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carbs Flashcards

1
Q

Biological significance of Carbohydrates

A
  • salicin and adriamycin Most abundant, naturally occurring class of biomolecules
  • energy storage
  • structural role (cellulose and chitin)
  • components of some drugs (salicin for anti-inflammatory, adriamycin for chemo)
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2
Q

4 types of large weight biopolymers

A
  • glycoproteins
  • proteoglycans
  • peptidoglycans
  • lipopolysaccharides
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3
Q

Glycoprotein

A

Glycoproteins: short-branched carbohydrate chains bonded to amino acids side chains
(receptors, recognition, cell interaction)
ex. blood group antigens A and B

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4
Q

Proteoglycans (mucopolysaccharides)

A

Proteoglycans: long, linear carbohydrate chains bonded to side chains of amino acids

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5
Q

Peptidoglycans

A

Peptidoglycans: long, linear carbohydrates cross linked by short oligopeptides (bacterial cell walls)

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6
Q

Lipopolysaccharides

A

Lipopolysaccharides: fatty acids linked to carbohydrates (outer envelope of gram negative bacteria)

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7
Q

Simple Sugar Formula

A

Empirical: C(H2O)
Molecular: Cn(H2O)n

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8
Q

Monosaccharide

A

carbohydrate that cannot be hydrolyzed in the lab (using H+/H20) to a simple carbohydrate

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9
Q

Monosaccharide Classification

  • number of carbons
  • carbonyl group present (aldose vs. ketose)
A
  • Prefix followed by -ose (e.g. triose, tetrose, pentose… etc). The first numbered carbon is closest to the carbonyl.
  • Aldoses have aldehyde group
  • ketoses have a ketone group on the 2nd carbon (unless otherwise specified).
  • Suffix -ulose can be used for ketoses*
    ex. pentulose vs. ketopentose (same)
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10
Q

Glyceraldehyde relationship between D/L and +/- of plane-polarized light

A

Discovered by Emil Fischer
ONLY can be used for GLYCERALDEHYDE!!!
D corresponds to + rotation (right handed)
L corresponds to - rotation (left handed)
-For all other sugars, there is no correlation.

2 enantiomers will rotate PPL to the same magnitude but opposite directions. HOWEVER, R/S configuration does not correlate with the direction of light rotation.

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11
Q

True/ False

Optical activity relationship of diastereomers can be predicted.

A

False

It cannot be predicted and Meso compounds do not rotate PPL (optically inactive)

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12
Q

D/L nomenclature for carbohydrates

A

When drawn in a Fischer projection, the OH group of the stereocentre (penultimate carbon) furthest from the carbonyl group
-D) is on the right
-L) is on the left
These two monosaccharides are a pair of enantiomers

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13
Q

Formation of Hemiacetals -

A
  • hydroxyl and carbonyl react together
  • exclusively intramolecular, more favourable than intermolecular
  • OH is most commonly on the penultimate carbon
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14
Q

Furanose vs. pyranose

A
  • Furanose: five membered ring, cyclic monosaccharide

- Pyranose: six membered ring, cyclic monosaccharide

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15
Q

Drawing Haworth Projections from Fischer Projections

A
  1. Rotate Fischer projection 90 degrees clockwise
  2. Draw template of ring
  3. walk along putting OH in, if on left = top, right= bottom
  4. For a D-sugar, the CH2OH is always up, and vice versa.
    * stereochemistry of anomeric carbon is undetermined*
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16
Q

Anomeric Carbon

A

-alpha vs. beta
New stereocentre formed upon hemiacetal formation, two possible stereoisomers known as anomers (are also diastereomers)
-alpha) OH opposite face to the last carbon (trans)
-beta) OH same face to the last carbon (cis)

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17
Q

True/False

L and D of the same sugars are not anomers

A

TRUE

L and D have different configurations at the penultimate carbon
-anomers have the same configuration for all carbons EXCEPT anomeric carbon

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18
Q

Mutarotation

A

Conversion between alpha and beta anomers of a monosaccharide in acidic and neutral (aqueous) conditions via open chain form.

