Biotechnology
A
Living factories
Yeast is a microscopic single-celled fungus. It is found naturally on many
types of fruit such as grapes.
Yeast is now used to make many useful products. Its usefulness stems from
its ability to use glucose as a source of energy. It does this in a process called
fermentation.
The word equation for fermentation is
glucose
yeast
energy + carbon dioxide + ethanol
Anaerobic respiration
You may have noticed that the fermentation equation is fairly similar to
another equation you have come across, namely, aerobic respiration.
Compare the two equations
glucose
yeast
glucose +oxygen
energy + carbon dioxide + ethanol
energy + carbon dioxide +water
Both of these two types of process can be performed by yeast. When oxygen
is available, yeast performs aerobic respiration. When oxygen is not available
yeast performs anaerobic respiration (fermentation).
The table below compares the two type of respiration:
Aerobic respiration
Oxygen required
No energy left on products
Release a lot of energy
Anaerobic respiration
No oxygen required
Ethanol still contains energy
Release some energy
Yeast at work in baking
Two beakers are set up as follows and left until the following day:
A
Yeast, flour
& glucose
B
flour &
glucose
The results were as follows:
A
B
Conclusion
When yeast ferments, it makes two important products, ethanol and carbon
dioxide. In baking the carbon dioxide bubbles make the dough rise. The
ethanol is burned off during the baking process.
Yeast at work in brewing
We have seen that when yeast is deprived of oxygen, it produces carbon
dioxide and ethanol. The following equipment can demonstrate this:
Results
The temperature rose from 22oC to 29oC.
The bicarbonate indicator changed from red to yellow, showing carbon
dioxide had been made.
Ethanol could be smelled.
Conclusion
Fermentation has occurred.
Commercial brewing
In beer making, fermentation is carried out on a larger scale using
fermenters.
To make beer that can be sold to the public, commercial brewers must give
the yeast the best growing conditions:
1.
2.
3.
a food supply – starch in barley grains is converted to maltose I a
process called malting
a suitable temperature – a thermostat ensures that a constant
temperature is maintained
no competition – all microorganisms except yeast are killed off to
prevent competition and possibly contamination.
The malting of barley
Barley contains starch. This starch cannot be used by yeast as a food so the
brewers must first germinate the barley grains. Enzymes in the grains then
convert the starch to the sugar maltose that the yeast can then use.
Modern brewing involves malting and batch processing.
Batch processing
This is the technique used by commercial brewers to provide the best
conditions for fermentation.
All the raw materials are added at the start.
The system is left untouched until fermentation ends.
The process is monitored and controlled to ensure that optimum conditions of
temperature etc are maintained.
When the process of fermentation is finished the products can be removed.
The fermenter is then cleaned and sterilised ready for the next batch of beer.
The souring of milk
Bacteria and a sugar, lactose, are present in fresh milk. The bacteria feed on
the sugar and cause the milk to sour. The souring of milk is a fermentation
process.
lactose
bacteria
lactic acid
Samples of milk of various ages were tested with pH paper:
Age of milk pH number
1
7
2
6.5
3
5
4
4.5
5
3
Conclusion
The pH of milk decreases as the milk gets older. Lactose is sugar in milk.
The souring of milk is brought about by fermentation carried out by bacteria.
The lactose sugar is converted to lactic acid.
How yoghurt and cheese are made
Cheese and yoghurt are made by curdling milk.
Lactic acid is needed to curdle the milk.
Manufacturers add certain strains of bacteria to the milk. Different types of
bacteria give the different types of cheese and yoghurt.
B
Problems and profit with waste
Problems with untreated sewage
Sewage is mostly organic waste and is produced in large amounts by humans.
To avoid disease, it must be dealt with safely and quickly.
Untreated sewage decreases the pH and the oxygen content of the river
water.
Sewage and health
In the first half of the 19th century, untreated sewage was dumped into the
rivers that were then used as drinking water and for washing. This often
resulted in disease and death. Even in modern Britain, a natural disaster like
flooding could disrupt the sewage treatment systems and the threat of such
disease could return. Some diseases that could be spread by untreated
sewage or a failure to wash hands after a visit to the toilet are
Typhoid
Diphtheria
Cholera
Food Poisoning
Polio
Sewage treatment
The main process in the treatment of sewage is its breakdown by the action
of micro organisms to products harmless to the environment.
