Final - Carbohydrates, Lipids, Nucleic Acids, Drugs Flashcards
What is the molecular formula of carbohydrates(monosaccharides?)?
CnH2nOn
When a sugar is a ketone, where is the group assumed to be?
Assumed to be in position/Carbon 2 on sugar (from top)
Break down the names aldohexose and pentulose.
Aldohexose: an aldose carbonyl group present, and 6 Cs.
Pentulose: 5 Cs and a ketone carbonyl group present. Could also be called ketopentose, or 2-ketopentose.
Which of D and L is the naturally-occurring carbohydrate?
What distinguishes them?
D
Determined by the position of OH on the penultimate Carbon.
In D vs L enantiomers, every stereocentre changes.
D= OH on right
L = OH on left
What’s special about the classification technique for glyceraldehyde?
Glyceraldehyde is an aldotriose, that is chiral and thus rotates PPL. This is the ONLY situation where S/R configurations match with D/L configurations and direction of PPL rotation.
When -OH is at Right(D), it’s R, and [a]=+.
When -OH is at Left(L), glyceraldehyde is S, and [a]= - .
Do R/S and rotation of PPL corroborate?
NO! except for glyceraldehyde.
Direction of PPL is experimentally determined.
Relation between D/L and PPL direction.
You won’t know which +/- and D/L match up, but once experimentally determined, you’ll know that:
ENANTIOMERS!! rotate PPL to same magnitude, but opposite direction.
This is not the case for diastereomers.
And it’s not the same for meso compounds because they don’t even rotate PPL.
What are enantiomers?
What would be the enantiomer pair of L-(+)-Arabinose?
What would be one of its diastereomers?
Every chiral centre has the opposite configuration as its pair.
Non-superimposable mirror images.
Enantiomer pair: D-(-)-Arabinose.
Diastereomer: L-(-)-Xylose or D-(+)-Xylose == same molecular formula, but different arrangement.
What distinguishes the alpha and beta anomers in hemiacetals?
How did the anomers come about?
In hemiacetal formation, the penultimate C binds to the top or the bottom of C1 (carbonyl group) because it is flat(sp2) and thus makes the OH on the new stereocentre at C1…
- TRANS to C6 (CH2OH) == ALPHA anomer
- CIS to C6 (CH2OH) == BETA anomer
anomers=diastereomers
In Haworth projections and in rotated Fischer projections, how can you tell a D from an L sugar?
The CH2OH (C6) is up for D, and down(bottom face) for L.
Do hemiacetals/anomers mutarotate? How can you tell?
How do you determine which anomer is present at higher quantities at equilibrium?
Anomers (=DIASTEREOMERS) have different [alpha]s. But after they’ve interconverted, they have the same [alpha]s.
When you’ve measured the [alphas] before and after, whichever one’s number has jumped the LEAST is present in higher concentrations.
Usually there’s more beta in the equilibrium mixture because its cis is more favourable.
This mutarotation can happen in acidic and neutral aqueous solutions.
What are pyranose and furanose?
Furanose: Five-membered ring
Pyranose: 6-membered ring
What’s another word for acetals of sugars?
Glycosides, or O-glycosides because the hemiacetal reacts with another alcohol which has a nucleophile OH. Or N-glycosides (which are found in nucleosides) when the hemiacetal reacts with an amine (now there’s no O at that C1).
What is the difference of Glycoside Formation (from hemiacetal formation)?
(how do you name glycosides? What conditions? Structural difference?)
Properties of acetals.
Glycosides= acetals of sugars that are formed via the acid-catalyzed SN1 rxn (using ___OH eg, CH3OH).
Formed from a hemiacetal and another alcohol to give sugar with the anomeric carbon’s OH being O__ instead (eg, OMe)!
Forms alpha and beta anomers, but they do not mutarotate or go back to their open-chain forms unless enzyme comes or strong acid, because they are stable in neutral and basic conditions! They’re also not reducing sugars because of this.
Naming: “Methyl alpha-D-glucopyranosIDE”
What’s the condition of hemiacetal equilibrium?
Hemiacetals are in equilibrium with their open-chain forms! Because they are unstable in basic and neutral conditions.
What are the oxidants that can oxidize sugars to Aldonic Acids?
What functional group(s) are oxidized?
