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Файл:Биотехнология = Biotechnology. Учебное пособие по английскому языку
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Now, some enzymes require small cofactors or coenzymes associated with
the protein to facilitate the reaction. These are small molecules, some of them
are known as hemes or flavins, or indeed other prosthetic groups such as metal
ions, which are bound in the active site of the enzyme.
Enzyme catalytic cycles are multistep catalytic cycles. They involve the
binding of reactants in the so-called enzyme active site. So, substrates or reactants are assembled within the active site where the chemical catalysis can take
place. The second part of the catalytic cycle is the process of bond making and
bond breaking, the so-called catalytic part of the reaction cycle. And then
products are then released from the active site at the end of the catalytic cycle to
enable another round of catalysis to then proceed following substrate binding.
Now, many of these processes are facilitated by the natural flexibility, conformational flexibility, of enzyme molecules. This conformational flexibility is
often required to optimally position substrates in the enzyme active site, and
also to provide an optimal environment for catalysis, for example, through
the exclusion of water from the active site.
There are various models of enzyme catalysis that have been advanced
over the years that include this flexible behavior of enzyme molecules. One is
the so-called induced fit model of catalysis, where an exposure of an enzyme to
a substrate, or the analogy would be a key, causes the active site of the enzyme,
or the lock, to change shape in order to allow the enzyme and substrate to bind
forming an enzyme-substrate complex. And this is demonstrated with a simple
cartoon here on the right where we have the perfect fit of a lock and key shown
on the left, and the analogous situation whereby a substrate molecule is nicely
fitting into the active site of an enzyme shown on the right.
Part II. Enzymes are ideal catalysts for the production of fine chemicals
and pharmaceuticals due to their relatively mild reaction conditions under
which they operate, and also because of the very high catalytic rates that they
support and the high degree of reactant specificity.
This, therefore, maps very nicely into the green chemistry agenda, where
industrial biotechnology can reduce, for example, the production of the accumulation of toxic waste products. We can have energy efficient processes. And
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we're very much using natural bioprocesses for the production of a whole range
of finer specialty chemicals using biological catalysis.
Use of enzymes in biotechnology of course is not new. Pre-1970s, enzymes were being used in a number of classical production methods, for example fermentation processes. Purified enzymes were used in selected industrial
processes. And the properties of a number of enzymes were being modified
through chemical treatment.
Much took off in the 1980s as we ushered in the molecular biology era,
where through the ability to clone genes and genetically change their sequence,
then ushered in the protein engineering era, where we can modify in a very directed way the properties of a biological catalyst.
And we can also get an appreciation of how those manipulations can alter
the overall structure of the protein molecule, and therefore, it's catalytic ability,
using techniques such as x-ray crystallography. In the post-genomics and genomics era, post 2000, what we now see are enzymes being used extensively in
metabolic engineering processes and industrial biotechnology. We're also seeing the development of synthetic biology, and enzymes played a major role here
in the bespoke design of biological organisms toward industrial processes, and
even the design of artificial organisms.
So, in the synthetic biology approach, that is very much a product of new
technologies that have evolved over the last few years, we can now begin to assemble whole biosynthetic pathways in microorganisms from enzymes taken
from a whole range of different sources, or indeed engineered enzymes that
have been manipulated to have different properties. This gives us the possibility
of designing processes that enable the production of a whole range of high value
chemicals, from cheap feed stocks or renewable feed stocks, and to generate
new and high value chemicals which are new to nature by modifying the natural
pathways and enzymes present in these biosynthetic pathways. And, of course,
what we can do is then to optimize host organisms to improve productivity, and
therefore, introduce scalable processes based on the new biology that can be
used to make a whole range of industrial and valuable products.
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Video 3
Part I. Hello, I'm Peter Budd. I'm a Professor of Polymer Chemistry here
in Manchester. I'm interested in polymers, giant molecules, and in other new
materials like graphene. But I'm interested in applying those materials to help
solve big problems and to improve people's lives. In this presentation, I'm going
to talk about new membrane materials and the way in which they can be applied
in industrial biotechnology.
One area of my research is the development of new materials for membrane processes. That is, processes that use thin films to enable industrially imported separations to be carried out efficiently and economically. I'm going to
tell you about the potential of membrane processes in industrial biotechnology.
Industrial biotechnology is you should all now know, is about using microorganisms or enzymes on an industrial scale to make useful products from biofeedstocks, from agricultural crops or better from organic waste materials. Fuels
provide the energy that keeps our society moving. Biofuels are fuels that started
out as something growing in the recent past as opposed to fossil fuels, where
geology has worked on organic matter over millions of years. Biofuels include
biodiesel, produced from oils or fats by a transesterification process, biogas,
methane generated by anaerobic digestion of all sorts of organic materials and
bioalcohols, resulting from fermentation of sugars or sugar-based materials.
