Carbohydrates
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- Created by: LBCW0502
- Created on: 29-11-17 12:13
What are carbohydrates?
Polyhydroxy aldehydes or ketones
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What are the roles of carbohydrates?
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What is the general formula for simple carbohydrates?
C.H2O
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What is the simplest monosaccharide in the 2-ketose family?
Ketotriose/dihydroxyacetone
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In the 2-ketose family, when do the monosaccharides become chiral?
When a second carbon is added (from ketotetrose onwards)
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How do you calculate the number of stereoisomers for a particular molecule?
2^n (where n is the number of chiral carbons)
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What is the simplest monosaccharide in the aldose family?
Aldotriose/glyceraldehyde
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How do you distinguish between a D-isomer and an L-isomer?
D isomer (chiral C furthest away from the functional group e.g. aldehyde has an OH attached on the right). L isomer (chiral C furthest away from the functional group e.g. aldehyde has an OH attached on the left)
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What are diastereoisomers?
Non-superimposable images
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What are epimers?
Any two diastereoisomers that differ only in the configuration around a single carbon atom
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Give examples of epimers (3)
D-threose and D-erythrose, D-glucose and D-galactose, D-glucose and D-mannose
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What are anomers?
Isomeric forms of the monosaccharides that differ only in their configuration about the hemiacetal or hemiketal carbon (hemiacetal/carbonyl carbon is known as the anomeric carbon). There are alpha or beta anomers
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Do monosaccharides exist in a linear form or a cyclic form?
Cyclic form
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What is the difference between a furanose and a pyranose?
A furanose is a cyclic sugar containing a five (carbon) membered ring. Pyranose is a cyclic sugar containing a six (carbon) membered ring
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What are the three representations required to know?
Fischer projection, complete Haworth projection (includes Hs) and incomplete Haworth projection (no Hs) - need to be able to state configurations
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How do you convert a linear form of a monosaccharide to a cyclic form?
Determine if the structure will be a furanose or pyranose. The CH2OH is in the D configuration (up). Other groups on the right point down and groups on the left point up.
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Describe the general structure of a monosaccharide in the chair conformation
Groups can be axial (perpendicular to the plane) or equatorial (parallel to the plane). More accurate structure
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Which type of enzymes are used in reactions involving ATP?
Kinase enzymes
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Describe a kinase catalysed formation of sugar phosphates (e.g. Beta-D-glucose)
ATP donates a phosphate group to Beta-D-glucose to make the molecule less stable/more reactive. The phosphate group covalently bonds to glucose to form glucose-6-phosphate (good source but very stable). Glucokinase used
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Describe the formation of NDP sugars (e.g. beta-D-galactose-1-phosphate)
Deoxyribonucleotide used (A, T, C, G). Two phosphate groups donated to beta-D-galactose-1-phosphate. Pi lost, forming UDP galactose. Nucleotidyl transferase used
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Describe the Haworth projection for sucrose
Sucrose is disaccharide formed from glucose (pyranose) and fructose (furanose). Alpha glycosidic bond C1-C4.
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Describe the Haworth projection for lactose
Lactose is a disaccharide formed from glucose (pyranose) and galactose (pyranose). Beta glycosidic bond C1-C4
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Why is sucrose a non-reducing sugar?
Sucrose does not contain any free ends
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Why is lactose a reducing sugar?
Lactose contains free ends (on glucose - aldehyde group)
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Describe the structure of cellobiose
Homogeneous disaccharide. Beta glycosidic bond C1-C4. Contains beta-glucose monomers in D configuration
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Describe the structure of maltose
Homogeneous disaccharide. Alpha glycosidic bond C1-C4. Contains alpha-glucose monomers in D configuration
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Describe the structure of isomaltose
Homogeneous disaccharide. Alpha glycosidic bond C1-C6. Contains alpha-glucose monomers in D configuration
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What are enantiomers?
A pair of mirror images which are non-superimposable (optically active)
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What are monosaccharides?
Single polyhydroxy aldehyde or ketone units
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What are disaccharides, oligosaccharides and polysaccharides?
Disaccharides contain two monosaccharide units. Oligosaccharides are short chains of monosaccharide units. Polysaccharides contain 20 or more monosaccharide units
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What is the general formula for polysaccharides?
Cx(H2O)y
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How are polysaccharides characterised? (3)
Identity of glycosyl monomers, nature of glycosidic linkages between them, sequence of glycosyl residues
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What is the difference between homopolysaccharides and heteropolysaccharides?