  • Monitoring of the percentage present at equilibrium monitored by optical rotation. Resting equilibrium proportions cannot be predicted.
  • calculate percentage using weighted average.
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19
Q

Alpha or beta more favoured?

A

Beta is more favoured because it is more stable. Hydroxyl in equatorial position is favoured.

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20
Q

Glycosides (acetal)

A

Reaction of alcohols as an oxygen nucleophile (O-glycosides) with a hemiacetal (acid-catalyzed SN1 reaction)

  • Names: name of group on oxygen, ending with -ide
  • stable in basic and neutral pH, only reverts with glycosidase enzyme/strong acid
  • can also react with amines to form N-glycosides
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21
Q

Oxidation to Aldonic Acids

A

Aldehyde group oxidized into carboxylic acid with a weak oxidant (named -onic acid)
-common oxidants: Bromine dissolved in water (Br2 into two Br- ions), Tollen’s Reagent (formation of silver mirror) or Benedict’s/Fehling’s Reagents (formation of Cu2O red solid)

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22
Q

Reducing Sugars

A

Presence of an aldehyde group on a sugar that gets oxidized into a carboxylic acid while the oxidant becomes reduced.
i.e.reagents reduces the oxidants and get oxidized themselves.

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23
Q

Oxidation to Aldaric Acids

A

Stronger oxidizing agents like nitric acid (HNO3) oxidizes both the aldehyde and primary alcohol into carboxylic alcohols. Not secondary alcohols. (Named -aric acid)
Can be used to provide structural information about the original sugar as meso compounds are optically inactive.

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24
Q

Oxidation to Uronic Acid

A

Oxidation of only the primary alcohol of a carbohydrate, and not the aldehyde (named -uronic acid). Done with enzymes.

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25
Q

Glucuronic Acid

A

Used in the liver to detoxify toxic substances containing hydroxyl groups. Reaction between the two to form a glucuronide (excreted in urine).
-examples of a ironic acid reaction

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26
Q

Reduction to Alditols

A

Reduction of the carbonyl group into an alcohol using reducing agents H2/metal, NaBH4, LiAlH4. (Named -itol)

  • sugar alcohols are poorly absorbed and metabolized by the body (e.g. sorbitol and xylitol)
  • if a ketose is reduced, a new stereocentre is formed (racemic mixture/diastereomers)
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27
Q

Epimers

A

subclass of diastereomers differing at only one stereocenter

In basic solution, sugars undergo epimerization (isomerization) through enolate anions to result in diastereomers that differ in the C2 stereocentre, and another constitutional isomer (ketose) via tautomerization.
-results in a false positive test for ketoses because they slowly isomerize to aldehydes which reacts with Benedict’s Reagent.

28
Q

Mechanism for epimerization and isomerization

A
  1. Base Deprotonates alpha carbon
  2. Alpha carbon becomes carbocation
  3. Able to tautomerize
29
Q

Aldol Reactions

A

Enolates can attack other aldehydes or ketones in a nucleophilic addition reaction and forms a new carbon-carbon bond
-results in a beta-hydroxy carbonyl compound, nucleophile retains carbonyl, electrophile becomes alcohol

30
Q

Aldolase Catalyzes reversible formation of fructose-1,6-biosynthesis in glycolysis.

A
  • DHAP attacks GAP to form F-1,6-BP

- the reverse mechanism is called the retro-aldol reaction, actually takes place in glycolysis

31
Q

Acylation (or acetylation) of OH Groups (Esterification)

A

Addition of acyl groups to the alcohols to form acetyl esters by nucleophilic acyl substitution. OH of the monosaccharide is the nucleophile.
-use of acetic anhydride, alcohols are acetylated.

