Exam Three Content

What is the formula of sugar and its annotation

• -Ose suffix

• C_n(H₂O)_n

D-Ribose

• information molecule

• building block of nucleic acids

Epimer, Diastereomer, Enantiomer

Epimer: Carbohydrates with the same formula but a variation in one asymmetrical carbon

Diastereomer: Carbohydrates with the same formula but variation in more than one asymmetrical carbon

Enantiomer: D and L Glucose are mirror images, D is more biologically common

Chair vs Boat vs Haworth

Haworth projection: makes the ring look flat

Chair/Boat: Six membered rings will pucker into either the chair or boat

• chair is more stable

Aldose and Ketose

Aldose: Carbonyl is an aldehyde on C1

Ketose: Carbonyl is a ketone on C2

Cyclization of Glucose

Chemical reaction where linear (Fischer Projection) glucose forms a ring and is favored when you have at least 4 carbons

• C5 hydroxyl attacks C1 aldehyde producing a cyclic hemiacetal

• The carbon that used to the be the carbonyl carrbon becomes the anomeric carbon

Beta Anomer: When the C6 CH₂OH and the C1 (Anomeric) OH are on the same side

Alpha Anomer: When the C6 Ch₂OH and the C1 (Anomeric) OH are on opposite sides

Fructose Forms

Can exist in linear or two cyclical forms (4 or 5 carbon rings)

• Furanose = 5 membered ring

  • Favored??

• Pyranose = 6 membered ring

  • More rare???

Glycosidic Bonds + common Disaccharides

Two monosaccharides combine via a condensation/dehyddratio reaction, forming disaccharides

lactose: β-1,4-Glycosidic bond

• β-D-galactopyranosyl-(1→ 4)-D-glucose

• Bond between galactose and glucose

Maltose: α-1,4 Glycosidic Bond

• α-D-Glucopyranosyl-(1→4)-D-glucose

Hemiacetal to Full Acetal

• Free cyclic glucose has an anomeric OH, making that carbon part of a hemiacetal

• When this anomeric OH participates in the formation of a glycosidic bond, that carbon becomes an acetal

Glucose → Pyruvate

• Pyruvates are partially oxidized via the removal of electrons

• Glucose = more reduced

• Pyruvate = more oxidized

• Glucose → pyruvate, overall, carbons are more oxidized

High GI Foods

• High HI = glucose enters the blood rapidly

• High GI foods can cause rapid blood-glucose spike → insulin resistant patients should avoid them!

  • Amylopectin have more ends and enzymes will be able to better pull off the glucose, increasing glucose release

  • Insulin resistant patients should avoid foods with a higher amylopectin:amylose proportion

Amylose, Amylopectin, Glycogen

Amylose: Plant glucose storate

• α(1→ 4) bonds, unbranched

Amylopectin: Plant glucose storage, branched

• Main chain: α(1→ 4)

• Branches: α(1 → 6)

glycogen: Animal glucose storage

• resembles amylopectin but is more branched

Significance of branching

• more branches → more ends → more places for glucose to release simultaneously

• Due to glycogens many branches and ends for glucose release, it can release stored glucose quickly

Chain length is determined by — and structures have a —

Enzymes, protein anchor within

NAD+

• NAD+ is two nucleotides connected through their phosphate groups via a phosphoanyhdride bond and a nicotinamide ring derived from a niacin

• Electron carrier in oxidized state

• A co-factor; not covalently attached to the protein but can freely associate and dissociate

Where does redox chemistry occur + what happens to NAD+

• Nicotinamide ring

• Substrate oxidation is the removal of two hydrogen equivalents, NAD+ will receive one Hydride (H-)

  • NAD+ + 2H → NADH + H+

  • The other proton is released into the solution

• This reaction is readily reversible

How does the N+ charge disappear

• Nicotinamide ring starts as NAD+ with a formal positive charge

• the hydride H- is transferred onto a carbon of the nicotinamide ring

• The H- with 2 electrons is going to change the bonding/electron distribution of the conjugated nicotinamide ring and through rearrangement of the π electrons/resonance, the nitrogen is no longer left electron deficient with the formal +1 charge

NAD+ and NADP+

NAD+/NADH → mainly catabolic reactions

NADP+/NADPH → mainly anabolic reactions

• the electron transfer still occurs at the nicotinamide ring

Glyceraldehyde 3-phosphate mechanism

• Phase 2 pay off - step 6 in glycolysis

Reaction: G3P → 1,3-biphosphoglycerate and NAD+ → NADH

• G3P is losing electrons, getting oxidized

• NAD+ gains electrons, getting reduced

GAPDH Mechanism: Catalyzed by the enzyme glyceraldehyde-3-phosphate dehydrogenase

• Has an important active-site reside (Cys)

• G3P will react with the Cystine (-SH) and form a covalent thiohemiactal between the cysteine sulfur and the aldehyde of the G3P

1. G3P Binds:

   1. G3P enters the active site

   2. NAD+ is already there in its oxidized state

2. Cys attacks G3P:

   1. The reactive cysteine sulfur attacks the aldehyde carbon of G3P

   2. A thiohemiacetal covalent enzyme-substrate intermediate forms

3. The redox step:

   1. The substrate transfers a hydride H- to NAD+

      1. Substrate is oxidized and NAD+ is reduced

   2. release of NADH:

      1. NADH leaves the active site and is replaced by another molecule of NAD+

   3. Phosphate Enters:

      1. Phosphate enters and the covalent thioester linkage between the substrate and enzyme undergo phosphorylysis, releasing the second product, 1,2-biphosphoglycerate

GADPH structure + how it helps

• Quaternary homotetramer → 4 proteins subunits and they are the same type of subunit

• Positions the G3P and NAD+ very closely together and in the correct orientation so that the hydride can transfer efficiently from substrate to the nicotinamide ring