B2.5 Proteins and Enzymes

Home Learning Pack Due for 2nd September (whether we have a lesson or not!)

Name:

Target Grade:

Grade:

Heya,

Your task over the summer is to teach this topic to yourself. You will have to hand in this booklet as evidence of your work and you will be sitting a test in the first week back.

This topic will not be covered in class so failure to complete the work will result in a Faculty detention of 1 hour with myself and Mr Patel.

On a more positive note, learning like this will prepare you for the rigour expected from you during your A-levels and whatever higher education or training you choose to undertake.

If you are struggling with anything in this topic I can be reached via:

mswrightscience.wordpress.com

swright@nautical.lambeth.sch.uk

Good luck,

Miss Wright

Topic:   B2.5 Proteins                                       

Date Specification Content Comments B2.5 Proteins – their functions and uses Proteins have many functions, both inside and outside the cells of living

organisms. Proteins, as enzymes, are now used widely in the home and in industry. You should use your skills, knowledge and understanding to: Evaluate the advantages and disadvantages of using enzymes in the

home and in industry.

B2.5.1 Proteins

a) Protein molecules are made up of long chains of amino acids. These long chains are folded to produce a specific shape that enables other molecules to fit into the protein. Proteins act as: Structural components of tissues such as muscles. Hormones. Antibodies. Catalysts.

b) Catalysts increase the rate of chemical reactions. Biological catalysts are called enzymes. Enzymes are proteins.

B2.5.2 Enzymes

a) The shape of an enzyme is vital for the enzyme’s function. High temperatures change the shape.

b) Different enzymes work best at different pH values.

c) Some enzymes work outside the body cells. The digestive enzymes are produced by specialised cells in glands and in the lining of the gut. The enzymes then pass out of the cells into the gut where they come into contact with food molecules. They catalyse the breakdown of large molecules into smaller molecules.

d) The enzyme amylase is produced in the salivary glands, the pancreas and

the small intestine. This enzyme catalyses the breakdown of starch into sugars in the mouth and small intestine.

   

Topic:   B2.5 Proteins                                       

Date Specification Content Comments

e) Protease enzymes are produced by the stomach, the pancreas and the

small intestine. These enzymes catalyse the breakdown of proteins into amino acids in the stomach and the small intestine.

f) Lipase enzymes are produced by the pancreas and small intestine. These

enzymes catalyse the breakdown of lipids (fats and oils) into fatty acids and glycerol in the small intestine.

g) The stomach also produces hydrochloric acid. The enzymes in the stomach work most effectively in these acid conditions.

h) The liver produces bile, which is stored in the gall bladder before being released into the small intestine. Bile neutralises the acid that was added to food in the stomach. This provides alkaline conditions in which enzymes in the small intestine work most effectively.

i) Some microorganisms produce enzymes that pass out of the cells. These enzymes have many uses in the home and in industry. In the home: Biological detergents may contain protein-digesting and fat-digesting

enzymes (proteases and lipases). Biological detergents are more effective at low temperatures than other

types of detergents. In industry: Proteases are used to ‘pre-digest’ the protein in some baby foods. Carbohydrases are used to convert starch into sugar syrup. Isomerase is used to convert glucose syrup into fructose syrup, which

is much sweeter and therefore can be used in smaller quantities in slimming foods.

j) In industry, enzymes are used to bring about reactions at normal temperatures and pressures that would otherwise require expensive, energy-demanding equipment. However, most enzymes are denatured at high temperatures and many are costly to produce.

Proteins and Enzymes (The absolute basics) Proteins are made from long chains of smaller molecules called amino acids. These long chains are folded into particular shapes. This is important in relation to how antibodies and enzymes work.

Enzymes are biological catalysts. There are optimum temperatures and pH values at which their activity is greatest. Enzymes are also proteins. If the shape of an enzyme changes, it may no longer work (it is said to have been 'denatured').

Amino acids to proteins Proteins are polymers. They are built up in cells when monomers called amino acids join together end to end:

Lots of amino acid molecules → a protein molecule

There are only about 20 different naturally occurring amino acids. However, each protein molecule has hundreds, or even thousands, of them joined together in a unique sequence. This gives each protein its own individual properties.

Different proteins The long chains of amino acids fold to give each type of protein molecule a specific shape. Proteins act as:

Structural components of tissues (such as muscles) Hormones (such as insulin) Antibodies (part of the body's immune system) Biological catalysts (enzymes)

The particular shape that a protein molecule has allows other molecules to fit into it. This is particularly important for antibodies and enzymes.

Enzymes are biological catalysts - substances that increase the rate of chemical reactions without being used up. Enzymes are proteins folded into complex shapes that allow smaller molecules to fit into them. The place where these substrate molecules fit is called the active site.

The animation shows how this works. In this example, two small molecules join together to make a larger one.

If the shape of the enzyme changes, its active site may no longer work. We say the enzyme has been 'denatured'.

