Biomolecules - Carbohydrates Flashcards
Intro to carbohydrates
Glucose - aldehyde
Fructose - ketone
*D represents a right handed carbohydrate (OH is on the right side of the chiral carbon). The opposite is an L carbohydrate. D and L are enantiomers (mirror images at every chiral carbon)
*we can digest the D sugars
*epimers are diastereomers that differ at only one carbon
Mutarotation - six membered ring for glucose is opening and closing
Alpha configuration is less favoured for glucose because it creates steric hindrance, but the beta anomer is the one with the anomeric oxygen in the cis position in relation to the last oxygen
Disaccharide: two monosaccharides linked together by a glycosidic linkage
Lactose: glucose + galactose; beta, 1,4 glycoside bond
Maltose: glucose + glucose; alpha, 1,4 glycoside
Sucrose: glucose + fructose; non reducing sugar
Cellulose: repeating glucose units formed by beta, 1,4 glycoside bond. Starch is alpha. We can break down the linkages in starch,
Glycogen: dry branched, alpha, 1,4 glycoside
*keto form is favoured unless enol form is particularly stable
* The body has more NAD+ than NADH and more NADPH than NADP+
From practice Qs
*the heaviest carbohydrate deflects the least in mass spectrometer
*fructose is a furanose in its cyclical form
*an aldose has an aldehyde functional group where a ketose has a ketone
Gluconeogenesis and Glycolysis
*In the fasted state, the body uses glycogen and gluconeogenesis to keep blood glucose levels constant (uses proteins and lactate)
*There are fast and slow acting forms of regulation
*fast acting: includes Le Chataliers principle and allosteric regulation (positive or negative; e.g. ATP is an allosteric regulator of many steps in glycolysis and AMP signals the cell to stop gluconeogenesis)
*slow acting: transcription (up regulates the transcription of necessary enzymes)
*hormonal regulation: the body produces certain hormones to determine whether gluconeogenesis and glycolysis are on or off - glucagon (promotes gluconeogenesis) and insulin (promotes glycolysis)
*glycolysis has a negative free energy change overall, but some steps are both positive and negative free energy change
Km and Kcat
Km is the substrate concentration at which the rate of conversion of reactant to product is half the maximum rate. The lower the Km for an enzyme, the faster it converts reactants to products at non-saturating substrate concentrations.
The Kcat of an enzyme is defined as the number of molecules of substrate converted to product per molecule of enzyme per second.