Br2 (bromine dissolved in water) gives two Br- ions when reduced. KETONES ARE NOT OXIDIZED BY Br2!!!
Tollen’s Reagent : Ag+ gives a silver metal when reduced. (to tell oxidation of aldehyde to corresponding ketose)
Benedict’s Reagent: Cu2+ gives a red solid Cu+(s) when reduced. (to tell oxidation of aldehyde to corresponding ketose, aka carboxylic acid)
CHO—> COOH @C1
What is used to oxidize sugars to Aldaric Acid?
What functional group(s) are oxidized?
HNO3 oxidizes the CHO @C1 and the primary alcohol (CH2OH) @C6. It’s too weak to oxidize the other 2ndary alcohols (OHs).
It makes them both COOH which could potentially create meso compounds because the product would be symmetric, —> optically inactive!
Explain the oxidation of sugars to Uronic Acid.
Give a biologically significant example.
Can only be done using enzymes.
Oxidizes only the primary alcohol (CH2OH).
Glucuronic acid is used by liver to detoxify it from toxic substances. It does this by binding to the toxins (THC, anabolic steroids, morphine) and is then excreted in urine.
Drug tests look for this metabolite.
Explain the reduction of sugars to Alditols.
Give a biological relevance of these.
What happens if the sugar is a ketose?
Use catalytic hydrogenation (H2/Pd or Pt), NaBH4, LiAlH4 – which are both hydride donors.
Reduces CHO into CH2OH (into a sugar alcohol).
Sugar alcohols are poorly absorbed by body, metabolize and pass through body quickly, making them low-calorie sugars. (eg, Sorbitol and Xylitol in sugar-free gum).
That ketone group is also reduced into normal OH and H, which could be on either side. == creating new stereocentre.
Explain Epimerization
A pair of epimers are diastereomers where only one stereocentre is different. Epimerization involves this switch of one stereocentre of the ALPHA CARBON.
See mechanism in notes.
Explain Isomerization.
Constitutional isomers have the same molecular formula, just different arrangement.
Isomerization of aldehyde to ketone involves an ene-diol rearrangement of the ALPHA CARBON under BASIC conditions with successive(2) tautomerizations (movement of double bond position and a proton).
See mechanism in notes.
What happens in Aldol Reactions?
Name 2 related biologically significant aldol rxns.
Enolates attack other aldehyde or ketone to form a product of both the nucleophile (enolate) and electrophile (next ald/ket).
In combined product: the nucleophile keeps it C=O, while the electrophile becomes the alcohol.
Aldol=aldehyde+alcohol
See mechanism in notes.
Aldol rxn catalyzed by aldolase in the formation of fructose-1,6-biphosphate in glucose byosynthesis; and the reverse Retro-aldol Rxn.
Explain the Acylation of OH Groups
Addition of acyl groups to alcohols for form acetyl esters by a nucleophilic substitution rxn.
We acetylated cellulose in lab, creating cellulose acetate.
Only the OHs get acetylated (must have an H on it)
See mechanism of acid-catalyzed acetylation using acetic anhydride in notes.
Explain the Kiliani-Fischer Synthesis of Monosaccharides
It lengthens the monosacc by 1 C from the top (added on top of the aldehyde), creating a new stereocentre, a new C1. The key (and beginning) step is the addition of CN- to the aldehyde forming a cyanohydrin. The CN at the top eventually gets replaced to an aldehyde again.
Traditional Method:
- have to convert CN to COOH to lactone (C=O) to -onic acid (COO-Na+); all so that then we can separate the diastereomers formed from the new stereocentre produced into 2 separate flasks - convert -onic acid back to lactone using acid, then reduced to an aldehyde using Na/Hg (VERY TOXIC)
Modern Method uses 3 steps, and no toxins:
- use catalyst H2, Pt/BaSO4 to reduce nitrile (CN) to imine (HC=NH) (the Barium stops the rxn from going all the way to an amine).
- hydrolyze imine to aldehyde (HC=O) then separate the diastereomers using HPLC
What linkage connects 2 monosaccharides?
Glycosidic linkage (acetal) with at least 1 anomeric C involved
What are the relative stabilities of hemiacetals and acetals in different pH conditions?
What are the conditions for hemiacetal mutarotation?
