Carbohydrates Flashcards
Whats a monosaccharide?
simple carbohydrate of only one sugar unit
(C based molecule with many hydroxyl groups)
CH2O(n)
Aldose VS ketose:
aldose = contains aldehyde (RCH=O)
Ketose = contains ketone (RC=O)
Monosaccharides are
aldoses or ketoses with 2 or more hydroxyl groups
Whats an “epimer” isomer?
- Diastereomers (isomers that are NOT mirror images)
- differ at only 1 asymmetic carbon atom (glucose vs mannose)
Whats an enatiomer?
- stereoisomer (same attatchment order but differ in spatial arrangement)
- non superimposable mirror image (L vs D forms)
whats an anomer?
- diasteromers (not mirrors)
- differ at a new asymmetric carbon atom formed on ring closure
whats an anomeric centre?
the C1 atom where the ring closure occurs
where is the OH on C1 in alpha anomers?
alpha = OH group on anomeric carbon is below the plane
(down)
where is the OH on C1 in beta anomers?
beta = OH group on anomeric carbon is abobe the plane
(up)
Why does ring closure happen?
ketone and alcohol groups react within an open chain sugar to form a ring
Pyran =
6 membered ring of monosaccharide
(pyranose)
Furan =
5 membered ring of monosaccharide
(furanose)
4 common monosaccharides are
- ribose (4C)
- glucose (5C)
- mannose (5C)
- galactose (5C)
What is a glycosidic bond?
the bond between the anomeric carbon of one monosaccharide and the alcohol of another
what are 3 common disaccharides?
- maltose (2 glucose)
- sucrose (glucose + fructose)
- lactose (galactose + glucose)
What are reducing sugars?
sugars that react with oxidizing agents because of the aldehyde group
are all monosaccharides reducing
yes, even the ketose (fructose) b/c they can tatomerize into aldoses
which dissacharides are reducing?
- maltose
- lactose
(sucrose is NOT)
why isnt sucrose reducing?
both anomeric centres are locked in a glycosidic bond
Structure + function of glycogen
- homopolymer of glucose
- mostly a-1,4 glycosidic bonds
- branches every 10 units by a-1,6 GBs
Function = energy storage
hollow helix structute
Structure and function of starch?
- homopolymer of glucose
- amylose (linear) a-1,4 GB
- amylopectin (branched) [1 a-1,6 GB per 30 1,4 GB]
nutritional reservoir in plants
hollow helix structure
structure and function of cellulose?
- homopolymer of glucose
- linear (B-1,4-GBs)
- H bonds between parallel chains
How do carbs attatch to proteins?
anomeric carbon of the carb to N or O of AA to form glycosidic bond
What is O linked glycosylation?
carbs attached to side chain hydroxyl OXYGEN of serine or threonine
What is N linked glycosylation?
carbs attatched to side chainamide NITROGEN of asparagine
How does glycosylation change the properties of a protein?
adds additional chemical information for a variety of functions
what are the classes of glycoproteins?
- glycoproteins
- proteoglycans
- mucins
Glycoproteins (composition)
Protein > carbohydrate (by weight)
- N or O linked
Proteoglycans (composition)
Carbohydrate > protein (by weight)
- glycosaminoglycans
Glycosaminoglycans
Mucins (composition)
carbohydrate > protein
- extensively O linked
proteoglycans (function)
lubricants + structural components in connective tissue by absorbing water
- proteins attatched to glysaminoglycans (repeating units of glycosamine and galactosamine
Mucins (function)
mucus material; bind water to lubricate and protect insteninal tract
What are lectins?
- proteins that specifically bind carbohydrates by non covalent interactions
- slectins help immune cells bind to site of injury through this binding method
