L6 - Glycosylation 1 Flashcards
(30 cards)
what are most proteins embedded in membranes
glycoproteins or proteoglycans
= hexose sugars added
define the glycocalyx
the layer of carbohyrdartes that surround a cell
= first thing ecountered when entering a new cell
we know very littel about the glycocalyx
what determines different blood groups - example of glycosylation
terminal hexose sugar determined by glycosylation
- a3 sugar is different
what is different in hexose sugars - simple monosaccharide
location of OH group - all hexose sugars are very similar
= almost always found in ring form - folded up
give one reason the glycolyax is so hard to study
lots of possible shapes hexose susgars can take
= all are very similar and take different forms
= isomers
what is the most common monosaccharide
D-glucose
compare glycoproteins vs proteoglycans
glycoproteins:
fewer,shorter,branched sugars bound –> main component of glycocalyx
proteoglycans:
long unbrached chains of sugars bound –> make up ECM
what do proteoglycans bind huge amounts of
water
= form huge complexes bound to water and found in conncetive tissues + ECM
technical abbreviation for carbohyrdrate
CHO
what are Glycosaminoglycans (GAGs)
long, unbranched sugar chain made of repeating disaccharide units.
- Hyaluronic acid/hyaluronate = simplest
- Chondroitin
describe Hylauronic acid
simplest GAG
forms a β3-β4 discahride
not sulfated and not covalently bound to proteins
= acts as a ‘space filler’ in case of injury due to long length of
describe a common feature of GAGs
most are sulpfated - negatively charged
discahride units
bind lots of water and cations (-)
name the 1 GAG not sulphated
Hyaluronate/hyaluronic acid
how do we make proteoglycans - GAGs
GAGs usally covalently linked to Serube side chain on core protein
major function of GAGs
shock absorber
in feet and hands –> able to bind lots of water
what is a glycosidic bond
between sugar and somthing else
what must first be done before a glcyosidic bond can be made between a sugar and somthing else
Monosacharides need to be activated
–> mono/diphosphates do tgis
active forms known as ‘Nucleotide sugars’ –> UDP-glucose is an example
what are O-linked sugars
class of sugars where there is ‘somthing’ bound to the oxygen sidechain
- threonine/serine amino acid
- lysine but must be ‘hydroxylated’ first
what must be done to lysine residues before O-linked sugars can be added to them in glycoslyation
hydroxylated
= defects in hydroxylates prevents glycosylation
= collagen of ECM is less stable = curly
name a disease caused by incorect glycolsation patterns
Scurvy - Vit C defieincy
lysine hydroxylates use Vitamin-C as a cofactor –> defincy prevents hydroxylation
= lysines cannot be gycosylated –> collagen is less stable –> bleeding gums
what are N-linked sugars
attached via nitrogen group to Asn sidechain
= needs a specific protein motif Asn-x-Ser/Thr
= X can be anything BUT proline
where does glycosylation of proteins begin
Endoplasmic reticulum
= need a signal sequence on N-terminus –> directed into ER traslocator
No signal = No entry to ER = No glycoslyation
describe what happens when N-terminus signal sequence for glcyoslaytion is on proteins
enters ER translocator
14-mer ogliosacharide transffered ‘en bloc’ = in mass
14-mer is modified to become either of 2 ogliosacharides :
- High mannose
- complex
why is there a common core in both high mannose and complex oglioscaharides
N-linked oglioscaharides all start ar the same 14-mer
