20 WJEC Biology AS Level - Marianne Izen - 2nd Edition Flashcards
What is important when write about cellulose in the cell wall?
When you write about cellulose in the cell wall, always state ‘plant cell wall rather than just ‘cell wall’ because the cell walls of fungi and most prokaryotes do not contain cellulose
Describe the structure of cellulose at an individual molecule level
An individual cellulose molecule consists of a long chain of ẞ-glucose units.
These glucose monomers are joined by ẞ-1,4-glycosidic bonds to make a straight, unbranched chain.
The ẞ-link rotates adjacent glucose molecules 180°.
Describe the structure of cellulose at microfibril level
Hydrogen bonds form between the (OH) groups of adjacent parallel chains of cellulose, contributing to cellulose’s structural stability.
These parallel cellulose molecules become tightly cross- linked by hydrogen bonds to form a bundle called a microfibril.
Describe the structure of cellulose at ‘fibre’ and ‘cell wall’ level
The microfibrils of cellulose are, in turn, held in bundles called fibres.
A cell wall has several layers of fibres, which run parallel within a layer but at an angle to the adjacent layers.
This laminated structure also contributes to the strength of the cell wall.
Describe the features of glycogen
The main storage product in animals is glycogen.
It used to be called animal starch because it is very similar to amylopectin.
It also has a-1,4 and a-1,6 bonds.
The difference is that in glycogen, the a-1,6 bonds occur every 8-10 glucose molecules.
This means glycogen has shorter a-1,4-linked chains than amylopectin and so it is more branched.
Describe the features of cellulose
Cellulose is a structural polysaccharide
Its presence in plant cell walls makes it the most abundant organic molecule on Earth.
Cellulose is freely permeable, because 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.
Cellulose is a fibrous molecule.
It is a carbohydrate and is the main component of the
of plants.
How does starch and glycogen provide energy where it is needed?
Both starch and glycogen are readily broken down by hydrolysis to a-glucose, which is soluble and can be transported to where energy is needed.
What does the word “cellulose” refer to?
We use the word ‘cellulose’ to refer to the chains of ẞ-glucose, i.e. the cellulose molecules and also for the bulk material that they make.
