2.3 Proteins

The diagram below shows the process of translation.

Identify molecule A.

(1)

Explain how molecule A controls the process of translation.

(3)

Describe the importance of molecule B in protein synthesis.

The following table shows the mRNA codons and their amino acids.

A mutation in the gene that codes for molecule C changes one of the DNA base triplets on the antisense strand from TCA to TCT.

Which of the following describes the effect that this mutation will have on molecule C? 

(1)

The gene coding for molecule C consists of 495 DNA bases. After transcription was completed, 39 bases were removed from the molecule which ultimately produced molecule A.

Calculate the number of amino acids that molecule C would consist of after translation.

(2)

Explain the effect that a change in the DNA base sequence of a gene can have on the protein for which it codes.

The following diagram shows an example of a dipeptide.

Identify the peptide bond in this molecule by drawing around it on the diagram.

(1)

Describe how a peptide bond forms between two amino acids.

(2)

Proteins can have four structural levels. The following diagram shows an example of a protein.

State the level(s) of protein structure that is visible in the diagram.

(1)

Compare and contrast the chemical bonds found at each level of protein structure identified at part (b) (i).

(2)

The protein in the diagram at part (b) is an example of a globular protein.

Explain using a named example, how the structure of a globular protein enables it to perform its function.

People suffering from anaemia are generally lacking in dietary iron. It is recommended that they consume more red meat and green leafy vegetables to increase the iron levels in their blood.

Based on your knowledge of haemoglobin, explain why one of the symptoms of anaemia would be fatigue.

Bromelain is an enzyme found in the fruit and stems of pineapples.

It is a protease and is able to break down protein such as collagen. Topical bromelain is often applied to burn wounds as a form of treatment.

Deduce the way in which bromelain may act as a treatment.

The activity of bromelain was investigated by placing a small amount of the enzyme with a known concentration of protein.

The graph below shows the progress of this reaction when it is carried out at 25 °C.

Calculate the initial rate of the reaction. Show your working.

(2)

The investigation was repeated with a higher concentration of bromelain.

Predict the expected result by drawing a curve on the graph.

(1)

The investigation was extended to compare the initial reaction rates of bromelain and papain. Papain is similar to bromelain but found in papaya.

State two possible advantages of calculating the initial reaction rates of enzyme catalysed reactions here rather than the reaction rates at another point during the experiment.

The table below shows the results of an investigation into the effects of temperature on the reaction rate of amylase. Note that a.u. denotes arbitrary units.

Calculate the percentage increase in the reaction rate between 10°C and 40°C.

Plot a graph of the results in part (a) on the axes below. Indicate on the graph at which temperature the rate of reaction was the highest.

(2)

Which of the following provides the most accurate description of the results? 

(1)

The scientists repeated their investigation with some adjustments in order to obtain a more accurate result of the temperature at which the reaction rate is highest.

State two adjustments that they could make to their investigation to obtain these results.

Enzymes are very sensitive to temperatures above 40°C.

Using your knowledge of enzyme structure, explain why the reaction rate of amylase decreased after 40°C.