C1. Intro
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Fundamental units of carbs? why? - general formula?
• monosaccharides (simple sugars) because not hydrolyzed by acid to form a smaller unit • C_x(H_2O)_x –> corresponds to hydrates of carbon
most common monosacs have what molecular formula? - 3 monosacs? - exist primarily in what form?
• C6H12O6 • glucose, galactose, fructose • cyclized form
disacs consits of what linked by what bond? - 3 disaccharides: from what? + characteristic
• 2 simple sugars linked by covalent glycosidic bond (ether linkage R - O - R) • maltose: glucose + glucose –> common enzymatic hydrolysis product of starch • sucrose: glucose + fructose –> common table sugar • lactose: glucose + galactose –> major sugar in cow’s milk
what are oligosaccharides? - 2 examples –> formed of what?
• 3 to 10 monosaccharides linked together by glycosidic bonds • raffinose (trisaccharide): galactose, glucose and fructose • stachyose (tetrasaccharide): glucose, fructose and 2 galactose
polysaccharides are what? - 5 examples
• polymers of monosacs that have a chain length > 10 units • starch, cellulose, glycogen, pectin and xanthan gum
4 common roles of carbs in living systems? + from what type of carb?
• energy source in seeds: starch for germination • structural component: cellulose and hemicellulose (plant cell wall) • ready supply of energy: mono and disacs • short term energy supply for muscles: glycogen
3 functionality of mono and disacs in food?
• sweetening agents • coloring agents (caramel colour) • production of flavors (caramelization/Maillard reaction)
7 functionality of polysacs in food?
• thickening agents • gelling agents • emulsion stabilizers • water holding/binding agents • anticaking agents • producing edible films • encapsulate flavors
• how many carbons do monosacs have? range • 2 functional groups of monosac in their linear form?
• C3H6O3 to C7H14O7 • alcohol group + ketone (C2) OR aldehyde group (C1)
which compound is used as reference compound to determine __-___ isomerism? - how? - vs other sugars?
glyceraldehyde! - D-L isomerism - aldehyde group on top, OH to right = D-isomer vs OH to left = L-isomer - other sugars: carboxylic group on top (C1), OH on C at (n-1) position determines D or L
what are epimers?
optical isomers involving asymmetric carbons other than the carbon at the n-1 position (ie only difference at C2 for a 6 carbon monosac)
isomers can be generated through _______ or ________ _________
acid or base catalysis
describe number of carbon + ketone vs aldehyde - ketohexose - aldohexose - aldopentose
• ketohexose: C6 ketone • aldohexose: C6 aldehyde • aldopentose: C5 aldehyde
cyclization is due to the formation of internal _______ and _________ - reactions are intra/intermolecular? explain
• hemiacetals • hemiketals • intramolecular: alcohol group attacks aldehyde or ketone group of the same molecule
• hemiacetal formation of glucose –> what ring? • hemiketal formation in fructose –> what ring? • which is more stable?
• hemiacetal –> pyranose • hemiketal –> furanose ring • pyranose is most stable!
cyclization results in an additional __________ carbon at the ___ position, termed ________ carbon, leading to 2 optical isomers, termed ________ - what are the 2 isomers?
• asymmetrical carbon at C1 position, termed anomeric carbon • anomers! • alpha form: OH group at anomeric carbon is on opposite side of ring as C6 • beta form: OH group at anomeric carbon is on same side as C6
3 different projections/conformation for monosacs?
• Fischer projection (linear/planar) • Haworth projection (hexagone) • chair conformation
in solution there is a _________ equilibrium between which 3 forms? - how can it be observed?
• dynamic equilibrium! • a, b and open chain
how can dynamic equilibrium between a, b and open form be observed? - when pure a-D-glucopyranose is dissolved in water, ______ ______ starts are ____° and gradually changes to ___° - when pure b-form dissolved in water, _______ _______ starts at ___ and gradually changes to ____° - this phenomenon is termed what?
• observed by following the optical rotation of plane-polarized light by a solution of sugar • alpha: optical rotation starts as 112° –> 53° • alpha: optical rotation starts as 19° –> 53° • mutarotation
mutarotation is the result of (2) - equilibrium between a, b and open chain of glucopyranose? (percentages) - vs of fructose?
• cyclic form opening up • recyclizing, coming to equilibrium with its anomer - 62% b-D-glucopyranose + 37% a-D-glucopyranose + 1% open chain form - fructose –> equilibrium is more complicated bc cyclization via formation of hemiketal can produce furanose OR pyranose
aldehyde group present on ________ has strong what? explain
• aldoses has strong reducing power • aldehydes are capable of reducing metal ions (oxidation-reduction reaction that converts aldehyde to a carboxylic acid)
as a group, monosacs are generally termed ________ sugars and can be tested for and quantified by specific what reactions? - most common test? involves what?
• reducing sugars • by oxidation/reduction reactions • Fehling’s test –> reduction of Cu(II) (blue) in form of copper tartrate to Cu(I) oxide (reddish brown precipitate)
Fehling’s reagent only reacts with what? - accordingly, only reacts with what form of monosac? - although only _% of sugar is in that form, when that form is depleted, what happens?
• free aldehyde groups • open-chain form • 1% of sugar is in open-chain form –> when open-chain form is depleted by above reaction, it is replenished by opening of the ring forms (with which it is in equilibrium)
is fructose a reducing sugar?
even if it is a ketose sugar and has no aldehyde group, it is still a reducing sugar - because fructose is converted into glucose (ketose –> aldose) (enolization) –> glucose can then react with Fehling’s solution