L4+5: Glycobiology building blocks

What is the general formula for carbohydrates?

Cn(H20)n

What is the simplest carbohydrate in a cell?

Monosaccharides

What are the two forms of carbonyl monosaccharides?

Aldoses and ketoses

What is an important structural feature of monosaccharides?

They have chiral carbons (4 different functional groups attached)

What are the two forms of enantiomers and what does this classification mean?

L (levo), left- Inactive

D (dextro), right- active

Describes the position of the OH group

What are structural isomers?

Same atoms, but linked together differently

What are stereoisomers?

The same atoms and formula, but different arrangement in space

Which monosaccharides are ketoses?

Fructose

Which monosaccharides are aldoses?

Glucose and galactose

What are the two classifications of stereoisomers?

Enantiomers- non-superimposable mirror images, D is metabolically active

Diastereomers- anomers or epimers, not mirror images

What are the differences in the alpha and beta forms of the cyclic structures of monosaccharides?

Alpha- OH group projects downwards (opposite side to CH2OH)

Beta- OH group projects upwards (same side to CH2OH)

What is a disaccharide?

Two monosaccharides joined together by a glycosidic (covalent) bond in a condensation reaction

What enzymes hydrolyse which glycosidic bonds?

Maltase hydrolyses maltose (2 alpha glucose)

Sucrase hydrolyses sucrose (glucose and fructose)

Lactase hydrolyses lactose (glucose and galactose)

What is a homopolysaccharide?

A polysaccharide with only one type of monosaccharide

What is a heteropolysaccharide?

A polysaccharide with two or more types of monosaccharide

What is the function of glycogen?

Animal energy store in liver and muscle cells

Which enzymes hydrolyse glycogen?

Alpha 1-4- glycogen phosphorylase

Alpha 1-6- debranching enzyme

How does glycogen produce energy in the liver and muscles

Slow release energy

• In the liver- glucagon breaks down glycogen to glucose

• In the muscles- adrenaline can trigger glycogen break down (faster)

What is starch made up of? Describe the structure of these molecules

• Amylose- unbranched, alpha 1-4 glycosidic bonds

• Amylopectin- branched, alpha 1-4 and 1-6 glycosidic bonds

What are amylose and amylopectin hydrolysed by?

Both hydrolysed by amylase, into disaccharides

Describe the structure of cellulose

• Component of plant cell walls

• Unbranched

• Beta 1-4 glycosidic bonds

• Rigid structure- more difficult to break than alpha bonds

How is cellulose digested in ruminants?

Digested by bacteria possessing cellulases, in the forestomach of ruminants

Describe the structure of chitin

Similar structure to cellulose (beta 1-4)

Exoskeletons of invertebrates

Structural- difficult to break bond

What is the difference between glycoproteins and proteoglycans?

The main component of glycoproteins is protein. The main component of proteoglycans is sugar

What is the function of glycolipids?

• Specific recognition sites on phospholipid bilayer

• Allow cells to survive in hydrophilic environments

What is the function of glycoproteins?

• Blood clotting

• Reproduction

• Immune system recognition

• Form protective coats around viruses to protect from immune system

What are the two forms of glycoproteins?

O linked and N linked (sugar and protein joined with oxygen or nitrogen)

What is the function of proteoglycans?

• Provide viscosity and tensile strength

• Clinical example: can be injected into joints to increase lubrication