carbohydrates
What is the H:O ratio in carbohydrates?
2:1
What is the H:O ratio in lipids?
larger than 2:1
What elements are found in proteins?
carbon (C), hydrogen (H), oxygen (O), nitrogen (N) and sometimes sulfur (S)
How would you test for the presence of proteins in food?
Condensation reaction ;
Hydrolysis reaction;
How to make a triglyceride molecule?
A triglyceride is formed from one glycerol and three fatty acids by condensation reaction.
Name some food that is rich in proteins
meat, fish, eggs, beans, milk, dairy products (e.g. cheese)
If starch is present, the iodine solution turns from brown to blue-black.
i) starch
ii) fructose
iii) lactose
i) rice, wheat, potatoes, taros
ii) fruits, honey
iii) milk, dairy products such as cheese and yogurt
Name some food that is rich in lipids.
Fatty meat, seeds, nuts, milk, dairy products (e.g. cheese)
What is the basic building block of proteins? Describe its structure.
Amino acid;
Each amino acid has an amino group, a carboxyl group and a side chain. Different amino acids have different side chains.
How would you test for the presence of reducing sugars in food? What is the positive result? Can you use this test to detect sucrose?
- If reducing sugar is present, a brick-red precipitate will form.
- Sucrose is not a reducing sugar so no.
Name three polysaccharides and state their functions.
Starch - major energy source in our diet
Glycogen - energy storage in animals
Cellulose - a component of plant cell walls
Name 4 functions of lipids
- as energy reserves
- as a shock absorber
- as a heat insulator
- produce hormones
- a component of cell membrane
- involved in the absorption, transport and storage of lipid-soluble vitamins
State 3 functions of proteins.
- for growth and repair
- to produce enzymes, antibodies, haemoglobin and some hormones
- as a source of energy when carbohydrate and lipid storage are used up in body
State 4 significance of water in living organisms.
- provide a medium for chemical reactions to take place
- a good solvent and a good transport medium
- act as a cooling agent
- provide lubrication (e.g. in joints)
- provide buoyancy for aquatic organisms
Describe how you would carry out a test to detect the presence of lipids in food.
- Put a drop of food sample onto a piece of filter paper and let it dry.
- A translucent spot will remain on the filter paper if lipids are present.
- If this translucent spot is formed by lipids, it will disappear if we put it into an organic solvent (e.g. ethanol). This is because lipids are insoluble in water but soluble in organic solvents.
What determines the final shape of a protein? Use an example to illustrate why its unique shape is important to its function.
The sequence of amino acids determines the final shape of a protein.
Its shape is important. For example, enzymes have unique active sites which fit with specific substrates. Changes in the shapes of the active sites (i.e. denaturation) causes enzymes to lose their functions.