This Homework Task Is All About Applying Your Biology Knowledge to a New Situation. Read

Homework task HB2.18.1 Lesson reference: B2.18 Enzymes in industry

Enzymes in industry

Learning objectives:  Understand why enzymes are used in industry.  Consider some examples of using enzymes in industry.  Evaluate the advantages and disadvantages of using enzymes in industry. Suggested time: 30 minutes

Name: ______Date: ______

This homework task is all about applying your biology knowledge to a new situation. Read the passage below and then answer the questions.

Making leather  Leather is made from animal skins or hides. The hides have to be cured and tanned to make them clean, flexible, and resistant to decay.  The first stage is to cure the hides by immersing them in salt solution. This removes water from the hides and prevents bacteria decomposing the collagen protein in the hides.  Then the hides are soaked in clean water to remove the salt and to rehydrate them.  The hides are then treated with a strong alkaline solution and some other chemicals to remove the fats, alter the condition of the collagen proteins, and remove the hairs. The hairs of the fur contain a protein called keratin. There are many bonds between the sulfur groups of amino acids called cysteine.  These bonds are hard to break. They make the protein structure very stable. The chemicals added break these bonds and weaken the hairs, so they can be scraped off the hide.  Next, the pH of the hides is lowered, by adding salt and sulfuric acid.  This neutralises the alkaline pH produced by the alkaline solution. Now protease enzymes can be added to soften the leather.  The leather is then soaked in a solution of tannins, aluminium salts, and egg yolk. Tannins are obtained from plants, for example oak trees. They coat the collagen so it is less water soluble and less susceptible to bacterial action. This also makes the leather flexible. Finally the leather is waxed.

170 © Oxford University Press 2011 This document may have been altered from the original. A By what process is water removed form the hides when they are soaked in strong salt solution?

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B Why do you think strong salt solution prevents bacteria from decomposing the hides?

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C When the sulfur bonds between adjacent cysteine amino acids in the chain are broken, what will happen to the structure of the keratin protein molecules?

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D Why does the pH have to be lowered before the protease enzymes are added to the hides?

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E Why do you think coating the leather in tannins prevents bacterial action?

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171 © Oxford University Press 2011 This document may have been altered from the original. F Until the 19th century, tanneries (where leather is made from animal skins) used urine and dog or pigeon faeces to treat the hides. This practice had been carried out since ancient times. Scientists now know that it was the protease enzymes in the faeces that helped cure the hides.

i Why are faeces a good source of protease enzymes?

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In Victorian times some children were employed to collect dog faeces from the streets.

ii Why do you think dog faeces were used as opposed to horse faeces, which would also have been readily available from the streets?

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G If you worked in a modern tannery and came across a new source of protease enzymes, what investigations would you do to find out if these enzymes would be suitable to use in making leather?

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