Chapter 8: Carbohydrates Flashcards
Formula for Carbohydrates, n=?
(C ∙ H2O)n, where n ≥ 3.
basic carbohydrate unit? How do they differ?
-monosaccharides
-differ in their number of carbon atoms and in the arrangement of the H and O atoms attached to the carbons.
Monosaccharides can be strung together in almost limitless ways to form?
Polysaccharides.
Monosaccharides are classified according to?
the chemical nature of their carbonyl group and the number of their C atoms.
What are the 2 carbonyl groups and their sugars
Aldehyde, aldose
Ketone,ketose
The smallest monosaccharides, those with three carbon atoms, are? Those with four, five, six, seven, etc. C atoms are?
-trioses.
- tetroses, pentoses, hexoses, heptoses, etc.
How to determine possible stereoisomers?
All but two of its six C atoms, C1 and C6, are chiral centers, so D-glucose is one of 2 4= 16 possible stereoisomers.
How to differentiate between D and L sugars/determine stereochemistry?
If OH on the bottom chiral centre points to the right it is a D-
If OH on the bottom chiral centre points to the left it is a L-
has to be farthest from carbonyl group
D- and L- sugars are what kind of isomer
enantiomers, L sugars are the mirror images of their D counterparts.
why is the the D prefix is often omitted?
Because L sugars are biologically much less abundant than D sugars,
what are epimers
Sugars that differ only by the configuration around one C atom
difference between aldehyde and ketone
difference is the presence of a hydrogen atom attached to the C-O double bond in the aldehyde. Ketones don’t have that hydrogen
alcohols react with the carbonyl groups of aldehydes and ketones to form?
hemiacetals and hemiketals,
The hydroxyl and either the aldehyde or the ketone functions of monosaccharides can likewise react intramolecularly to form
cyclic hemiacetals and hemiketals
chiral center in a carb?
carbons that have both hydrogen and hydroxyl
what are anomers. what are the two types?
when the hydroxyl attacks the carbonylit can do so from either side, thus generating two different stereoisomers
It can either attack from this side, pushing the new hydroxyl down, resulting in the alpha anomer, or
it can attack from this side pushing the new hydroxyl up, resulting in the beta anomer,
If a cyclic monosaccharide has a six-membered ring we will call it a ?
pyranose
Sometimes the hydroxyl on carbon four can do the attacking, resulting in a five-membered ring which we will call a?
furanose
Haworth projections are used to draw?
cyclic monosaccharides
a way in which cyclic sugars can convert from one anomer to another?
This alpha glucose might go back to the linear form and then cyclize again to form the beta anomer.
why is glucose the most abundant monosaccharide in nature.
Only β -D-glucose can simultaneously have all five of its non-H substituents in equatorial positions.
which anomer is preferred for glucose? !
In fact, for glucose, the beta anomer is preferred because the hydroxyl on the anomeric carbon will be in the equatorial position versus axial in the alpha anomer.
Oxidation of an aldose converts its aldehyde group to a carboxylic acid group, called an? end in?
aldonic acid
-onic acid
Oxidation of the primary alcohol group of aldoses yields? end in?
uronic acids
-uronic acid
changes most bottom Carbon
Aldoses and ketoses can be reduced under mild conditions—for example, by treatment with NaBH4 —to yield polyhydroxy alcohols known as? end in?
alditols,
-itol
Monosaccharide units in which an OH group is replaced by H are known as ?
deoxy sugars.
In ____ one or more OH groups have been replaced by an amino group, which is often acetylated.
amino sugar
The bond connecting the anomeric carbon to the alcohol oxygen is
a glycosidic bond
Saccharides bearing anomeric carbons that have not formed glycosides are termed ?
reducing sugars
The identification of a sugar as nonreducing is evidence that?
it is a glycoside.
what are polysaccharides?
Polysaccharides, which are also known as glycans, consist of monosaccharides linked together by glycosidic bonds.
Polysaccharides are classified as either ?
homopolysaccharides or heteropolysaccharides if they consist of one type or more than one type of monosaccharide.
most well known disaccharides? how many sugars? which is more abundant
lactose and sucrose, 2 each, sucrose
is glucose a reducing sugar ?
Ye
what is sucrose
the major form in which carbohydrates are transported in plants. Sucrose is familiar to us as common table sugar.
Cellulose,
the primary structural component of plant cell walls (Fig. 8-8), accounts for over half of the carbon in the biosphere:
Chitin
is the principal structural component of the exoskeletons of invertebrates such as crustaceans, insects, and spiders and is also present in the cell walls of most fungi and many algae. It is therefore the second most abundant biomolecule, after cellulose. Chitin is a homopolymer of β (1→4)-linked N-acetyl-Dglucosamine residues:
Cellulose and Chitin Are what kind of Polysaccharides
Structural
Starch and Glycogen Are what kind of Polysaccharides
Storage
Starch and Glycogen Are what kind of Polysaccharides
Storage
Glycogen,
the storage polysaccharide of animals, is present in all cells but is most prevalent in skeletal muscle and in liver, where it occurs as cytoplasmic granules