Methanol, ethanol, propanol, and butanol can all be used as fuels. Bioehtanol is
widely used in places like Brazil. For the future there is increasing interest in
biobutanol, which is considered as a direct replacement for gasoline. Butanol
comes in four chemical forms, isomers of which three are commercially important, 1-butanol, isobutanol, and tert-butanol. Biobutanol is produced by bacterial fermentation in a process known as ABE fermentation. Because the butanol, B, comes together with a couple of other products, acetone, A, and
ethanol, E.
So the product you want has to be separated from a complex mixture. Incidentally, the systematic name for acetone is propanone, but industry often mistakes the old names. The old names for butanol and ethanol are butyl alcohol
and ethyl alcohol. The bacteria used in ABE fermentation are generally strains
of bacteria from the class Clostridia. The University of Manchester played
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an important role in the history of ABE fermentation. In 1912, a senior lecturer
at the university, Chaim Weizmann was working on how to produce useful
products by fermentation. He isolated the bacterium Clostridum acetobutylicum
that led to a patent for the first ABE process. Chaim Weizmann himself later on
to become the first President of Israel. During the first World War, the ABE
fermentation process became extremely important not for the B, but for the A.
It was used for acetone production, essential to the British war industry as
a solvent employed in making cordite, a replacement for gunpowder. Later
the ABE process fell out of favor because acetone, butanol and ethanol could be
produced more cheaply from petroleum. But now there is renewed interest for
biobutanol production. Any biofuel starts out as a biomass of one sort or another.
The biomass is subjected to some combination of chemical, enzymatic or fermentation processes. And what we generally end up with is a mixture of the
product we want, along with other things in a lot of water. We need to separate
and purify the fuel we want. And the separation and purification stages typically represent 60 % to 80 % of the overall production cost. If we can save energy,
save costs in the separation and purification stages, it may make the difference
between whether or not the whole process is economically viable.
Part II. Separation processes that are commonly used in industrial biotechnology include distillation, extraction, adsorption and crystallization. And
there is a growing interest in the potential of membrane processes. Membrane
processes could be much more energy efficient than distillation for example and
lend themselves well to continuous rather than batch processing.
There are many different membrane processes that can be used for molecular separations. They all rely on a membrane, a thin film which may have
a complex structure, but is more permeable to one component in a mixture than
to others. Membranes may come in various forms: as flat sheets, coiled up in
spiral round modules or as hollow fibres packed into long tubes.
Whatever the process and whatever the form, the principle is the same.
A mixture, the feed, is applied to the one side of the membrane and the permeate is withdrawn from the other side. And if the membrane has done its job, the
permeate has a different composition to the feed. Of course for the process to
work at all, there must be a driving force for permeation through the membrane,
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a concentration gradiant or the pressure gradiant. Depending on the process,
the feed may be a liquid mixture or a gaseous mixture and the permeates may
be a liquid or a vapor. One membrane process of interest for industrial biotechnology is pervaporation. Pervaporation is a combination of permeation and
evaporation. The feed is a liquid mixture. It could be for example, a mixture of
butanol and water.
Either vacuum or an inert sweet gas is applied to withdraw the permeate as
a vapour. Either water or the organic compound may be pulled through as
the permeate, depending on the nature of the membrane. Like distillation, pervaporation involves a change of phase, from liquid to vapor. But it can be carried out at lower temperatures than distillation.
If we have a feed that is a mixture of vapors, then we can apply, a vapor
permeation process in which there is no change of phase. Nanofiltration is
a process in which the feed is a liquid mixture and pressure is applied to force
the permeate to the membrane as a liquid.
It is used to separate small molecules or ions from larger molecules or ions.
Another membrane process that could prove useful in industrial biotechnology,
although it is not yet well-developed is pertraction. Pertraction is a combination
of permeation and extraction.
It can be called membrane assisted liquid-liquid extraction. In pertraction,
a solid is transferred via a membrane from an aqueous phase to an organic
phase. The key to every membrane process is the membrane, which provides
selectivity for the components of interest which must also allow enough stuff to
permeate, give a high enough flux for the process to be economic. We are seeking to develop new membrane materials that combine good selectivity with
high flux. Membrane materials can be divided into two groups. Those that like
water, hydrophilic, and those that like organic compounds, organophilic.
Both types of membrane can be useful in industrial biotechnology and for
both types of membrane new materials are being developed at the University of
Manchester. For hydrophilic membranes, a new material of interest is graphene
oxide. Rahul Nair, working with the Nobel Prize winner Andre Geim, in our
school of physics, showed that multilayer graphene oxide membranes, could let
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water through as easily as through an open surface. But it's in the dry state that
they were impermeable to even the smallest gases.
