Carbohydrates Flashcards
What is a chiral carbon?
Carbon with 4 different groups attached to it
Which of the ff amino acids DOES NOT have a chiral carbon?
(a) valine (b) tryptophan (c) glycine (d) phenylalanine
(c) glycine
* Glycine is the ONLY non-chiral amino acid. (It has 2 H’s attached to its alpha-carbon)
What is mutarotation?
Conversion between alpha- and beta-anomers
RECALL: alpha-anomer is the form with -OH below and beta-anomer is the form with -OH above the plan of the molecule
What is the form of carbohydrates naturally occurring in nature?
D-carbohydrates such as D-glucose, D-mannose, etc
What is the most stable conformational isomer for a 6-C sugar?
(a) boat (b) chair (c) envelope
(b) chair
The chair conformation does not have any steric strain, and has the most stable angles (60 degrees) in its structure.
What the reactive groups in carbohydrates? (also forms a basis of classification)
Aldehydes and ketones
Carbohydrates can be classified as either aldoses or ketoses.
Which among the following is an aldose-ketose pair?
(a) glucose-fructose (b) glucose-mannose (c) fructose-ribulose
(a) glucose-fructose
(b) glucose and mannose are both ALDOSES and (c) fructose and ribulose are both KETOSES
Carbohydrates can also be classified according to the number of carbons.
If ribose has 5 carbons, how will you name it?
Pentose
Which among the ff are monosaccharides? How would you classify those which are NOT monosaccharides in the choices?
Fructose, maltose, glucose, galactose, lactose
Glucose, galactose and fructose are MONOSACCHARIDES.
Maltose and lactose are DISACCHARIDES.
What monosaccharides make up maltose?
Glucose-glucose
What monosaccharides make up lactose?
Galactose-glucose
What monosaccharides make up sucrose?
Glucose-fructose
What bond joins 2 monosaccharides?
Glycosidic bond
What is a polysaccharide?
A polymer of monosaccharides
Examples of polysaccharides
Glycogen, cellulose, starch
Differentiate heteropolysaccharides and homopolysaccharides. Give 1 example each.
Heteropolysaccharides: made up of more than 1 type of monosaccharide
ex. peptidoglycan (found in bacterial cell walls)
Homopolysaccharide: made up of 1 type of monosaccharide only
ex. glycogen, starch
Difference between starch and cellulose?
Starch forms alpha (1-4) bonds. Cellulose forms beta (1-6) bonds.
Starch has 2 kinds of glycosidic bonds, alpha (1-4) and alpha (1-6). Which forms linear chains, and which gives rise to branches?
Alpha (1-4): for linear chains
Alpha (1-6): forms branches
What are reducing sugars?
Sugars with a free anomeric carbon (meaning that the aldehyde group is free and not involved in a glycosidic bond to form a cyclic structure).
A solution, when added with a solution of Cu2+ ions, formed a precipitate with Cu+ as one of its components. Did the solution contain a reducing sugar?
YES
Cu2+ was reduced to Cu+, therefore the solution contained reducing sugars.
What are optical isomers?
Isomers that can either rotate plane-polarized light to the right (dextrorotatory, small letter d) or the left (levorotatory, small letter l).
What are stereoisomers?
Isomers wherein the hydroxyl group attached to the penultimate carbon (or the last chiral carbon, C5 if the sugar is a hexose) is either on the right (D) or the left (L).
What are enantiomers?
Isomers which are mirror images of each other.
What are epimers?
Isomers whose structures differ only in their configuration around 1 carbon atom
Glucose forms many epimers, which are called C-(number) epimers of glucose. In the choices below, match the correct carbon number with the epimer.
C-2 and C-4
mannose and galactose
C2: mannose
C4: galactose
This means that glucose would have exactly the SAME structure with mannose and galactose except at carbon # 2 (for mannose) and carbon # 4 (for galactose).
One monosaccharide derivative is phosphate esters, such as glucose-6-phosphate. Why is there a need for phosphorylation?
Attaching a phosphate group makes the molecule CHARGED. Once it is charged, the molecule would not be as easily diffusible through the LIPID bilayer, thus trapping the molecule inside and committing it to specific pathways.
Another monosaccharide deriviative is acids. Which carbons are oxidized to become acids?
C1 and C6
If only C1 is oxidized, what is the acid derivative called?
Aldonic acid
ex. gluconic acid
If only C6 is oxidized, what is the acid derivative called?
Alduronic acid
ex. glucoronic acid
If BOTH C1 and C6 are oxidized, what is the acid derivative called?
Aldaric acid
ex. glucaric acid
If carbonyl groups in a monosaccharide are reduced, what is the derivative called?
Alditols
ex. mannitol
How are amino sugars derived? Example of an amino sugar?
The -OH group is replaced with an amino (-NH2) group at C2. An acetyl group may also be added to give rise to N-acetyl-sugars.
ex. N-acetyl-neuraminic acid (sialic acid)
Glycosides are also monosaccharide derivatives. Examples of glycosides?
Ouabain, amygdalin
What are proteoglycans?
Glycosaminoglycans + protein
Proteoglycans form a “bottlebrush” look. Sulfate and acetyl groups from glycosaminoglycans have negative charges that repel each other and make the strands look “stiff.”
Used as a lubricant by the body (because its negative groups attract water)
Examples of glycosaminoglycans?
Heparan sulfate, chondroitin sulfate, heparin
What is the most prevalent glycosaminoglycan?
Chondroitin sulfate
What are glycoproteins?
In glycoproteins, there is a protein core with carbohydrate groups attached to it.
In glycoproteins, carbohydrates link to proteins either through O-glycosidic bonds or N-glycosidic bonds. Through which amino acids do they form these links?
O-glycosidic bonds: serine and threonine
N-glycosidic bonds: asparagine
Carbohydrates serve as informational molecules, T/F?
T. For interaction with one another and with other cell types (attachment, migration).
Carbohydrates play a role in cell recognition, T/F?
T. Found in self, non-self recognition process by immune cells of the body, apoptosis, cell differentiation, recognition of the egg by the sperm.
Deficiency in galactokinase?
Galactosemia (accumulates in the blood)/galactosuria (accumulates in the urine)
Deficiency in fructokinase?
Fructosuria
What enzyme is deficient in lactose intolerance?
Lactase
