Chapter 8: Carbohydrates Flashcards
Name two structural properties of carbs
1) chiral, non superimposable on their mirror images
2) D-configuration is most common
3) Often ketose or aldose families of sugars
The enantiomer of a D configuration sugar is ____
and L configuration sugar
If you switch the group closest to “CHO” on D-glyceraldehyde to a ketone, and “CHO” to CH2OH, you get ______
D-hydroxyacetone
What is an aldose
carbonyl group is an aldehyde
what is a ketose
carbonyl group is a ketone and not at the end of the carbon chain.
For aldoses, what is the general formula to determine how many stereoisomers a sugar has?
possible # of steroisomers have 2^#of chiral centers.
ex/ glucose has 4 chiral centers, therefore, 2^4= 16 possible steroisomers
What is an epimer?
sugars that differ only by the configuration around one atom that isn’t the anomeric carbon. If you were to change the configuration at the anomeric carbon, it would just chnage from alpha to beta anomers. Ex, d-glyceraldehyde and d-dehydroxyacetone are epimers, or glucose vs mannose
define epimerization? Does this happen readily in biological systems?
the conversion between epimers. This does not occur under physiological conditions without some sort of enzyme
6 membered monosaccharides form _____rings and 5 membered monosaccharides form _____ rings
pyranose rings, furanose rings
define anomeric carbon
the carbonyl carbon where the monosaccharide cyclizes, the carbon that is bonded to both an oxygen and an OH group.
name the two possible configurations of anomers
alpha: when the OH substituent of the anomeric carbon is on the opposite side of the ring from the CH2OH group at the C5 (in hexose)
beta: when the OH substituent of the anomeric carbon is on the same side of the ring of the CH2OH group at c5 ( in hexose)
beta dglucose is the preferred conformation because all the hydroxyl groups are in ____ position, minimizing ______
equatorial position, minimizing steric hinderance
What is mutarotation?
the conversion between alpha and beta anomers through the open chain form, but beta is still favored. This doesn’t happen a whole lot because open chain form is almost never present.
draw d-ribose haworth projection, furanose ring
alpha or beta
draw d-glucose hawroth projection pyranose ring
alpha or beta
draw d-fructose haworth projection furanose ring
alpha or beta
in a fischer projection, if the OH on the bottom chiral center points to the right, the sugar is ______, if the oH on the bottom chiral center points to the left, the sugar is _____
sugar is D, sugar is L
T/F you can oxidize a ketose
false
why can you oxidize an aldose?
aldehydes are oxidizable and is therefore a reducing sugar because they have a free anomeric hydroxyl.
Draw a fischer projection of glucose vs its oxidized form, gluconate
CHO group at the top should be reduces
Draw a fischer projection of glucose vs its oxidized form, gluconate
CHO group at the top should be reduced to COOH
What is an alditol
formed through the reduction of an aldose
if an aldose is reduced to an alditol, the CHO group at the top becomes :
CH2OH
What is a deoxysugar
a sugar where one of the OH groups, usually at the 2’ position is replaced by an H
What is an amino derivative of sugar
a sugar where one of the OH groups are replaced by an NH2 group.
what group would you form if you oxidize the alcohol bottom group in an aldose?
form a “uronic acid”
If an aldolse’s alcohol group on the bottom was oxidized rather than its aldehyde, the alcohol group becomes :
CH2OH –> COOH
What’re the 6 top derivatives of monosaccharides
1) phosphate esters
2) Lactones/ oxidation products
3) alditols
4) Uronic Acids
5) Deoxysugars
6) amino derivatives
When can a ketone become a reducing sugar?
only when they undergo tauteromerization. If they remain in the ketose form, they will not undergo reduction because they do not have any free aldehyde or ketones
When can a ketone become a reducing sugar?
only when they undergo tauteromerization. If they remain in the ketose form, they will not undergo reduction because they do not have any free aldehyde or ketones at the anomeric position.
What bond links the anomeric carbon to another compound, regardless of it being another sugar or not? What kind of reaction takes place?
a glycosidic linkage. Formed through the CONDENSATION of an anomeric group and another compound, causing an elimination of an H20
If the anomeric carbon bonds to an amine, it forms an ______ bond
N-glycosidic bond
T/F an anomeric carbon involved in a glycosidic bond cannot freely convert between alpha and beta anomeric forms
true.
In terms of bonding, what is a reducing sugar?
a saccharide that has not formed a glycosidic bond on its anomeric carbon
in terms of bonding, define disaccharide
two monosaccharide linked with each other via a glycosidic bond
Draw beta(1–>4)galactose and glucose, which forms lactose. Is this a reducing reducing sugar?
yes, lactose is a reducing sugar because glucose portion has a free reducing sugar.
Is beta(1–>2)glucose+fructose, which forms sucrose, a reducing sugar?
no, the 1 and 2 positions on the monosaccharides correspond to anomeric carbon portions, therefore, sucrose is not a reducing sugar.
two main functions of a polysaccharide, what is the main bonding difference?
structural material and energy sources. Storage poly saccharides are alpha and structural polysaccharides are beta
What’re the two main starches?
alpha amylose and amylopectin
define starch
a mixture of glycans that plants use as a principle ENERGY SOURCE
Is starch a structural carbohydrate?
no
what is the bonding of alpha amylose
alpha(1-4)glu polymer.
