11. Carbohydrate structure and function Flashcards
which biological macromolecule is the most abundant
carbohydrates
besides cell respiration, list some of the other roles of carbs
structural elements of cell walls or animal connective tissues, cell-cell recognition, cell adhesion or signaling, support skeletal joints
how many monomeric units do monosaccharides have
1
how many monomeric units do disaccharides have
2
how many monomeric units do oligosaccharides have
2-20
how many monomeric units do polysaccharides have
20+
what are carb polymers sometimes referred to as
glycans
what is a glycan
a name used to refer to carb polymers
what is a homoglycan
identical monomers
what is a heteroglycan
different monomers
what are glycoconjugates
carbohydrates covalently attached to another molecule (ie non-sugar molecules such as proteins)
what 2 functional groups will a monosaccharide be bonded to
aldehydes or ketones
what is the name for a monosaccharide with an aldehyde
an aldose
what is the name for a monosaccharide with a ketone
a ketose
what shape is the backbone of most common monosaccharides
linear chains
in a monosaccharide structure, what are the carbons bound to
one will be bound to a double bond (aldose or ketose), and all the other carbons will be bound to OH and H
how do you determine the type of enantiomer a monosaccharide is
look at the chiral carbon farthest from the carbonyl carbon, and see which side the OH is on
which side is the OH for the D enantiomer
right
which side is the OH for the L enantiomer
left
how do you get the name of a 4C or 5C ketose
often, you just add “ul” to the name of the corresponding aldose
define epimers
two diastereomers that differ only in the configuration at one carbon
how do cyclic structures form for monosaccharides
the carbonyl carbon can react with an intramolecular hydroxyl group
what is the resulting structure of a monosaccharide cyclizing
the O of the OH is incorporated into the cycle = hemiacteals or hemiketals, and a new chiral center is formed
how many stereoisomers are produced when a monosaccharide cyclizes
2
how are the stereoisomers of cyclization denoted
alpha and beta (OH pointing up is beta, OH pointing down is alpha)
since the two stereoisomers of cyclization only differ at the hemiacetal/hemiketal carbon, what are they called
anomers
what are the 2 names of 5 and 6 membered rings with one oxygen
furanoses and pyranoses
what is a furanose
a 5 membered ring with an oxygen
what is a pyranose
a six membered ring with an oxygen
to convert a cyclic drawing to a linear drawing, which way does a sub going below the plane go on the linear drawing
down = right left = up
what is mutarotation
when the alpha and beta anomers interconvert configurations. It involves breaking bonds and opening up the ring temporarily
what is the product of mutarotation (in glucose solution)
1/3 alpha-D-glucose
2/3 beta-D-glucose
a teeny bit of linear glucose
a teeny bit of glucofuranose
what are the two haworth projections
chair or boat
T or F: you can turn the planar ring into the chair or boat conformation without breaking any bonds
true
what are the 4 non-polymerized monosaccharide derivatives
sugar phosphates, deoxy sugars, amino sugars, and acidic sugars
what are sugar phosphates
phosphate esters
what is the charge of sugar phosphates at neutral pH
negative
what is the purpose of sugar phosphates
phosphorylation of sugar tends to trap sugar in a cell, as there aren’t many transporters for phosphorylated sugars
what is a deoxy sugar
one of the OH groups is replaced with H
what is an amino sugar
one of the OH groups is replaced with an amino group
what is an acidic sugar
a carbon is oxidized (this will often be the aldehyde carbon)
how are disaccharides produced
by condensing two monosaccharides into a glycoside with the formation of a covalent O-glycosidic bond
in monosaccharide condensation, which parts of the monosaccharides interact
the OH of one sugar reacts with the anomeric carbon of the other
what is maltose a major component of
dried cereal grains
what is the structure of maltose
two D-glucose residues joined by an 1,4 alpha-glycosidic bond. The anomeric carbon of glucose on the left is locked in an alpha conformation while one on the right can freely rotate between a and b conformations
what is lactose a major component of
milk
what is the structure of lactose
D-galactose and D-glucose joined by an 1.4 beta-glycosidic bond
describe lactose intolerance
arises from insufficient levels of lactase (which breaks down lactose). When the undigested lactose passes into the large intestine, high lactose concentration retains water, and the lactose is eventually fermented
what is the structure of sucrose
D glucose and D fructose joined by an 1,2 glycosidic bond
how is an N-glycosidic bond made
an N atom of a molecule can react with an anomeric carbon of a cyclic sugar
how are nucleosidases made
with N-glycosidic bonds
what is a homoglycan
a glycan with all the same monosaccharide subunit
what is a heteroglycan
a glycan with different monosaccharide subunits
what polysaccharides store glucose monomers for future cell respiration
starch and glycogen
how is starch and glycogen stored in a cell
stored in large and heavily hydrated clusters or granules
what are the two forms of starch
amylose and amylopectin
describe the structure of amylose
unbranched polymer of 100-1000 D-glucose residues connected by (α1→4) glycosidic linkages
describe the structure of amylopectin
branched, and branching occurs every 24-30 residues. Branches are attached via (α1→6) glycosidic bonds to linear chains of residues linked by (α1→4) glycosidic bonds. amylopectin may contain 300-6000 glucose residues
describe the structure of a starch granule
it may have double helical chains of amylose/amylopectin and amylopectin/amylopectin.
what happens to the structure of starch when fuels need to be mobilized
glucose molecules at the non reducing ends are enzymatically removed when fuels need to be mobilized
describe the structure of glycogen
its a polymer of (α1->4) linked D-glucose subunits with (α1->6) branches. Its more branched + compact
where in the body is glycogen mainly present
in the liver and skeletal muscle and cytosolic granules
what happens to the reducing ends of glycogen
degradative enzymes hydrolyze glucose molecules from the non reducing ends of branches simultaneously
give the formula for the number of glucose reducing ends available
n branches = n+1 reducing ends available
why is glucose stored as glycogen
glycogen = insoluble while glucose = soluble. If we stored it as glucose, cell osmolarity would be high and water would rush in = cell bursts
what is cellulose
tough, fibrous, and water insoluble glucose homoglycan. Its the major component of cell walls
describe the structure of cellulose
linear unbranched glucose chains with a (β1->4) glycosidic linkage
what are glycosidases
enzymes that catalyze the hydrolysis of glycosidic bonds, which is essential for sugar digestion
describe the role of a-amylase
it’s an endoglycosidase: breaks internal glycosidic bonds for (α1→4) glycosidic linkages. It breaks downs starch and glycogen
describe the role of cellulase
it’s an endoglycosidase: it breaks (β1→4) terminal glycosidic bonds in cellulose to release maltose
describe the structure of chitin
a linear unbranched polymer. The monomers are N-acetylglucosamine (GlcNAc) linked by (β1→4) glycosidic linkages
how are chitin bundles/fibrils formed
the GlcNAc residues of adjacent strands of chitin form hydrogen bonds with each other
how do polysaccharides fold
a chain of monomers formed by covalent bonds will be stabilized into a shape by weaker interactions
T or F: there is free rotation around the glycosidic linkage of polysaccharides
true; but steric hindrance limits the number of viable bond angles
T or F: phi and psi angles can be used to describe the 3D polysaccharide structure and its dihedral angles
true
what is the most stable structure for the α1->4 linked chains of starch and glycogen
a tightly coiled helix
what is the most stable conformation of cellulose
where each glucose chair is 180 degrees from it’s neighbor, which produces a straight and extended chain with all OH groups available for H bonding to other chains
