Complex carbohydrates

Question 1

What are the features of a polysaccharide/complex carbohydrate structure (6)

Answer 1

1. simple carbohydrate systems = single units called monosaccharides. Two units joined together with a covalent bond = disaccharides.
2. In the covalent bond between two units = oxygen or ethyl linkage between two carbon atoms (glycosidic bond).
3. In alpha glucose, the OH substitute is positioned axially = OH group points down from the chair structure.
4. In beta glucose, the OH substitute is positioned equatorially = OH group points up from the chair structure.
5. glycosidic linkages are a (1→4) - carbon 1 and carbon 4.
6. These linkages promote a helix structure in which hydrogen bonds form between the oxygen bound at the 2 carbon of one glucose and the carbon 3 of the next glucose.

Question 2

What is the role of complex carbohydrates in nature, e.g. energy storage and structure (5)

Answer 2

1. Storage - starch, glycogen
2. structural - cellulose, chitin
3. protective - hyaluronic acid (connective tissue)
4. cellular recognition - blood group systems
5. specific agents - heparin (anti-coagulant)

Question 3

How are complex carbohydrates metabolised (1)

Answer 3

glycoside hydrolases hydrolyse dissacharides into monosaccharides

Question 4

How is amylose metabolised (2)

Answer 4

1. salivary alpha-amylase in animals splits alpha(1→4) glucosidic linkages within the molecules of amylose and produces monomers of glucose atoms
2. beta-amylase in plants and microorganisms (exoamylase) cleaves disaccharide units from the non-reducing end of chains to form dimers of maltose units

Question 5

How is glycogen metabolised in the muscle and liver (4)

Answer 5

1. Hydrolysed by Glycogen phosphorylase to release glucose-1-phosphate.
2. Insulin (a hormone) stimulates conversion of glucose to glycogen)
3. Glucagon (a hormone) stimulates conversion of glycogen to glucose)
4. Glucagon triggers the release of glucose into the blood to power cells throughout the body.

Question 6

What is a mixed glycan polysaccharide and its medical use (4)

Answer 6

1. It is a repeating unit with nitrogen present.
2. A long-chain polymer of a Nacetyl-glucosamine - β-(1→4) linkages
3. Component of the cell walls of fungi, the exoskeletons of arthropods such as crustaceans (e.g., crabs, lobsters and shrimps) and insects.
4. Chitin’s flexibility and strength make it useful as a surgical thread, which is biodegradable and wears away with time as the wound heals.

Question 7

What are the functions of glycoproteins (8)

Answer 7

1. Structural – collagen
2. Lubricants and protective agents **– synovial fluid, mucins
3. Metal Transport molecules **– transferrin that transportsiron through theblood, binding tightly but reversibly.
4. Defence against infection **– immunoglobulins, selectins, complement proteins, interferons
5. Hormones – Human chorionic gonadotropin(hCG) for the maternal recognition of pregnancy produced by trophoblastcells that surround a growing embryo, which eventually form the placenta afterimplantation.
6. Cell-cell recognition **– fibronectin, laminin 111, chondronectin
7. Structural **- Cadherin, which helps skin hold together. Mediate cell-cell adhesion and recognition.
8. Enzymes - various proteases, nucleases, glycosidases

Question 8

Role of glycoproteins in blood group substances (6)

Answer 8

1. The importance of glycoproteins is the blood group antigens (substances)
2. Present on the surface of red blood cells.
3. The ABO blood groups are based on slight differences in glycoprotein structure.
4. Involves tetrasaccharides linked to cell wall protein
5. Blood group O is the most common blood group in the UK.
6. When the substances in the blood, antigens and antibodies of one type are added to those of a second type, they induce a clumping of red blood cells.

Question 9

What is present in type A, B, O, AB and O- blood (5)

Answer 9

1. In type A antigens, there is an N-acetylgalactosamine present, as well as galactose, fructose and N-acetyl glucosamine.
2. type B antigens - Galactose antigen present as well as galactose, fructose and N-acetyl glucosamine
3. type O antigens - only galactose, fructose, and N-acetyl glucosamine are present with no additional saccharides.
4. Type AB blood contains both tetra-saccharides
5. Type O- contains neither.

Question 10

What is the structure of Glycoproteins (5)

Answer 10

1. Proteins with oligosaccharides covalently linked to their polypeptide backbone
2. Oligosaccharide units usually less than 15 monosaccharide units
3. Molecules can contain between 1 and 85% carbohydrate.
4. Found in most organisms – animals, plants, bacteria, fungi, viruses
5. Many functions….

Question 11

What is the structure of Heteroglycans (7)

Answer 11

Heteroglycans, in nature, contain other sugars with an anomeric centre:

1. alpha-glucose (pyranose form)
2. alpha-galactose (pyronose form)
3. alpha-mannose (pyranose form)

Important acylated aminoglycan molecules with an anomeric centre:
(often found in glycoproteins)

1. N-acetylglucosamine (GIcNAc) in the N-glycosidic bond, we have N-acetylglucosamine linked to asparagine.
2. N-acetylgalactosamine (GaINAc)

Question 12

What is microcrystalline cellulose (MCC) and its uses (6)

Answer 12

1. found in cell walls of plants, microcrystalline cellulose (MCC) is a term for refined wood pulp and is used as a:
2. texturiser, an anti-caking agent and dry binder, drug disintegrant
3. a fat substitute, emulsifier, filler and diluent
4. extender, bulking agent in food production
5. the most common form is used in vitamin supplements or tablets
6. excipient most widely used for direct compression-anti-adherent

Question 13

What is the nature of glycoprotein bonds (4)

Answer 13

1. Asparagine bonds (most common) - N-glycoside
2. Serine bonds - O-glycoside
3. Hydroxylysine bonds (uncommon) - O-glycoside
4. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation.

Question 14

What is the nature of N-glycosides (3)

Answer 14

1. Asn exists as part of an Asn-X-Ser(Thr) sequence.
2. Simple – contains only mannose and GlcNAc – common in primitive organisms.
3. Complex – same core as simple but with outer chains containing Sialic acid, Galactose and Fucose residues linked to the core – only in higher animals

Question 15

How do surface decorations dictate immunogenicity (3)

Answer 15

1. Recognition of self versus non-self
2. Invader versus host material
3. Surface decorations illicit immune response

Question 16

What is Glycomics and Glycoproteomics (3)

Answer 16

1. The term “glycomics” currently describes studies designed to define the complete repertoire of glycans that a cell or tissue produces under specified conditions of time, location, and environment.
2. glycoproteomics describes this glycome as it appears on the cellular proteome.
3. Glycoproteomics determines which sites on each glycoprotein of a cell are glycosylated and ideally includes the identification and quantitation of each glycan structure at each site on the heterogeneous glycoforms in the cell.

Question 17

What are the analytical methods of glycomics and glycoproteomics (4)

Answer 17

1. MS (mass spectrometry)
2. Ion mobility - determine the shape
3. LC (liquid chromatography)
4. CE (capillary electrophoresis) and CE-MS (capillary electrophoresis mass spectrometry)

Question 18

What is Chitin and its uses (5)

Answer 18

1. a structural heteroglycan polymer of GlcNAc with repeating unit with nitrogen present
2. A long-chain polymer of a Nacetyl-glucosamine - β-(1→4) linkages
3. Component of the cell walls of fungi, the exoskeletons of arthropods such as crustaceans (e.g., crabs, lobsters and shrimps) and insects.
4. Chitin’s flexibility and strength make it useful as a surgical thread.
5. Biodegradable - wears away with time as the wound heals.