For organophilic membranes, we are working with a new class of polymers
called polymers of intrinsic microporosity or PIMs that were invented in Manchester by Neil McKeown and myself. The basic idea of a PIM is that if we design the polymer backbone so that it is like a molecular scale ladder, and build in
something that makes it twist and turn into a contorted shape. We have a polymer
that cannot pack together, and fills space in the solid state.
It ends up with lots of little spaces that small molecules can get into. It behaves like a molecular sieve. The first membrane forming PIM that was synthesized, we called PIM-1. PIMs are potentially useful for a variety of membrane
processes. For gas separations, such as air separation, they have been shown to
be amongst the best performing polymers. And PIMs really love organic compounds, they have been shown to be much better than other polymers at pulling
neutral dyes out of ethanol solution. In pervaporation, PIMs can, for example,
pull mostly butanol out of a butanol water mixture. Although research has continuing to improve the selectivity further. By applying chemistry to PIMs, we
can create a range of materials with different selectivities.
For example, carboxylated PIM-1 will preferentially pull cationic organic
compounds out of water. While ethanolamine-modified PIM-1 will preferentially pull out anionic, organic compounds. There is still much to do, but here in
Manchester and elsewhere, we're working hard to create the next generation of
membranes, for more efficient and economic separation processes in industrial
biotechnology.
Video 4
Hello, my name is Patricia Thornley, and I am a professor in sustainable
energy systems at the Tyndall Center for Climate Change Research. I'm based
in the School of Mechanical, Aerospace, and Civil engineering at the University
of Manchester. Most of the work that I do is in bioenergy. So today, we're going
to be talking about the challenges of making bioenergy development sustainable.
Challenges of sustainable bioenergy development. Climate change is the biggest
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global challenge that mankind faces. Our current trajectory is likely to see global
mean surface temperatures rise by at least two degrees centigrade by the end of
this century. And that will result in the hottest days in parts of the world being
ten degrees centigrade hotter than today. Sea level rises that will obliterate low
lying states, agricultural productivity being decimated in parts of the world
where food security is already an issue, under much higher frequency of
extreme weather events, with well documented consequences. The UK
government has therefore committed to challenging long-term targets to reduce
our greenhouse gas emissions by 80 % by 2050. These emissions are dominated
by fossil fuel use for energy. And so switching to renewable energy provision is
a key part of this strategy. There's also a commitment to provide 15 % of UK
energy consumption from renewables by 2020.
Bioenergy is low carbon because the carbon dioxide released when biomass is converted has been sequestered from the atmosphere relatively recently
when the plant grew. So releasing it is more akin to recycling CO2 and provided that the biomass resource is sustainably managed, this doesn't increase
the long term atmospheric burden of greenhouse gases.
Studies by the UK government have shown that bioenergy could provide
up to 50 % of the UK's renewable energy across heat, transport fuels, and electricity by 2020. So it is important that we think carefully about the wider impacts and challenges of using biomass for energy.
Well lots of people talk about using things sustainably. It all sounds very
positive, but it can be difficult sometimes to know what they really mean. One
definition was formalized in the Bruntland Report by the World Commission on
Environment and Development. And it said that sustainability meant meeting
the needs of the present without compromising the ability of future generations
to meet their own needs. But of course, means that we need to protect the environment. So that means preserving our fuel reserves and biodiversity, while
avoiding pollution and dangerous greenhouse gas levels, but there's more to it
than that. If we think holistically about our environment as the place where we
exist, we realize that there's also a social dimension to this and so sustainable
development should be just and equitable. For example, not exploiting the resources of one group to provide the needs of another. In the society we inhabit
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today, there is global interaction and trade. Also, necessary, sustainable activity
contributes in some way to economic growth. We cannot indefinitely continue
something if it has a significant uncompensated financial cost. So, we think of
sustainable development as taking place in a space that has constrained by environmental protection, economic growth and social justice. We call these
the three pillars of sustainability.
Now let's get back to biomass. Biomass is any organic matter of recent
biogenic origin used to supply energy or materials. Now this can range from
purpose grown crops such as short rotation coppice, and to energy grasses,
through to the biodegradable fraction of municipal waste. What all of these materials have in common is that they contain carbon atoms that have relatively
recently been sequestered from the atmosphere. When we use the material to
provide energy and convert the hydrocarbon to carbon dioxide and water, we
are only returning the carbon dioxide that was recently removed from the atmosphere. It doesn't actually increase the net long-term burden of CO2 in
the atmosphere. Anthropogenic climate change is caused by an accumulation of
greenhouse gases in the atmosphere. If we have a net transfer of the carbon
stock sequestered by plants in the ecosphere to the atmosphere, that would be
a problem. This could for example, occur with unsustainable logging practice.
