Quiz 8 Flashcards
The smallest sugars are
aldoses and ketoses
formula (C x H2O)n
monomers cyclize to form
a or B anomers
monosaccharides can be linked to other or to other molecules by
glycosidic bonds
monosaccharides, or simple sugars are synthesized from smaller precursors that are derived from
CO2 AND H2O by photosynthesis
monosaccharides
not broken into simpler sugars under mild conditions
oligosaccharides
oligo “a few” usually 2 to 10 simple sugar residues
polysaccharides
polymers of simple sugars
aldoses and ketoses contain
aldehyde and ketone functions
chiral monosaccharides
- aldoses with 3 or more carbon atoms
- ketoses with 4 or more carbon atoms
D,L designation refers to
the configurations of the highest numbered chiral center
D sugars
predominate in nature
steroisomers that are mirror images of each other are
enantiomers
diasteromers
pairs of isomers that have opposite configurations at one or more chiral centers but are NOT mirror images of each other
epimers
two sugars that differ in configuration at only one chiral centers
cyclic form of glucose is a
pyranose (6-membered ring)
cyclic form of fructose is a
furganose (5-membered ring)
glucose (an aldose) can cyclize to form
a cyclic hemiacetal
fructose (a ketose) can cyclize to form
a cyclic hemiketal
when hemiacetals and hemiketals are formed,
the carbonyl carbon atom becomes a new asymmetric center
isomers of monosaccharides that differ only in their configuration about that new asymmetric carbon are called
anomers
equilibrium between linear and cyclic forms means
anomers interconvert
“reducing sugars” have
free anomeric carbons which fluctuate between circular and linear forms
silica acid on a mucosal cell membrane glycoproteins is the
binding site for the flu virus
sugar alcohols
are formed by mild reduction of sugars
deoxy sugars
are constituents of DNA
sugar esters
phosphate esters like ATP are important for energy
amino sugars
contain an amino group in place of a hydroxyl group
acetals, metals and glycosides
basis for oligo- and polysaccharides
disaccharides
are the simples oligosaccharides : two monosaccharides linked by a glycosidic bond
each unit in an oligosaccharide is termed a
residue
each of the disaccharide structures is a
mixed acetal
with one hydroxyl provided from one monosaccharide and one hydroxyl from the other monosaccharide
each of these except for sucrose possesses one
free anomeric carbon and is thus a reducing sugar
sucrose is not
a reducing sugar, because it does not have a free anomeric carbon
homopolysaccharide
a polysaccharide that contains only one kind of monosaccharide
heteropolysaccharide
a polysaccharide made up of different monosaccharides
starch and glycogen are
storage molecules
chitin and cellulose
are structural molecules
starch is a
plant storage polysaccharide
amylose has
a(1->4) links, no branches, one reducing end
the branches in amylopectin are
a(1->6), every 12-20 residues, one reducing end
iodine fits into the helices to produce a
blue color, diagnostic of amylose
suspensions of amylose in water adopt a
helical conformation
iodine can into the
hydrophobic middle of the amylose helix to give a blue color that is characteristic and diagnostic for starch
glycogen is the
glucose storage device in animals
glycogen constitutes
up to 10% of liver mass and 1-2% of muscle mass
glycogen constitutes
up to 10% of liver mass and 1-2% of muscle mass
a(1->4) backbone, a(1->6)
branches every 8-12 residues
the composition of structural polysaccharides
is similar to storage polysaccharides: glucose units
structural: cellulose consists of B(1->4) linkages
amylose(storage) prefers
a helical conformation due to its bent a(1->4) linkages
cellulose,(structural) with
b(1->4) linkages can adopt a fully extended conformation
cellulose is a
structural polysaccharide
- found in cell walls of nearly all plants
giraffes, cattle, deer and camels are ruminant animals that are able to metabolize
cellulose, thanks to bacterial cellulase in the rumen, a large first compartment in the stomach of a ruminant
chitin is found in the
exoskeletons of crustaceans, insects and spiders, and cell walls of fungi
- it is a similar to cellulose but C-2s are N-acetyl
cellulose strands are
parallel
chitin strands can be
parallel or antiparallel
glycosaminoglycans
repeating disaccharides with amino sugars and negative charges
glycosaminoglycans are