Acidic conditions: hemiacetals and acetals are formed and degraded.
Neutral conditions: hemiacetals are unstable, acetals are stable.
Basic conditions: hemiacetals are unstable and thus can mutarotate, acetals are stable.
If one part of molecule is a hemiacetal, the whole molecule collectively can mutarotate, and be a reducing sugar.
What are the 2 disaccharides of D-glucose?
Are either of them reducing sugars?
Maltose: alpha(1,4) glycoside linkage
- reducing &; mutarotates bc has hemiacetal
Cellobiose: beta(1,4) glycoside linkage
- reducing &; mutarotates bc has hemiacetal
They differ only by the configuration of the anomeric C (aka, cis vs trans)
What is the bond configuration of Lactose?
Lactose: beta(1,4) glycoside linkage btwn D-glucose and D-galactose.
These monos only differ by configuration on C4.
This bond can be cleaved by lactase enzyme
What is the bond configuration of Sucrose?
What is the effect of the hydrolysis of sucrose?
What is meant by “invert sugar”?
D-glucose and D-fructose.
alpha(1,2) @ glucose
beta(2,1) @ fructose
If you hydrolyze sucrose, it creates 1:1 mixture of D-gluc and D-fruc ==> “invert sugar”. = hydrolyzed product rotates PPL in opposite direction
- means that the mixture rotates PPL in different direction (left) from Sucrose (+66) - this mixture is sweeter than sucrose, and has a longer shelf life (aka, it won't crystallize at high concentrations) - sucrose is not a reducing sugar, but when it's hydrolyzed it creates 2 hemiacetals, making it reducing.
What are the two types of starch?
What are they used for?
What is their structure?
- types of polysacc starches that are used as energy storage for plants
Amylose: UNbranched chains of D-glucose joined by alpha(1,4) glycosidic bonds, forming a hollow helical structure
Amylopectin: Branched polymer of D-glucose with alpha(1,4) linkages in chain, and then branches start with alpha(1,6) bonds.
Describe Glycogen
Energy/carb storage for animals. stored in liver and muscle tissues.
Same as amylopectin, except more branches for easier access. Alpha(1,4) and Alpha(1,6)
Describe Cellulose.
What is its structure? Its bigger structure.
How can it be degraded?
In plant cell walls.
similar to amylose – unbranched, BUT linear straight chain of BETA(1,4) (thus config of anomeric C is different)
Bundles up to form chain bundles (in a crystalline arrangement via H bonding – because every 2nd unit is rotated for extra bonding)–> microfibrils–> fibrils –> fibres= can be found in cotton, paper, wood.
The H bonding makes cellulose very water-insoluble, even though glucose is soluble.
Cellulase Enzyme breaks it down into D-glucose EXTRACELLULARLY (outside the microorganism). But only cellulase-producing microorganisms can do this. So humans can’t get carbs from plants, but cows can because they’re in a symbiotic relationship with these microorganisms.
What’s a practical place you see Cellulase Enzyme?
In laundry detergent. It breaks down cellulose (which is 90% of cotton), so it’ll take care of pilling.
Describe glycolysis in general.
Glucose + 2NAD+ +2 ADP + 2 PO43- —–> 2 pyruvates + 2 ATP + 2 NADH
Anaerobic process
10 enzymatic steps (1-5 energy consumption, 6-10 energy production)
What are the 2 phases of glycolysis?
Steps 1-5: energy consumption. glucose + 2ATP –> 2G3P
Steps 6-10: energy production. 2 G3P —> 2 pyruvates +4 ATP
What happens in Step 1 of glycolysis with hexokinase (glucose-> G6P)?
Hexokinase converts glucose into G6P by adding a P from ATP (CH2OH to CH2OPO3 2-).
USES Mg2+ on ATP O-s!!!
What happens in Step 2 of glycolysis with phosphoglucose isomerase(G6P -> Fruc6P)?
G6P to Fruc6P
Hemiacetal to aldehyde form, then isomerizes it to a ketone via ene-diol rearrangement step.
What happens in Step 3 of glycolysis with phosphofructokinase (Fruc6P -> Fruc-1,6-bisphosphate)?
this enzyme can only act on the BETA anomer of Fruc6P, so if it’s in alpha, it’ll mutarotate to beta.
This is a rate-determining step, and a control point int he pathway.
