Homework

1. Make a table to contrast the features of fibrous and globular proteins (see next slide)

2. Worksheet protein structure and carbohydrate questions

3. Complete question sheet from todays practical

Protease practical

Proteins - Fibrous v globularFibrous Globular

Shape

Structure

Solubility

Stability

Function

Examples

Proteins - Fibrous v globularFibrous Globular

Shape Long chains Ball

Structure Tightly wound secondary structure, tertiary twisted again quaternary multi chains loop around each other

Secondary usually a mixture of alpha helix and beta sheet, tertiary wound into a globular shape, can be quaternary structure

Solubility Insoluble – chains are h bonded to each other so few exposed groups to interact with water molecules

More soluble – forms a colloid – interactions between hydrophillic R groups and water

Stability So many h bonds that it takes a lot to disrupt the structure. Stable

Easily disrupted – denaturedLess bonds holding it together

Function Structural e.g. hair etc. Metabolism (chemical reactions in cells)

Examples Collagen – tendonsKeratin hair

Haemoglobin, antibodiesEnzymes, some hormones

pH2

pH4

pH10

pH8

pH6

pH7

Fastest = pH7Next = pH63rd = pH104th = pH85th =pH4Denatured = pH2

Results pH Time taken for

solution to clear/m

Rate = 1/timeIn m-1

1087642

Graph

• Independent variable on the x axis =• Dependent variable on y axis =

Worksheet questions 1. Remember the change in absorbance takes place because the enzyme is

digesting the protein in the milk powder solution. What is happening in the cuvette at pH7? Use the words protein, amino acids, soluble, insoluble, hydrolysis, enzyme =protease (neutrase) in your answer. (3 marks)

2. Which is the optimum pH for neutrase? (1 mark) What is the evidence from the data for this?(1 mark)

3. The textbook value for optimum pH for neutrase is 5.5-7.5. Do your results agree with this? (1 mark)

4. Why is using the colorimeter better than just taking the time the milk takes to clear by eye for each pH?(1 mark)

5. Can you criticise any of the plot lines (e.g. are they all smooth)? (1 mark)6. Why may these anomalies have occurred? (2 marks)7. How could you make the experiment more reliable? (3 marks)8. Why did we use buffer solutions? (1)