3.1.2 Carbohydrates Flashcards
How are disaccharides formed? Explain using the examples: maltose, sucrose and lactose.
- Disaccharides are formed by the condensation of 2 monosaccharides.
- E.g. maltose, sucrose and lactose
- Glucose + glucose = maltose
- Glucose + fructose = sucrose
- Glucose + galactose = lactose
Define the term isomer
When molecules have the same molecular formula but the atoms are arranged differently.
How many isomers does glucose have?
Glucose has 2 isomers, alpha-glucose and beta-glucose.
What are the differences between the 2 isomers of glucose?
. Alpha-glucose: OH groups below C1 and below C4.
* Beta-glucose: OH groups above C1 and below C4 i.e. position of OH on C1 is reversed compared to alpha glucose.
What is the function of glycogen?:
Energy store in animal cells.
What is the structure of glycogen?
- Polysaccharide of alpha-glucose.
- C1-C4 and C1-C6 glycosidic bonds so branched.
How is the structure of glycogen related to its function?
- Branched; can be rapidly hydrolysed to release
glucose for respiration to provide energy. - Large polysaccharide molecule; can’t leave cell.
- Insoluble in water; water potential of cell not affected i.e. no osmotic effect.
What is the function of starch?
Energy store in plant cells.
What makes up starch?
- Polysaccharide of alpha-glucose.
- Made of amylose and amylopectin.
What is the structure of amylose?
1,4 glycosidic bonds and unbranched
What is the structure of amylopectin?
1,4 and 1,6 glycosidic bonds branched.
How does the structure of amylose related to its function?
- Helical; compact for storage in cell.
- Large polysaccharide molecule; can’t leave cell.
- Insoluble in water; water potential of cell not affected i.e. no osmotic effect.
How does the structure of amylopectin relate to its structure?
- Branched; can be rapidly hydrolysed to release glucose for respiration to provide energy and compact to fit more molecules
- Large polysaccharide molecule; can’t leave cell.
- Insoluble in water; water potential of cell not affected i.e. no osmotic effect.
What is the function of cellulose?
Provides strength and structural support to plant/algae cell walls.
What is the structure of cellulose?
- Polysaccharide of beta glucose
- 1,4 glycosidic bond
- Straight and unbranched chains
- Chains are linked in parallel by hydrogen bonds forming microfibrils.
How does the structure of cellulose relate to its function?
- Every other beta glucose chain is inverted in a long, straight chain, unbranched chain.
- Many hydrogen bonds link parallel strands to form microfibrils (strong fibres)
- Hydrogen bonds are strong in high numbers, so it provides strength.
What are reducing sugars?
- All monosaccharides
- Some disaccharides e.g. maltose/lactose
What are non-reducing sugars?
- No monosaccharides
- Some disaccharides e.g. sucrose
Describe how to carry out the Benedict’s test for reducing sugars
- Add benedict’s reagent (blue) to food sample.
- Heat in a boiling water bath.
- Positive = green / yellow / orange / red precipitate (reducing sugar present).
* If negative result (Benedicts reagent doesn’t change colour) then test for non-reducing sugar.
Describe how to carry out the Benedict’s test for non-reducing sugars
- Add an equal volume of sample and dilute hydrochloric acid to hydrolyse the sugar.
- Heat in a boiling water bath.
- Neutralise with sodium bicarbonate.
- Carry out normal benedict’s test.
- Non-reducing sugar present = green / yellow / orange / red precipitate.
Suggest a method to measure the quantity of sugar in a solution:
- Carry out Benedict’s test then filter AND dry.
- Find mass/weight
Explain how the concentration of glucose in a sample can be determined.
- Produce a dilution series of glucose solutions of known concentrations.
- Perform a Benedict’s test on each sample (use same amount of solution for each test) and remove any precipitate (e.g. by centrifuging).
- Using a colorimeter, measure the absorbance of each sample to establish a calibration curve.
- Repeat with unknown sample and compare the absorbance to the calibration curve to determine glucose concentration.
Describe the test for starch
- Add iodine dissolved in potassium iodide to solution and shake/stir.
- Blue-black colour = starch present.
