Lecture 11 - Carbohydrates Flashcards
what are carbohydrates?
-sugar, saccharides
what is a monosaccharide?
singel sugar molecules
what are polysaccharides/glycans?
polymeric sugar
carbohydrates are all _____
-polyalcohols
is every carbon chiral?
yes
except C=O at the end of the chain
why are sugars with 5 or 6 carbons most important biochemically?
-they can cyclize
how do sugars cyclize?
-via the formation of hemiacetals or hemiketals into rings
what is special about 5 or 6 member rings?
-almost no ring strain
what are 5 atom ring sugars called?
furanose
what are 6 atom ring sugars called?
pyranose
in anomeric forms of cyclic sugars, why is one of the atoms always an O?
came from the attacking OH
What happens to the original C=O during cyclization?
becomes -OH hanging off side of ring
what are the two optical isomers?
-alpha (below)
-beta (above)
anomeric forms
cyclic sugars are ____ in solution and there is only _____ between
- metastable
- slow interchange
- anomeric forms
how can sugars be modified?
covalently
what can glycosidic bonds be made into? how?
- an amine (N-linked) or alcohol (O-linked)
- via the anomeric carbon
polysaccharides (glycans)
purpose:
ex:
- structural
- cellulose, chitin
glycosaminoglycans
purpose:
ex:
- viscous or lubricating agent
- vitreous humor (eye)
proteoglycans
purpose:
ex:
- structural
- cartilage
peptidoglycans
purpose:
ex:
- structural
- bacterial cell walls
glycoproteins
purpose:
ex:
- modifies protein properties
- most proteins are glycosylated
how are disaccharides formed?
-when a glycosidic bond is formed between one sugar (via its anomeric carbon) and one -OH group on another sugar
whate are teh two anomeric forms of disaccharides?
- lactose = galactose + glucose
2. sucrose = glucose + fructose
what is cellulose?
the key structural fiber for plants