32
Q

Kiliani-Fischer Synthesis of Monosaccharides

A

Extension of monosaccharide by one carbon (new carbon-carbon bond) to synthesize rare sugars that are difficult to isolate.
-nucleophilic addition of cyanide (CN-) to the aldehyde to form a cyanohydrin after protonation.
-new stereocentre is formed (two diastereomers present, epimers)
Note: C1 in the original sugar became C2 in the 2 new sugars

Problem? How to separate them (2 methods)

33
Q

Traditional Method of Kiliani-Fischer Synthesis

create salts to separate

A

Addition of NaCN (extends carbon chain, new stereocentre)

  • Acid: hydrolysis of nitrite, CN into carboxylic acid
  • carboxylic acid spontaneously forms a lactone, which can be hydrolyzed with base. Yields two diastereomeric aldonic acid salts that can be separated by recrystallization.
  • After separation, they are converted back to lactones with acid
  • Reduced to an aldehyde with Na/Hg amalgam
34
Q

Modern Method of Kiliani-Fischer Synthesis

create imine hydrolyze to aldehyde and separate using HPLC

A
  • Addition of NaCN (extends carbon chain, new stereocentre)
  • Use of H2 and Pd/BaSO4 to generate an imine (HC=NH), BaSO4 poisons the Pd to weaken catalytic activity.
  • addition of H+/H2O, hydrolysis of imine into aldehyde.
  • generates epimers that can be separated by HPLC
35
Q

Disaccharides

A

Two monosaccharides connected using an acetal linkage (i.e. glycoside).

  • at least one of the anomeric carbons must be involved in the acetyl linkage, sometimes both may be involved.
  • formed and degraded in acidic conditions. Stable in neutral or basic conditions.
  • do not mutarotate, nor are they reducing. However, if one part of the molecule is a hemiacetal (free anomeric carbon), it can mutarotate and be a reducing sugar.
36
Q

Maltose and Cellobiose

A

Connection of two D-glucose via a 1,4 glycosidic linkage. Can both mutarotate and are reducing sugars.

  • maltose: alpha(1,4) glycoside bond
  • cellobiose: beta(1,4) glycoside bond
37
Q

Lactose

A

‘Milk sugar’ comprises of 5% of the weight in milk. Connection of D-galactose joined beta(1,4) to D-glucose.

  • D-glucose can still mutarotate, possesses reducing power.
  • lactase cleaves the beta-galactose linkage.
38
Q

Sucrose

A

Table sugar from sugar cane made up of D-glucose and D-fructose connected by both anomeric carbons. Alpha(1,2) for glucose and beta(2,1) at fructose.

  • no hemiacetal, does not mutarotate and not reducing.
  • hydrolysis into D-glucose and D-fructose by invertase or acid, results in sweeter taste and less likely to crystallize at high concentration (longer shelf life)
  • gives positive reducing sugar test upon hydrolysis
39
Q

Invert Sugar

A

1: 1 mixture of glucose and fructose
- named because the mixture rotates light to the left (-39) while the optical of sucrose is +66.5. After hydrolysis, the direction of optical rotation inverts. -

40
Q

Dextrose and Levulose

A

Dextrose: another name for D-glucose. This is because the equilibrium mixture has a rotation of +52.7.
-Levulose: another name for D-fructose. This is because the equilibrium mixture has a rotation of -92.

41
Q

Starch

A

Used for energy storage in plants and can be divided into two types: amylose and amylopectin.
-polymers made up of only D-glucose

42
Q

Amylose vs. Amylopectin

A

Amylose: continuous, unbranched chains of D-glucose units joined by alpha(1,4) linkages. Forms hollow, helical structure where other molecules can fit inside. (hydrophobic)
-Amylopectin: branched polymer of D-glucose that has alpha(1,6) branches every 24-30 units in addition to alpha(1,4) glycoside linkages.

43
Q

Glycogen

A

Used for energy storage in animals (350g in humans equally between liver and muscle)
-branched polymer of D-glucose using alpha(1,4) linkages and alpha(1,6) branches but more branched in comparison to amylopectin.

44
Q

Cellulose

A

Primarily used for structural functions and is comprised of a linear polymer of D-glucose linked beta(1,4). No branching.

