carbohydrates (polysaccharides) Flashcards
(24 cards)
what are polysaccharides?
polysaccharides are large polymers of monosaccharide molecules
what are three examples of polysaccharides and how are they formed?
the polysaccharides cellulose, starch and glycogen are polymers of glucose and are formed by the joining of glucose molecules during condensation reactions
how do polysaccharides differ?
polysaccharides differ in the number and arrangement of the glucose molecules they contain
what are two properties of polysaccharides?
they are unsweet to taste and relatively insoluble in water
what are the functions of polysaccharides?
they function as storage or structural molecules
are polysaccharides reducing or non reducing?
they are non reducing giving a negative result in the benedict’s test
what type of polysaccharide is cellulose, where is it found and what does it provide?
cellulose is a fibrous polysaccharide found in the cell wall of plants, which provides rigidity and shape to the cell
what is the monomer in cellulose?
the monomer in cellulose is beta (β) glucose
how is cellulose formed and what is it’s structure?
cellulose is a polysaccharide of beta glucose molecules joined together by glycosidic bonds, formed in condensation reactions to form a long, straight chain. cellulose is made up of a single type of polymer because only a single type of glycosidic bond is possible, the beta 1-4 glycosidic bond. due to this difference, every other beta glucose monomer is inverted.
how is a microfibril formed?
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
how are macrofibrils formed and what is their structure?
- microfibrils are grouped into larger bundles known as macrofibrils
- macrofibrils in one layer are orientated in the same direction
- macrofibrils in successive layers are orientated in a different direction
what are two properties of macrofibrils and why?
- 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 type of polysaccharide is starch and where is it found?
starch is the storage carbohydrate found in plants, consisting of long branched chains of alpha (α) glucose molecules. Two types of polymer make up starch
what two types of polymer make up starch?
amylose and amylopectin
what are amylose and amylopectin a result of?
amylose is the result of alpha 1-4 glycosidic bonds
amylopectin 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 ideally suited to it’s function as a storage compound?
- it is insoluble and therefore osmotically inactive (it does not draw water into a cell by osmosis which could lead to cell damage)
- the molecule has a helical shape forming a compact store
how is starch hydrolysed and what does this produce?
starch is hydrolysed by the enzyme amylase to produce the disaccharide maltose
starch (polysaccharide) + water —Amylase–> maltose (disaccharide)
how can starch be detected?
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 type of polysaccharide is glycogen and where is it found?
glycogen is a storage carbohydrate found in the cytoplasm of animal cells
what is glycogen sometimes referred to as and why?
glycogen is sometimes referred to as ‘animal starch’ due to similarities in structure and function between the two molecules
what is glycogen a polymer of?
glycogen is a polymer of glucose, similar to starch
what are three properties of glycogen?
- glycogen is similar to starch but with more branches (free ends), which means it can be hydrolysed rapidly to release glucose for respiration and there’s more free ends for enzymes to bind to
- it is insoluble and osmotically inactive which are ideal storage properties
where is glycogen stored?
glycogen is stored in large amounts in liver and muscles tissues
