Ch 4 Carb Structure And Function Flashcards
Monosaccharides
Most basic structural unit of carbs
Formula is Cn(H2O)n
Trioses
Tetroses
Pentoses
Hexoses
Simplest monosaccharides containing three Cs
Tetroses contain 4 Cs
Pentoses contain 5
Hexoses contain 6
Aldoses
Carbs that contain aldehydes as their most oxidized functional group
Ketoses
Carbs that contain alcohols with ketones as their most oxidized functional group
Glyceraldehyde
Simplest Aldose - an aldotriose
A polyhydroxylated aldehyde
Dihydroxyacetone
Simplest ketose also participates in glycosidic bonds
Commonly tested carbs
D-Fructose
D-glucose
D-galactose
D-mannose
Optical isomers
Also called stereoisomers
All share chemical formula
Enantiomers
Share chemical formula and are nonsuperimposable, nonidentical, mirror images of each other
Same sugar in different optical families
D and L naming convention
D-+ has a positive rotation
L-+ has negative
All D sugars in Fischer projection have hydroxide of their highest numbered chiral center on right and L sugars have that hydroxide on the left
Diastereomers
Two sugars that are in the same family (both ketoses or both aldoses with same number of carbons) that are not identical and are not mirror images
Epimers
A special subtype of diastereomers that differ in configuration at exactly one chiral center
Equation for number of stereoisomers with a common backbone for a given molecule
2 to the power n
Where n = number of chiral carbons.
Hemiacetals
And hemiketals
Monosaccharides have an Oh group (nucleophile) and a CO group (electrophile)
And can therefore undergo intramolecular reactions to form cyclic hemiacetals (from aldoses) and hemiketals (from ketoses)
Pyranose
And furanose
Six-membered and 5-membered rings respectively - only cyclic molecules that are stable in solution due to ring strain
Anomeric carbon
Carbonyl carbon that becomes chiral in the process of formation of either a hemiacetal or hemiketal
Anomers
Two molecules that differ at the anomeric carbon
Alpha anomer
In glucose, has the oh group is C-1 trans to the -CH2OH substituent (axial and down)
Left
Beta anomer
Has -OH group of C-1 cis to the -CH2OH substituent (equatorial and up)
Right
Haworth projection
When converting a Fischer projection to this everything on the right will point down
Mutarotation
Spontaneous change of configuration of hemiacetals around C-1
Exposing them to water causes them to cycle bt open and closed forms forming either alpha or beta anomer
Occurs rapidly when catalyzed with acid or base
Aldonic acids
Oxidized aldoses
Monosaccharides switching between anomeric configurations and spending time in open chain aldehyde form are oxidized to carboxylic acids to form aldonic acids
Because they can be oxidized they are reducing agents
Reducing sugar
Any monosaccharide with an acetal ring
Lactone
When aldose is in ring form oxidation yields a lactone
Contains a cyclic ester (O as part of the ring)
Vit C is an example
Tollen’s reagent
Utilizes Ag(NH3)sub2+1charge as an oxidizing agent In positive Tollen’s test aldehydes reduce Ag+ to metallic silver
Benedict’s reagent
Aldehyde group of aldose is readily oxidized
Indicated by a red precipitate of Cu2O
Tautomerization
Rearrangement of bonds in a compound usually by moving a hydrogen and forming a double bond
The ketone group picks up a hydrogen while the double bond moves between two adjacent carbons forming an enol
Enol
Compound with double bond and alcohol group
Aditol
When the aldehyde group of an aldose us reduced to an alcohol
Deoxy sugar
Contains a hydrogen that replaces a hydroxyl group on the sugar
Phosphorylation
Extremely important metabolic reaction of glycolysis in which a phosphate group is transferred from ATP to glucose
Acetals
Hemiacetals react with alcohols
Glycosidic bonds
Anomeric hydroxyl group is transformed into an alkoxy group yielding a mixture of alpha and beta acetals with water as the leaving group
These are the resulting C-O bonds
Glycosides
Hemiacetals react with alcohols to form acetals. The resulting acetals are held together in mixture with alpha and beta acetals via C-O bonds called glycosidic bonds. And the acetals are known as glycosides.
Furanosides
Glycosides derived from furanose rings
Pyranosides
Glycosides derived from pyranose rings
Disaccharide
Glycosidic bonds formed between two monosaccharides result in formation of this
The hydroxyl group on the anomeric carbon of one reacts with hydroxyl
Important disaccharides
Maltose - two glucose molecules linked by alpha 1,4 glycosidic bond
Sucrose - glucose - alpha - 1,2 - fructose
Lactose - galactose - beta - 1,4 - glucose
Homopolysaccharide
A polysaccharide entirely composed of one type of molecule such as glucose
Heteropolysaccharide
Polymer made of more than one type of monosaccharide
Three most important biological polysaccharides
Cellulose, starch, and glycogen
Cellulose
Main structural component of plants. Homopolysaccharide chain of beta D glucose linked by beta 1,4 glycosidic bonds
Humans cannot digest
Starches
Polysaccharides that are more digestible by humans because they are linked alpha D glucose monomers
Plants store it primarily as amylose
There is also amylopectin
Amylose
Starch
Linear glucose polymer linked via alpha 1,4 glycosidic bonds
Degraded by alpha-amylase and beta-amylase
Amylopectin
Starts with the same type of linkage that amylose exhibits but also contains branches via alpha 1,6 glycosidic bonds
Debranching enzymes help degrade this
Beta-amylase
Cleaves amylose at the nonreducing end of the polymer (the end with the acetal) to yield maltose
Alpha-amylase
Cleaves randomly along the chain to yield shorter polysaccharide chains, maltose and glucose
Glycogen
Carb storage unit in animals
Similar to starch except or had more alpha-1,6 glycosidic bonds which makes it highly branched which optimizes energy efficiency and makes it more soluble in solution allowing more glucose to be stored in the body
Glycogen phosphorylase
Functions by cleaving glucose from the nonreducing end of a glycogen branch and phosphorylating it and producing glucose 1-phosphate which plays an important role in metabolism