C1. Intro Flashcards
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
what is the intermediate between conversion of aldose to ketose?
endiol (deprotonierte form)
when is reducing power of a sugar lost?
when OH at anomeric carbon of cyclic form is covalently bonded to another group –> prevents ring from opening
(conversion to open-chain form requires that an OH group bound to anomeric carbon to revert back to an aldehyde group)
maltose vs sucrose –> which is non-reducing vs reducing?
- why?
- what linkage?
- maltose = reducing –> 2nd glucose is not involved in the glycosidic bond –> ring opening can occur at one end of molecule –> but only has 1/2 reducing power of glucose bc one of the 2 anomeric carbons is used in glycosidic bond
- maltose = a-1-4 glycosidic linkage
- sucrose = not reducing –> both anomeric carbons (C1 and C2 of fructose) are tied up in the glycosidic bond, so ring opening cannot occur
- sucrose = a-1-2 glycosidic linkage