Uses of enzymes in industry

Enzyme  Use 

Protease  Used to pre‐digest proteins during the manufacture of baby foods 

Lipase  Used ‐ together with protease ‐ in biological detergents to break down (digest) the substances in stains into smaller, water soluble substances 

Carbohydrase  Used to convert starch syrup, which is relatively cheap, into sugar syrup, which is more valuable ‐ for example, as an ingredient in sports drinks 

Isomerase  Used to convert glucose syrup into fructose syrup ‐ fructose is sweeter than glucose, so it can be used in smaller amounts in slimming foods 

Enzymes can be denatured by high temperatures or extremes of pH. Note that it is wrong to say the enzyme has been killed. Although enzymes are made by living things, they are proteins and not alive.

Temperature, pH and enzymes The activity of enzymes is affected by temperature and pH.

Temperature and enzymes As the temperature increases, so does the rate of reaction. 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.

pH and enzymes Changes in pH also alter an enzyme’s shape. Different enzymes work best at different pH values. The optimum pH for an enzyme depends on where it normally works. For example, intestinal enzymes have an optimum pH of about 7.5. Enzymes in the stomach have an optimum pH of about 2.

Enzymes and their reactions catalysed

Enzyme Reaction catalysed Where produced

Amylase Starch → sugars Salivary glands, pancreas, small intestine

Protease Proteins → amino acids Stomach, pancreas, small intestine

Lipase Lipids → fatty acids + glycerol Pancreas, small intestine

Stomach acid The stomach produces hydrochloric acid. This helps to begin digestion, and it kills many harmful microorganisms that might have been swallowed along with the food. The enzymes in the stomach work best in acidic conditions - in other words, at a low pH.

Bile After the stomach, food travels to the small intestine. The enzymes in the small intestine work best in alkaline conditions, but the food is acidic after being in the stomach. A substance called bile neutralises the acid to provide the alkaline conditions needed in the small intestine. Bile is produced by the liver and stored in the gall bladder.

1. Babies find it difficult to digest proteins in their food. Baby food manufacturers use enzymes to ‘pre-digest’ the protein in baby food.

(a) Use words from the box to complete the following sentences.

amino acids amylases fatty acids

proteases glucose lipases

Proteins are ‘pre-digested’ using enzymes called .........................................

The pre-digestion of protein produces ........................................................... (2)

(b) A baby food manufacturer uses enzyme V to pre-digest protein. He tries four new enzymes, W, X, Y and Z, to see if he can reduce the time taken to pre-digest the protein.

The graph shows the time taken for the enzymes to completely pre-digest the protein.

The manufacturer uses the same concentration of enzyme and the same mass of protein in each experiment.

(i) How long did it take enzyme V to pre-digest the protein?

................ minutes (1)

(ii) Which enzyme, V, W, X, Y or Z, would you advise the baby food manufacturer to use?

Enzyme (1)

(Total 4 marks)

2. The diagram shows the apparatus used to investigate the digestion of milk fat by an enzyme. The reaction mixture contained milk and the enzyme.

In Experiment 1, bile was also added. In Experiment 2, an equal volume of water replaced the bile.

In each experiment, the pH was recorded at 2 minute intervals.

The results of the two experiments are given in the table.

Time in minutes pH 

Experiment 1: with bile  Experiment 2: without bile 

0  9.0  9.0 

2  8.8  9.0 

4  8.7  9.0 

6  8.1  8.8 

8  7.7  8.6 

10  7.6  8.2 

(a) Milk fat is a type of lipid.

Explain why the pH changed in experiment 2.

........................................................................................................................

........................................................................................................................

........................................................................................................................ (2)

(b) (i) For Experiment 1, calculate the average rate of fall in pH per minute, between 4 minutes and 8 minutes.

Show clearly how you work out your final answer.

...............................................................................................................

...............................................................................................................

................................. pH units per minute (2)

(ii) The average rate of fall in pH per minute for Experiment 2 was 0.1 units of pH per minute.

Explain the difference in the rate of fall in pH when bile is present.

...............................................................................................................

............................................................................................................... (1) (Total 5 marks)

 

1. What are the monomers that make up proteins?

2. What causes proteins to hold their shape?

3. What is the name of the bond between 2 monomers in a protein

4. Draw the repeat unit for the 2 monomers below. Give the other product formed

5. Explain the function of a catalyst and how it is able to do this.

6. Define an enzyme

7. Why do high temperatures stop enzymes working?

8. What is the ideal pH for Amylase?

9. Link the 3 digestive enzymes with their respective organs and food groups.

10. Which chemical is used to neutralise stomach acid?

11. Which 2 types of digestive enzymes do biological washing powders contain?

12. Why do biological washing powders save you money?

13. Why is Isomerase commercially important?

14. Which enzyme is added to baby food? Why?

15. Give 2 advantages and disadvantages to using enzymes in industry

6 mark questions:

1. Protein is required for a number of systems within the body. Giving specific examples explain why a protein deficiency is unhealthy. _______________________________________________________________________________

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2. Justify the use of enzymes in industry despite the restrictive conditions required. _______________________________________________________________________________

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3. When a person becomes ill their internal body temperature is raised. Why can sustained periods of fever inducing illness make the patient predisposed to weight loss? You must refer to at least 2 organs. _______________________________________________________________________________

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4. Write your own 6 mark question with mark scheme. Remember that you must have more

than 6 potential marking points. _______________________________________________________________________________

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