Oxygen is required by the micro organisms and this is usually provided at the
treatment works by using compressed air.
The complete breakdown of sewage is only possible under aerobic conditions.
Under anaerobic conditions, sewage is only partly broken down leaving some
harmful products. If these products were released into the river they would
provide food for other bacteria that would then use up the oxygen in the
water.
Sewage is a mixture of many organic compounds. Each species of micro
organisms can only break down a few substances and therefore a range of
different micro organisms are required to completely remove all sewage
materials.
Working with micro organisms
Microbes can help in the manufacture of food and drink, treating sewage and
can cause disease.
Many microbes are always present in the air, in all surfaces and inside open
containers so precautions must be taken to prevent unwanted microbes
growing (contamination).
Therefore when working with micro organisms in the laboratory, it is
important to adopt a safe practice.
1. Petri dishes of agar jelly must be kept closed until ready for use so that
no unwanted microbes can contaminate the agar.
2. Hands must be washed before and after experiments so that no
bacteria are transferred into or outside the laboratory.
3. Petri dishes are sealed after being inoculated so that no bacteria are
accidentally spilled.
4. After use, petri dishes are first sterilised in an autoclave and then
disposed of safely. An autoclave heats the dishes to a very high
temperature to kill all bacteria.
Contamination
Contamination is the presence of unwanted, perhaps harmful, micro
organisms. Beer production is one area where contamination may occur.
In between batches, manufacturers sterilise all their equipment and then
check to make sure each it is indeed sterile.
Particular care has to be taken to remove unwanted fungal and bacterial
spores. This is done by
1. regular checks for contamination.
2. the use of high temperature steam.
3. chemicals such as caustic soda.
Microbes and decay
When an organism dies, its tissues decay, mainly due to the action of certain
micro organisms. The micro organisms use the dead tissue as a source of
energy. These micro organisms are also known as decomposers.
Microbes and recycling
Recycling is not new. Nature has been recycling or millions of years.
To keep an ecosystem in balance materials must be recycled. The two main
cycles are the carbon and the nitrogen cycles.
Carbon cycle
CO2 is added to the atmosphere by respiration
CO2 is removed from the atmosphere by photosynthesis. Bacteria feed on
dead remains and faeces and release CO2 back into the air during respiration.
Nitrogen cycle
Bacteria are involved in many stages of the nitrogen cycle:
Nitrogen-fixing bacteria (4) – plants such as peas and beans have nodules on
their roots that contain these bacteria. The bacteria convert nitrogen from the
air into nitrate and thus such plants have their own ‘fertiliser factory’ with
them.
Nitrifying bacteria (2) – they convert ammonium compounds to nitrite and
then to nitrate
Denitrifying bacteria (3) – remove nitrogen compounds from the soil and put
nitrogen back into the air
Fuels from fermentation
There are advantages to using fermentation fuels rather than fossil fuels.
Fermentation fuels – methane, ethanol, biogas
Fossil fuels – coal, oil and gas
Fermentation fuels
Harmless to the environment
Easy to obtain
Cheap to obtain
Renewable
Fossil fuels
Harmful to the environment
Difficult to obtain
Expensive to obtain
Non-renewable
Upgrading waste
Upgrading waste is a means of obtaining useful products from unwanted
waste material that would otherwise have to be disposed of and. might harm
the environment. Microorganisms are used to change the waste into
substances which can be used as an energy source or high quality protein
food.
Example 1 Biogas
This can be made by the decomposition of farm yard manure and household
rubbish by microbes. The biogas can then be burned as a source of energy.
Example 2 Whey
Whey is the waste liquid from cheese making. Whey can be used as a
component of cattle feed or in biscuits and cakes.
Example 3 Fruit pulp
Fruit pulp is the waste from making fruit juices.
Manufacturers now add the enzyme pectinase to the waste fruit pulp.
Pectinase breaks down the pectin in the plant cell walls releasing more juice.
