Protein synthesis

The sequence of bases on one strand of a section of DNA is

TAC CGT AAT TAT

Which of these is the complementary sequence of DNA on the other strand of the double helix?

Which of these is the correct summary of the processes occurring during protein synthesis?

The table shows different mRNA codons for some amino acids.

UUU-AUG-UGU is one combination of codons that codes for the sequence of amino acids W–X–Y.

Give the number of other combinations that code for the same amino acid sequence.

Explain why most genetic mutations have no effect on the phenotype of an organism.

Use the information in the table and your own knowledge in your answer.

State one way that the incidence of mutations can be increased.

Cells use genetic information when carrying out protein synthesis.

Give the difference between a gene and a genome.

Describe the process of transcription.

Explain why a change in the sequence of bases in the DNA does not always result in a change in enzyme function.

Some characteristics are determined only by the genes, and some are determined by a combination of the genes and the environment.

Give an example of each type of characteristic in humans.

determined only by the genes

determined by the genes and the environment

Mutation can cause changes in the enzymes produced during protein synthesis.

State what is meant by the term mutation.

Explain the different effects that a single base mutation can have on transcription and translation and the production and activity of an enzyme.

Scientists investigate the rate of spontaneous mutations in yeast. They record the number of mutations per cell during mitosis and during meiosis. They count the mutations in three different strains of yeast and repeat each count. The mutation rates are counted per division per cell.

Calculate the mean mutation rate for strain 5207 during meiosis.

mean rate =_........ × 10⁸ per division per cell

Suggest why the mutation is calculated per division per cell rather than just per cell.

Comment on the differences in rates of mutation for mitosis and meiosis in the different yeast strains.

Diagram 1 shows part of a DNA molecule.

Strand 1 G G C T A G T T G

Complete Diagram 1 by writing the letters of the missing bases in the empty boxes for strand 2.

Give the maximum number of amino acids that are coded for by this DNA strand (strand 2).

The original DNA strand is used to produce mRNA.

Complete the empty boxes in Diagram 2 to show the mRNA coded for by this DNA strand.

DNA G G C T A G T T G

A length of DNA consists of 25 000 base pairs.

This makes a total of 50 000 bases.

In this length of DNA, 30% of the bases are adenine (A).

Determine the number of thymine (T) bases, cytosine (C) bases, and guanine (G) bases in this length of DNA.

Describe the differences between the process of transcription and the process of translation.

The diagram shows part of a molecule of DNA.

State what is meant by the term genome.

Describe the differences between the structure of DNA and the structure of RNA.

Describe the roles of RNA in protein synthesis.

Rabies is a dangerous disease caused by a virus.

The rabies virus is a pathogen.

Which other groups of microorganisms include pathogens?

Rabies is transmitted to humans when they are bitten by an infected animal. Domestic dogs are dogs kept by people as pets or as working animals. Dogs and some wild animals are known to transfer rabies to humans.

In the 1940s, a rabies vaccine for animals was introduced in the United States and most domestic dogs were vaccinated.

The graph shows the number of cases of human rabies and domestic dog rabies in the United States from 1938 to 2018.

Number of domestic
Number of dog cases
human cases

The immune system of dogs works in a similar way to the immune system of humans.

Explain how the rabies vaccine prevents dogs from developing rabies.

Discuss the effects of the use of the rabies vaccine to immunise domestic dogs on the number of cases of rabies in humans.

Use information from the graph to support your answer.

A new RNA vaccine is being developed to treat rabies.

RNA that codes for parts of the rabies virus protein coat are injected into the body. Cells then take up the RNA and produce the viral proteins.

Describe how the cells use the RNA to produce the viral proteins.

Beta thalassaemia is a genetic condition caused by a mutation in a gene for haemoglobin. People with beta thalassaemia produce less haemoglobin and fewer red blood cells than people without the condition.

Explain why people with beta thalassaemia may experience severe tiredness.

A new treatment for beta thalassaemia has been developed that edits the haemoglobin gene. These are the steps in the treatment.

• remove blood stem cells from a patient’s bone marrow

• put a strand of RNA and an enzyme into the blood stem cells to correct the haemoglobin gene

• use drugs to destroy the patient’s remaining bone marrow cells

• replace the patient’s bone marrow cells with the modified stem cells

The modified stem cells that are in the bone marrow now produce red blood cells containing sufficient haemoglobin.

The strand of RNA used in this treatment is complementary to one strand of the DNA in the haemoglobin gene.

Give the base sequence of RNA that is complementary to this sequence of DNA.

DNA strand A A T G G C G G C T C A

Protein synthesis of the modified gene will produce haemoglobin.

Describe the stages of this protein synthesis.

The standard treatment for beta thalassaemia is a weekly blood transfusion.

The new treatment has so far been tested on two patients, with these results.

• both patients started making large numbers of red blood cells with sufficient haemoglobin

• both patients experienced serious side effects from the drugs used, needing to spend several months in isolation in hospital before recovering

• 15 months after the treatment, neither patient required further blood transfusions

• both patients were able to exercise normally without feeling tired

Evaluate the use of the new treatment compared to weekly blood transfusions.

6 (a) The diagram shows one strand of DNA from a section of a gene. ATTCCGAGT What would be the complementary sequence of bases on the messenger RNA produced from this strand of DNA?

The diagram shows a stage during protein synthesis.

Which row gives the correct names for the stage of protein synthesis shown and the sequence of bases labelled X?

Explain how a mutation in a gene can affect the phenotype of an organism.

