Chapter 7: Carbohydrates Flashcards
What is the formula of a Carbohydrate?
C_n(H2O)_n
What functions do carbohydrates fulfill?
- Energy source and storage
- Structural component of cell walls and exoskeletons
- informational molecules in cell-cell signaling
How would you classify a carbohydrate with the following number of carbons?
- 5
- 3
- 4
- 7
- Pentose
- Triose
- Tetrose
- Heptose
Be able to know what an oligosaccharide is:
A carbon with more than one sugar
Ex: Disaccharide
How do Constitutional Isomers differ?
They differ in the order of attachment of atoms
Ex: Two molecules can have the same formula (C3H6O3) but they aren’t the same due to the way they are arranged
What are Stereoisomers? What other isomers are direct variants of them?
Stereoisomers differ in spatial arrangement but are in the same order as each other. The two variants are Enantiomers (Nonsuperimpossable mirror images, D vs L formation) and Diastereomers (Isomers that are not mirror images)
What are epimers and anomers?
Epimers are isomers that differ at one of several asymmetric carbon atoms.
Anomers are isomers that differ at a new asymmetric carbon atom formed on ring closure (α vs ß formation)
What is a Ketose? What is an Aldose? How can you change between them?
Ketoses are carbohydrates with Ketone functionality, and Aldoses are carbohydrates with Aldehyde Functionality. You can swap between them by using an Enediol Intermediate.
How do you determine in a non-cyclic sugar if it is in D or L conformation?
Look at the chiral center furthest away from the carbonyl carbon. If it has the OH group on the right, it is D-formation. If the OH group is on the left, it is in the L-formation.
For a carbon to be chiral what requirements must it meet?
It must be attached to four different groups.
Hexose is in which conformation mostly in living organisms?
D-conformation
Can epimers also be classified as diastereomers?
Yes as Epimers are also not mirror images (be careful on some questions as one of the answers may be “more” correct)
How can you determine the number of stereoisomers a given carbohydrate will have?
The # of Stereoisomers = 2^n
n = # of chiral centers
A carbohydrate with 4 chiral centers will have 2^4 stereoisomers which is 16
What are the common carbohydrates in Biochemistry?
Ribose - The Standard 5 Carbon Sugar
Hexose - The Standard 6 Carbon Sugar
Galactose - Epimer of Glucose
Mannose - Epimer of Glucose
Fructose - Ketose Form of Glucose
If a chiral molecule has a mirror image isomer what is that called? What if it has a non-mirror image isomer?
If it has a mirror image isomer, it is an enantiomer
If it has a non-mirror image isomer, it is a diastereomer
Aldehyde and Ketone Carbons are ________philic
Electrophilic
When aldehydes are attacked by alcohols, what is formed? What about when ketones are attacked?
Hemiacetals
Hemiketals
What is the name for six-membered oxygen-containing rings? What about those with five members?
Pyranose
Furanose
In a cyclic carbohydrate, if the anomeric carbon has an alcohol group pointing down, which form is it in? (Alpha or Beta)
It is in the Alpha formation
As temperature increases, does the equilibrium shift towards the furanose or pyranose form for cyclization?
Equilibrium shifts in the direction of the furanose form, and this causes the sweetness of the solution to decrease.
What is mutarotation?
Mutarotation is where a carbohydrate in solution inter-converts between the linear form and four cyclic conformation
Which sugars are reducing?
All sugars with a free anomeric carbon are reducing sugars. This means all monosaccharides are reducing sugars.
How are two sugars joined?
They are joined via a glycosidic bond between an anomeric carbon and a hydroxyl carbon. This bond (which is an acetal) is more stable and less reactive than the hemiacetal at the second monomer.
What are the two types of glycosidic bonds?
O-glycosidic bond and N-glycosidic bond
What are disaccharides linked by?
O-Glycosidic Bonds
Which enzymes are responsible for linking monosaccharides?
Glycosyltransferases
What happens when two sugar molecules are joined together via their anomeric carbons?
They become a nonreducing sugar
What is the difference between homopolysaccharides and heteropolysaccharides?
Homopolysaccharides are all made up of the same monomer subunit while heteropolysaccharides are made up of multiple monomer subunits.
Do polysaccharides have a defined molecular weight? Why?
No, because they do not have a template to follow to make them