Single cell protein
Most microorganisms can reproduce much faster than plant and animal cells
can by asexual reproduction where the cell simply divides in two.
1 cell
2 cells
4 cells and so on
By this method these cells can increase in number in a matter of hours and
make them ideal for growing food etc.
Single cell protein - some kinds of yeast produce a rich supply of oil. In the
future it is hoped that this yeast can be grown to supply a source of human
food.
Mycoprotein – some fungi produce mycoprotein which is thread-like. This can
be used to mimic meat and provides a vegetarian source of protein. It is at
present sold under the brand name Quorn.
C
Reprogramming Microbes
Bacteria
Bacteria cells are much smaller than animal cells.
Both bacterial cells and animal cells have a nucleus but some bacterial cells
have extra chromosome material called plasmids which can be transferred
from one bacterial cell to another. Just like other cells, the normal control of
the bacterial cell’s activities depend on its chromosome material.
Genetic engineering
Genetic engineering is very important to biotechnology. It enables us to direct
microbes to make products they would not normally make eg human genes
can be placed into microbes to make substances useful to humans.
Pieces of chromosome can be transferred from a human cell into a bacterial
cell and allow the bacteria to make a new substance.
First the chromosome material is removed from a human cell. One gene is
removed. The plasmid is carefully removed from a bacterial cell and the ring
is opened. The human gene is inserted into the plasmid. Lastly the altered
plasmid is placed back into the bacterial cell.
The bacterial cells multiply and produce large quantities of whatever protein
the gene was the instruction for. This protein is now produced more quickly
with less expense.
Useful products of genetic engineering
Insulin - this hormone is produced by the pancreas and regulates the amount
of sugar in the blood. People who cannot produce this hormone sufficiently
suffer from diabetes. More people are living longer and the number of people
being diagnosed with diabetes is increasing. Thus the demand for insulin has
risen sharply. Before biotechnology the insulin was obtained from pig
pancreases. Many people were allergic to the pig insulin. Now human insulin
can be mass produced using genetic engineering and bacteria.
Growth hormone – Many children if diagnose early enough can benefit from
doses of human growth hormone so the reach a more average height.
Genetic engineering versus selective breeding
Both of the above methods can alter the genotype of species that are useful
to man.
Selective breeding
Years of careful selection of required
characteristics
Breeding over many generations
Genetic engineering
Alters the characteristic immediately
Improves an already present
characteristic
Species has a completely new
characteristic
Immediately new species
Biological detergents
Some detergents are called biological detergents. This means that they
contain enzymes such as proteases and lipases that will breakdown stains like
egg, milk or blood. These enzymes have been extracted form soil bacteria.
The use of enzymes in such detergents have meant that washing clothes can
now be done at much lower temperatures, saving time and energy. It also
allows delicate fabrics to be cleaned better with less damage to the fabrics.
Antibiotics
In 1928 a Scotsman called Alexander Fleming discovered that a substance
made by a fungus prevented the growth of bacteria. This substance was
penicillin and was the first known antibiotic. Since then many other antibiotics
have been discovered and used against diseases caused by bacteria.
A range of antibiotics is required because no one antibiotic is effective against
all bacterial diseases as the following experiment shows. A multidisc has
different antibiotics on each “spoke”
G, C, TE and S all can combat this bacteria but antibiotics P and E are
ineffective.
Immobilising enzymes
In most enzyme reactions the following takes place:
{substrate + enzyme} mixture
{product + enzyme} mixture
Separating the enzymes from the products can be expensive for some
industries and sometimes the enzyme cannot be reused.
A new technique called immobilisation has saved industries a lot of time and
money because it allows the enzyme to be reused again and again and the
products are easily separated from the mixture.
This is achieved by trapping the enzymes or yeast cells in jelly, immobilising
them:
Continuous flow processing
In some industries, continuous flow processing is more efficient and cost
effective than batch processing.
1.
2.
3.
4.
The enzyme does not have to be separated from the enzyme
The expensive enzyme can be reused.
Valuable time is not lost during change over of batches.
The problem of waste disposal is reduced as possibly harmful
substances are not released into the environment because the
enzymes are not thrown away.