Biology Revision Cards

Potassium - Important in nerve transmission and active transportation of molecules.

Calcium - Component of cell walls (calcium pectate).

Magnesium - Constituent of chlorophyll, needed for photosynthesis.

Iron - Essential for the formation of haemoglobin to carry oxygen around the body.

Hydrogen Carbonate - Acts as a buffer, resists changes in pH.

Nitrate - Amino acids

Phosphate - ATP production, nucleotides and phospholipids membrane.

PRIMARY - long chains of individual amino acids, in a specific sequence, joined together as a polypeptide, with peptide bonds.

SECONDARY - the single polypeptide chain bent or twisted to give a(alpha) helix or b(beta) pleated sheets, these are held in place with hydrogen bonds.

TERTIARY - this is a 3D structure, the polypeptide chain is twisted and held in a specific 3D shape due to bonding (ionic, covalent, disulphide and weak hydrogen bonds), this is a globular structure and is typical of enzymes.

QUATERNARY - when there is more than one type of polypeptide chain and a non-protein component e.g. haemoglobin.

REDUCING SUGARS- add benedicts reagent and heat in a waterbath for a few minutes, the colour should change from blue to green to orange to red, for a positive result.

NON REDUCING SUGARS - the benedicts test wont work unless you hydrolyse the bonds with hydrochloric acid then neutralise the solution. if you do the benedicts test after this you will get a positive result and the same colour change as above.

STARCH - add dilute iodine to the substance or solution and there will be a colour change from orange to blue/black.

PROTEIN - (make sure the solid is dissolved in a liquid or the protein is in solution) then add a little of Biuret 1 reagent (sodium hydroxide) and then a few drops of Biuret 2 reagent (copper sulphate), a blue/purple ring forms on the top of the solution and when shaken the solution is a light purple for a positive result.

LIPIDS - grind up the sample, add ethanol and shake the test tube, decant the liquid into a test tube of water leaving any undissolved substance between them, if there are lipids present they will precipitate in the water forming a cloudy white emulsion.

POLYMERASE CHAIN REACTION

• in DNA replication, the two strands of the double helix come apart (high temperatures of about 90 degrees break hydrogen bonds).
• they are cooled, but to stop the strands reforming primers are added.
• free nucleotides in the nucleus, join up to the exposed bases by specific base pairing.
• DNA polymerase catalyses the polymerisation of deoxyribonucleotides into a DNA strand.
• Replication is semi-conservative (in each new daughter DNA molecule, one strand is original and the other strand is new).
• specific base pairing ensures that 2 identical copies of the original DNA have been formed.

• enzymes are organic catalysts which speed up reactions in organisms by lowering the activation energy of a reaction (this is the energy required to start a reaction).
• enzymes are globular proteins.
• the 3D structure of an enzyme confers specificity i.e. only the correct substrate molecule can fit into the active site on a specific enzyme molecule.
• the active site is a number of amino acids in the coiled polypeptide chain which makes up the enzyme.
• enzymes are specific.
• 'lock and key' hypothesis.
• 'induced fit' hypothesis.
• enzyme reactions are reversible.
• enzymes will be denatured at high temperatures due to their protein structure (as the temp increases the rate of reaction increases up to an optimum temperature, above this temp the enzyme is denatured).
• changes in pH affect the enzyme shape and reduce the rate of reaction.
• changes in substrate concentration affect the rate of reaction (rate of reaction will increase with substrate conc. until all the enzyme active sites are occupied and the reaction rate levels off).
• changes in enzyme concentration, the more enzyme molecules the more active sites, which should increase the rate of reaction.

This controls the passage of different substances into and out of the cell. the basic structure is described as the FLUID MOSAIC MODEL, mosaic because there are many proteins in the membrane dotted around in a mosaic pattern, and fluid because the pattern of proteins is continually changing due to the fluidity of the PHOSPHOLIPID BILAYER.

The PHOSPHOLIPID BILAYER consists of phospholipids with hydrophilic phosphate heads (water loving) and hydrophobic fatty acis tails (water hating). the bilayer forms a barrier to water soluble substances although lipid soluble substances and gases can pass through freely. therfore it is said to be 'partially permeable'.

The Protein molecules have a variety of functions:

• they form hydrophilic pores allowing small water soluble chemicals to pass through.
• they play a role in active transport and facilitated diffusion.
• they act as specific receptor sites to hormones etc.
• the glycoproteins have a role in cell recognition e.g. the immune system.