  • because of configuration, adopts straight chain instead of curved like amylose.
  • every second unit rotated to allow extra hydrogen bonding to occur.
  • multiple chains associate very tightly by hydrogen bonding, results in insoluble properties. Forms supramolecular structure that can form microfibrils, fibrils, then fibres.
  • Break down fabric? Acetylation with anhydride changes OH to ester to destroy hydrogen bonding)

-broken down outside of the cell (extracellular degradation) by cellulase

45
Q

Break down cellulose?

A

Acetylation with anhydride changes OH to ester to destroy hydrogen bonding)

46
Q

Cellulase

A

Enzyme produced by fungi and bacteria that breaks down cellulose.

  • not excreted by humans, we cannot obtain carbs from cellulose (do not excrete cellulase)
  • However, some animals degrade cellulose into D-glucose via symbiotic relationship with cellulase producing microorganisms (but don’t produce their own cellulase)
47
Q

Glycolysis: net reaction

A

Glucose converted to pyruvate in 10 steps

  • anaerobic process
  • C1 of pyruvate come from C3 and C4 of glucose

Glucose + 2NAD+ + 2(PO4)3- + 2ADP into 2 Pyruvate + 2NADH + 2ATP

48
Q

Glycolysis: energy consumption phase

A

Glucose and 2ATP into 2 G3P, involves converting aldose to ketose

  • addition of ATP replaces C6 OH with phosphate
  • isomerization from pyranose to furanose
  • addition of ATP replaces C1 OH with phosphate, out of cyclic form.
  • retro-aldol reaction by aldolase that breaks into DHAP (eventually isomerizes to G3P) and G3P
49
Q

Glycolysis: energy production phase

A
  • Oxidation (NAD+) and phosphorylation of C1 G3P into 1,3BP.
  • Dephosphorylation (energy recovery, regeneration of ATP) of C1
  • movement of phosphate from C3 to C2
  • loss of water to form an enol compound (highly unstable)
  • second energy recovery, dephosphorylation of C2 into pyruvate.
50
Q

Glycolysis: Glucose into G6P mechanism

A

Requires Mg2+ cofactor, regulation by hexokinase.

  • Sixth carbon OH after deprotonation attacks phosphate of ATP
  • up and down carbonyl action to complete phosphorylation into G3P, ADP leaving group
51
Q

Glycolysis: G6P into F6P mechanism

A

Hemiacetal into aldehyde, then isomerization into ketone via ene-diol. Regulation by phosphoglucose isomerase.

  • decyclize (deprotonation of anomeric OH, protonation of anomeric carbon)
  • enolization mechanism, conversion to ketone
  • cyclize into fructose with phosphate (F6P)
52
Q

Glycolysis: F6P into F1,6BP mechanism

A

Enzyme only acts on the beta anomer! Identical to the hexokinase reaction. Regulation by phosphofructokinase.

  • beta anomer OH is deprotonated and attacks the phosphate of ATP.
  • up and down mechanism to complete phosphorylation of carbon 1.
  • Control point of glycolysis as phosphofructokinase is heavily regulated.
53
Q

Glycolysis: F1,6BP into DHAP/G3P mechanism

A

Retro-aldol reaction to split fructose into two, three-carbon products (DHAP and G3P). Regulated by aldolase.

  • decyclization
  • carbonyl is the electron acceptor in fungi/ bacteria. Conversion to OH to be more electrophilic carbon, breaking of carbon-carbon bond.
  • carbonyl reforms to make DHAP while aldehyde forms on other counterpart to make G3P.

Aldolase in plants and animals

Uses iminium ion (Schiff base) with a lysine side chain of enzyme instead of carbonyl.

  • lysine attaches to ketone spot to become a better electron acceptor
  • retro-aldol reaction happens to split into G3P and modified DHAP
  • modified DHAP reacts wit H2O to convert back to DHAP.
54
Q

Glycolysis: DHAP to G3P conversion

A

Isomerization of DHAP into G3P, done by Triosephosphate isomerase
-enolization mechanism of ketose into aldehyde using acid-base reactions, into enol state

55
Q

Glycolysis: G3P into 1,3biphosphoglycerate

A

Oxidation and phosphorylation of G3P.

