Carbohydrates Flashcards
What are carbohydrates made of?
- Carbon
- Oxygen
- Hydrogen
Monomer definition
Smaller units from which larger molecules are made
Monosaccharides
Monosaccharides are the monomers of carbohydrates. Examples include glucose, fructose and galactose
Isomer definition
Same molecular formula
Different arrangement of atoms
Isomers of glucose
- Alpha-glucose
2. Beta-glucose
Differnce between alpha glucose and beta glucose
Diagrams
Condensation reaction
This is where two or more molecules join together. Chemical bond is formed between molecule / molecules, Molecule of water is released per chemical bond formed
Glycosidic bond
Chemical bond formed when two or more monosaccharides join together via a condensation reaction. Molecule of water released per glycosidic bond formed
Disaccharide
Where 2 monosaccharides join together in a condensation reaction. Glycosidic bond formed between the 2 monosaccharides and a molecule of water is released
Disaccharide examples
- Sucrose: Glucose + fructose
- Maltose: a-glucose + a-glucose
- Lactose: glucose + galactose
Hydrolysis
Splitting of a chemical bond via addition of water
Test for reducing sugars
All monosaccharides + some disaccharides are reducing sugars
- Add some benedicts reagent to sample
- Heat sample in boiling hot water bath
- If reducing sugar is present, there will be a coloured precipitate - Blue, green, yellow, orange, brick red (BGYOB)
- The higher the conc of reducing sugar, the further the colour change goes
- This can be used to compare the conc of reducing sugar in different solutions
Test for non-reducing sugars
Non reducing sugars: All polysaccharides + some disaccharides
If reducing sugar not present, a non-reducing sugar may be present
Non-reducing sugar must be hydrolysed into its constituent monosaccharides (reducing sugar), then carry out test as normal for reducing sugar, if reducing sugar present, that means non-reducing sugar present
- Add dilute HCl to sample in boiling hot water bath. If non-reducing sugar is present, the glycosidic bonds between the monosaccharides will be hydrolysed. We now have a reducing sugar
- Neutralise test sample with sodium hydrogen carbonate
- Carry out test as normal for reducing sugar
- If reducing sugar present, coloyred precipiate BGYOB
What is the result if no reducing sugar is present?
Solution remains blue
Polysaccharide Definition
When more than two monosaccharides join together in a condensation reaction. Glycosidic bonds formed between the monosaccharides and a molecule of water is released per glycosidc bond formed
Three important carbohydrates
- Starch
- Cellulose
- Glycogen
Function of starch
- Energy storage molecule / stores excess glucose in plants. Plants store excess glucose as starch. Plants release energy from glucose. When plant cells need energy and there is no glucose, starch is broken down, glucose is released and energy is released from glucose during respiration
Structure of starch and how it is related to its function
Starch is made up of two polysaccharides of alpha-glucose. One is called amylose and the other is called amylopectin.
Amylose
- Long, Unbranched polysaccharide of alpha-glucose
The angles of the glycosidic bonds between the a-glucose monosaccharides gives amylose its coiled structure, allowing it to be compact, making it better for storage of glucose
Amylopectin
- Long, branched polysaccharide chain of a-glucose.
- Lots of side branches. This allows enzymes to reach the glycosidic bonds between the a-glucose monosacchairdes quicker and hydrolyse these bonds quicker, leading to quicker release of glucose and therefore, quick energy release in plant cells
Starch is insoluble
This means that no water enters / leaves via osmosis
Prevents cell from chance of swelling / bursting
Better for storage of glucose
Function of glycogen
Storage of excess glucose in animal cells.
Animal cells release energy from glucose.
However, when there is no glucose, they break down glycogen and glucose is released. They then release energy from this glucose during respiration.
Structure of glycogen and how its related to its function
Glycogen consists of one long branched polysaccharide of a-glucose monosaccharides. Lots of side branches allows enzymes to reach glycosidic bonds quickly, hydrolyse these bonds and quickly release the glucose, leading to quick energy release in cells.
Glycogen is insoluble
This means that no water enters / leaves via osmosis
Prevents cell from chance of swelling / bursting
Better for storage of glucose
Function of cellulose
Provides structural support. For example, in cell walls
