Protein synthesis

Describe how mRNA is obtained from pre-mRNA.

Describe how RNA polymerase joins RNA nucleotides.

Figure 1 shows the energy contained in molecules during an enzyme-controlled reaction.

Which expression represents the activation energy (E_a) of this reaction?

Tick (✓) one box.

In 1914, a group of scientists investigated enzyme action.

After studying their results, the scientists reached the following conclusions:

Our current understanding of enzyme action is based on the induced-fit model.

Describe similarities and differences between the conclusions from 1914 and our current understanding of enzyme action.

Describe the roles of ribosomes, tRNA and ATP in the process of translation.

Describe and explain the adaptations of leaves that maximise gas exchange.

Do not refer to organelles in your answer.

Describe the pathway taken by blood between a kidney and the coronary arteries.

Include names of the major blood vessels (arteries and veins) and heart valves involved.

Give three structural differences between an mRNA molecule and a tRNA molecule.

Table 3 shows mRNA codons and the amino acid coded by each codon.

Figure 5 shows the mRNA base sequence produced when part of a gene coding for an enzyme is transcribed.

Use Table 3 to give the amino acids coded by the mRNA base sequence in Figure 5

A mutation occurred in the part of the gene transcribed in Question 06.2.

Figure 6 shows the mRNA base sequence produced when the identical part in the mutated gene is transcribed.

The amino acids coded by this mRNA base sequence form part of the enzyme’s active site.

Use all the information in this question to:

• name the type of mutation that occurred to produce the mutated gene

• give the change in DNA caused by this mutation

• explain the effect this mutation will have on the function of the enzyme.

Explanation of effect on function of enzyme

Define genome and proteome.

The classification system used in the early 20th century grouped different species of bacteria according to the position and shape of flagella on bacterial cells and by the number of flagella per cell. These were observed using an optical microscope. Each species of bacterium has a characteristic cell shape and arrangement of flagella. These characteristics may be shared with other species within a genus. Flagella are fragile, difficult to stain and may extend from the cell at any angle.

Consider the accuracy and limitations of the early classification of bacteria using the arrangement of flagella.

Suggest why several bacterial species have been renamed in recent years.

Figure 6 shows an image from an optical microscope of a single bacterial cell.

This bacterial cell is 2.3 μm long (excluding the flagellum).

Calculate the magnification of this image.

Show your working.

Complete Table 3 to give three differences between DNA molecules and tRNA molecules.

Scientists investigated ribosomal RNA in liver cells.

Figure 10 shows the method they used to isolate the ribosomes from the liver cells. The detergent dissolves lipids.

The scientists broke open the cells to produce a suspension of cell contents.

Describe how the scientists would remove large organelles from this suspension of cell contents.

Explain the position of the bands of ribosomes in tubes A and B in Figure 10.

Describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation.

Table 2 shows:

• mRNA codons and the amino acid coded for by each codon

• the type of bond formed by the R group of some of the amino acids.

Crystallin is a structural protein found in the human eye. An inherited disease that leads to blindness is caused by changes in properties of crystallin. The replacement of the amino acid Arg with the amino acid Gly causes these changes.

Use information in Table 2 to suggest why this amino acid replacement changes the properties of crystallin.

The amino acid replacement of Arg with Gly is caused by a single base substitution mutation in the DNA. The non-mutant DNA triplet is TCC.

Complete Table 3.

Give:

• the mRNA codon complementary to the non-mutant DNA triplet

• the mutated mRNA codon that could cause the change from Arg to Gly in the crystallin protein

• the DNA triplet complementary to this mutated mRNA codon.

Describe how mRNA is formed by transcription in eukaryotes.

Describe how a polypeptide is formed by translation of mRNA.

Define ‘gene mutation’ and explain how a gene mutation can have:

• no effect on an individual

• a positive effect on an individual.

Scientists collected data on 800 000 human births. The data showed the mass of each baby at birth and whether the baby needed to be transferred to a special care unit for very ill babies.

Their results are shown in Figure 5.

Use Figure 5 to explain how human mass at birth is affected by stabilising selection.

The scientists studied 1500 more births. They recorded the mass at birth of each baby and the nature of the KIR gene in the mother’s genome.

Some of their results are shown in Table 2.

The scientists used a statistical test to test the following null hypothesis:

‘The presence of KIR2DS1 in the mother’s genome does not affect the frequency of births above 4500 g’

Tick (✓) one box that gives the name of the statistical test that the scientists should use with the data in Table 2 to test this null hypothesis.

The scientists calculated a P value of 0.03 when testing their null hypothesis.

What can you conclude from this result? Explain your answer.

Mitochondrial DNA (mtDNA) is a small circular DNA molecule located in mitochondria. It is 16 569 nucleotides long and contains 37 genes and a control region.

Sports scientists investigated whether a mutation in the control region of mtDNA in human males was related to an ability to exercise for longer.

• The males in Group T had thymine at nucleotide position 16 519

• The males in Group C had a mutation resulting in cytosine at nucleotide position 16 519

The control regions of Group T and Group C were the same length.

Name the type of gene mutation that is most likely to have occurred at nucleotide position 16 519

Group T and Group C completed the same 8-week training programme. The following measurements were taken at the start of the 8-week programme, and again at the end.

1. VO 2 max (a measure of maximal oxygen uptake).

2. Citrate synthase (CS) activity (CS is an enzyme involved in the Krebs cycle).

The scientists then calculated the percentage increase in each measurement in both groups.

Figure 4 and Figure 5 show their results.

A student concluded from Figure 4 and Figure 5 that training has a positive effect on VO 2 max and CS activity.

Evaluate the student’s conclusion.

The mitochondrial DNA (mtDNA) control region is an area of mtDNA that is non-coding. This region stimulates the synthesis of both mtDNA and mitochondrial messenger RNA.

Use this information to suggest two reasons why the mutation at nucleotide position 16 519 could lead to the differences seen in Figure 5.

The sports scientists investigated whether there was a correlation between the percentage change in VO 2 max and percentage change in CS activity in Group T.

Figure 6 shows their results.

‘Having thymine at nucleotide position 16 519 in Group T causes an increase in ability to exercise for longer.’

Evaluate this conclusion.

Use all the data in this question.

Draw the general structure of an amino acid.

Table 1 shows mRNA codons and the amino acids coded for by each codon. It also shows some properties of the R group of each amino acid.

The genetic code is described as degenerate.

What is meant by this? Use an example from Table 1 to illustrate your answer.

A scientist investigated changes in the amino acid sequence of a human enzyme resulting from mutations. All these amino acid changes result from single base substitution mutations. This enzyme is a polypeptide 465 amino acids long.

Table 2 shows the result of three of the base substitutions.

What is the minimum number of bases in the gene coding for this polypeptide?

A change from Glu to Lys at amino acid 300 had no effect on the rate of reaction catalysed by the enzyme. The same change at amino acid 279 significantly reduced the rate of reaction catalysed by the enzyme.

Use all the information and your knowledge of protein structure to suggest reasons for the differences between the effects of these two changes.

Give the two types of molecule from which a ribosome is made.

Describe the role of a ribosome in the production of a polypeptide. Do not include transcription in your answer.

Table 1 shows the base sequence of part of a pre-mRNA molecule from a eukaryotic cell.

Complete the table with the base sequence of the DNA strand from which this pre-mRNA was transcribed.

In a eukaryotic cell, the base sequence of the mRNA might be different from the sequence of the pre-mRNA.

Explain why.