Glycoconjugates Flashcards
Glycoconjugates?
Carbs covalently linked to other non-CHO biomolecules –> lipids and proteins
3 functions of glycoconjugates
- cell to cell communication and signaling
- labeling of proteins
- recognition sites for extracellular molecules
glycoconjugates commonly found on ? but also in ?
on exterior of plasma membrane but also intracellular
Glycosaminoglycans (GAG) structure? –> 2 monomers? some also contain ?
linear polymers of repeating disaccharide units
1st monomer: amino sugar: N-acetyl glucosamine/galactosamine
2nd monomer: negatively charged: uronic acid –> oxidized C6 OH into carboxylic group
- some also contain sulfate esters –> highly negative
GAG = extended hydrated molecule –> (increase or decrease) charge repulsion between inside of proteins
decrease
GAG can react with water –> role in ________ of ECM
viscosity
GAG forms meshwork with ________ proteins to form ________ –> plays role in (3)
- fibrous proteins
- extracellular matrix
- connective tissue, cartilage and lubrification of joints
Hyaluronate: ? + repeated how many times? + found in (2)
- no sulfate group!
- 50 000x
- articular cartilage and synovial fluid –> lubrification of ECM
Chondroitin-4-sulfate: repeated ? + found in?
- 20-60x
- cartilage around joints
Keratan sulfate: ? + repeated? + found in (3)
- no sugar acid uronic acid (replaced by galactose)
- 25 times
- cornea, cartilage and bone
Herapin: repeated ? + contains ? + is an ?
- 15-90x
- iduronic acid and sometimes GlcA
- Anticoagulant
Herapin (3) vs heparan sulfate (3)
herapin: in immune cells! more specific and more sulfated
heparan sulfate: heparin-like polysac but attached to proteins –> uniquitous –> less charged than heparin but same function!
Function of heparin/heparan sulfate (3)
- prevent blood clotting by activating protease inhibitor antithrombin
- bind to various cells regulates development and formation of blood vessels
- can also bind to viruses and bacteria to decrease their virulence
Heparan sulfate interaction to form blood clot
negative charge of sulfates interacts with positive charge of thrombin (essential for coagulation) and antithrombin (inhibits thrombin in presence of heparan sulfate)
Proteoglycans: what? where?
- rod-shaped protein “backbones” in cell membrane that are heavily glycosylated (covalently linked to GAGs)
- on cell surface or in extracellular matrix (ECM)
How to GAG bind to extracellular proteins to form proteoglycans? VS how do proteoglycans bind to membrane proteins?
- extracellular: through electrostatic interactions
- membrane: covalently
Proteoglycan components (3)
- core protein (Ser-Gly-X-Gly)
- tetrasaccharide bridge, linked to core protein from anomeric carbon of xylose (on bridge) to serine OH
- GAGs linked to core protein via tetrasaccharide bridge
Syndecan vs glypicans
Syndecan: protein has single transmembrane domain –> integral membrane protein
Glypican: protein is anchored (GPI anchor) to lipid membrane
Proteoglycan functions (3)
- interacts with variety of receptors from neighbouring cells and regulate cell growth
- act on tissue organizers and influence various cell activities
- bind to extracellular proteins through electrostatic interactions
Proteoglycan aggregates? covers what surface? for 2 fct
- enormous supramolecular assemblies of many core proteins all bound to hyaluronan
- covers joint surfaces –> articular cartilage: decrease friction and load balancing
which 2 GAGS form huge noncovalent proteoglycan aggregates? –> fct (2)
Hyaluronan and aggrecan: hold lots of water and provide lubrification
Feather like shape: what is the long thing au millieu? then branche? then feuilles?
- middle = hyaluronan
- branch = aggrecan core protein
- GAG link chondroitin sulfate
Glycoproteins found where?
outer surface of plasma membrane, in ECM or in blood
Glycoproteins have _____ (up to ?) ______________ joined covalently to _________
one or more (up to 10-12) oligosaccharides joined covalently to protein
How is CHO attached to protein? for glycoproteins. what bonds?
anomeric C of CHO attached to aa of protein.
- O-linked glycosidic bond: OH group of serine or threonine
- N-linked glycosidic bond: amide N of asparagine
Glycoproteins function?
CHO play role in protein-protein recognition
What proportion of mammalian proteins are glycoproteins? vs bacteria and viral proteins
- 50%
- bacteria: only some glycosylate proteins
- viral proteins: heavily glycosylated –> helps pathogens evade immune system
Glycolipids?
lipids with covalently bound oligosaccharides (exposed to cell’s outer surface
Glycolipids are components of what?
plant and animal cell membranes where head groups are oligossacharides
Oligosaccharides in glycolipids can be recognized by ?
Lectins –> recognize sugar motif of glycolipids and glycoproteins
2 functions of glycolipids
- nerve conduction and myelin formation
- signal transduction
Glycoproteins function?
CHO play role in protein-protein recognition
In vertebrae, ganglioside carbohydrate composition determines ?
blood groups
in gram negative bacteria –> lipopolysaccharides cover the ? –> 3 regions
peptidoglycan layer
1. Lipid A region –> endotoxic
2. core region
3. O-specific chain region –> gives serotype and leads immune response from hosts
Immune system identifies and targets specific species of bacteria by identifying species-specific ____________
lipopolysaccharides
How to conduct analysis of glycoconjugates?
through mass spectrometry
Extracellular matrix? gives (3) to tissues
material outside cell
- gives strength, elasticity and physical barriers to tissues
Main components of ECM (3)
- proteoglycan aggregates (aggrecan bound to hyaluronan)
- collagen fibers
- elastic/fibrous protein
ECM and tumour cells relationship
- ECM = barrier for tumours cells seeking to invade new tissues
- some tumor cells secret heparinase that degrade ECM
Some integral membrane protein are ___________ (type?) vs other integral membrane proteins are receptors for _______________ (type?)
- proteoglycans (syndecans)
- extracellular proteoglycans (integrins)
proteoglycans link cellular cytoskeleton to ECM and transmit signals into cell to regulate (4)
- cell growth
- cell mobility
- apoptosis
- wound healing
