biological molecules

Define the term polysaccharide

• composed of many / chain of / polymer of monosaccharides / sugar monomers;

• further detail eg. carbohydrate / branched or unbranched / macromolecule / glycosidic bonds / joined by condensation reactions;

State two structural differences between starch and cellulose.

• alpha, beta;

• branched, unbranched;

Describe the structure of cellulose.

• beta glucose;

• 1-4; glycosidic bonds;

• alternately oriented;

• unbranched;

• form hydrogen bonds with parallel chains;

Explain why cellulose is suitable as a component of plant cell walls.

• from fibrils and fibres;

• hydrogen bonding between molecules;

• linear; molecules lie parallel;

• strength to prevent bursting / withstand turgor pressure;

• fibres at angles / crisscross;

• many gaps between fibres, cell wall permeable;

• AVP eg. insoluble / -OH group for hydrogen bonding;

Define the terms saturated and unsaturated

• maximum number of hydrogen atoms;

• contains C=C double bonds;

Explain why lipids are useful as storage molecules

• does not dissolve in water; does not affect osmotic pressure;

• higher calorific value than carbohydrates; yield more energy per gram on oxidation;

• useful properties. buoyancy / insulation;

Describe the structure of a phospholipid

• fatty acids;

• glycerol;

• phosphate; with choline;

State two uses of lipids.

storage / protection / cell membrane / insulation / buoyancy / waterproofing;

Explain what is meant by the amphoteric property of amino acids.

molecules contain both acidic and basic groups;

Explain what is meant by tertiary protein structure

• polypeptide chain;

• folds extensively;

• into compact / globular structure;

Suggest the significance of sulphur in the properties of a protein.

increase stability to pH; temperature changes;

Explain how the structure of a collagen fibre provides the skin with strength

• covalent bonds between collagen molecules;

• strong covalent bonds;

• staggered molecules, so no weak area;

• fibres line up in layers, run in different directions;

• provides tensile strength;

Explain the role of hydrogen bonding in maintaining the tertiary structure of proteins.

• hydrogen bonds stabilise further folding of protein;

• forms between R groups with amine and carboxyl groups;

• amino acids that may be further apart in primary structure;

• maintain 3D structure / forms shape of active site;

Explain how hydrogen bonding occurs between water molecules

• water molecules are dipoles;

• $\delta$+ hydrogen and $\delta$- oxygen;

• positively charged hydrogen of one molecule attracted to negatively charged oxygen of another molecule;

• weak attraction between water molecules;

Suggest why water is an excellent solvent for ions.

• water molecules are polar;

• ions are charged;

• ref. attraction between water molecules and ions;

• AVP eg. oxygen $\delta$- faces positive ion;

Outline the importance of water as a solvent in plants.

• dissolves ions / minerals and polar molecules;

• transport in xylem and phloem;

• storage in vacuoles;

• metabolic reactions;

• dissolve carbon dioxide and oxygen for respiration / photosynthesis

Describe how to test for the presence of sucrose and protein in a solution.

• mix equal volumes of solution and dilute HCL;

• boil in water bath to hydrolyse sucrose;

• mix with equal volumes of Benedict’s reagent;

• boil in water bath;

• brick red precipitate appears;

• mix equal volumes of solution and dilute NaOH;

• add CuSO4;

• turns purple;

Describe how to carry out a test to detect the presence of protein in a solution

• add equal volume of dilute KOH solution to test solution;

• add few drops of CuSO4;

• presence of purple ring at interface;

• dissolves to form purple solution when shaken;

Describe a test to determine the presence of lipids in a sample solution.

• emulsion test, add equal volumes of ethanol and cold water;

• mix, white emulsion forms;

• Sudan III, add few drops of Sudan III;

• red fat droplets appear;

Describe how to compare the concentrations of glucose in a test solution to known standard concentrations of glucose solutions.

• same volumes;

• same volumes of glucose oxidase;

• incubate at stated time and temp;

• same volume of peroxide and indicator;

• read intensity of colour in photometer;

State why no colour change is observed when Benedict’s solution used to test a sucrose solution

• sucrose is non-reducing;

• no acid is used to break down sucrose to make reducing sugars;

• AVP eg. Cu2+ not reduced to Cu+ / cannot donate electrons / no free aldehyde, ketone group;