3.3 : Carbohydrates Continued ( Polymer ) Flashcards
What is starch ? How is it made?
Glucose made by photosynthesis in plant cells is stored as starch. It is made when many alpha glucose molecules are joined by glycosidic bonds.
What is the function of starch?
Chemical energy store in plants
What are the two forms of starch?
Amylose and amylopectin
Describe how amylose is made. What does it look like and what are its properties?
It is formed by alpha glucose molecules joined together only by 1-4 glycosidic bonds.
The angle of the bond means that this long chain of glucose twists to form a helix which is further stabilised by hydrogen bonding.
This makes it compact and less soluble than the glucose molecules used to make it.
Describe how amylopectin is made. What does it look like ?
It is made by 1-4 glycosidic bonds between alpha glucose molecules but there are also some glycosidic bonds formed by condensation reactions between carbon 1 and carbon 6.
This means it has a branched structure , with every 1-6 branching point occurring around one every 25 glucose subunits.
What is glycogen? Describe its structure and properties.
An energy storage molecule in animals and fungi.
It forms more branches ( and coils) than amylopectin. This means it is more compact and less space is needed for it to be stored. This is important as animals are mobile, unlike plants, so they need more energy.
The branching also means there are many free ends where glucose molecules can be added or removed. This speeds up the processes of storing or releasing glucose molecules.
What are the key properties of amylopectin and glycogen ?
Insoluble, branched and compact
What is a hydrolysis reaction? When is this needed?
It is the addition of water molecules.
Starch or glycogen undergoes it to release glucose for respiration.
The reactions are catalysed by enzymes.
Describe how cellulose is made and it’s structure
Beta glucose molecules can join together and form a polymer if alternative glucose molecules are turned upside down.
When a polysaccharide forms this way, it can’t coil or form branches. A straight chain molecule is formed called cellulose.
Describe the properties of cellulose and why it has them
- cellulose molecules make hydrogen bonds with each other, forming microfibrils
- these microfibrils join together to make macrofibrils, which combine to form fibres
- these fibres are strong, insoluble and used to make cell walls
- it is an important part of our diet, it is hard to break down into its monomers and forms the ‘fibre’ necessary for a healthy digestive system