Adds PO32- onto Carbon 1!!
What happens in Step 4 of glycolysis with Aldolase (Fruc-1,6-bisP –> DHAP + G3P)?
Retro-aldol rxn.
In plants and humans, the enzyme uses imine because it’s a better electron acceptor than the carbonyl that’s there. =NH+—Enzyme !! Creates DHAP and G3P.
What happens in Step 5 of glycolysis with Triosephosphate isomerase (DHAP –> G3P)?
DHAP gets isomerized into an aldehyde again via ene-diol mechanism
Step 6 of glycolysis: G3P dehydrogenase (G3P –> 1,3-bisphosphate)
Oxidative phosphorylation of G3P, with help of NAD+–> NADH. But it’s actually performed on the sulfur version of G3P == hemithioacetal (S-Enz at top).
What are the roles of NADH and NAD+ in REDOX?
coenzyme NADH is the reducing agent and hydride donor.
NAD+ is the oxidizing agent and hydride acceptor.,
Step 7 of glycolysis: Phosphoglycerate kinase: 1,3-bisphosphate –> 3-phosphoglycerate
Removes the PO32- on the C1 to create ATP and COO-.
Mg2+ is there as a cofactor.
Step 8 of glycolysis: Phosphoglycerate mutase (3-phosphoglycerate –> 2-phosphoglycerate)
How is this different in plants?
Moves Phosphate from C3 to C2 by adding a group to C3 and then removing the old one from C3. Enzyme uses a histidine residue
Plants take the one at C3 and put it on C2
Step 9 of glycolysis: Enolase (2-phosphoglycerate –> phosphoenolpyruvate)
An H and an OH is taken away to create an enol. Enols are usually very unstable and so are usually found in their keto forms. But this enol has no H on its phosphate so it can’t revert to its keto form!
The energy in this enol will be used to make ATP.
Step 10 of glycolysis: Pyruvate kinase: phosphoenolpyruvate —> pyruvate
transfer of phosphate to ADP gives ATP. so now the enol can tautomerize into its stable keto to make pyruvate.
What happens to pyruvate after glycolysis?
Pyruvate (3 Cs) undergoes OXIDATIVE DECARBOXYLATION which is a successive loss of CO2 using TPP and an oxidation of the C that’ll be attached to the CoA by lipoic acid —> into Acetyl-CoA (2 Cs).
Performed by the pyruvate dehydrogenase complex.
TPP—> TPP ylide —> ylide-pyruvate—> - CO2 —> ENAMINE attacks lipoic acid –> regenerated ylide + CO-oxidized lipoic acid —> transesterify with CoA-SH to make Acetyl-CoA
Explain the significance of Thiamine Pyrophosphate in oxidative decarboxylation.
What is a ylide?
Its active part is its thiazolium ring – weakly acidic and forms a YLIDE.
YLIDE = overall neutral compound with pos and neg charges adjacent to each other. (aka, a stabilized carbocation)
How is the lipoic acid oxidized?
FAD is a reducing agent/hydride acceptor that oxidizes lipoic acid. Turning FAD into FADH2
What are aminotransferases?
Name a medicinal relevance.
Aminotransferases are enzymes that move amino groups btwn alpha AAs and beta-keto acid carbohydrates and vice versa.
Tests for high levels of aminotransferases in blood indicate liver damage.
Describe aminotransferase (transamine) reactions.
What is PLP?
Distinguish btwn an imine of PLP and an imine of alpha-keto acid.
These rxns btwn AAs and alpha-keto acids require Pyrodoxal phosphate (PLP). PLP is a coenzyme that functions as an amino-group carrier.
In the first rxn, the amino group from AA is transferred to PLP, creating an imine of PLP (because its C is involved in C=N). The tautomerization of this imine gives Imine of alpha-keto acid. The hydrolysis of this imine releases pyruvate (alpha keto acid) from the PMP.
Rxn 2 is the reverse of rxn 1 except the amino group is moved onto a different alpha-keto acid. PLP is regenerated.
What makes a fatty acid water-insoluble?
When would be the only time that they are soluble in water?
Its long hydrocarbon hydrophobic tail.
If fatty acids are ionized (COO-) then they’ll be soluble in water.– but only a tiny amount because the pH drops, stopping further ionization.
