Ch 7.1-7.2Carbohydrates Flashcards
What is the most abundant biomolecule in the known universe?
D-Glucose
What is the general formula for carbohydrates?
(CH2O)n, where n > 3
Some roles of carbohydrates in cells
precursors for almost all other biomolecules, used to produce energy, linked to other molecules (ex: glycolipid, glycoprotein)
describe the classification and naming of carbohydrates
1) whether it is an aldehyde (aldose, aldo-) (more common in carbohydrates ) or a ketone (ketose, keto-)
2) number of carbon atoms:
3 (triose), 4 (tetrose), 5 (pentose), 6 (hexose), 7 (heptose)
ex: aldohexose or ketopentose
4) A monosaccharide is given D configuration if the -OH group of the penultimate carbon (that forms the hemiketal or hemiacetal) is on the same side as D-Glyceraldehyde.
5) A cyclic monosaccharide is given the α (alpha) designation if the -OH group of the anomeric carbon is on the same side as the oxygen atom on the highest numbered asymmetric carbon in the ring with a hydroxyl group (one below the penultimate carbon that forms the hemiketal or hemiacetal), β (beta) if it is on the opposite side.
.
Note: Designation of D or L relates the configuration of a given molecule and does not specify the sign (+ or -) of rotation of plane-polarized light.
what is the classification of D-Glucose?
aldohexose
what is the classification of D-Fructose?
ketohexose
what are the cutoff points for monosaccharides, oligosaccharides and polysaccharides?
Monosaccharide:
1 residue
Oligosaccharides:
2-10 residues
disaccharide - 2
trisaccharide - 3
tetrasaccharide - 4
Polysaccharide:
many residues (up to thousands)
monosaccharide
a sugar with one residue
oligosaccharide
a sugar with 2-10 residues
polysaccharide
a sugar with more than 10 residues (up to thousands)
enantiomer
stereoisomers that are a mirror images of each other.
ex: D-Glyceraldehyde and L-Glyceraldehyde
enantiomers rotate polarised light in opposite directions and DO NOT interact with the same binding sites on enzymes or proteins (lock-and-key hypothesis)
epimer
stereoisomers (specifically diastereomers) that differ in stereochemistry at only one chiral carbon, aside from
ex: D-Erythrose and D-Threose are 2-epimers of each other.
ex: D-Glucose and D-Galactose are 4-epimers of each other.
what is the numbering convention of carbohydrates?
For aldoses, C1 is the most oxidised carbon (the carbonyl carbon).
For ketoses, the carbonyl carbon is C2.
what is the simplest chiral carbohydrate?
Glyceraldehyde. Carbohydrates have three or more carbons: the ketotriose (dihydroxyacetone) is not chiral, but the aldotriose (glyceraldehyde) is.
what is a cyclic sugar with a five membered ring called?
furanose
what is a cyclic sugar with a six membered ring called?
pyranose
pyran
furan
pyranose
pyranose: a sugar with a six membered ring
furanose
furanose: a sugar with a five membered ring
hemiacetal
covalent bond between a hydroxyl group and an aldehyde
hemiketal
covalent bond between a hydroxyl group and a ketone
when a carbohydrate cyclises, which oxygen is responsible for the intracyclic oxygen?
the oxygen from the alcohol functional group of the hemiketal/hemiacetyl
when converting from a linear Fisher projection to a cyclised Haworth projection, what is the convention?
The intracyclic oxygen is at the top or upper-right of the ring in the Haworth projection. All subsituents on the left in the Fisher projection point up in the Haworth projection, conversely all substituents on the right point down. If the carbonyl oxygen (that is now a hydroxyl) points the opposite direction of the -OH group in the highest numbered chiral carbon with a hydroxyl, the new cyclic structure is said to be β (beta). If it points the same direction as that group it is said to be α (alpha).
When a cyclised carbohydrate interconverts from alpha to beta form it is called what?
mutarotation
what is the predominate anomer of glucose?
β (beta) anomer, due to steric hinderence. Most bulky groups can be placed on the equatorial positions of the ring in chair conformation using this mutarotation.
anomer
Two stereoisomers that differ only in their configuration about the anomeric carbon atom (the central carbon of an acetal or a hemiacetal)
describe the energy diagram of a pyranose in its various forms
45.2kJ/mol (10.8kcal/mol) from chair to half-chair
23kJ/mol (5.5kcal/mol) from chair to twist-boat
30kJ/mol (72kcal/mol) from chair to boat
D-Ribose
D-Glucose
D-Galactose
What is the structure of:
D-Ribose
D-Ribose
What is the structure of:
D-Glucose
D-Glucose
What is the structure of:
D-Galactose
D-Galactose
where is the intracyclic oxygen in the two chair forms of a pyranose?
describe the two chair forms of β-D-Glucopyranose
what is the difference between fructose and glucose?
fructose is the ketose form of glucose, which is an aldose (the carbonyl is on C2 in fructose and C1 in glucose)
D-Fructose
What is the structure of:
D-Fructose
glycerol
What is the structure of:
glycerol
2-Deoxy-β-D-ribofuranose
What is the structure of:
2-Deoxy-β-D-ribofuranose
N-acetyl-D-glucosamine
What is the structure of:
N-acetyl-D-glucosamine
what is the ketotriose called?
dihydroxyacetone
What is the aldotriose called?
glyceraldehyde (chiral!)
What is the difference between the ketotriose and the aldotriose besides the location of the carbonyl?
The ketotriose is achiral while the aldotriose is chiral