  • Sulphur hemiacetal from enzyme is converted into a thioester with G3P.
  • oxidation by NAD+ reforms the ketose.
  • A phosphate (nucleophile) then attacks the thioester via nucleophilic acyl substitution, kicks out sulphur to form high energy compound, 1,3 biphosphoglycerate.
56
Q

Glycolysis: 1,3-biphosphoglycerate into 3-phosphoglycerate

A

ADP stabilized by Mg2+ cofactor, negative oxygen attacks phosphate group. Regulated by phosphoglycerate kinase
-up and down mechanism on phosphate group leaves oxygen anion on 3 phosphoglycerate

57
Q

Glycolysis: 3 phosphoglycerate into 2 phosphoglycerate

-plants vs. animal

A

Regulated by phosphoglycerate mutase

  • In animals, phosphorylated (by ATP) histidine on enzyme transfers to C2 hydroxyl. The N on histidine attacks and removes the phosphate on C3 into a primary alcohol.
  • In plants, the C3 phosphate is removed by His first, and is returned to C2.
58
Q

Glycolysis: 2 phosphoglycerate into phosphoenolpyruvate

A

Regulated by enolase, protonation of C3 primary alcohol, base attacks hydrogen on C2 to allow for enolization of C2 and C3.
-higher energy than their kept counterparts, exist in very small concentrations at equilibrium. However, cannot revert back to keto because oxygen is phosphorylated.

59
Q

Glycolysis: phosphoenolpyruvate into pyruvate

A

Regulated by pyruvate kinase

  • ADP with Mg2+ cofactor, attacks C2 phosphate to generate ATP.
  • resulting enol form tautomerizes into more stable kept form (pyruvate).
60
Q

Pyruvate Dehydrogenase Complex

-two coenzymes

A

Carries out oxidative decarboxylation of pyruvate into acetyl-CoA.
-requires two co-enzymes: TPP and lipoic acid.

61
Q

TPP and mechanism of decarboxylation

A

Coenzyme to pyruvate dehydrogenase complex. Active part of TPP is the thiazolium ring which is weakly acidic and forms ylide.

  • ylide adds to pyruvate to form iminium ion, beta to carboxylate group
  • iminium group accepts electrons generated by decarboxylation to form an enamine
62
Q

Lipoic acid and mechanism of oxidation

A

Coenzyme to pyruvate dehydrogenase complex.

  • in SN2 like reaction, enamine attacks lipoid acid and displaces one sulphur. Formation of hemithioacetal.
  • elimination of ylide results in thioester.
  • conversion to acetyl-CoA by nucleophilic acyl substitution.
  • Lipoic acid is then regenerated using FAD, reduction to reform disulphide bridge.
63
Q

Aminotransferase (Transaminase)

-example

A

Enzymes that move amino groups between alpha-amino acids and carbohydrates that are alpha-keto acids.

  • example) transfer of amino group from alanine to alpha-ketoglutarate production pyruvate and glutamic acid.
  • low levels in blood indicative of liver damage
  • requires PLP, coenzyme that functions as an amino-group carrier, uses imine chemistry
64
Q

Aminotransferase reaction

A
  • First reaction: removal of amino group from amino acid to make alpha-leto acid (pyridoxal form/ PLP to pyrioxamine form/ PMP)
  • Second reaction: reverse of the first reaction, amino group is returned to a different alpha-keto acid (the carbohydrate).
65
Q

First step of Aminotransferase reaction (PLP to PMP)

A

Second step is simply the reverse

  • amine from amino acid attacks carbonyl (protonated water leaving group), formation of an imine of PLP (belongs to PLP because using PLP’s carbon).
  • base takes alpha-hydrogen from amino acid. Becomes imine of alpha-keto acid after movement of double bonds.
  • PLP double bond is reduced by acid.
  • hydrolysis of imine using water releases PMP and alpha-keto acid.

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