linear chains of repeating disaccharides in which one unit is an amino sugar and one or both is negatively charged
heparin, with very high negative charge is a natural
anticoagulant
hyaluronates are components of the vitreous humor of the eye and of synovial fluid,
the lubricant fluid of the body’s joints
chondroitin and keratan sulfate are found in
tendons, cartilage, and other connective tissue
glycosaminoglycans
are constituents of proteoglycans
proteoglycans
large glycosaminoglycan-containing proteins
peptidoglycan
bacterial cell walls consist of glycan chains cross-linked by peptides
glycoproteins
the oligosaccharide chains covalently attached to eukaryotic proteins play a role in protein structure and recognition
carbohydrates
may be N-linked or O-linked
O-linked carbohydrates are attracted to
side chain hydroxyl groups of usually serine residues on glycoproteins and proteoglycans
the difference between proteoglycans and glycoproteins in the type of sugars
- proteoglycans have O-linked glycosaminoglycans
- glycoproteins have N-linked and O-linked oligosaccharides
proteoglycans are a subset of glycoproteins whose carbohydrates are mostly, but not always solely
glycosaminoglycans
they are components of
animal cells, membranes, and the glycocalyx
they typically consist of
proteins with one or two types of glycosaminoglycan
cell surface and extracellular matrix [ECM] proteins
with covalently attached sulfated glycosaminoglycan chains
proteoglycan production and shedding is
part of cell-cell recognition and adhesion, cell proliferations
the carbohydrate groups of proteoglycans are predominantly glycosaminoglycans
O-linked residues on protein
structure of rat cartilage matrix proteoglycan
- highly hydrated
- compression of cartilage squeezes water out of the cartilage tissue
0 water is reabsorbed when the stress and compression diminishes
soluble protein component of the
extracellular matrix outside the cell membrane
structure of rat cartilage matrix proteoglycan
- chondroitin sulfate[green]
- keratan sulfate [blue]
- O-linked oligosaccharides [also blue]
- N-linked oligosaccharides [black]
modulation of cell growth processes
binding of growth factor proteins by proteoglycans in the glycocalyc
cushioning in joints
cartilage matrix proteoglycans absorb large amount s of water
bacteria cell walls are composed of
1 or 2 membranes a peptidoglycan shell
gram positive
one membrane a thick peptidoglycan outer shell made of a pentaglycine bridge connected by tetrapeptides
gram negative
two membranes with a thin peptidoglycan shell in between, with direct amide bonds between tetrapeptides
bacteria
peptidoglycan wall, lipopolysaccharides
animals
proteoglycans, glycoproteins and glycolipids
the peptidoglycan layer is a
fence or mesh of glycosaminoglycan heterosaccharide “rails” connected by tetrapeptides
gram negative cells are
“hairy”
lipopolysaccharide consiste of
a lipid group joined to a polysaccharide made up of long chains with various repeating monosaccharides.
animal cell surfaces contain an incredible diversity of
glycoproteins and proteoglycans
the polysaccharide structures regulate cell-cell
recognition and interaction with cell-surface receptors
the uniqueness of the “information”
in these structures is determined by the enzymes that synthesize these polysaccharides
N-linked glycoproteins are of three types
- high mannose, complex, and hybrid
the carbohydrate groups of glycoproteins may be linked to the protein by
serine or threonine residues [in the O-linked oligosaccharides]
function in many cases is to adopt an
extended conformation
bristle brush structure
extends functional protein domains up out of glycocalyx
the O-linked saccharides
often adopt extended conformations to life the functional domains of these proteins above the membrane surface
oligosaccharides can
- alter the chemical and physical properties of proteins
- can stabilize protein conformations and/or protect against proteolysis
- cleavage of monosaccharide units from N-linked glycoproteins in blood targets them for degradation in the liver
progressive cleavage of silica acid residues
- exposes gal residues. binding to liver receptors increases as more Gal is exposed
lectins are
the translators of the sugar code
selectin-carbohydrate interactions
modulate the rolling of leukocytes along the vascular wall, so that leukocytes can migrate efficiently to the sites of inflammation
