BIO Qs I missed
Name 3 properties of glycogen
- Insoluble, so it is osmotically inactive and doesn't affect the water potential
- Compact, a lot of genetic material can be stored in a small space
- Highly branched, so enzymes can act simultaneously upon the many branches and it can be broken down into glucose monomers for respiration
Describe the test for reducing sugars
1) Add 2cm3 of the food sample to a test tube and, if it isn't already in liquid form, add 2cm3 of water and grind it into a liquid
2) Add an equal volume of Benedict's reagent and place the tube in a gently boiling water bath for 5 minutes
3) If the solution turns brick-red, reducing sugars are present
Name and explain two properties of polysaccharides
- Large, so it cannot diffuse out of the cell membrane
- Insoluble, so it doesn't affect the water potential
Name the 4 roles of lipids
- Waterproofing, insoluble in water
- Insulation, poor conductor of heat
- Protection
- Source of energy, when oxidised, they produce 2x the energy as the same mass of a carbohydrate and they release water
Describe the general structure of amino acids
- COOH, Carboxyl group, acidic
- H, Hydrogen molecule
- NH2, Basic group
- R, Side group, variety of different chemical groups
How are triglycerides formed?
During condensation reactions, an ester bond is formed between three fatty acid tails and glycerol
Describe the secondary structure of polypeptides
Composed of a 3D, alpha-helix structure which has hydrogen bonds, the amino acids in the structure can form hydrogen bonds with nearby amino acids
Describe the rest for reducing sugars in disaccharides
1) If the sample is not already in liquid form, it must first be ground up in water.
2) Add 2cm3 of the food sample into a test tube with 2cm3 of Benedict's reagent and filter it to ensure any solid pieces of the sample do not remain.
3) Place the test tube in a gently boiling water bath for 5 minutes. If the Benedict's reagent remains blue, reducing sugars are not present.
4) Add another 2cm3 of the liquefied food sample to 2cm3 of HCl acid in a separate test tube and place the tube in a gently boiling water bath for 5 minutes. The dilute HCl acid will hydrolyse any disaccharide present into its constituent monosaccharides.
5) Slowly add some sodium hydrogen carbonate (NaHCO3) to the test tube to neutralise the HCl (Benedict's reagent will not work in acidic conditions).
6) Test with pH paper to ensure that the solution is alkaline
7) Re-test the resulting solution by heating it with 2cm3 of Benedict's reagent in a gently boiling water bath for 5 minutes
8) If a non-reducing sugar is present in the original sample, Benedict's reagent will now turn orange/brown. This is due to the reducing sugars that were produced from the hydrolysis of the non-reducing sugar.
Describe the structure of glycogen
- Straight, branched chains
- 1,6-glycosidic bonds
Describe the structure of enzymes
They are tertiary, globular proteins
Describe the test for proteins
1) Add 2cm3 of the food sample to a test tube and add a few drops of very dilute sodium hydroxide solution at room temperature
2) Mix gently
3) If it turns lilac, proteins are present, if it stays blue, no proteins are present
Describe the 4 points of the structure of triglycerides
- High ratio of energy-storing carbon-hydrogen bonds to carbon atoms = excellent source of energy
- Low mass to energy ratio = good storage molecules
- Large, non-polar = insoluble and don't affect the WP
- High ratio of hydrogen to oxygen atoms, so they produce water when oxidised = good source of water
Describe the test for detecting the presence of lipids
1) Add 2cm3 of the sample and 5cm3 of ethanol to a dry, grease-free tube
2) Shake thoroughly to dissolve any lipid present in the sample
3) Add 5cm3 of water and shake gently
4) A cloudy-white emulsion indicates the presence of a lipid
5) As a control, repeat the exp using water instead of a sample; the final solution should remain clear
Describe 5 properties of starch
Insoluble-> Osmotically inactive so it doesn't affect the WP
Large-> Cannot diffuse out of cell membrane
Compact-> Lots of DNA can be stored within a small space
When hydrolysed it can form alpha-glucose molecules which are easily transported and readily used in respiration
Branched form-> Has many ends which can be acted on by enzymes simultaneously and, therefore, glucose monomers can be produced rapidly
What is a dipeptide?
A pair of amino acids joined together by a peptide bond during a condensation reaction
Describe the tertiary structure of polypeptides
The secondary structure is further folded and twisted to form a complex, 3D structure.
The bonds involved are:
- Disulfide bridged
- Ionic bonds
- Hydrogen bonds
Describe hydrolysis
When water is added to a disaccharide under suitable conditions, it breaks the glycosidic bonds, releasing the constituent monosaccharides.
Describe how the structure of cellulose relates to it providing rigidity for the cell
- Molecules are made up of B-glucose and have 1,4-glycosidic bonds, so form long, unbranched chains
-The chains run parallel to each other and are crossed linked by hydrogen bonds
- Molecules are grouped to form microfibrils which, in turn, are grouped to form fibres
Describe the primary structure of polypeptides
The sequence of amino acids in a polypeptide, each amino acid pair is joined by a peptide bond