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26 Cards in this Set
- Front
- Back
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What are carbohydrates?
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They are organic compounds that are considered sugars.
Are significant source of dietary calories (55-60%). -Energy, structural component, and cell membrane |
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What are enantomers?
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Enantiomers are mirror images of each other
• D-forms of sugars are the predominant form in humans |
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What are the monomeric units of carbohydrates and what are the classifications?
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The monomeric units of carbohydrates are monosaccharides
• Based on the number of monomeric units carbohydrates can be classified as – Monosaccharides – Disaccharides – Oligosaccharides – Polysaccharides |
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How are monosaccharides further classified by their functional groups and number of C atoms? Can monosaccharides exist as isomers, what are isomers?
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Monosaccharidescanbefurtherclassifiedbased on
– Functional group • Aldoses (that have an aldehyde group) • Ketoses (that have a keto group) – Number of C atoms • Trioses (3C) • Tetroses (4C) • Pentoses (5C) • Hexoses (6C) • Heptoses (7C) • Monosaccharides may exist as isomers (compounds that have the same chemical formula but different structural formula) |
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What are Aldoses and ketoses?
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Aldoses have an aldehyde group on carbon 1, whereas ketoses have a keto group on carbon 2
Both are reducing sugars, aldoses react faster and ketoses slower. |
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What can carbohydrates do with a free aldehyde or free keto group?
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• Carbohydrates with a free aldehyde or keto group can react with cupric ions and convert them to cuprous ions (they can act as reducing sugars). Aldoses react faster and ketoses react slower, but both are reducing sugars
• Detection of sugars in urine is based on the reducing property of sugars |
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Are sugars normally found in urine? and how are they detected?
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• Sugars are normally NOT found in urine
• Presence of monosaccharides in urine is detected based on the reducing property of the aldehyde or keto group in the monosaccharide (Benedicts test) or Clinitest |
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What are some clinical conditions where sugars are found in the urine?
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Diabetes mellitus – characterized by high blood glucose levels. Glucose is found in urine when the blood glucose is greater than 170-180mg%. Most common clinical condition in which glucose (sugar) is present in urine
– Fructosuria and hereditary fructose intolerance – inherited disorders of fructose metabolism. Fructose is present in urine – Galactosemia – inherited disorder of galactose metabolism. Galactose is found in urine |
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What is benedict's test and what are dipsticks.
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Test's for reducing sugars in the urine, same for dipstick but is more specific for whether the the sugar is glucose or something else.
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Why does the cyclization of monosaccharides occur?
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• Monosaccharides with 5 or more C atoms rarely exist in the acyclic form. They are predominantly present in the cyclic form in solution.
• As a result of cyclization, two anomeric forms can exist (α and β forms). The two forms are interconvertible and this process is known as mutarotation • β-form of glucose is predominant in solution |
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What are epimers?
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They are compounds of the same forumla but differ at position of hydroxyl group at carbon -1 atom (sugar).
Carbohydrate isomers that differ in the configuration around one of the asymmetric C-atoms are known as epimers |
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Glucose and galactose are ____ epimers?
Glucose and manose are ____ epimers? What are epimerases? |
• Glucose and galactose are C-4 epimers
• Glucose and mannose are C-2 epimers • But galactose and mannose are not epimers of each other! Enzymes that interconvert epimers are known as epimerases (galactose metabolism) |
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What are Ribose and Deoxyribose?
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• Ribose (RNA) and deoxyribose (DNA) are components of nucleic acids
• The pentose sugar is linked to the purine or pyrimidine base by a β-N-glycosidic linkage to form a nucleoside • Pentose sugar + purine or pyrimidine base + phosphate = Nucleotide |
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What are sorbitol?
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• Sorbitol is a sugar alcohol (POLYL) formed from glucose. Sorbitol is formed from glucose in the nerve tissues, retina and the lens of the eye, when the blood glucose level is elevated for a prolonged period of time (prolonged hyperglycemia)
• Sorbitol formation is partly responsible for some of the chronic complications of diabetes mellitus |
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What is galactitol?
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Galactitol is formed from galactose in the lens in children with untreated galactosemia
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What are disaccharides - Lactose?
