Topic 1.2 - Carbohydrates Flashcards
What are monosaccharides?
Monomers from which larger carbohydrates are made
Give 3 common examples of monosaccharides
- Glucose
- Fructose
- Galactose
What are disaccharides and how are they formed? (2)
- 2 monosaccharides joined together with a glycosidic bond
- Formed by a condensation reaction, releasing a water molecule
Give 3 common examples of disaccharides
- Maltose
- Sucrose
- Lactose
How is maltose formed?
Glucose + glucose
How is sucrose formed?
Glucose + fructose
How is lactose formed?
Glucose + galactose
What are polysaccharides and how are they formed? (2)
1) Many monosaccharides joined together with glycosidic bonds
2) Formed by many condensation reactions, releasing water molecules
What is the function of starch?
Energy store in plant cells
What is the structure of starch? (3)
1) Polysaccharide of a-glucose
2) Amylose - 1,4-glycosidic bonds -> unbranched
3) Amylopectin - 1,4- and 1,6-glycosidic bonds -> branched
What is the function of glycogen?
Energy store in animal cells
What is the structure of glycogen? (2)
1) Polysaccharide made of a-glucose
2) 1,4- and 1,6- glycosidic bonds -> branched
How does the structure of starch relate to it’s function? (3)
1) Helical -> compact / fit more molecules in a small area
2) Large, insoluble polysaccharide molecule
3) Insoluble in water -> water potential of cell not affected
How does the structure of glycogen relate to its function? (4)
1) Branched -> compact / fit more molecules in a small area
2) Branched -> more ends for faster hydrolysis -> release glucose for respiration to make ATP for energy release
3) Large, insoluble polysaccharide molecule -> can’t leave cell / cross cell membrane
4) Insoluble in water -> water potential of cell not affected
What is the basic function of cellulose?
Provides strength and structural support to plant / algal cell wall
What is the structure of cellulose? (3)
1) Polysaccharide of B-glucose
2) 1,4-glycosidic bond -> straight, unbranched chains
3) Chains linked in parallel by hydrogen bonds forming microfibrils
How does the structure of cellulose relate to its function? (4)
1) Every other B-glucose is inverted in a long, straight, unbranched chain
2) Many hydrogen bonds link parallel strands to form microfibrils
3) Hydrogen bonds are strong in high numbers
4) So provides strength to plant cell walls
Give examples of reducing sugars (3)
1) Monosaccharides
2) Maltose
3) Lactose
Describe the test for reducing sugars (3)
1) Add Benedict’s solution (blue) to sample
2) Heat in a boiling water bath
3) Positive result = green / yellow / orange / red precipitate
Give an example of a non-reducing sugar
Sucrose
Describe the test for non-reducing sugars (5)
1) Do Benedict’s test and stays blue / negative
2) Heat in a boiling water bath with acid
3) Neutralise with alkali
4) Heat in a boiling water bath with Benedict’s solution
5) Positive result = green / yellow / orange / red precipitate
Suggest a method to measure the quantity of sugar in a solution (2)
1) Carry out Benedict’s test, then filter and dry precipitate
2) Find mass / weight
Suggest another method to measure the quantity of sugar in a solution (6)
1) Make sugar solutions of known concentrations
2) Heat a set volume of each sample with a set volume of Benedict’s solution for same time
3) Use colorimeter to measure absorbance of each known concentration
4) Plot calibration curve - concentration on x axis, absorbance on y axis and draw line of best fit
5) Repeat Benedict’s test with unknown sample and measure absorbance
6) Read off calibration curve to find concentration associated with unknown sample’s absorbance
Describe the biochemical test for starch (2)
1) Add iodine dissolved in potassium iodide and shake / stir
2) Positive result = blue / black