Chapter 10: Carbohydrates

Aldoses

glucose, galactose, ribose (aldehyde)

Ketose

fructose, ribulose (ketones)

Constitutional Isomers

same molecular formula, atoms connected differently

Horizontal Bonds

in front of plane

Vertical Bonds

behind plane

Epimers

Stereoisomers that vary at 1 chiral carbon

Hemicetal

Aldehyde + alcohol

Hemiketal

Ketose + alcohol

Anomeric carbon

New stereocenter made upon ring closure

Anomer

Isomers that differ only in configuration of the anomeric carbon

α

anomeric -OH below ring

β

anomeric -OH above ring plane

Furanose

5 carbon ring

Pyranose

6 Carbon ring

Ogliosaccharides

contain 2 or more monosaccharides linked by O-glycosidic bonds

Glycosidic Bonds

formed when hydroxl group reacts w alcohol

Glycosyltransferases

forms glycosidic bonds

Sucrose

a1 —> B1

glucose + fructose

cannot act as reducing sugar

Lactose

B1 —> 4

galactose + glucose

reducing sugar

Maltose

a1 —> 4

glucose + glucose

reducing sugar

Glycogen

a1 —> 4 chain

a1 —> 6 branch (every 12 residues)

animals

Amylose

linear a1 —> 4 (no branches)

starch/ plants

Amylopectin

branched a1 —> 6 every 30

starch/plants

Humans can only break down __ linkage:

a(1 —>4) linkage

a linked

curved/ coiled

B linkage

straight

Cellulose

B1 —> 4 linkage

linear

H bonding —> high tensile strength

plant

Chitin

B1 —> 4 N-acetyl glucosamine

exoskeleton + fungal cell walls

plant

N- glycosidic bond

binds to Asp (Nitrogen —> Aspargine)

O-glycosidic

Binds to Ser/ Thr

Glycosyltransferases

Adds carbs to proteins

Glycoproteins

mostly proteins

O-Ser/Thr / N-Asp links

stability, signaling, trafficing

EPO

3 N-linked

1 O-linked (Ser)

increase protein ½ life

glycosylation triples half-life in blood —> enhances stability to prevent fast degredation

I-Cell Disease

causes build-up of lysosomes in blood

mannose-6-phosphate tags are prevented from being made

inclusion bodies are formed

Proteoglycans

more carbs than proteins

long GAG chains that react well with negative molecules

sulfonated —> negative charge

structural roles, lubricants

Mucins/ Mucoproteins

Predominantly carbs

lots of GalNAc → Ser/Thr O-linked bonds

Major components of mucus

overexpressed in cystic fibrosis and bronchitis