 1-deoxy fructose.
- Glycated hemoglobin levels are higher in diabetic patients.
Sugar Derivatives
- Sugar acids are formed when the aldehyde group at C1 or the hydroxyl group at C6 is oxidized to a carboxylic acid (like gluconic or glucuronic acid).
- Sugar alcohols lack an aldehyde or ketone group (like ribitol).
Disaccharides
- Disaccharides contain glycosidic bonds formed between monosaccharides.
- These bonds are readily hydrolyzed by acid, not by base, often requiring boiling in dilute acid.
- Three common disaccharides are sucrose, maltose, and lactose.
- Sucrose is a non-reducing sugar, while maltose & lactose are reducing sugars.
Maltose
- Maltose is a reducing sugar formed from two glucose molecules linked by an α(1→4) glycosidic bond.
- It is also called maltobiose or malt sugar
Isomaltose
- Isomaltose is a reducing sugar.
- It consists of two glucose units linked by an alpha 1-6 glycosidic bond.
- It comes from the hydrolysis of glycogen or amylopectin.
Lactose
- Lactose is a reducing sugar.
- It has a beta (1-->4) glycosidic bond joining galactose and glucose.
Sucrose
- Sucrose is a non-reducing disaccharide of glucose and fructose.
- It's formed from plants, not animals.
- The anomeric carbons are involved in the glycosidic bond.
Cellobiose
- Cellobiose is a reducing disaccharide made of two glucose molecules joined by a β(1→4) glycosidic bond.
- It comes from the hydrolysis of cellulose.
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Description
Explore the intricacies of carbohydrates, focusing on simple sugars and their reactions including oxidation, reduction, and formation of oligo- and polysaccharides. Understand the distinction between reducing and non-reducing sugars, and the significance of hemiacetals. This quiz covers essential concepts from carbohydrate chemistry.