Homopolysaccharides contain one type of monosaccharide. Heteropolysaccharides contain two or more different types of monosaccharides
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Describe the structure of cellulose
Homopolysaccharide. Beta-glucose monomers bonded by beta C1-C4 glycosidic linkage. High H bond capacity (form fibrils)
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Describe the structure of starch amylose
Homopolysaccharide. Alpha-glucose monomers bonded by alpha C1-C4 glycosidic linkage. Form helices
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Describe the structure of starch amylopectin
Homopolysaccharide. Alpha-glucose monomers bonded by alpha C1-C4 and C1-C6 glycosidic linkage. Form branches
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What is the function of the enzyme alpha amylase?
Cleave every alpha glycosidic C1-C4 bond (produce source of reduced carbon)
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What is the function of the enzyme beta amylase?
Cleave every second residue
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Are the enzymes to break down branching?
No
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Describe the structure of starch glycogen
Homopolysaccharide. 1-6 branching. Remove glucose from non-reducing end
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Describe the conversion of glycogen to glucose
Phosphorolysis of alpha 1-4 glycosidic linkage (phosphate group attached to one of the glucose monomers)
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Describe the structure of glycosaminoglycans
Heteropolysaccharide. Repeating disaccharide of hyaluronic acid. Amino group attached to every other monosaccharide. Beta 1-4 bonds and beta 1-3 bonds
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Describe the structure of proteoglycans
Heteropolysaccharide. Consisting of heparin (prevents blood clotting). Four different monomers. Alpha 1-4 bonds. Some monosaccharides contain a sulfonate group
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State the main components in glycoproteins (3)
Polypeptides, oligosaccharide prosthetic group and covalent linkages
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What are the uses of glycoproteins? (10)
Hormones, antibodies, enzymes, receptor proteins, transport proteins, cell adhesion, growth control, cell recognition, confer blood group characteristics, confer structural stability to multi-molecular aggregates
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Gives examples where there are oligosaccharide groups in some glycoproteins (5)
Glycoprotein isolated from membrane of glomerulus, blood group determining (in pigs), glycoproteins in membrane of erythrocytes, antibodies, antifreeze protein
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How many species of haemoglobin are present in adult human blood?
3. HbA (normal). Five other forms - HbA-HbA0, HbAla1, HbAla2, HbA1b,HbA1c
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What are glycosylated haemoglobins?
Forms of Hb have the same alpha and beta composition but the beta chains in the four minor forms have simple sugars attached
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What are glucoconjugates?
Complex carbohydrate polymers covalently bonded to proteins or lipids
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Describe the solubility of monosaccharides in polar and non-polar solvents
Monosaccharides are soluble in polar solvents but insoluble in non-polar solvents
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Which functional group is present in an aldose?
Aldehyde
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Which functional group is present in a ketose?
Ketone
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Monosaccharides with four, five, six or seven carbons in their backbone are called what?
Tetroses, pentoses, hexoses and heptoses
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What are hemiacetals and hemiketals?
Derivatives formed when aldehydes or ketones react with alcohol. They contain an additional chiral carbon (two stereoisomers formed)
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What is mutarotation?
Alpha and beta anomers intercovert in aqueous solution (e.g. D-glucose)
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Oxidation of the aldehyde of glucose to carboxylic level produces what?
An aldonic acid
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Oxidation of carbon at C6 of glucose to carboxylic level produces what?
A uronic acid (forms an intermolecular bond with aldonic acid to produce lactone)
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What is the test for reducing sugars?
Fehling's test
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What happens when an anomeric carbon is involved in a glycosidic linkage?
Sugar residue cannot take the linear form and becomes a non-reducing sugar
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What is a reducing end?
A free anomeric carbon - not involved in the glycosidic bond
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What are dextrans?
Bacterial and yeast polysaccharides with alpha 1-6 linked poly-D-glucose, alpha 1-3 branching and alpha 1-2 or alpha 1-4 branching
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Describe the structure of chitin
Linear homopolysaccharide. Composed of N-acetyl-D-glucosamine residues with beta linkage. Able to form fibres
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What are the interactions with stabilise polymers? (5)
Hydrogen bonding, hydrophobic, van der Waals, charged sub units, electrostatic interactions
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Other cards in this set
Card 2
Front
What are the roles of carbohydrates?
Back
-
Card 3
Front
What is the general formula for simple carbohydrates?
Back
Card 4
Front
What is the simplest monosaccharide in the 2-ketose family?
Back
Card 5
Front
In the 2-ketose family, when do the monosaccharides become chiral?
Back
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