So, forest derived materials are only sustainable if the forest area is being maintained through harvest periods. However, as long as the carbon is being cycled
from ecosphere to atmosphere on a relatively short cycle time, there is no net
long term increase in atmospheric GHG concentrations. However, there will be
steps along the bioenergy chain where we emit greenhouse gases.
For example, there will be carbon dioxide emissions released during
transport or nitrous oxide emissions released from soils while plants are
growing. And we generally carry out a hole system greenhouse gas balance to
access if bioenergy is really contributing to carbon reductions or not. Now biomass resource is very dependent on land availability, food production, industrial
activity, and a whole host of other things. And we can model what this might
look like in the future, as has been done here by researchers at the University
of Manchester.
One very clear message we get is that under a whole range of possible future conditions, the biomass resource that we have available for use will be
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dominated by waste. So, we really need to focus on better ways of using and
making the most of waste if we want a really sustainable bioenergy future.
I said that we look at greenhouse gas balances along the whole supply
chain. When we do that, we use a technique which is called lifecycle assessment,
and this involves looking at a product. In this case, the product is a unit of energy. From the cradle where it is produced, in this case that's in a field where the
biomass is grown. Through its whole life cycle to its end use point when it delivers energy to the consumer. By doing this, we can establish the greenhouse
gas impact of that unit of energy compared to a reference level.
For example, we might compare it to the current fossil fuel energy use.
And so these graphs that you can see here show the carbon emissions associated
with using biomass in different ways. The one on the left shows that woodchip
boilers, small and
large electricity plants, all give similar, very significant reductions. But if
we frame things differently and instead consider the greenhouse reductions that
are achieved per unit of biomass. So that's taken into point the efficient use of
the biomass resource, we need up with quite a different rank ordering.
Again, this shows that it is important to understand what exactly the environmental policy objective is at the outset when considering the use of biomass
to encourage fire policy mechanisms. Of course, I've just been talking about
greenhouse gases and carbon, and I showed earlier the three pillars of sustainability. When we think in that scale, we need to be thinking about an awful lot
more than just greenhouse gases. Bioenergy systems have a whole host of ecological impacts, many of which are related to the production on land. So, when
we look at the impacts for bioenergy we need to think about the toxicity impacts of pesticides used in plant production. The biodiversity impacts of introducing new species. The hydrological impacts of planting crops and forests.
Now as we saw a few moments ago, sustainability isn't just about the environmental. There are social and economic impacts too. These can be pretty
wide ranging especially when we're dealing with biomass that may have been
produced overseas where it may be difficult to confirm the production conditions or where different working practices are prevalent.
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So we may need to think about whether biomass production is encouraging
forest clearance for land grabs. And how farm workers are treated on biofuel
plantations compared to the conditions they would experience on other land.
There are a huge number of things that could be considered. On a comprehensive, sustainability assessment really should take all of these into account.
Although depending on the resource and geographic region, some things may
be more important than others. And it may make sense to focus on some, rather
than all, of the criteria that you can see here.
Now this graph shows a semiquantitative assessment of all the criteria
I showed you on the previous slide for a particular bioenergy system. The way
to think about this is that the blue circle is the reference system, in this case it's
a fossil fuel diesel system and if we stretch that circle then that equates to being
more sustainable. And as you can see some parameters score well on the bioenergy system that's the purplish colored one, actually a first and more sustainable choice for parameter number 1, number 4, 11 and so on.
But for other parameters the bioenergy system is actually less sustainable
and this commit policy making very challenging. his sort of system can also
help us to inform system improvements.
We might try to redesign the bioenergy system to address some of those
most negative impacts. As we saw on that previous slide, when we implement
bioenergy, some things can be more sustainable, and some things can be less.
And really, bioenergy has potential to offer immense benefits, in terms of
greenhouse gas savings, employment creation, global trade opportunities, especially when we're looking at developing countries. But there are also risks, risks
of undesired social conditions and ecosystem impacts.
So we need to think very carefully about how we balance those risks and
rewards when we're engineering the systems. Sustainable engineering is about
balancing these in a context appropriate way where we think about the users on
the things surrounding it. That's the end of this module session. If you would
like any further information on this topic, you will find a lot of papers and a lot
of information and links to the UK Institutes doing work on this at the SUPERGEN Bioenergy Hub website www.supergenbioenergy.net. My contact details,
Patricia Thornley at Manchester are listed here as well. Thank you for listening.
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