cellulose, glycogen and starch Flashcards
What is the animal version of starch?
glycogen
Where is glycogen found?
in animals and bacteria
Describe the structure of glycogen
Glycogen has a similar structure to amylopectin, containing many alpha 1–6 glycosidic bonds that produce an even more branched structure.
What is the difference between the structure of glycogen and the structure of starch?
Glycogen have shorter chains and is more highly branched
Glycogen is less dense and more soluble than starch, and is broken down more rapidly. This indicates the higher metabolic requirements of animals compared with plants.
Why is glycogen called “animal starch”?
because it is the major carbohydrate storage product of animals
How is glycogen stored in animals?
as small granules mainly in the muscles and the liver
Why is the mass of carbohydrate that is stored, relatively smaller in animals?
because fat is the main storage molecule in animals
Why does Glycogen’s structure and properties, make it suitable for storage?
- it is insoluble and therefore does not tend to draw water into the cells by osmosis
- being insoluble, it does not diffuse out of cells
- it is compact, so a lot of it can be stored in a small space
- more highly branched than starch and so has more ends that can be acted on simultaneously by enzymes. hence, more rapidly broken down to form glucose monomers, which are used in respiration - important to animals, which have a higher metabolic rate and therefore respiratory rate than plants because they are more active.
What type of molecule is cellulose, what makes it different from glucose and what is its properties as a result of this?
Polysaccharide, also a polymer of glucose, but the bonding between the glucose unit is different, making the cellulose molecules are long and straight.
In what major way does cellulose differ from glycogen and starch?
made up of beta glucose instead of alpha glucose
Describe the structure of cellulose
it has straight, unbranched chains, which run parallel to one another,
allowing hydrogen bonds to form cross-linkages between adjacent chains, which add collective strength.
these molecules are grouped to form microfibrils which in turn are grouped to form fibres all of which provide yet more strength
Ever second beta glucose is rotated
How are cellulose molecules arranged and what bonds are they held together by?
Arranged side by side to form microfibrils and held together by many weak hydrogen bonds.
Even though hydrogen bonds are individually weak, why do they still make a considerable contribution to strengthening cellulose?
Because the sheer overall number of them adds to the strength
Where is cellulose found and how does its structure help?
Plants - strengthen the plant cell wall
What is the role of the cell wall?
- provides rigidity
- also prevent the plant cell from bursting as water enters it by osmosis
How does the cell wall prevent the plant cell from bursting?
it exerts an inward pressure that stops any further influx of water. As a result, living plant cells are turgid and push against one another making non-woody parts o the plant semi-rigid
Why is it important that stems and leaves maintain their turgid state?
so that they can provide the maximum surface area for photosynthesis
What are lipids and what do they contain?
Oils and fats. Contain carbon, hydrogen and oxygen
What are the properties of lipids?
insoluble in water
are soluble in organic solvents such as alcohols and acetone
What group of lipids are plant oils and animal fats mostly made up of?
triglycerides
Starch is a store of glucose. What happens when glucose is needed by the plant cell? Why is the process to obtain glucose from the starch quick?
water is used to break the glycosidic bonds (hydrolysis reaction).
This is done quickly because the enzymes that break down starch act at the ends of the molecules.
Since amylopectin has a lot of branches, it has a lot of ends, allowing the enzymes to break down starch rapidly
How is starch adapted for its main role, energy storage?
its insoluble and therefore doesn’t affect water potential, so water is not drawn into the cells by osmosis
being large and insoluble, it does not diffuse out of cells
its compact, so a lot of it can be stored in a small space
when hydrolysed it forms alpha glucose, which is both easily transported and readily used in respiration
the branched form has many ends, each of which can be acted on by enzymes simultaneously meaning that glucose monomers are released very rapidly
What makes starch molecules very compact
the unbranched chain in the structure, which is wound into a tight coil that makes the molecule very compact.
What type of molecule is starch and where is it only found and in what form?
It is a polysaccharide only found in plants in small grains - intracellular grains in organelles called plastids
What properties of starch molecules make it ideal for storing glucose?
They are insoluble and compact
Describe the properties of amylopectin
It is soluble in both hot and cold water
It does not resist digestion
It shows extensive branching
It gives reddish-brown color with iodine solution
Describe the structure of amylopectin
A
polymer of alpha glycose joined by 1-4 glycosidic bonds
has a branch every 25-30 alpha glucose molecule. This branch is connected to the main chain by a glycosidic bond but between carbon 1 of an alpha molecule and carbon 6 of another one (1 6 glycosidic bond)
Describe the properties of the amylose component of starch (mention something about its coiled structure
It is insoluble in cold water
It is more resistant to digestion due to packed helical structure
It limits the infiltration of water in starch
It gives dark blue/black color with iodine solution
Angles of the glycosidic bonds = coiled structure → makes it compact = can fit more into a small space (= good for storage)
Describe the structure of amylose
polymer of alpha glucose molecules
compact cylindrical polysaccharide
Glycosidic bond linking the α-glucose molecules is an α-1,4 glycosidic bond.
Twisted into a complex helix with hydrogen bonds forming between glucose molecules along the chain
