Polysaccharides

Created by

mayesha

Cards (24)

whats a polysaccharide?
they are large, complex polymers that are formed from very large numbers of monosaccharide units (which are their monomers) linked by glycosidic bonds
whats a polymer?
a large molecule comprising repeated units, monomers, bonded together
whats a monomer?
single repeating unit of a polymer
why is glucose not the best storage option?
its water-soluble so it would increase the concentration of the cell contents, and consequently draw water in by osmosis
why are starch and glycogen better storage products than glucose?
they are insoluble so they have no osmotic effect
they cant diffuse out of the cell
they are compact molecules and can be stored in a small space
they carry a lot of energy in their C-H and C-C bonds
where can starch be found?
starch is the main store of glucose for plants and starch grains are found in high concentrations in seeds and storage organs such as potato tubers
what is starch built up of?
a-glucose molecules bonded together in 2 different ways, forming the 2 polymers, amylose and amylopectin
whats the structure of amylose?
linear, unbranched molecule
has a-1,4 glycosidic bonds forming between the 1st carbon (C1) on one glucose monomer and the 4th carbon (C4) on the adjacent one
this is repeated, forming a chain, which coils into a helix
whats the structure of amylopectin?
has chains of glucose monomers joined with a-1,4 glycosidic bonds
they are cross-linked with a-1,6 glycosidic bonds and fit inside the amylose
when a glycosidic bond forms between the C1 atom on one glucose molecule and the C6 atom on another, a side branch is seen
these occur every 24-30 glucose molecules
a-1,4 glycosidic bonds continue on from the start of the branch
so amylopectin is branched
whats glycogen?
the main storage product in animals
whats the structure of glycogen?
it has a-1,4 and a-1,6 glycosidic bonds (makes it very similar to amylopectin)
the a-1,6 glycosidic bonds occur every 8-10 glucose molecules
this means glycogen has shorter a-1,4-linked chains than amylopectin and so its much more branched
whats cellulose?
its a structural polysaccharide and its presence in plant cell walls makes it the most abundant organic molecule on earth
what does an individual cellulose molecule consist of?
a long chain of b-glucose unit
how are the glucose monomers in cellulose joined?
they are joined by b-1,4 glycosidic bonds to make a straight, unbranched chain
what do the b-links in cellulose do to the adjacent glucose molecules?
they rotate the adjacent glucose molecules by 180 $^.$
what forms between the OH groups of adjacent parallel chains and how do they help?
hydrogen bonds form between these groups and they help contribute to cellulose’s structural stability
whats a microfibril?
a bundle caused by parallel cellulose molecules becoming tightly cross-linked by hydrogen bonds
what are fibres?
they are microfibrils, in turn, held in bundles
how are the fibres in cellulose structured in a cell wall?
a cell wall has several layers of fibres
they run parallel within a layer but at an angle to the adjacent layers
how does the laminated structure of cellulose contribute to the cell?
it increases the strength of the cell wall
why is cellulose freely permeable and what can penetrate through?
its freely permeable as there are spaces between the fibres
water and its solutes can penetrate through these spaces in the cell wall, all the way to the cell membrane
whats chitin and where is it found?
its a structural polysaccharide and is found in the exoskeleton of insects and in fungal cell walls
what are the characteristics of chitin?
its strong, waterproof and lightweight
whats the structure of chitin?
resembles cellulose with its long chains of b-1,4-linked monomers but has groups derived from amino acids added, to form a heteropolysaccharide
like cellulose, the monomers are rotated through 180 $^.$ in relation to their neighbours
the long parallel chains are cross-linked to each other by hydrogen bonds, forming microfibrils