Glycoconjugates

what are glycoconjugates

they are carbohydrates covalently linked to other, non-carbohydrate molecules

what are the functions of glycoconjugates

cell to cell communication and signaling, labelling of proteins (transport, destruction), recognition sites for extracellular molecules

where are glycoconjugates found

there are commonly found on the exterior of a plasma membrane but can also be intracellular

what are the 3 main types of glycoconjugates

proteoglycans (glycosaminoglycans), glycoproteins, glycosphingolipids

what are proteoglycans

they are rod-shaped protein backbones in a cell membrane that are heavily glycosylates (covalently linked to carbohydrates)

what types of proteoglycans are linked to carbohydrates

glycosaminoglycans are linked to them

what are glycosaminoglycans

they are linear polymers of repeating disaccharide units that are highly negatively charge and form a meshwork with fibrous proteins to form extracellular matrix.

what does the extended hydrated molecule on glycosaminoglycans do

they minimize charge repulsion

what are the components of glycosaminoglycans

an amine sugar monomer (N-acetyl-glucosamine or N-acetyl-galactosamine)

uronic acid monomer (C6 oxidation, except keratan sulfate)

sulfate esters (except hyaluronate, only some glycosaminoglycans)

where are glycosaminoglycans found

they are found in articular cartilage and synovial fluid, cornea, bone, and can even be an anticoagulant

what are the characteristics of hyaluronate

it has about 50,000 disaccharides per chain, it has no sulfate groups, is not covalently bound to protein and is found in articular cartilage and synovial fluid

what are the characteristics of chondroitin 4-sulfate

it has 20-60 disaccharides per chain and is found in cartilage around joints

what are the characteristics of keratan sulfate

it has about 25 disaccharides per chain, it has no sugar acid (no uronic acid) and is found in the cornea, cartilage, and bone

what are the characteristics of heparin

it has 15-90 disaccharide per chain, sometimes if GLcA and is an anticoagulant

what is heparin

it is a linear polymer, 3-40 kDa

what is heparan sulfate

it is a heparin like polysaccharide but attached to proteins

what do heparin and heparan sulfate do

they prevent blood clotting by activating protease inhibitor antithrombin

their binding to various cells regulate development and formation of blood vessels

they can bind to viruses and bacteria and decrease their virulence

what is the structure of proteoglycans like

they are different glycosaminoglycans linked to a core protein through a carbohydrate polymer know as a tetrasaccharide bridge and the core protein generally consists of the amino acid sequence Ser-Gly-X-Gly

where is the linkage between glycosaminoglycans and core proteins in proteoglycans

it is from the anomeric cartoon of xylose to serine hydroxyl

what are the characteristics of syndecans

they are a protein that has a single transmembrane domain (integral membrane protein)

what are the characteristics of glypicans

they are a protein that is anchored to a lipid membrane (GPI anchor) in the membrane

what are the functions of proteoglycans

they are a molecule of the cell-surface of ECM that interact with a variety of receptor from neighboring cells and regulate cell growth

they are tissue organizers and influence cellular activities like growth factor activation and adhesion

they bind to extracellular proteins through electrostatic interactions

what are proteoglycan aggregates

they are enormous supramolecular assemblies of many core proteins all bound to hyaluronan that hold a lot of water, provide lubrication and cover joint surfaces

what can hyaluronan and aggrecan for

they can form huge noncovalent aggregates

what are the main components of the ECM

proteoglycan aggregates, collagen fibers, elastin (fibrous protein)

what is the function of the ECM

strength, elasticity an physical barrier in tissues that can prevent invasion from tumor cells

what do some tumor cells secrete

they secrete heparin's that degrades the ECM

what make up the integral membrane

some have the proteins proteoglycans (syndecans) others have proteins that are receptors for extracellular proteoglycans (integrals)

what do the integral membrane proteins do

they link cellular cytoskeleton to the ECM and transmit signals into the cell to regulate cell growth cell mobility, apoptosis, and wound healing

which group of carbohydrates in unique in that its members are strong anions, containing a significant concentration of carboxylate and sulfate

glycosaminoglycans

which glycosaminoglycan is found in the synovial fluid of joints

hyaluronate

where are glycoproteins

they are in the outer surface of the plasma membrane in the ECM and blood

what are glycoproteins

they are one or more oligosaccharides joined covalently to a protein (branched or unbranched) and the carbohydrate is O-linked (Ser of The) of N-linked (Asn)

what do carbohydrates play a role in in glycoproteins

they play a role in protein protein recognition and have high affinity binding by carbohydrate-binding proteins (lectins)

why are viral proteins heavily glycosylated

because being heavily glycosylated helps evade the immune system

what are glycolipids

they are lipids with covalently bound oligosaccharides and are components of plant and animal cell membranes where the head groups are oligosaccharides

what are glycospingolipids

they are oligosaccharides bound to a sphingolipid in the cell membrane

what do oligosaccharides act as

they act as specific sites for recognition by lectins

what are the functions of glycolipids

they function in nerve conduction and myelin formation (neurons) and signal transduction

what does ganglioside carbohydrate composition determine is vertebrates

they determine the blood groups and can be attached to a protein or lipid

what do lipopolysaccharides do in gram-negative bacteria

they cover the peptidoglycan layer

what are the regions of a lipopolysaccharide

the lipid A region: can be endotoxic in some species producing the toxic effects for hosts

the core region

the o-specific chain region: identified by the immune system

describe proteoglycans

they are glycoconjugates in which sulfates glycosaminoglycans are covalently attached to a core protein: adhesion, recognition, info transfer

describe glycoproteins

they contain oligosaccharides covalently liked to Asn or See/Thr residues: cell surface or extracellular proteins and most secreted proteins

describe glycolipids

in addition to glycosphingolipids in plants and animals and lipopolysaccharides in bacteria, are components of the cell envelope with oligosaccharide chains exposed on the cell’s outer surface

what lipids are modified with oligosaccharides

sphingolipids