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Questions and Answers
Two monosaccharides have the same chemical formula but differ in the spatial arrangement of atoms around a chiral center. They are non-superimposable mirror images. Which type of isomers are they?
Two monosaccharides have the same chemical formula but differ in the spatial arrangement of atoms around a chiral center. They are non-superimposable mirror images. Which type of isomers are they?
- Diastereomers
- Epimers
- Enantiomers (correct)
- Constitutional isomers
During the formation of a cyclic monosaccharide, the reaction between an aldehyde group and an alcohol group results in the formation of a hemiacetal. Which carbon atom becomes the anomeric carbon in this process?
During the formation of a cyclic monosaccharide, the reaction between an aldehyde group and an alcohol group results in the formation of a hemiacetal. Which carbon atom becomes the anomeric carbon in this process?
- The carbon farthest from the original aldehyde carbon.
- The carbon that was part of the alcohol group.
- The carbon that was originally the aldehyde carbon. (correct)
- The carbon adjacent to the original aldehyde carbon.
A biochemist identifies a disaccharide that does not react with Fehling’s solution. What conclusion can be drawn about the disaccharide's structure?
A biochemist identifies a disaccharide that does not react with Fehling’s solution. What conclusion can be drawn about the disaccharide's structure?
- It contains only α-1,4-glycosidic bonds.
- It is likely a component of glycogen.
- It lacks a free anomeric carbon. (correct)
- It has a free anomeric carbon.
A researcher is studying a modified glucose molecule found in a metabolic pathway. Upon analysis, it is determined that a phosphate group is attached to the sixth carbon of the glucose. What type of monosaccharide modification is this?
A researcher is studying a modified glucose molecule found in a metabolic pathway. Upon analysis, it is determined that a phosphate group is attached to the sixth carbon of the glucose. What type of monosaccharide modification is this?
Which characteristic of the α-1,6-glycosidic bond contributes to the structure of glycogen?
Which characteristic of the α-1,6-glycosidic bond contributes to the structure of glycogen?
Cellulose and glycogen are both polysaccharides of glucose, but they have distinct structural and functional properties. Which statement correctly describes a key difference between them?
Cellulose and glycogen are both polysaccharides of glucose, but they have distinct structural and functional properties. Which statement correctly describes a key difference between them?
A researcher is analyzing a sample from the extracellular matrix and finds a molecule composed of a core protein with a high proportion of glycosaminoglycans. Which type of molecule is most likely present in the sample?
A researcher is analyzing a sample from the extracellular matrix and finds a molecule composed of a core protein with a high proportion of glycosaminoglycans. Which type of molecule is most likely present in the sample?
In N-linked glycosylation, what specific amino acid residue on a protein does the carbohydrate molecule attach to?
In N-linked glycosylation, what specific amino acid residue on a protein does the carbohydrate molecule attach to?
A scientist is studying a newly discovered glycosaminoglycan. Which structural feature would be expected in this type of molecule?
A scientist is studying a newly discovered glycosaminoglycan. Which structural feature would be expected in this type of molecule?
Heparin is a glycosaminoglycan known for its anticoagulant properties. What structural feature of heparin contributes to its biological activity?
Heparin is a glycosaminoglycan known for its anticoagulant properties. What structural feature of heparin contributes to its biological activity?
Flashcards
Constitutional Isomers
Constitutional Isomers
Isomers with the same molecular formula but different atomic connectivity.
Stereoisomers
Stereoisomers
Isomers with the same connectivity but different spatial arrangements.
Enantiomers
Enantiomers
Non-superimposable mirror images.
Diastereomers
Diastereomers
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Epimers
Epimers
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Anomers
Anomers
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Reducing Sugars
Reducing Sugars
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Non-reducing Sugars
Non-reducing Sugars
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Glycoproteins
Glycoproteins
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Proteoglycans
Proteoglycans
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Study Notes
- Monosaccharides are simple sugars that can exist in different isomeric forms.
Isomers of Monosaccharides
- Constitutional isomers have the same molecular formula but different connectivity of atoms.
- Stereoisomers share the same connectivity but differ in spatial arrangement.
- Enantiomers are stereoisomers that are non-superimposable mirror images, such as D- and L- forms.
- Diastereomers are stereoisomers that are not mirror images.
- Epimers are diastereomers that differ at only one asymmetric center.
- Anomers are cyclic forms of monosaccharides that differ at the anomeric carbon (α and β forms), which is formed during ring closure.
Cyclic Forms of Monosaccharides
- Monosaccharides form cyclic structures via hemiacetal (aldehyde + alcohol) or hemiketal (ketone + alcohol) reactions.
- Glucose typically forms a six-membered pyranose ring.
- Fructose can form either a five-membered furanose or a six-membered pyranose ring.
- The anomeric carbon determines the sugar configuration: α (OH group is below the ring) or β (OH group is above the ring).
Reducing and Non-Reducing Sugars
- Reducing sugars possess a free anomeric carbon that can reduce oxidizing agents; glucose is an example, reacting with Fehling’s solution.
- Non-reducing sugars do not have a free anomeric carbon; sucrose is an example.
Modifications of Monosaccharides
- Glycosidic bond formation involves linking sugars to alcohols (O-glycosidic) or amines (N-glycosidic).
- Phosphorylation is significant in metabolic pathways, exemplified by glucose-6-phosphate.
- Amino sugars and acetylation are found in glycosaminoglycans.
Disaccharides and Polysaccharides
- Common linkages in polysaccharides include α-1,4, β-1,4, and α-1,6.
- α-1,4 linkages are present in starch and glycogen, contributing to their linear structure.
- β-1,4 linkages are found in cellulose, resulting in a linear, rigid structure.
- α-1,6 linkages create branching in glycogen and amylopectin.
Impact of Linkage Type on Polysaccharide Structure
- Glycogen contains α-1,4 and α-1,6 linkages, is highly branched, and serves as a compact energy storage molecule in animals.
- Cellulose contains β-1,4 linkages, forming straight chains and fibers, providing structural support in plants and is indigestible by humans.
Glycoproteins
- Glycoproteins have protein as their major component and are involved in cell signaling and membrane functions.
- Proteoglycans are composed mainly of carbohydrates (glycosaminoglycans) and provide structural support in the extracellular matrix.
- Mucins are carbohydrate-rich and function as lubricants in mucus.
Carbohydrate Attachment to Proteins
- N-linked glycosylation involves carbohydrates attaching to asparagine (Asn).
- O-linked glycosylation involves carbohydrates attaching to serine (Ser) or threonine (Thr).
- All N-linked polysaccharides share a common pentasaccharide core consisting of three mannoses and two N-acetylglucosamines.
Glycosaminoglycans Features
- Glycosaminoglycans consist of repeating disaccharide units, with one amino sugar and one negatively charged sugar.
- They play a crucial role in connective tissue, cartilage, and the extracellular matrix.
- Examples of glycosaminoglycans include chitin (in insects), hyaluronic acid (in joints), and heparin (a blood anticoagulant).
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