What is the formula for a monosaccharide? Use an example to describe how monosaccharides link to form disaccharides correct answer: (CH2O)*n, where n is the number of carbons and must be greater than 3 (e.g. glucose has 6 carbons, C6H12O6). Glucose and fructose are both monosaccharides, which link...
BCH210 Exam Questions With
Complete Soes
What is the formula for a monosaccharide? Use an example to
describe how monosaccharides link to form disaccharides
correct answer: (CH2O)*n, where n is the number of carbons
and must be greater than 3 (e.g. glucose has 6 carbons,
C6H12O6). Glucose and fructose are both monosaccharides,
which link through a glycosidic bond to form sucrose, a
disaccharide
Name, classify and describe the two simplest monosaccharides
(3 carbons) correct answer: Glyceraldehyde: Aldo-triose,
aldehyde on one end bound to a chiral carbon (hydroxyl group
and hydrogen) which in turn is bound to the final carbon that's
attached to another hydroxyl group. The L-isomer has the chiral
hydroxyl group on the left, and the D-isomer has it on the right
Dihydroxy-acetone: keto-triose, achiral ketone carbon in
between two carbons both bound to their own hydroxyl groups
*In aldoses, the first carbon in the chain will be double bonded
to oxygen. In ketoses, the second will be double bonded to
oxygen instead*
How are carbohydrate carbons numbered? correct answer: In
aldoses, carbon 1 is the aldehyde carbon. In ketoses, carbons are
numbered relative to the ketone end, and the ketone carbon is
always carbon 2
,The biologically relevant carbohydrate isomers are D-isomers.
How is this nomenclature assigned? What is the relationship
between the number of chiral carbons in a carbohydrate and the
number of possible linear structures that could exist for that
amount of carbons? correct answer: The L- or D-isomer
terminology is assigned based on the chiral carbon furthest away
from the carbonyl on the sugar (i.e. if hydroxyl group on carbon
5 of glucose is to the left, it's an L-isomer). The amount of
possible linear stereoisomers given a number of chiral carbons is
2 to the power of the number of chiral carbons (e.g. aldopentose,
aldehyde with 5 carbons, 3 are chiral, therefore 2^3=8 possible
linear structures of aldopentose)
What is carbohydrate cyclization and how does it happen?
correct answer: The transformation of a linear carbohydrate into
a one of two cyclical structures in solution (reversible in
solution). Starting with a linear carbohydrate, the hydroxyl
groups on the last chiral carbon carries out a nucleophilic attack
on either the aldehyde or ketone carbonyl of the sugar. The
hydroxyl oxygen bonds with the carbonyl carbon (oxygen is
now part of the main ring structure), with the other electrons that
made up its former double bond going to a proton in water. The
carbonyl carbon is now bonded to its original hydrogen and
oxygen, in addition to the hydroxyl hydrogen which has now
bonded to the carbonyl oxygen. The new bond that is ultimately
formed in cyclization is either hemiacetal (aldehyde derivative)
or hemiketal (ketone derivative). These intramolecular reactions
form either a 5-member furan ring or a 6-member pyran ring
What are anomers? What is the difference between alpha and
beta cyclical carbohydrates? correct answer: Cyclization
, introduces a new chiral carbon to the molecular structure, which
can vary in the localization of their new hydroxyl groups. Alpha
cyclical anomers will have the newly formed hydroxyl group
below the ring (axial), while beta cyclical anomers will have it
above the ring (equatorial) (descriptions with respect to Haworth
projections). In solution, we typically find 66% beta anomers,
33% alpha, and 1% linear structures.
What is the main sugar in honey? What's special about it? Why
does heating a sugar impact its sweetness? correct answer: The
main sugar in honey is fructose (found along with glucose,
sucrose and water). Fructose is a 6-carbon ketose that can form
both a furan and a pyran ring. Heating sugars impacts their
properties by promoting the formation of linear structures
How do we determine the chirality of cyclic structures? correct
answer: Mutarotation, a change in optical rotation of polarized
light following the inter conversion between the alpha and beta
anomers
Define isomers, constitutional isomers, the different
stereoisomers and the different diastereomers correct answer:
Isomers: same molecular formula, different structure
Constitutional isomers: different order of functional group
bonding
Stereoisomers: same formula and order, but...
Enantiomers: non-superimposable mirror images (differ in
spatial arrangement at all asymmetric carbons)
Diastereoisomers: not mirror images
Different diastereoisomers:
Epimers: differ at one asymmetric carbon
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