Starch, Glycogen And Cellulose Flashcards
What is starch a polymer of?
Alpha-glucose
Where is starch found?
In plants
What is starch a mixture of?
Amylose and amylopectin
What is the function of starch in plants?
Main storage polysaccharide in plants
What bonds join alpha-glucose molecules in amylose?
1,4-glycosidic bonds
What structure is formed in amylose?
Helix
What bonds are present in the amylose helix?
Hydrogen
Why is amylose a good storage compound?
- It’s insoluble in water
- because of the compact shape it allows tight packing
What bonds join alpha-glucose molecules in amylopectin?
1,4-glycosidic bonds
In amylopectin what happens every 25 glucose molecules?
Adjacent chains are connected by 1,6-glycosidic bonds
What structure does amylopectin have?
Branched
What does amylopectin have?
Many protruding ends
What can happen to amylopectins many protruding ends?
They can be hydrolysed rapidly therefore allowing rapid release of glucose
What is the test for starch?
The iodine test
What is the reagent in the test for starch?
Iodine
How do you carry out the test for starch?
Add 2-3 drops of the iodine
What is a positive result of the test for starch?
Black/blue precipitate forms
What is starch digested to?
Maltose
What enzymes digest starch?
Salivary and pancreatic amylase
In the digestion of starch what bonds do alpha-amylase break?
1-4 links randomly
In the digestion of starch what bonds do beta-amylase break?
Alternative 1-4 links
What is maltose digested into?
Alpha glucose
What enzyme digests maltose?
Maltase found in intestinal juices
As well as branched, what is significant about the chains of amylopectin?
They are long
What is significant about the chains of amylopectin being long?
It reduced the amount of ends there are making amylopectin harder to break down, making it harder to digest
What is significant about starch being insoluble?
It is osmotically inactive
What is glycogen?
The main storage polysaccharide in animals
What is glycogen a polymer of?
Alpha-glucose
How does the structure of glycogen differ to that of amylopectin?
It is branched but has much shorter 1,4 chains and therefore many more branches
What is the significance of glycogen being highly branched?
Quick hydrolysis of glucose off of the branches
Is energy release quicker in plants or animals?
Animals
Why is energy release greater in animals?
They have a higher metabolic demand
What similarities to glycogen and amylopectin have?
They are both joined by 1,4-glycosidic bonds with 1,6-glycosidic bonds joining 1-4 linked chains
Where is glycogen found in mammals?
Liver and muscles
As a result of being a good storage molecule what role does glycogen play in mammals?
Regulates blood glucose levels
What is cellulose?
A polymer of beta-glucose
How is cellulose arranged?
In long straight chains
What is the role of cellulose?
Structural polysaccharide
Why is cellulose strong?
- has an inverted arrangement of successive glucose molecules meaning that hydrogen bonds
- the molecules are tightly cross-linked to form microfibrils
- microfibres form fibres
How are cellulose fibres arranged?
In layers, running across each other interwoven with other substances
How are chains of glucose linked?
1,4-glycosidic bonds
What is cellulose resistant to?
Enzyme hydrolysis?
How is cellulose resistant to enzyme hydrolysis?
Hydrogen bonding prevents water entering the molecule
Can humans digest cellulose?
No
Why can’t humans digest cellulose?
Humans dont produce cellulase
What is the significance of cellulose cell walls being strong?
They need to maintain turgidity so that leaves are held in a position to absorb maximum sunlight
What is chitin?
A polymer of glucosamine
What bonds link the glucosamine monomers?
Beta-1,4-glycosidic links
What is the significance of the amino group?
More hydrogen bonding between the chains than in cellulose therefore, chitin is extremely tough