What kind of structure do the alpha glycosidic bonds of alpha amylose allow it to form?
the alpha glycosidic bonds allow amylose to aggregate into loose helical coil formation.
Is amylose a reducing sugar?
yes, has a free anomeric carbon
What is the two types of bonding in amylopectin
alpha(1-4)glucose polymer with branched alpha (1-6)glucose polymers.
How does amylopectin prevent plant cells from lyses?
the large branched structures it renders helps reduce osmotic pressure because water will enter proportionally to the number of solute molecules at a given time.
If plants tried to store free little glucose molecules, lots of water would follow, but if plants stored one large molecule of amylopectin, only one water will follow, preventing swelling and lyses.
What is glycogen? and where in the body is it most commonly found?
a storage polysaccharide for animals. it is present most in skeletal and liver cells.
Is glycogen more similar to amylose or amylopectin? why?
more similar to amylopectin because they are both alpha(1-4)glucose polymers with branched alpha (1-6)glucose polymers.q
What permits quick mobilization of glycogen in the body?
it’s highly branched structure has a lot of non reducing ends, which is where enzymes that degrade glucose attach to.
Why would there not be a lot of glucose in your liver cells? Why is glycogen better?
1) would cause osmotic lyses because water enters proportionally to the glucose concentration
2) polymerized glucoses are safer stored because they cannot be reduced or undergo random chemical reaction
3) due to the alpha 1-4 linkages, the structure is very open and can be semi soluble in water, allowing h20 soluble enzymes access to mobilize non reducing end.
4) due to alpha 1-6 linkages, structure is highly branched and can be easily mobilized by even more enzymes working on the non reducing end.
Is glycogen water soluble? why?
water soluble due to alpha 1-4 and 1-6 linkages.
What’re the two main polysaccharides involved in structure?
chitin and cellulose
What is the function of cellulose? How is it bonded?
primary structure of cell walls linked by BETA (1-4) glucose linkages
How does its bonding allow cellulose to be a good structural component?
h bonding enables it to form flat sheets of glucose molecules. Hbonding occurs between neighbors, and between sheets. Hbonding allows cellulose to be flexible becuase the Hbonds can form and reform, but it does not allow cellulose to be stretchy because the covalent bond linking the sugars together is already at its max stretch and cannot be extended unless broken.
What is the function of chitin? How is it bonded and how does it differ from cellulose in terms of composition?
Chitin is the structural component of exoskeletonds in bugs and crustaceans. Like cellulose, it consists of Beta(1-4) linkages. However, instead of glucose, it uses N-acetyl-D-glucosamine residues.
It has the capacity to form structural sheets like cellulose
Why isn’t cellulose of chitin water soluble?
They already have extensive Hbonding occuring in their structures, and water cannot get in to Hbond with the hydrogens in the cellulose or chitin structure since they are all already interacting with each other. Thus, water cannot penetrate and dissolve cellulose
Bacteria cell walls are made of _____
peptidoglycan
what is peptidoglycan made of?
N-acetylmuramic acid, N-acetylglucosamine, and tetrapeptidesq
Why are gram negative bacteria antibiotic resistant?
because their thin peptidoglycan cell wall is covered by a complex outer-membrane that can exclude substances.
What is an oligosaccharide?
a large carb polymer that is involved in cell-cell recognition
What is a lectin?
a protein that is involved in cell-cell recognition that recognizes oligosaccharides
Glucan vs Glycan
Glucan: polysaccharide of D-glucose monomer
Glycan: polysaccharide of a large number of monosaccharides linked glycosidically, especially one that is part of a glycoprotein or a glycolipid.
What kind of interactions are usually used between oligosaccharide and protein interactions?
extensive hydrogen bonding and vanderwaal forces.
What is an N linked oligosaccharide? Where is an N linked oligosaccharide formed?
an oligosaccharide that is attached to asparagine Beta covalently at the amino group. Aparagine is always followed by X, and then Ser/Thr.
Formed cotranslationally: when the polypeptide is being formed, but can also be modified in the golgi apparatus.
What is an O linked oligosaccharide? Where is it formed?
An O liked oligosaccharide involves a BETA-galactosyl(1-3) N-acetylgalactosamine linked to the OH group of either SER OR THR
**beta 1-3 linkage is most important to remember, you do not need to remember the structure of the N-acetylgalactosamine compound ( found in chitin)
In an antigenic oligosaccharide, where would you find the A, B or H antigens?
On the non reducing end of the oligosaccharide.
How many different disaccharides of D-glucopyranose are possible?
- C1 of one glucopyranose can form α or β glycosidic linkages with C1, C2, C3, C4, or C6 of a second glucopyranose, which can also be in the α or β form. However, α-glucose-(1→1)-β-glucose is identical to β-glucose-(1→1)-α-glucose, so the total is 19 rather than 20.
Is amylose or amylopectin more likely to be a long-term storage polysaccharide in plants?
Amylose (it has only one nonreducing end from which glucose can be mobilized) whereas amylopectin is branched and has tons of non reducing ends
