Biology Paper 2 June 2016

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1. AThey copy an mRNA template into a single strand of complementary DNA for insertion into a vector.
2. BThey unwind the DNA double helix ahead of the replication fork so that both strands can be copied.
3. CThey cut DNA at specific recognition sequences, producing fragments so that a required gene can be removed and inserted into a vector.
4. DThey join two DNA fragments together permanently by forming new phosphodiester bonds across the gap in each strand of the sugar-phosphate backbone.

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1. AThey introduce kinks in the hydrocarbon tail that prevent the fatty acid chains from packing closely together, which lowers the lipid's melting point.
2. BThey add extra hydrogen atoms along the tail at the point where the double bond was, which raises the lipid's melting point and makes it solidify more readily at low temperature.
3. CThey let the fatty acid chains pack more tightly together in a regular lattice, which increases the lipid's density and melting point.
4. DThey replace the ester bonds linking the fatty acids to glycerol, which makes the lipid far more resistant to enzymic hydrolysis.

1. AUnsaturated fatty acids have lower melting points, so they keep the cell membrane fluid when the animal's body temperature falls in cold surroundings.
2. BUnsaturated fatty acids are broken down and respired more easily than saturated fatty acids, releasing extra metabolic heat that helps warm the cell in cold environments.
3. CUnsaturated fatty acids form stronger bonds with membrane proteins, making the membrane more rigid at low temperature.
4. DUnsaturated fatty acids increase the membrane's permeability to water, allowing the cell to osmoregulate faster in cold water.

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1. AIt supplies extra chemical energy directly to the reactant molecules, increasing the total energy that the reaction releases overall.
2. BIt permanently binds to the product formed at the active site, physically preventing the reverse reaction from taking place.
3. CIt raises the local temperature of the substrate molecules bound to it, giving them extra kinetic energy to react faster.
4. DSubstrate binds to the enzyme's active site, slightly changing the site's shape so that bonds in the substrate break more easily, which lowers the activation energy needed.

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1. AThey bind reversibly to the active site for a short time, briefly blocking substrate binding before dissociating.
2. BThey bind permanently to sulphydryl/disulphide bonds away from the active site, changing the enzyme's structure so that it precipitates and loses activity.
3. CThey compete directly with the substrate for the active site, blocking it there until the metal ion happens to be displaced again by an excess of substrate molecules.
4. DThey lower the kinetic energy of the enzyme molecule, slowing the reaction until the temperature is raised again.