Module 5 - Carbohydrates Flashcards Preview

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Flashcards in Module 5 - Carbohydrates Deck (15)
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1
Q

What are epimers?

A

Epimer is one of a pair of stereoisomers. The two isomers differ in configuration at only one stereogenic center.

2
Q

Describe the ABO blood group antigen in terms of its chemical structure and differences between the antigens.

A

ABO blood group antigen are glycosphingolipids on surfaces of red blood cells. A and B antigens differ from O antigen by one extra monosaccharides.

3
Q

What are C-type lectins? Mention an example and its function.

A

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.

4
Q

Explain the difference between aldose and ketose sugars.

A
  • 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.
5
Q

Describe the general reaction of a glycosyl transferase, which is responsible for oligosaccharide assembly.

A

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.

6
Q

Explain how the linkages between glucose units in cellulose and starch/glycogen give rise to their different properties.

A

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
7
Q

Explain with an example, how sugars can be a target for drug design.

A

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.

8
Q

What are glycoproteins? How are the components attached?

A

Glycoproteins are carbohydrate groups that are covalently attached to proteins. They can be assembled through two methods:

  1. Via Asparagine residues (N-glycans) - sugars are linked to amide chain of asparagine
  2. Via Serine or Threonine residues (O-glycans) - sugars are linked to the oxygen atom in the side chain of serine or threonine residues
9
Q

Explain the reactivity of the monosaccharides.

A

When in the planar orientation, monosaccharides are reducing agents, where the aldehyde group and can be oxidized to a carboxylic group.

10
Q

What are lectins?

A

Broad family of proteins which recognize carbohydrates

11
Q

List the amino acids that can act as glycosylation sites on proteins.

A

Asn, Thr, Ser

12
Q

A 6-membered ring is called the ________ ring.

A

pyranose

13
Q

What are monosaccharides?

A
  • 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
14
Q

Provide examples of three fundamentally different roles of sugars in biology.

A
  • major component of the cell surface
  • important in influencing the function of proteins
  • important in specific recognition interactions
15
Q

Explain the structural basis of the interconversion between the α and β anomers of cyclised sugars

A

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.