biochem carbohydrates and glycoproteins

carbohydrates

cell and protein can be coated in this usually for tissue formation, basis for human blood group, used by pathogens to gain access and has a lot of structural diversity

constitutional isomers

differ on the order of attachment of atoms (glyceraldehyde and dihydroxyacetone)

stereoisomer

atoms in same order but differ in spatial arrangement (enantiomer and diastereomers)

enantiomer

nonsuperimosable mirror image (D-glyceraldehyde and L-glyceraldehyde)

diastereomers

isomers that are not mirror images (anomers and epimers) (D-aldose and D-glucose)

anomers

differ at a new asymmetric carbon atom formed on ring closure (alpha-D-glucose and Beta-D-glucose)

epimers

differ at one several asymmetric carbon atom (D-glucose and D-mannose)

why does aldose have higher activity?

in reaction carbonyl group acts as nucleophile and groups attached are H so less steric hindrance

sucrose

major sugar produced by plants, combines glucose and fructose using alpha-1, beta-2 glycosidic linkage (non-reducing sugar)

lactose

“milk sugar” is made of a beta-D-galactose and an D- glucose (beta 1,4-glycosidic linkage) reducing sugar

maltose

disaccharide of glucose, repeating unit of amylose with an alpha 1,4 glycosidic linkage, reducing sugar

disaccharides example

sucrose, lactose, and maltose

polysaccharides examples

starch, glycogen, and cellulose

starch

storage polysaccharides in plants from a mix of amylose (10-20% alpha1,4 glucose link) and amylopectin (80-90% alpha 1,4 glucose with alpha 1,6 branches) once every 30 residues

glycogen

contains glucose chains by alpha 1,4 and alpha 1,6 linkage once every 10 residues

why is branched structure better for storage and breakdown

when enzymes break down these polysaccharides work from the non-reducing ends. with extensive branching there are more non-reducing ends for enzymatic cleavage so glycogens structure is better for hydrolysis

cellulose

structural polysaccharides, beta 1,4 glucose polymer which is fibril structure and indigestible by animals

glyconjugate examples

glycoproteins, proteoglycans, and mucins

glycoproteins

1-10% carbohydrate, cell membrane proteins, and secreted proteins

proteoglycans

glycosaminoglycans + proteins, mostly carbohydrates (80-95%), and structural components (cartilage). highly polar

example of proteoglycan

chondroitan 6-sulfate, heparin, dermatan sulfate, hyaluronate

mucins

found in mucus and lubricants mostly carbohydrates too (GALNAc)

why glycosylate proteins?

it increases complexity of the proteome and same genome can make different protein. it directs trafficking (where protein goes to the cell surface for secretion or to the lysosome (out of cell)), protein structure can contribute to structural strength

where does protein glycosylation happen

ER lumen and golgi, golgi will recognize the correct and incorrect glycosylation and send the molecules to different places

purpose of dolichol phosphate

liquid molecule that had to be utilized in ER as bait for assembly of adding sugar molecules to protein

UDP-glucose

precursor used in the biosynthesis of oligonucleotides destined to become protein modifications

erthropoietin

stimulates the production of red blood cells, 3-Asn residues that have been decorated by sugar molecules and 1-0 link decorated with ser 126

what does type A blood add

N-acetylgalactoamine

what does type B blood add

galactose

chitin

longer polymer of GlcNAc, % of sugar is more than glycoprotein

mucin

VNTR region of the proteins backbone has a high degree of glycosylation, forces it into an extended conformation, highly branched and adhere to ser/thr to act as barrier and hydration. usually attach to OH

lectin

bind to specific oligosaccharides or glycans. C type lectin have a ca2+- binding carbohydrate recognition domain. Ca2+ in the ER enable mannose- binding lectins to recognize glycoproteins targeted for the lysosome

selectins

C-type lectins that recruit immune sites of injury during the immune response that adhere to lymph node (L-type), endothelium (E-type), and blood platelets (P-type)

inclusion cell disease

effect in glycosylation interrupt protein trafficking change protein attachment and cannot be sent to lysosome. mannose- PO4 serves as a signal to direct protein to the lysosome, defects cause a build up of undigested cellular component called “inclusions”

influenza virus infects cells

recognizes sialic acid at glycoprotein terimini. the flu virus has hemagglutinin that bind sialic acid on cell surface glycoproteins and is engulfed by the cell. virions replicate, resemble, and bud again using sialic acid. neuraminidase cleaves sialic acid glycosidic bond to free virus