Glycobiology

Question 1

Functions of Carbs

Answer 1

1. Energy source
2. Energy storage (glycogen)
3. Structural component of cell membranes, bacterial cell, walls and exoskeletons
4. Nucleotide biosynthesis
5. Lipid biosynthesis

Question 1

Carbohydrates: formula

Answer 1

Cn(H2O)n -> Carbon and Water

produced from CO2 and H2O

Question 2

Monosaccharides (one sugar)

Answer 2

Oxygen atoms are found in hydroxyl group or part of a carbonyl group:
1. Aldoses:
if the sugar has C=O as the last C is an Aldehyde group, and it is known as an aldose
2. Ketoses:
if the sugar has C=O as an internal C, it is a ketone group and it is known as a ketone.

Sugars are named in relation of carbons.

Question 3

Cyclic structures

Answer 3

when typically >5 Cs.

• Pyranoses and Furanoses
  named based upon the shape
  Pyranose is a six-membered ring with 5 carbons and 1 oxygen.
  Furanoses is a five-membered ring with 4 carbons and 1 oxygen.
• alfa e beta forms
  alfa is formed OH on opposite side.
  beta is formed OH on same side.

Question 4

Isomers

Answer 4

two forms:
1. structural isomers
2. stereoisomers
divided in enantiomers (non-superimposable mirror images) and in diastereomers (Epimers = differs in only one chiral centre & Anomers = differs at the acetal/hemiacetal C.

Question 5

Disaccharides

Answer 5

Definition:
two monosaccharides joined together via a condensation reaction.

The OH group of one combines with the H of another releasing a molecule of water and forming a covalent bond known as a glycosidic bond.

Question 6

Types of Disaccharides

Answer 6

• Trehalose
  is a different linkage of two glucose molecules. Two α glucose molecules bonded C1 and C1. Requires different enzyme trehalose to hydrolyse.
• Sucrose
  is a disaccharide of one fructose and one glucose molecule.
  α-glucose and β-fructose, bonded between C1 and C2. Hydrolysed by sucrase.
• Lactose
  is a disaccharide of one galactose and one glucose molecule.
  Both β, bonded between C1 and C4. Hydrolysed by lactase.

Question 7

Polysaccharides

Answer 7

long chain of monosaccharides linked by glycosidic bonds. Can be branched or unbranched.

• Homopolysaccharides = single type of monosaccharides.
• Heterpolysaccherides = different kinds.

Question 8

Polysaccharides: Glycogen

Answer 8

It is a branched polymer of glucose monomers, with alfa1.4 glycosidic bonds in chain and alfa1.6 glycosidic bonds in branch points.

• the storage form of glucose
• stored in liver and muscle cells

in liver:
whenever blood glucose levels decrease, the hormone glucagon is released causing glycogen broken down via hydrolysis to release glucose monomers

in skeletal muscle:
adrenaline can cause glycogen breakdown to be used locally in fight or flight situations.

Question 9

Polysaccharides: Starch

Answer 9

is a mixture of 2 homopolysaccherides of glucose:
- amylose
- amylopectin

Starch is hydrolysed by alfa-amylase into: maltose, maltotriose and the alfa1.6 linkages are left as dextrins (maltase and isomaltase).

Question 10

Polysaccharides: Cellulose

Answer 10

unbranched chains of glucose monomers linked by beta1.4 glycosidic bonds.

Result in a long, straight, non-helical chains, that are cluster together to form parallel bundles that are held together by hydrogen bonds.

Vertebrates cannot hydrolysed it:
- molecules passed by bacteria and hydrolysed during fermentation -~ forestomachs and hindgut fermenters

Question 11

Fermentation of Cellulose

Answer 11

Different species of bacteria and yeasts.

Glucose is broken down to pyruvate by glycolysis by the microbes. Then, pyruvate is converted to VFAs by>
- Acetate
- Propionate
- Buriate

Question 12

GlycoLipids

Answer 12

lipids modified with a carbohydrate component.

Cell membranes lipids in which the hydrophilic head groups are polysaccharides, that act as specific sites for recognition by carbohydrate binding proteins.

ENDOTOXIN
The dominant surface feature of the outer membrane of gram-negative bacteria such as Escherichia coli.

Question 13

GlycoProteins

Answer 13

proteins with one or several oligosaccharides of varying complexity covalently attached.

Found:
- on the outer face of the plasma membrane in the extracellular matrix of the blood
- in specific organelles inside cells (Golgi complexes and secretory glands

Question 14

Types of Glycosylation

Answer 14

• O-linked glycosylation is attached at its anomeric carbon through a glycosidic link to the OH of a serine or threonine residue
• N-linked glycosylation is attached at its anomeric carbon through an N-glycosyl link to the amide nitrogen of an asparagine residue

Question 15

Functions of Glycoproteins

Answer 15

1. Found on the surface of the lipid bilayer of cell membranes
2. Hydrophilic nature - function in the aqueous environment
3. Hormones may be glycoproteins
4. Blood clotting depends on the glycoprotein’s prothrombin, thrombin and fibrinogen
5. Reproduction
6. Immune system recognition

Question 16

Proteoglycan

Answer 16

are macromolecules of the cell surface or extracellular matrix.
The basic unit consists of a “core protein” attached to glycosaminoglycans.

They are major components of connective tissue. They are secreted into the extracellular matrix.

AGGRECAN
major component of cartilage.
it consists of:
- Hyaluronan
- core protein
- Glycosaminoglycans of chondroitin sulphate and keratan sulphate

Question 17

Glycosaminoglycans

Answer 17

are long unbranched polysaccharides consisting of a repeating disaccharide unit.

They provide viscosity, adhesiveness and tensile strength to the extracellular matrix.

Question 18

Heparin: what is it? Disorders treated?

Answer 18

Anticoagulant.
Activates protease inhibitor.

Physiologically: prevents clots within vessels.

Disorders treated:
- cardiac, aortic, arterial thrombosis
- pulmonary thrombosis
- disseminated intravascular coagulation
- systemic thrombotic or “hyper coagulable” syndromes (haemolytic anaemia, pancreatitis, neoplasia, protein losing disorders).