carbohydrates ( polysaccharides ) Flashcards
what are polysaccharides?
polysaccharides are large polymers of monosaccharide molecules
name three polysaccharides
cellulose, starch and glycogen
how are cellulose, starch and glycogen formed?
they are polymers of glucose and are formed by the joining of glucose molecules during condensation reactions
how do polysaccharides differ and what is their function?
polysaccharides differ in the number and arrangement of the glucose molecules they contain. they function as storage or structural molecules.
are polysaccharides reducing or non reducing?
non reducing - giving a negative result in the benedict’s test
what are some properties of polysaccharides?
they are unsweet to taste and relatively insoluble in water
what is cellulose?
cellulose is a fibrous polysaccharide found in the cell wall of plants, which provide rigidity and shape to the cell
draw the structure of beta glucose
see diagram
how is cellulose formed and what is it formed from?
cellulose is a polysaccharide of beta glucose molecules joined together by glycosidic bonds. these bonds are formed in condensation reactions to form a long, straight chain. cellulose is made up of a single type of polymer, this is because only a single type of glycosidic bond is possible (beta 1,4 glycosidic bond).
what does the beta 1,4 glycosidic bond form?
it causes every other beta glucose monomer to invert
what is the structure of cellulose in the cell wall?
hydroxyl (OH) groups which project from either side of the beta glucose chain form hydrogen bonds with the hydroxyl (OH) groups of other adjacent chains producing a three dimensional structure known as a microfibril.
microfibrils are grouped together in larger bundles known as macrofibrils.
macrofibrils in one layer are oriented in the same direction.
macrofibrils in successive layers are oriented in a different direction.
macrofibrils of these different layers are interwoven, and embedded in a matrix providing rigidity.
the cellulose cell wall is usually fully permeable due to minute channels between the different layers of macrofibrils.
what is starch?
starch is the storage carbohydrate found in plants, consisting of long, branched chains of alpha glucose molecules
what polymers make up starch?
amylose, which is the result of alpha 1,4 glycosidic bonds and amylopectin, which is the result of both alpha 1,4 and alpha 1,6 glycosidic bonds
where is starch stored?
starch is stored in starch grains (amyloplasts) in the cytoplasm
how is starch suited to it’s function as a storage compound?
it is insoluble and therefore osmotically inactive (doesn’t draw water in by osmosis which could lead to cell damage).
the molecule has a helical shape forming a compact store.
why is starch branched and what is the benefit of this?
starch is branched as a result of alpha 1,6 glycosidic bonds and the benefit is that there’s more free ends for enzymes to attach to
how is starch hydrolysed?
starch is hydrolysed by the enzyme amylase to produce the disaccharide maltose
how do you test for the presence of starch?
starch can be detected in a sample by using the iodine test. add 2-3 drops of iodine solution. if starch is present a blue/black colour is produced. if no starch is present the iodine solution remains orange/yellow.
what is glycogen?
glycogen is the storage carbohydrate found in the cytoplasm of animal cells. it is sometimes referred to as ‘animal starch’ due to similarities in structure and function between the two molecules.
what is glycogen a polymer of and how does this differ to starch?
glycogen is a polymer of alpha glucose, similar to starch but with more branches (free ends), which means it can be hydrolysed rapidly to release glucose for respiration
what properties of glycogen make it a suitable storage compound?
it is insoluble and osmotically inactive, like starch
where is glycogen found?
it is stored in large amounts in liver and muscle tissues
