Glycobiology Flashcards
Functions of Carbs
- Energy source
- Energy storage (glycogen)
- Structural component of cell membranes, bacterial cell, walls and exoskeletons
- Nucleotide biosynthesis
- Lipid biosynthesis
Carbohydrates: formula
Cn(H2O)n -> Carbon and Water
produced from CO2 and H2O
Monosaccharides (one sugar)
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.
Cyclic structures
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.
Isomers
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.
Disaccharides
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.
Types of Disaccharides
- 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.
Polysaccharides
long chain of monosaccharides linked by glycosidic bonds. Can be branched or unbranched.
- Homopolysaccharides = single type of monosaccharides.
- Heterpolysaccherides = different kinds.
Polysaccharides: Glycogen
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.
Polysaccharides: Starch
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).
Polysaccharides: Cellulose
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
Fermentation of Cellulose
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
GlycoLipids
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.
GlycoProteins
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
Types of Glycosylation
- 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
Functions of Glycoproteins
- Found on the surface of the lipid bilayer of cell membranes
- Hydrophilic nature - function in the aqueous environment
- Hormones may be glycoproteins
- Blood clotting depends on the glycoprotein’s prothrombin, thrombin and fibrinogen
- Reproduction
- Immune system recognition
Proteoglycan
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
Glycosaminoglycans
are long unbranched polysaccharides consisting of a repeating disaccharide unit.
They provide viscosity, adhesiveness and tensile strength to the extracellular matrix.
Heparin: what is it? Disorders treated?
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).
