Mistakes on additional questions Flashcards
What is ribose
is it a monosaccharide
(b) State two structural differences between starch and cellulose.
starch contains α-glucose, cellulose contains β-glucose;
starch linked by α- glycosidic links, cellulose by β-glycosidic links; starch may contain branched chains, cellulose is unbranched;
(c) What is meant by tertiary protein structure?
polypeptide chain;
bends/folds extensively;
into a compact/globular structure;
Describe how you would carry out a test to detect the presence of protein in an unknown sample solution.
add equal volume of (dilute/5%) potassium hydroxide solution to test solution; (down side of test tube) add a few drops of (1%) copper sulphate solution; presence of a purple ring at interface;
which dissolves to form a purple solution on shaking, indicates protein;
(b)(i) What does the “R” represent?
rest of the molecule/side chain;
(ii) Give an example of an “R” group.
hydrogen/methyl group/any correct group;
(iii) What is the name of the bond that links two adjacent amino acids?
(iii) peptide;
(c) “Amino acids are amphoteric”. What does this mean?
(c) their molecules contain both acidic and basic groups;
(a) Describe the structure of a phospholipid.
(a) fatty acids joined to; glycerol; phosphate also attached; reference to alcohol/choline attached to phosphate; (b) (i) (fatty acid) side chain polar head
(c) Give two uses of lipids, other than storage.
Any 2 of:
waterproofing/protection qualified/cell membrane structure/insulation/give buoyancy;;
(a) (i) What do the terms saturated and unsaturated mean?
saturated means that the molecule contains the maximum number of hydrogen atoms;
unsaturated means that the molecule contains fewer hydrogen atoms than it might/contains double bonds;
(ii) In what ways do the properties of saturated and unsaturated fats differ?
unsaturated fats have lower melting points than saturated fats;
unsaturated fats form oils but saturated fats are solid; 2
(b) Why are lipids useful as storage molecules?
b Any four of:
don’t dissolve in water/body fluids/
therefore don’t affect osmotic balance of cells/tissues/
have higher calorific value than carbohydrates/
can yield more energy per gramme on oxidation/
reference to other useful properties/buoyancy/insulation;;;; 4
Why is it important to have these two differing forms?
leads to greater chemical variety/biochemical division of labour; alpha glucose/starch is respiratory;
whereas beta glucose/cellulose is structural;
A solution which tested negative for reducing sugars was thought to contain sucrose and protein. Describe how you would find out whether this was so.
mix equal volumes of solution and dilute hydrochloric acid;
boil in a water bath (for 2 minutes) to hydrolyse sucrose (to glucose and fructose); mix with equal volumes of Benedict’s reagent;
boil in water bath (for 2 minutes);
if brick red precipitate appears then sucrose is present;
mix equal volumes of solution and (dilute/5 %) sodium hydroxide;
run dilute/1% copper sulphate solution into the solution;
a purple ring at the interface indicates protein is present;
What polymer contains nitrogen and always contains a phosphate group
(a) X - nucleic acid/DNA/RNA/ATP/nucleotide;
What polymer contains nitrogen and may not contains a phosphate group
Y - protein/amino acid/polypeptide;
(b) Starch is a mixture of two polymers. Name them and say how they differ structurally from each other.
amylose is an unbranched chain but amylopectin is branched; 1
(b) amylose; amylopectin;
(c) Cysteine is a sulphur containing amino-acid. Suggest the significance of this in:
(i) protein structure.
(ii) protein properties.
i, forms covalent/sulphur bonds;
holding adjacent polypeptides together/contributes to secondary/tertiary structure;
(ii) increases protein’s stability to pH change; increases protein’s stability to temperature change; (allow 1 mark if just refer to ‘strong bonding’)
What can be hydrolysed to smaller units
starch, prooien and DNA
(b) Describe a Benedicts test to detect the presence of glucose in a sample solution.
Any three of:
mix together equal volumes of solution and Benedicts reagent/ boil in a waterbath for (2 minutes)/
presence of brick red precipitate indicates glucose;;;
(c) The concentration of glucose in solutions can be measured using the glucose oxidase technique.
The solution to be tested is incubated with glucose oxidase and then with peroxidase and an indicator which changes colour when oxidised in the reaction. Peroxidase breaks down the hydrogen peroxide formed by the glucose oxidase, releasing oxygen which changes the colour of the indicator.
The intensity of the colour produced is directly proportional to the concentration of glucose in the solution.
Describe how you would use this method to compare the concentration of glucose in a test solution to a known standard concentration of glucose solution.
use same volumes of test and standard solutions;
add same volume of glucose oxidase solution to each;
incubate for a standard/stated time at a suitable/stated temperature; add same volume of peroxide and indicator;
read intensity of colour in photometer;
]calculate answer using formula Concentration of test Concentration of standard = Reading of Test Reading of Standard ;
(b) What is the name of the chemical bond which joins these two hexose units together?
(b) 1,4-glycosidic/alpha link;
(d) State one function of the carbohydrate shown above in living cells. (maltose)
(d) respiration/energy substrate;
Two glucose molecules binding forms a what bond
(ii) (1, 4 -)glycosidic beta link;
(b) In some membranes absorption involves active transport. Explain why cells in these membranes:
(ii) possess large quantities of cholesterol and other lipids in their cell membranes.
ref. cholesterol will mix with water and allows passage of some water soluble substances; will accelerate diffusion/entry of non-polar substances;
e. g. oxygen/carbon dioxide;
