Lecture 7: Plastics from Plants Flashcards
advantages of plastics from plants:
- plants produce a lot of biomass
- biodegradable product
- renewable resource
problems with plastics from plants:
- plastic is low value therefore the product myst be very cheap to be commercially viable
- previous productions of bioplastics has proven uneconomic
types of plastics that can be made from plants:
Several different sorts of plastic can remade POLY-HYDROXYALKANOATES (PHA)
Polyhydroxybutyrate (PHB) is synthesised as a storage polymer by the..
bacterium Ralstonia eutropha
negative properties of polyhydroxybutyrate (PHB)
- brittle
- low melting point
- it thermally degrades just above its melting point which introduces problems when it is used to make products
synthesis of polyhydroxybutyrate (PHB) synthesis in plants requires…
3 genes to be transferred from the bacterium to the plant, phbA, phbB, phcC
polyhydroxybutyrate is a…. similar to…
biodegradable plastic with similar properties to polypropylene
why isn’t polyhydroxybutyrate (PHB) commercially produced?
- not a commercially valuable product
- yields in plants are low
lipid metabolism can be averted into PHB production by
introducing three genes
transgenic plants expressing pub genes accumulate
PHB
-synthesis directed to chloroplast, normal site of starch synthesis
transgenic plants expressing pub genes accumulate _____ BUT::
-yields are low,
-leaves are a poor atria for large scale production
-PHB is not a commercially suitable product
(brittle, stiff, difficult to work with )
What plastic is related to polyhydroxybutyrate (PHB)
polyhydroxybutyrate-co-valerate (PHB-V) is a much more commercially useful product but plants DO NOT produce it
using same pathway as PHB how can Polyhydroxybutyrate-co-valerate be produced?
for PHB (C4) lipid metabolism can be diverted by introducing three genes, PHB-V (C5) can be produced if significant quantities of propionyl CoA are present
3 problems with producing PHB-V. PROBLEM 1:
1) phbA prooien won’t use propionyl coA as a substrate, so a second form of the enzyme Beta-ketothiolase gene (BktB) was isolated from Ralstonia eutropha
3 problems with producing PHB-V. PROBLEM 2:
plants don’t contain enough propionyl-coA
Solution= increase flux into the pathway by increasing the amount of substrate 2-ketobutyrate. this was achieved by engineering the plants to contain threonine deaminase
3 problems with producing PHB-V. PROBLEM 3:
plant threonine deaminase is inhibited by isoleucine, a metabolite of 2-ketobutyrate.
Solution: used a mutated form of threonine deaminase isolated from Eschericia coli. This only shows weak inhibition by isoleucine
to make plant produce OHB-V, numerous steps are involved:
- pick a suitable plant - oil seed rape
- use promoters to direct synthesis to the seeds
- -ease of harvest
- -minimal impact on the rest of plant growth
- -high yield
- modify the coding regions so that the enzymes are made in the oil-storing plastids (leucoplasts)
- introduce genes which will synthesis PHB-V
- introduce genes to modify metabolism so that plenty of the correct substrates are produced
is it economic? Use of green plants as industrial factories and commercial application of ‘green chemistry’ relies on
1) primary metabolic issues
2) cheap oil
3) plastic properties
is it economic? PRIMARY METABOLIC ISSUES
- can the polymer be produced in plants at high enough concentrations for industrial extraction?
- can enough polymer production be maintained in plants over multiple generations?
is it economic? CHEAP OIL
- limited global resource BUT massive scale production
- plastics derived from petrochemicals = inexpensive
- economics >important > environment credentials
is it economic? PLASTIC PROPERTIES
-must be similar to petrochemicals competitors
Biopol is PHB produced by
fermentation of plant sugars and oils
long history of bioplastics science & production:
1941 onwards, long process.
-process requires investment from company for a long time
metabolix (is a company) trilling bioplastic PRODUCING plants examples
- Camelina (brassica) in Canada. Achieved 10-20% PHAs in seed weight, but still not enough
- Switchgrasee in Massachusetts. Produced up to 3.7% leaf weight as PHB. Needed to be 5% too be economically viable
- Sugarcane in Australia