What is it, how is it cleaved and why should it be avoided? |
• Made up of two monosaccharides linked by a glycosidic linkage
• Lactose (milk sugar)= Glucose + Galactose linked by a β1→4 glycosidic linkage • Lactose is a reducing sugar • Dietary lactose is cleaved to the component monosaccharides by intestinal lactase (brush border disaccharidase) • Lactose avoidance in the diet is advised for patients with lactose intolerance and galactosemia |
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What is disaccharide's - sucrose?
What is it, how is it cleaved, and why should it be avoided? |
• Sucrose (cane sugar)= Glucose + Fructose
• Sucrose is a non-reducing sugar, as the C1 of glucose and C2 of fructose are involved in the glycosidic linkage (aldehyde and keto group is not free) • Dietary sucrose is cleaved to the component monosaccharides by intestinal sucrase (brush border disaccharidase) • Sucrose avoidance in the diet is advised for children with hereditary fructose intolerance 17 |
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What is Fructose?
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It is a monosaccharides and is a kethexose.
• It is a component of fruits, honey • High fructose corn syrup (HFCS 55) contains fructose (55%) and glucose (42%) – used as a sucrose substitute in soft drinks • HFCS is ingested as a mixture of monosaccharides (fructose and glucose) compared to sucrose that is digested by sucrase in the intestine • The fructose : glucose ratio is 1 in sucrose; whereas in HFCS, the fructose: glucose ratio is greater than 1 |
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What is disaccharides maltose?
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Maltose (present in malt) = 2 glucose units
• The two glucose units are linked by an α1→4 glycosidic linkage. • Maltose is a reducing sugar • Maltose is formed as one of the products of digestion of dietary starch by amylase • Maltoseiscleavedtoglucose by intestinal maltase (brush border disaccharidase) |
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What are polysaccharides?
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10-20 monosaccharide units
Polysaccharides • Polysaccharides can be classified as – Homopolysaccharides (similar monosaccharide units) – Heteropolysaccharides (different monosaccharide units) • Homopolysaccharides – Starch and glycogen (made up of glucose units) • Heteropolysaccharides – Glycosaminoglycans |
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What is glycogen, where is it found?
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Glycogen is a storage polysaccharide in humans. It is present in liver and muscle as cytosolic glycogen granules
• It is made of glucose units • The glucose units in the linear chain are linked by α1→4 glycosidic linkages. Glucose units at the branch point are linked by α1→6 glycosidic linkages |
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What is starch?
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Starch is a dietary polsaccharides
• Starch is made up of two components • Amylose (linear unbranched polymer of glucose) • Amylopectin (branched polymer of glucose) • Starch is made up of glucose units in the linear chain linked by α1→4 glycosidic linkages. Glucose units at the branch point are linked by α1→6 glycosidic linkages • It is digested by salivary and pancreatic amylase |
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How does amylopectin and glycogen differ?
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• Amylopectin (branched polymer of glucose) has fewer number of branches compared to glycogen
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What are glycosaminoglycans?
What are some examples of GAGs? |
They are made up of repeating disaccharide units.
• Sugar acid (glucuronic acid) and an amino sugar (glucosamine or galactosamine) • Examples of glycosaminoglycans are hyaluronic acid and heparin |
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What is cellulose?
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It is the majority carbohydrate dietary fiber that cannot be digested and helps to facilitate peristalsis.
Examples are cellulose and pectin • Cellulose is a homopolysaccharide containing glucose units linked by β 1→4 glycosidic linkages • β 1→4 glycosidic linkages in cellulose cannot be cleaved by digestive enzymes in the human gut • Remember: lactase can hydrolyze the β 1→4 glycosidic linkages only in the disaccharide lactose and NOT in cellulose!! |
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What are glycoproteins?
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They are oligosaccharide chains (glycan) that are attached to a polypeptide side chain.
Glycosylation may occur as either one type of linkage or with both on the same protein • O-linked – Glycosylation on the OH group of Ser/Thr – Often found as extracellular proteins or as membrane bound proteins – Glycan groups always face extracellular side • N-Linked – Glycosylation on the Asn (asparagine) residue (not Gln) – Either of two types (high mannose, or complex) |