In an accident at a nuclear power station, radioactive material was released into the surrounding areas of land. Scientists investigated the impact of this on a species of butterfly.

Samples of adult butterflies were collected from an area near the power station two months after the release of the radioactive material. The percentages of butterflies with abnormalities were calculated. The butterflies were then mated in the laboratory and the percentage of offspring with abnormalities calculated. The experiment was repeated with butterflies collected from the same area, 10 months after the release of the radioactive material.

Describe how the scientists could have sampled the population of butterflies in the area.

The results of the investigation are shown in the table.

The scientists concluded that the increased level of radioactivity has led to an increased rate of mutation of DNA. Discuss the scientists’ conclusion referring to data from the table to support your answer.

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow.

Haemolytic disease

Haemolysis is the term used to describe the bursting of red blood cells. Haemolytic disease occurs when the red blood cells burst in the body of a foetus in a pregnant woman. The bursting of the red blood cells affects the development of the foetus into a baby.

The red blood cells burst when certain antibodies from the mother pass across the placenta. The antibodies attach to protein molecules called antigens. These antigens are on the surface of the foetal red blood cells. The protein antigen is called the rhesus factor and is made using the genetic code found on the dominant allele, D, during the production of red blood cells in bone marrow.

Homozygous dominant and heterozygous individuals have cells with the antigen. These individuals have the rhesus positive blood group. Homozygous recessive individuals have cells that do not have the antigen. These individuals have the rhesus negative blood group.

During the birth of a rhesus positive baby, some red blood cells may leak into the circulatory system of the mother. This happens as the placenta pulls away from the wall of the uterus. A rhesus negative mother will make antibodies that destroy rhesus positive red blood cells. This is not a problem for the child that has just been born. However, if the mother becomes pregnant again with another rhesus positive foetus, the antibodies will harm the foetus.

Haemolytic disease can be avoided by treating a rhesus negative woman at risk of having a second rhesus positive child. This treatment involves the mother having an injection during and after pregnancy. The injection destroys rhesus positive cells in the mother's blood before the cells can cause an immune response.

If the foetus is rhesus positive, the pregnancy is carefully monitored for signs of haemolytic disease. Monitoring includes regular ultrasound scans of the foetus and measuring the amount of antibody in the mother's blood. A change in the concentration of the antibody in the mother’s blood, due to her secondary immune response, can lead to dangerous haemolysis. If a foetal blood test confirms a low number of red blood cells, a blood transfusion can be done in utero to replace the burst foetal red blood cells.

Explain why bursting of red blood cells affects the development of a foetus (lines 3 and 4).

The dominant allele codes for the production of the protein that will act as an antigen.

Describe how the dominant allele leads to the production of RNA during protein synthesis (lines 7 to 9).

Give the reason why proteins cannot be made by red blood cells (lines 7 to 9).

Give one piece of evidence from the passage that shows that antibodies are smaller than red blood cells.

A mother who is homozygous recessive for the rhesus factor has a child with a father who is heterozygous.

Give the genotypes of the mother, the father, their gametes and the possible genotypes of the child.

Give the probability that the child will be rhesus positive.

Explain why the concentration of the rhesus antibody in the mother's blood rises quickly to harmful levels if she has a second child who is Rhesus positive (lines 16 to 19).

Suggest what is meant by the term in utero (line 30).

A foetus with haemolytic disease can be given a blood transfusion.

Suggest the blood group of the source of the cells used for this transfusion (lines 29 and 30).

A DNA strand has this sequence of bases.

C A T T C A A T T C A T T T C

How many amino acids does this sequence of bases code for?

Write down the complementary mRNA code for this sequence of bases.

A student reads that DNA codons are non-overlapping.

Suggest what is meant by the term non-overlapping.

You should refer to the sequence of bases in your answer.

Describe what happens in the translation stage of protein synthesis.

State what is meant by the genome of an organism.

A scientist investigates the effect of growth hormone (GH) on the body mass of rats.

This is his method.

● give one rat a GH solution every day for 500 days

● give another rat a control solution every day for 500 days

● measure the mass of each rat each week for 500 days

The graph shows his results.

Suggest how the control solution differs from the GH solution.

Calculate the average rate of growth of the rat given GH solution from 100 days to 500 days.

Give your answer in g per day.

rate of growth =_........ g per day

The scientist controlled all the variables in his investigation.

Suggest two abiotic variables he controls.

The scientist repeats his investigation using more rats.

Explain why using more rats improves his investigation.

GH increases transcription in cells.

Explain why this affects the growth of rats.

DNA and RNA are involved in the processes of transcription and translation.

State three ways in which the structure of a DNA molecule differs from the structure of an RNA molecule.

Describe the differences between the processes of transcription and translation.

The DNA molecule codes for the amino acids used to make proteins.

There are four different bases in DNA and 20 amino acids used to make proteins.

Use this information to show that a minimum of three bases on the DNA molecule is needed to code for each amino acid.

The molecules RNA and DNA are both involved in inheritance and protein synthesis.

Give two differences between the structure of a DNA molecule and the structure of an RNA molecule.

This sequence shows the order of bases on a DNA strand.

CATCATCCTCATCTA

Give the sequence of bases in the mRNA that would be produced from this strand.

The sequence of bases in the mRNA is used to code for the amino acids in a protein.

Calculate the number of bases required to code for an amino acid chain of 1400 amino acids.

A mutation results in a change in the sequence of bases in a DNA strand.

Discuss what effect a change in the sequence of bases could have on the functioning of the enzyme produced.

Give one way that the incidence of mutation could be increased.