Module 5 - Carbohydrates Flashcards
What are epimers?
Epimer is one of a pair of stereoisomers. The two isomers differ in configuration at only one stereogenic center.
Describe the ABO blood group antigen in terms of its chemical structure and differences between the antigens.
ABO blood group antigen are glycosphingolipids on surfaces of red blood cells. A and B antigens differ from O antigen by one extra monosaccharides.
What are C-type lectins? Mention an example and its function.
C-type lectin uses calcium as a bridge between the protein (carboxylate) and the sugar (hydroxyl group)
Selectin, involved in cell-cell adhesion. Able to bind to WBC to sites of injury and allow movements of cells from blood stream to site of infection.
Explain the difference between aldose and ketose sugars.
- Ketoses are monosaccharides with a ketone group, while aldoses are monosaccharides with an aldehyde group.
- Ketoses form hemiketal rings and aldoses form hemiacetal rings.
- In aldoses, the carbonyl group is in the number one position. In ketoses, carbonyl carbon has number two.
Describe the general reaction of a glycosyl transferase, which is responsible for oligosaccharide assembly.
Nucleotide-monosaccharide reacted with an acceptor (carbohydrate) with the help of a glycosyl transferase to form a monosaccharide-Acceptor and a nucleotide.
Note: monosaccharide is transferred from the nucleotide sugar to the non-reducing end of the carbohydrate acceptor.
Explain how the linkages between glucose units in cellulose and starch/glycogen give rise to their different properties.
Cellulose:
- Glucose residues are linked by (β-1,4) glycosidic bonds
- structure stabilized by H bonds
- result is long flat molecule, and chains of cellulose can form interchain H bonds
- important structural support
Glycogen:
- Glucose residues are linked in (α-1,4) glycosidic bonds
- leads to an open helix structure
- provides an accessible store of sugar
Explain with an example, how sugars can be a target for drug design.
Neuraminidase Inhibitor (Relenza) inhibits the enzyme neuraminidase of a flu virus. Neuraminidase cleaves the sialic acid receptors that hold on to the hemagglutinin preventing its release. The inhibitor is a sugar which binds to the the neuraminidase receptors in the virus, preventing its release.
What are glycoproteins? How are the components attached?
Glycoproteins are carbohydrate groups that are covalently attached to proteins. They can be assembled through two methods:
- Via Asparagine residues (N-glycans) - sugars are linked to amide chain of asparagine
- Via Serine or Threonine residues (O-glycans) - sugars are linked to the oxygen atom in the side chain of serine or threonine residues
Explain the reactivity of the monosaccharides.
When in the planar orientation, monosaccharides are reducing agents, where the aldehyde group and can be oxidized to a carboxylic group.
What are lectins?
Broad family of proteins which recognize carbohydrates
List the amino acids that can act as glycosylation sites on proteins.
Asn, Thr, Ser
A 6-membered ring is called the ________ ring.
pyranose
What are monosaccharides?
- basic unit of carbohydrates
- aldehydes/ketones that have two or more hydroxyl group
- most naturally occurring sugars belong to D-series
- have more or equal to 3 carbon atoms
Provide examples of three fundamentally different roles of sugars in biology.
- major component of the cell surface
- important in influencing the function of proteins
- important in specific recognition interactions
Explain the structural basis of the interconversion between the α and β anomers of cyclised sugars
α and β anomers of cyclised sugars arise because when the hydroxyl group on C-5 attacks the C-1, there is 2 possible orientation of the aldehyde group. α anomer is when C-1 OH- group lies below the plane, and vice versa for β anomer.
