Chapter 9: Carbohydrates Flashcards
what are the other two names for carbohydrates?
sugar
saccharide
what is a carbohydrate?
aldehyde or ketone compounds where every carbon in the structure is an alcohol except for one: the carbonyl
why are carbohydrates so named?
they have the general chemical structure (C*H2O)n
what is a monosaccharide?
a single monomer unit of sugar
what is a oligosaccharide?
a small polymer of monosaccharides
what is a polysaccharide?
a large polymer of monosaccharides groups linked together
what is a glycoprotein?
oligosaccharides linked to protein
what is a glycolipid?
oligosaccharides linked to lipids
draw the line structure for glucose
…
which form of sugar is the biologically relevant form: linear or ring?
ring
How do you know whether a carbohydrate is a D or and L carbohydrate?
you look at which way the second to last alcohol is pointed
Which carbohydrate is L carbohydrate?
the one whose second to last alcohol is pointing to the left
Which carbohydrate is D carbohydrate?
the one whose second to last alcohol is pointing to the right
which form of sugar is the biologically relevant form: L or D?
d
What kind of carbonyl does a ketose carbohydrate have?
ketone
What kind of carbonyl does a aldose carbohydrate have?
aldehyde
Are carbohydrates optically active and chiral?
yea
In Fischer projection, which lines are dashed?
the vertical ones
In Fischer projection, which lines are wedged?
the horizontal ones
which sugar did Dr. Shimko describe as being the foundation for all other sugars?
D-Glyceraldehyde
Why did Dr. Shimko describe D-Glyceraldehyde as being the foundation for all other sugars?
because it is the bases for how we assign stereochemistry to all carbohydrates
what is the second to last carbon in a carbohydrate called?
Penultimate carbon
is ‘glucose’ a common name or a systematic name?
common
why do biochemists use the penultimate carbon to determine carbohydrate stereochemistry instead of the R S system?
So that they don’t have to determine the R and S for every single chiral center
Which carbohydrate is primarily found in nature as L even though carbohydrates are more often found in nature as D?
L-arabinose
what is L-arabinose involved in?
photosynthesis
when you draw the D version of an L carbohydrate (or vice versa) do you have to reverse all the chiral centers or just the penultimate chiral center?
all the chiral centers
it’s like a complete mirror image
what 4 prefixes do you need to know to identify the number of carbons in a carbohydrate?
triose
tetrose
pentose
hexose
what is D-Glyceraldehyde involved in?
glycolysis
What are D-Erythrose and D-Xylose involved in?
pentose phosphate pathway
what is D-Ribose involved with?
its building block for RNA and DNA
what is D-Glucose involved in?
it gets broken down directly by glycolysis
What (biological process) are D-Mannose and D-Galactose involved in?
they get broken down in the glycidic cycle?????
What are epimers?
molecules that are identical except for rotation around one asymmetric carbon
on which carbon is a carbohydrate’s ketone located?
C2
what are Dihydroxyacetone and D-Fructose involved in?
glycolysis
what are D-Erythrulose, D-Erythrulose, and D-Xylulose involved in?
pentose phosphate pathway
what is the 2nd most important sugar after glucose?
D-Fructose
is furanose a 5 membered ring or a 6 membered ring?
5
is pyranose a 5 membered ring or a 6 membered ring?
6
are ringed carbohydrates aromatic?
no
what is a hemiacetal?
what you call it when a sugar converts from its linear form to a ring structure by nucleophilic attack of the carbonyl by an alcohol
which carbon is the anomeric carbon in a ringed carbohydrate?
the one that adopted a new stereocenter during the formation of the hemiacetal
what is an intermolecular hemiacetal?
what you call it when a sugar converts from its linear form to a ring structure by nucleophilic attack of its carbonyl by one of its alcohols
what’s a Haworth projection?
a simplified method of drawing ring structures with the plane of the ring perpendicular to the page
what is the limitation of Haworth projections?
they are not geometrically precise
What is an anomer?
A pair of stereoisomers that differ only in
conformation around the anomeric carbon (the carbonyl carbon in the linear form)
what is an α-anomer?
what you call it when the OH substituent of the anomeric carbon is on the opposite face of the ring from the CH2OH group which helps to define D/L-stereochemistry
alphas are down right dirty (OH points down in the ring and right on the line structure)
what is a β-anomer:
what you call it when the OH substituent of the anomeric carbon is on the same face of the ring as the CH2OH group that helps to define D/L-stereochemistry
(betas point up in the ring and left in the line structure)
I imagine Anne and MC Hammer standing on the same plane of a ring, but in secret…on the down low
what is mutarotation?
is the process of interconverting between α and β
anomers THROUGH THE LINEAR INTERMEDIATE to reach equilibrium
note the spelling: mutant rotation
What has to be true about a sugar’s anomeric carbon in order for mutarotation to occur?
the anomeric carbon must have an alcohol as a substituent
what does it mean to say that a sugar is a reducing sugar?
