DNA & the genome

Describe how a quaternary protein is formed from its monomers.

Do not include the process of translation in your answer.

Describe the structure of DNA and the structure of a chromosome.

Mutation can result in an increase in genetic variation within a species.

Describe and explain the other processes that result in increases in genetic variation within a species.

Describe how a sample of chloroplasts could be isolated from leaves.

Scientists grew two groups of plants:

control plants with all the inorganic ions needed

iron-deficient plants with all the inorganic ions needed but without iron ions.

After 1 week, the scientists measured the mass of protein and the mass of chlorophyll in the chloroplasts isolated from samples of leaves of these two groups of plants.

Table 4 shows the scientists’ results.

Some proteins found inside the chloroplast are synthesised inside the chloroplast.

Give one feature of the chloroplast that allows protein to be synthesised inside the chloroplast and describe one difference between this feature in the chloroplast and similar features in the rest of the cell.

Structural difference

The ratio of protein to chlorophyll in control plants is 9:1

Use the information in Table 4 to calculate the ratio of protein to chlorophyll in iron-deficient plants.

The scientists also observed the chloroplasts from the samples of leaves using an electron microscope.

Figure 6 shows a chloroplast from a control plant (image A) and a chloroplast from an iron-deficient plant (image B).

Figure 6

This source has been removed due to third-party copyright restrictions.

Use Figure 6 to suggest why iron-deficient plants have a reduced growth rate.

Complete Table 2 to show three differences between DNA in the nucleus of a plant cell and DNA in a prokaryotic cell.

Scientists investigated the genetic diversity between several species of sweet potato. They studied non-coding multiple repeats of base sequences.

Define ‘non-coding base sequences’ and describe where the non-coding multiple repeats are positioned in the genome.

The percentage similarities in the non-coding multiple repeats of base sequences of four species of sweet potato are shown in Table 3.

Use the information in Table 3 to complete the phylogenetic tree shown in Figure 8.

Write the letter that represents the correct species into each box.

The scientists studied five individuals from each species. Within the five individuals of species T they found a percentage similarity of 66%.

Use Table 3 to evaluate how this information affects the validity of the phylogenetic tree.

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.

Give two pieces of evidence from Figure 1 that this cell was undergoing mitosis. Explain your answers.

When preparing the cells for observation the scientist placed them in a solution that had a slightly higher (less negative) water potential than the cytoplasm. This did not cause the cells to burst but moved the chromosomes further apart in order to reduce the overlapping of the chromosomes when observed with an optical microscope.

Suggest how this procedure moved the chromosomes apart.

The dark stain used on the chromosomes binds more to some areas of the chromosomes than others, giving the chromosomes a striped appearance.

Suggest one way the structure of the chromosome could differ along its length to result in the stain binding more in some areas.

In Figure 2 the chromosomes are arranged in homologous pairs. What is a homologous pair of chromosomes?

Give two ways in which the arrangement of prokaryotic DNA is different from the arrangement of the human DNA in Figure 1.

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.

In women, the first division of meiosis produces one daughter cell that has almost all of the cytoplasm. The other daughter cell consists of a nucleus surrounded by a very small amount of cytoplasm and a cell-surface membrane. This very small daughter cell is called a polar body. Polar bodies do not usually divide. The same process occurs in the second division of meiosis, resulting in one egg cell and two polar bodies.

The diagram in Figure 3 shows the formation of an egg cell and two polar bodies during meiosis. It also shows what happens to one pair of homologous chromosomes. This pair carries two alleles of gene A.

Complete Figure 3 by putting A or a in the boxes. One box has been completed for you with A.

combination of alleles on the chromosome in the first polar body in Figure 3.

A scientist measured the diameter of a polar body and the diameter of the nucleus inside it. The diameter of the polar body was 10.4 µm and the diameter of the nucleus was 7.0 µm. The density of mitochondria in the cytoplasm of the polar body (outside of the nucleus) was 0.08 mitochondria per µm³.

Calculate the number of mitochondria in the polar body. You should assume polar bodies and nuclei are spherical.

The formula for the volume of a sphere is πr³ where π = 3.14

Show your working.

Mitochondrial diseases are caused by faulty mitochondria. All of a person’s mitochondria are inherited from their mother via the egg cell. An egg cell contains

One proposed treatment to prevent passing on faulty mitochondria involves

• removing the nucleus from an egg cell donated by a woman with healthy mitochondria

• replacing this nucleus with the contents of the polar body from a woman whose egg cells are affected by mitochondrial disease.

Suggest how this treatment prevents inheritance of mitochondrial diseases.

If most of the mitochondria in a cell are faulty, this prevents many important enzyme-catalysed reactions taking place or slows them down.

Suggest and explain one reason why.

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