| Date | May 2016 | Marks available | 1 | Reference code | 16M.3.HL.TZ0.9 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Outline | Question number | 9 | Adapted from | N/A |
Question
Succinate is industrially produced by continuous fermentation. It is used as a raw material in the production of flavour enhancers, drugs and industrial chemicals. One method of increasing the production of succinate is to genetically modify E. coli to express high levels of formate dehydrogenase (FDH1). This results in the production of higher concentrations of NADH. The engineered pathway is shown as a bold dotted line in the image.
Using the diagram, suggest a reason for high concentrations of NADH favouring the production of succinate.
Predict one metabolite other than succinate that will be produced in greater amounts if the amount of NADH available is increased.
Outline the process of continuous culture fermentation.
Outline one reason this process, to increase the production of succinate, represents pathway engineering.
Markscheme
NADH is required as a reducing agent/electron donor/hydrogen donor/co-enzyme/limiting factor for the production of succinate
High levels of FDH1 produce greater quantities of NADH which is required for conversion of glucose «via intermediates» to succinate
Lactate/ethanol
CO2 «favoured by high FDH1 levels»
Raw materials are supplied in continuous amounts
Products/wastes are continuously extracted
Conditions are monitored/regulated to keep variables at a steady state
Genetic processes/rate limiting chemicals/regulatory processes are being optimized
Examiners report
This was fairly well answered with many able to achieve the mark, usually for noting that NADH was a reducing agent or electron donor.
This was an easy question with almost all candidates able to predict one metabolite using the diagram.
The process of continuous culture fermentation seemed to be familiar to all candidates selecting this option with many scoring the 2 marks.
This was discriminating as many found it difficult to clearly show why the given process represented pathway engineering.