Sugars that have not formed a bond through their anomeric carbon (read: linear sugars) may act as a reducing agents and may be referred to as reducing sugars
sugars that can act as reducing agents because their anomeric carbon is, having it’s carbonyl (C=O bond) in tact, can be oxidized (by metals)
what do you call a reducing sugar that has been oxidized?
modified sugar
Do both ends of a reducing sugar able to be reducing agents?
no
One end is reducing and the other end is non reducing
Do we refer to sugars as ‘reducing’ when they’re in their ring form?
No
It the reudcy-ness only applies to the linear form, as it still has it’s carbonyl
how is directionality established in reducing sugars?
we read the sugar from the NON reducing end to the reducing end
what does it mean to say that a metal gets reduced by a reducing sugar?
the metal receives electrons from the sugar
the sugar gives electrons to the metal
Why/how are monosaccharide derivatives examples of modified sugars?
yes
Are dehydroxy sugars and phosphorylated sugars examples of monosaccharide derivatives/modified sugars?
yes
which sugars can be reducing sugars?
any sugar that can get into its linear form
what is the difference between regular glucose and the modified glucose ‘glucosamine’?
glucosamine has NH2 group on the C2
what is the difference between regular glucose and the modified glucose ‘GlcNaC’?
GlcNaC has an acetylene group on its C2 that turns glycosidic bond into an amide linkage
what is the difference between regular glucose and the modified glucose ‘GlcNaC’?
GlcNaC has an acetylene group on its C2 that turns glycosidic bond into an amide linkage
what is a glycosidic bond?
what you call it with you link sugars together with covalent bonds through their anomeric carbon
(like how peptide bonds/amide bonds exist between amino acids)
what is the difference between regular glucose and the modified glucose ‘GalNaC’?
GalNaC has an amine at the C2 position
what is GalNaC actually called?
N-acetylgalactosamine
what is GlcNaC actually called?
N-Acetylglucosamine
what is chitin for?
exoskeleton
can a sugar engage in mutarotation after it’s reacted its anomeric carbon to make a glycosidic bond?
no. The new glycosidic bond is so stable that the anomers can no longer interconvert by mutarotation
why can’t sugars do mutarotation anymore after they’ve made glycosidic bonds?
it would require breaking a carbon-oxygen bonds, which is highly unlikely to occur without intervention from an agent like a glycosidase enzyme
what does a glycosidase enzyme do?
enzymes that selectively cleave glycosidic bonds
why can’t sugars do mutarotation anymore after they’ve made glycosidic bonds?
it would require breaking a carbon-oxygen bond
(ether linkage), which is highly unlikely to occur without intervention from an agent like a glycosidase enzyme
can alpha and beta glycocidic bonds be broken with the same glycosidases?
no
alpha glycocidic bonds require alpha glycosidase
beta glycocidic bonds require beta glycosidase
can alpha and beta glycocidic bonds be broken with the same glycosidases?
no
alpha glycocidic bonds require alpha glycosidase
beta glycocidic bonds require beta glycosidase
Do humans make both alpha glycosidase
and beta glycosidase?
No.
We primarily make alpha (which is why we can’t break down disaccharide sugars that are beta)
Do humans make both alpha glycosidase
and beta glycosidase ?
No.
As adults, we primarily make alpha (which is why we can’t break down milk fat)
What is an N-glycosidic bond?
a glycocidic bond linked through a nitrogen
what mechanism do sugars to do generate glycocidic bonds with one another?
condensation
what mechanism is the reverse of the one sugars to do generate glycocidic bonds with one another?
hydrolysis
what is maltose?
what you get when you bind 2 glucoses together
Does stereochemistry define common glucose disaccharides (like maltose and cellobiose)?
yes
slides p 14
Are there multiple types of glucose-glucose disaccharides ?
yes
what is maltose the disaccharide unit for?
it’s the disaccharide unit of starch (α-linkage)
what is starch?
Starch is a polysaccharide formed by units of glucose and the storage form of carbohydrates in plants.
what is cellobiose the disaccharide unit for?
Cellobiose is the disaccharide unit of cellulose (β-linkage
what is cellulose?
an insoluble substance which is the main constituent of plant cell walls and of vegetable fibers such as cotton.
what does it mean to say you have a 1-4 glycidic bond?
it means the anomeric carbon from one sugar (C1) is bound to the C4 carbon of the other sugar
what is the difference between a 1-4 linked maltose and a 1-4 linked cellobiose?
in the maltose, the anomeric carbon (C1) is alpha.
in the cellobiose, the anomeric carbon (C1) is beta
can the reducing end of a maltose or cellobiose do mutarotation?
yes. As long as they still have their alcohol substituents on their anomeric carbons, they can still do mutarotation
Can humans break maltose and cellobiose into their monomers in order to free the glucose and use it for energy production?
