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Class 11 Biology Notes Chapters Chemical Coordination and Integration
Typology: Study Guides, Projects, Research
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03 Enzymes
#21 Enzymes and reactions
Many chemical reactions can be speeded up by substances called catalysts. Within living organisms, these reactions (metabolic reactions) are controlled by catalysts called enzymes. Enzyme molecules are proteins.
Enzymes and reactions
Most enzyme names end in – ase, e.g. lipase, protease.
Temperature, pH and enzymes
The activity of enzymes is affected by temperature and pH.
Effect of temperature on enzymes
The optimum (best) temperature for enzyme-controlled reactions is 37^0 C (body temperature).
As the temperature increases, the rate of reaction increases. But very high temperatures denature enzymes.
The graph shows the typical change in an enzyme's activity with increasing temperature.
The enzyme activity gradually increases with temperature up to around 37ºC, or body temperature. Then, as the temperature continues to rise , the rate of reaction falls rapidly as heat energy denatures the enzyme. Most enzymes are denatured above 500 C.
Effect of pH on enzymes
The pH of a solution is how acidic or alkaline it is. Different enzymes work best at different pH values. The optimum pH for an enzyme depends on where it normally works. It is around neutral ( pH= 7 ) for most enzymes but there are some exceptions.
#22 Enzymes - 'Lock and key' model
Enzymes are very specific, each kind of enzyme catalyse one kind of reaction only. To catalyse a reaction, enzyme molecule and substrate molecule need to meet and joint together by a temporary bond.
Each molecule has a special shape and an active site into which its substrate molecule fits exactly.
This enzyme is amylase , and its active site is just the right size and shape for a substrate molecule ( starch in this case).
The starch slots into the active site.
The starch is split into maltose molecules.
The enzyme is unaltered, and ready to accept another part of the starch molecule
# 23 Role of enzymes in germinating seeds
Seeds contain stored food in the cotyledons to provide energy and materials
for growth. This is usually in the form of starch – a large, insoluble molecule
(long chain of glucose), that keeps the food immobile. The starch needs to be
changed into a soluble molecule ( sugar ) with help of enzymes for the seeds
to make use of.
In the presence of H 2 O , Gibberellin or gibberellic acid (GA) stimulates the
production of amylase.
Amylase breaks down starch to maltose , allowing for the formation of ATP
(via glucose).
The energy produced in the embryo is used to facilitate germination.
The glucose produced may also be used to synthesis cellulose - for cell wall
formation.
Warmth helps speed up the process.
Do it your self
Boil two standard eggs together, and push two teaspoons into the yolks so that there is some yolk left on the spoons.
Dissolve equal amounts of ordinary and 'biological' detergents in two separate glasses of water, and leave a yolk-stained spoon in each glass. After some time you will see that the spoon in the ordinary detergent still has yolk on, but the yolk on the other spoon has been digested by the 'biological' detergent. This will happen if the 'biological' detergent really contains enzymes that break down the proteins in egg yolk.
Try this
Figure above shows a box of biological washing powder.
a) Explain why: i) The presence of protease and lipase would make the washing powder more effective than ordinary detergent [3 marks]
ii) The powder should not be used in boiling water [2 marks]
b) Silk is a material made from protein. Explain why the biological washing powder should not be used to wash silk clothes [2 marks]
Answer:
a) i) Protease and lipase are enzyme They break down stains better than ordinary detergent Protease breaks down protein; lipase breaks down fat ii) Enzymes are denatured at high temperature b) There is protease in the biological washing powder This would digest the protein in the silk so the clothes would get spoiled.
Benefit from using enzymes in cleaning products, toothpaste and other products in our home.
Additional resources:
http://www.saasta.ac.za/biosciences/enzymes.html http://isbibbio.wikispaces.com/biological+washing+powders+and+enzymes
#25 Use of enzymes in the food industry
Enzymes are an integral component of modern fruit juice manufacturing and are highly suitable for optimising processes. Fruit juices are extracted using an enzyme called pectinase.
Pectin is a substance which helps to stick plant cells together. Fruits like apple or orange contain a lot of pectin. The braking down of pectin makes it much easier to squeeze juice from the fruit.
Pectinase is widely used in order to:
Enzymes are sometimes used when making baby foods. Proteases are used to treat some high-protein foods, they break down proteins to polypeptides and amino acids for young baby to absorb the food easier.
The enzymes produced by the microorganisms may be extracellular or intracellular:
Explain words:
_ Molasses (syrup):_* Thick, dark brown, uncrystallized juice obtained from raw sugar during the refining process.
_Corn-steep liquor_* : a concentrated fluid obtained by soaking corn grains in water (containing 0,2% SO 2 ) for 36 — 40 hours at 46 — 50°C.
#27 Use of microorganisms to manufacture antibiotic penicillin
Three colonies of a Penicillium mold growing on an agar medium.
Antibiotics are substances which kill bacteria without harming human cells. They help to cure bacterial infections. Penicillin is made by growing the fungus Penicillium in a large fermenter.
Often, it is easier to use the whole microorganisms rather than extract its enzymes from it. The microorganism is grown in a fermenter, its enzymes convert a substrate to a desired product. The production of antibiotic penicillin is one example.
History (not included in the syllabus)
Thousands of glass fermentation vessels like this one were used in Glaxo (now GlaxoSmithKline) laboratories to produce penicillin.
Credits: Science Museum
The penicillium mould was grown on the surface of a liquid filled with all the nutrients it needed. This approach was replaced by the method of growing the mould within large industrial fermenters. The antibiotic was first used in the early 1940s and saved the lives of many soldiers during the Second World War.
Discovering of Penicillin
Sir Alexander Fleming, 1952 (photo AP)
Penicillin was discovered by chance. Alexander Fleming - the Scottish bacteriologist - accidentally left a dish of staphylococcus bacteria uncovered for a few days. He returned to find the dish dotted with bacterial growth, apart from one area where a patch of mould (Penicillin notatum) was growing. The mould produced a substance, named penicillin by Fleming, which inhibited bacterial growth and was later found to be effective against a wide range of harmful bacteria.
However, it was not until World War II that penicillin, the first antibiotic, was finally isolated by Howard Florey and Ernst Chain. Fleming, Florey and Chain received a Nobel prize in 1945, for their discovery which revolutionised medicine and led to the development of lifesaving antibiotics.
Additional sources: Royal Society of Chemistry sciencemuseum
Reactions catalysed by enzymes work fastest at a particular pH. The optimum
pH for most enzymes is around pH7 (neutral), but some have an optimum pH much higher or lower than this.
Extremes of pH cause enzyme molecules to lose their shape , so they no longer
bind with their substrate.
Amylase is found in seeds. When the seed begins to germinate , the amylase is
activated and catalyses the breakdown of insoluble starch to soluble maltose in the seed. The maltose is used by the growing embryo as an energy source and to make cellulose for new cell walls.
Biological washing powders contain enzymes, often obtained
from microorganisms such as bacteria or fungi. The enzymes break down proteins or fats on the fabric, forming watersoluble substances that can be washed away.
Pectinase is used to break down cell walls in fruits , making it easier to
extract juice from them.
The antibiotic penicillin is made by cultivating the fungus Penicillium in a fermenter. The fermenter is kept at the correct pH and temperature for the enzymes of the fungus to work well.
