Parkinson’s disease is one of the most common neurodegenerative disease worldwide, yet it has no cure.

Researchers are investigating whether stem cells can be used to replace nerve cells in patients diagnosed with Parkinson’s. 

Explain why researchers are obtaining these stem cells from the bone marrow. 

Stem cells can also be obtained from embryos. 

Name one other potential source of human stem cells. 

Embryonic stem cells are used in the development of an embryo.

Explain the role of these stem cells. 

Describe an ethical issue associated with the use of embryonic stem cells. 

In multicellular organisms, specialised cells become organised into tissues and organs. 

Explain the difference between muscle and muscular tissue. 

Adult stem cells are found in the bone marrow and are used to regenerate damaged tissues in the muscles.

Describe the features of adult stem cells that make them suitable for regenerating tissues in the muscles. 

Embryonic stem cells can be used in research to investigate the development of organisms.

Give three ways that research using embryonic stem cells has benefits for our understanding of biology. 

Severe combined immunodeficiency (SCID) is a group of disorders that affect the immunity of affected individuals.

Researchers are investigating whether stem cells from umbilical cords can be used to treat children with SCID. 

Give two features of stem cells. 

Suggest one reason why stem cells might be suitable to treat damage to the immune system in children with SCID. 

Steroid hormones, such as oestrogen, can influence the genome of a cell.

What is a genome?

In the cytoplasm, oestrogen binds to a specific androgen receptor.

Suggest and explain why oestrogen only binds to specific receptors.

The binding of oestrogen to an androgen receptor changes its shape, causing the oestrogen-receptor complex to enter the nucleus and stimulate gene expression.

Suggest how the oestrogen-receptor complex could stimulate gene expression.

Oestrogen can stimulate the growth of some types of breast tumour.

A drug known as tamoxifen can be used to treat these tumours.

In the liver, tamoxifen is converted into a substance known as endoxifen which has a similar shape to oestrogen.

Suggest how endoxifen may reduce the growth rate of breast tumours.

In eukaryotes, transcription of target genes can be stimulated or inhibited by the addition or removal of chemical groups.

Complete the table below by placing a tick to show whether each mechanism of action stimulates or inhibits the process of transcription.

Methyl groups bind to DNA to influence transcription.

Where do acetyl groups bind to?

Methyl and acetyl groups are described as epigenetic marks.

Describe what is meant by epigenetics.

Increased methylation of DNA can lead to the formation of tumours.

Explain how.

Tumours can be classified as either benign or malignant.

Describe one way in which benign tumours differ from malignant tumours.

Describe two ways both benign and malignant tumours may damage the body.

Mutations in tumour suppressor genes can cause cancer.

Explain how.

Research suggests that several cancers result from epigenetic changes.

Treatment with drugs may be able to reverse these epigenetic changes.

Suggest and explain how.

Small interfering RNA (siRNA) is involved in RNA interference (RNAi).

HIV particles have a specific protein on their surface that allows them to bind to receptors on human cells and invade them. This HIV protein can then be found on the surface of infected human cells.

siRNA can be used to inhibit expression of a specific HIV gene inside infected cells.

siRNA is attached to a carrier molecule that allows entry into infected human cells. One type of carrier involves a lipid molecule.

Suggest why combining siRNA with a lipid increases uptake of siRNA into cells.

Suggest and explain why siRNA only inhibits gene expression in cells infected with HIV.

The carrier molecule attached to siRNA may be able to prevent infection of cells by HIV on its own.

Suggest how.

Sickle cell anaemia is one of a group of inherited disorders known as sickle cell disease.

Patients with this disease have sickle-shaped red blood cells.

A single base substitution mutation causes sickle cell anaemia.

Explain how a single base substitution causes a change to the structure of a polypeptide.

Treatment for sickle cell disease can involve the use of stem cells.

Give two characteristic features of stem cells.

Scientists have investigated how different types of stem cell could be used to treat sickle cell disease.

Suggest one reason why embryonic pluripotent stem cells might be suitable to treat sickle cell disease.

Haematopoietic stem cell transplantation is a long-term treatment for those with sickle cell disease.

Treatment involves the patient receiving stem cells from the bone marrow of a donor without sickle cell disease.

Before treatment, any faulty bone marrow cells need to be destroyed.

Explain how this transplant is an effective treatment for sickle cell disease.

The diagram below shows how DNA methylation changes as an embryo develops from a zygote.

Embryo development involves totipotent, multipotent, and pluripotent stem cells.

Describe the differences between totipotent, multipotent, and pluripotent stem cells.

What is meant by the term DNA methylation?

Describe and explain the trend shown in the diagram above. 

Increased methylation of the promoter region of a tumour suppressor gene can cause a type of throat cancer.

This methylation is caused by an enzyme known as DNMT.

Research suggests that a chemical, called EGCG, is a competitive inhibitor of DNMT.

Suggest how EGCG allows expression of the tumour suppressor gene.

RNA produced from one gene can give rise to more than one type of protein.

The diagram below shows a part of this process.

Use the diagram above to explain how RNA from one gene can produce more than one type of protein.

Beta cells in the pancreas produce the protein insulin to control blood glucose concentration.

Transcription factors are involved in the activation of the insulin gene.

Explain how transcription factors activate this gene.

Explain why beta cells can produce insulin but other cells within the pancreas cannot.

The diagram below shows the mechanism of action for a transcription factor that increases transcription.

Name region A in the diagram above. 

Name enzyme B in the diagram above. 

Use the diagram above to explain how transcription factors can increase the rate of transcription.

Some transcription factors are activators, meaning they increase the rate of transcription.

Explain how a transcription factor may function as a repressor.

The diagram below shows how hormones and transcription factors can control transcription of a gene.

Name region X in the diagram above. 

Use the diagram above to describe how transcription can be controlled in eukaryotes.

Explain how gene expression can be regulated after the process of transcription.