11870973
Descripción
Fichas por J yadonknow, actualizado hace más de 1 año
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Creado por J yadonknow
hace casi 7 años
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| Pregunta | Respuesta |
| What are Oligosaccharides? | Short chain of monosaccharides under 20 residues |
| Why are carbohydrates sweet? | Tongue receptors interact with OH group of carb residues via hydreogen bonding |
| What are the two families of carbohydrates? | Aldoses and Ketoses |
| What is the general formula for the number of chiral centres a molecules can have? | n=number of centres 2^n |
| What are the main conformation of carbs? How can you identify this conformation? | Carbohydrates mainly exist in the D conformation If the chiral centre furthest away from CHO is on the right then it's a D sugar |
| Compare Aldoses and Ketoses (8) | Hexose / Hexose CHO at end of the chain / C=O at C2 Reducing sugars / Reducing C2,C3,C4 and C5 / C3,C4 and C5 L/D conformation is based on the spatial arrangement of the C5 groups 16 isomers / 8 isomers Benedicts reduces OH to COOH / naught. Cyclic in aq / Cyclic in Aq |
| Draw the structure of an aldose | Glucose structure, straight chained |
| Draw D-Glucose and two of its epimers, explaining what an epimer is | D-Mannose (epimer at C2) D-Galactose (epimer at C4) OH group in opposite orientation on a chiral centre then it's an epimer. |
| How can you identify a reducing sugar? | Sugar is oxidised to COOH with Benedict's reagant Cu2+->Cu blue to red (BR=CuSO4/Citrate.) |
| How does the sugar form a COOH? What is a "false positive" here? | The C=O of the carbonyl destabilises the 2' OH below it. The OH is oxidised to form another ketone group - giving a false positive as it forms an Endiol |
| How are ring structures formed from monosaccharides? | Aldotetroses and all monosaccharides >5C exist as cyclic structures in aq solution Covalent bond forms between the carbonyl group and an O: atom of an alcohol group. |
| What does this covalent bonding form? | A new chiral centre known as an anomer |
| Draw a diagram showing D-Glucose forming 2 different ring structures | a-d-g b-d-g |
| Describe the changes in bonding that occurs to the carbonyl group | C=O goes from 3 ligand to 4 ligand, generating an anomer, bond angle increases from 120' to 109.5' |
| Why do different ring structures form from the glucose? | As the O: can attack the carbonyl carbon from different angles, creating different orientation arrangements |
| How does most of glucose exist? | Exists in cyclic form, only linear form reacts as the OH group is free |
| How can Le Chatelier's principle be applied to this system? | Reaction is in equilibria When linear reacts to form COOH in a oxidation reaction with Benedict's, the reaction shifts to the left, over time all cyclic is converted to linear form |
| Draw the formation of a Haworth Projection of D-Fructose | D-fructose to a-d-frucofuranose |
| Draw a Haworth Projection of B-D galactose, what is this an epimer of? | C4 epimer of Glucose |
| Describe the conformation of pyranose rings | Saturated C has bond angles of 107' Tetrahedral geometry of saturated carbons produce Non-Planar structures c1-c5 close ring Axial Substituents sterically hinder each other as big bulky groups orientate away from each other to form a more energetically favourable conformation |
| Describe the conformation of a furanose ring | Not planar c1-c4 close ring Either C2/C3 is out of plane Conformation is known as enveloped form |
| What conformation predominates in B-D-Glucopyranose? | Chair form, as all axial positions are occupied by H atoms. |
| Give an example of a sugar derivative formed by the addition of a sulphate group | Heparin, anticoagulant |
| Give an example of a sugar derivative formed by the addition of an amine group | Glucosamine - found in connective tissue |
| How is a glycosidic bond formed? | Formed when an OH group reacts with the anomeric carbon, due to their lone pair of electrons |
| What sort of sugars have glycosidic bonds | Non-reducing sugars, as sugar is trapped in a non-cyclic form. |
| What are N-glycosidic bonds | Glycosidic bonds formed when the anomeric carbon reacts with nitrogen, as seen in nucleotides and glycoproteins |
| What monosaccharides is the olignosaccharide Lactose formed from? | GalB1-4Glu |
| What monosaccharides is the olignosaccharide Trehalose formed from? | Glua1-1aGlu |
| What monosaccharides is the olignosaccharide Maltose formed from? | Glua1-4Glu |
| What monosaccharides is the olignosaccharide Sucrose formed from? | Glua1-2BFru |
| Which sugars are non-reducing and why? | Sucrose and trehalose as the anomeric carbon is involved in the glycosidic bond and not available for bonding |
| Draw the formation of a glycosidic bond for Maltose | Hemiacetal group+OH group Forms a-D-Glucopyranosyl-(1->4)-D-Glucopyranose |
| What is a hemiacetal? | A compound deriving from the addition of an OH to an Aldehyde or Ketone, anything with a hemiacetal is a reducing sugar |
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