We make the alpha glycosidase enzyme needed to break maltose but not the beta glycosidase enzyme to break cellobiose
how does the body use broken down maltose?
we absorb into the intestinal cells and transfer to the blood stream to be moved around the body for energy production
what is the sucrose (table sugar) disaccharide composed of?
a glucose and a fructose with an alpha 1- beta 2 glycosidic linkage
Why doesn’t the disaccharide ‘sucrose’ have any reducing ends?
because both anomeric carbons are tied up in the glycosidic bond; neither of them have the OH substituent needed to allow them to engage in mutarotation
is sucrose a reducing sugar or non reducing sugar?
non reducing
what enzyme do humans use to break down sucrose into its constituent pieces (glucose & fructose)?
sucrase enzyme
what is another name for lactose?
milk sugar
what is the lactose disaccharide composed of?
a galactose sugar with a beta 1-4 linkage to glucose
which part of the lactose is the NON reducing end?
the galactose end
Is lactose the only disaccharide with beta linkage that adult humans can digest?
yes children make beta galactosidase enzyme that breaks the linkage in the lactose
some adults’ beta galactosidase is non-functional but their gut bacteria can break down the lactase (but the bacteria make gas in the process).
what mechanism does glycosidase use?
hydrolysis
what is the difference between exoglycosidase enzymes and ENDOglycosidase enzymes?
exoglycosidases bind to a sugar at the non-reducing and and cleave sugar monomers off of the chain one at a time as they make their way towards the reducing end of the sugar chain.
ENDOglycosidase can bind to a sugar chain anywhere (such as in the middle of the sugar chain)
are digestive enzymes examples of exoglycosidase enzymes or ENDOglycosidase enzymes?
endo
what is the type, repeating unit, and linkage for amylose?
type: homopolysaccharide
repeating unit/linkage: alpha 1-4 glucose; linear/no branches
what is amylose polysaccharide found in?
energy storage
what is amylose polysaccharide used for?
energy storage in plants
does amylose have a threadlike structure or a spiral like structure?
spiral
why is the release of energy from amylose slow?
amylose does NOT have branches and thus does not have many non-reducing ends for glycosidase enzymes to bind to and perform hydrolysis (cleavage of sugar monomers at the glycosidic linkages) for the purposes of releasing energy.
what is the type, repeating unit, and linkage for amylopectin?
type: homopolysaccharide
repeating unit/linkage: alpha 1-4 glucose in the main chain, alpha 1-6 glucose in the branched chains
How frequent are the branches in amylopectin?
About every 24-30 sugar residues
How is amylopectin r/t amylose?
Amylopectin is derived from amylose and is very similar except that it has branches and amylose does not.
what is amylopectin polysaccharide used for?
energy storage in plants
why is the release of energy from amylopectin relatively fast?
amylopectin has many branches and thus has many non-reducing ends for glycosidase enzymes to bind to and perform hydrolysis (cleavage of sugar monomers at the glycosidic linkages) for the purposes of releasing energy.
what two polysaccharides together comprise starch?
amylose and amylopectin
what is the type, repeating unit, and linkage for glycogen?
type: homopolysaccharide
repeating unit/linkage: alpha 1-4 glucose in the main chain, alpha 1-6 glucose in the branched chains
How frequent are the branches in glycogen?
About every 8-12 sugar residues
what is glycogen polysaccharide used for?
energy storage in bacteria and animal cells
primary storage for excess glucose
of the 5 polysaccharides you have to memorize, which 2 have branches?
amylose and glycogen
what small peptide makes glycogen?
glycogenin
what is the cleaving enzyme for glycogen?
glycogen phosphorylase
why is the cleaving enzyme for glycogen (glycogen phosphorylase ) so named?
it cleaves by phosphorolysis instead of hydrolysis
what is phosphorolysis?
is the cleavage of a compound in which inorganic phosphate is the attacking group
similar to hydrolysis
why is the release of energy from glycogen relatively fast?
glycogen has many branches and thus has many non-reducing ends for glycosidase enzymes to bind to and perform hydrolysis (cleavage of sugar monomers at the glycosidic linkages) for the purposes of releasing energy.
what is the type, repeating unit, and linkage for cellulose?
type: homopolysaccharide
repeating unit/linkage: beta 1-4 glucose in the main chain
does cellulose have a threadlike structure or a spiral like structure?
threadlike
what is the cleaving enzyme for cellulose?
May be broken up by cellulases: enzymes secreted by
some fungi, bacteria, and protozoa
why is cellulose useful as a structural material for plant cell walls?
Its thread orient themselves in an intricate repeating pattern is rigid and fibrous
what is the type, repeating unit, and linkage for chitin?
Type: homopolysaccharide
repeating unit/linkage: beta 1-4 GlcNAc in the main chain
what is chitin found in?
fungal cell walls and arthropod exoskeleton
why is chitin so useful as a structural sugar?
its sugar monomers pack tightly and orient themselves such that they can engage in hydrogen bonding without the need for water as a solvent. This give the chitin polymer rigidity.
what gives amylose a spiral shape (instead of a threadlike shape)
the stereochemistry of its anomeric carbons
what are the two main reasons that forming sugar polymers from monomers is favorable?
Polymers reduce the concentration of glucose based molecules (from 0.4 M in the monomer, glucose form
to 0.01 µM in the polymer glycogen form), and thereby:
- reduces osmotic stress on the cell (because the tightly packed subunits can orient themselves such that they can facilitate H bonding w/o water)
- makes it easier for the cell to regulate glucose, move it in & out of the cell, and take in/store excess glucose in the form of glycogen the lower concentration
gradient for glucose uptake
