Carbohydrates Flashcards
What is a carbohydrate?
Molecules which only consist of hydrogen, carbon and oxygen.
A single monomer is called a monosaccharide, with a pair of them being called a disaccharide and many of them a polysaccharide.
These are all joined together with a glycosidic bond, formed in a condensation reaction.
What are the 3 types of monosaccharides?
Glucose
Galactose
Fructose
How do you make maltose?
glucose + glucose
How do you make sucrose?
Glucose + fructose
How do you make lactose?
Galactose + glucose
Polysaccharides
Formed from many glucose units joined together
Glycogen and starch formed by the condensation of alpha glucose
Cellulose formed by the condensation of beta glucose
What is the function of starch?
To store energy in plants
Why do plants not store excess glucose?
Contains hydroxyl groups making it very soluble
This means that if glucose is inside a cell, water would enter via osmosis
The cell would lyse (burst) if there was lots of glucose
Structure of starch
Mixture of amylose and amylopectin
Amylose
• Unbranched chain of glucose joined by 1,4 glycosidic bonds
• Coiled so very compact to store a lot of energy
Amylopectin
• Branched, made up of glucose molecules joined by 1,4 and 1,6 glycosidic bonds
• Many side branches for enzymes to act upon
Some key properties of starch
• Insoluble so will not affect water potential
• When it is hydrolysed the released alpha glucose can be transported easily
What is the function of cellulose
• Gives rigidity and prevents cell bursting due to osmosis
• Due to its function it is a structural polysaccharide not storage
Structure of cellulose
Straight Unbranched Chain (SUB)
Has cross links that form microfibrils - this gives it its turgidity
What is the difference between a reducing sugar and a non reducing sugar?
Reducing sugar - Can donate electrons to other molecules
Eg monosaccharides and maltose and lactose
Non reducing sugar - Cannot donate electrons to another molecule
Eg sucrose
Test for reducing sugars
1) Add benedicts solution to sample and heat to 95 degrees
2) If there is only a very small amount of reducing sugar, only a small amount of red precipitate forms (green appearence)
3) If there is more reducing sugar present more red precipitate forms - yellow appearence
Glycogen
Main storage molecule in humans, formed from many molecules of alpha glucose, joined by 1,4 and 1,6 glycosidic bonds
Very branched so can be hydrolysed by enzymes quicker
Relatively large but compact molecule maximising the amount of energy it can store
Insoluble so does not affect water potential and cannot diffuse out of cell
