Gene expression - Mutations and cancer

What is a mutation?

A change in DNA sequence

What are the different type of mutations?

- Deleterious

- Addition

- Duplications

- Inversions

- Translocations

What are inversion and translocation mutations?

- Inversion - sequence of nucleotides are separated and then reattached in the reverse order (ATC|GTC → ATC|CTG)

- Translocations - A sequence of nucleotides break off and are then reattached at a different position on the chromosome or on a different chromosome altogether

What may mutations cause?

- Change in protein structures

- Change likelihood of certain cancers

- Cause genetic disorders

What is the gene that causes cystic fibrosis?

CTFR gene

What is a mutagen?

A chemical or physical agent that increases the rate of mutation in DNA

Give examples of mutagens.

- UV radiation

- Ionising radiation

- Deaminating agents

- Alkylating agents

Explain how UV radiation acts as a mutagen.

It causes errors in DNA replication

Explain how ionising radiation acts as a mutagen.

It can cause DNA to break. Errors can then be introduced when cells try to repair the DNA

Explain how deamiating agents act as mutagens.

They remove the amine (NH3) group from bases which leads to the conversion of cytosine to uracil

Explain how alkylating agents act as a mutagen.

They add methyl (CH3) groups to the phosphodiester backbone of DNA. This means guanine pairs with thymine rather than cytosine.

What is cancer?

Uncontrolled cell division that results in the formation of a tumour

What are acquired mutations?

Mutations that occur in adulthood

Where do acquired mutations usually take place and what do they result in?

They usually take place in genes responsible for cell division. This may lead to uncontrolled cell division/cancer

What is the definition of a tumour?

A group of abnormal cells that form lumps or growths

What are the two different types of tumour?

Benign and malignant

What are cancerous tumours?

They are tumours that grow very rapidly and are able to invade surrounding tissue (can metastasise)

How can cancer cells be distinguished from normal cells?

Cancer cells are darker in colour and more irregular in shape. They may also have different antigens on their surface.

What are the two types of gene that regulate cell division?

Tumour suppressor genes

Proto-oncogenes

What do tumour suppressor genes do?

They slow down cell division by creating proteins that limit the rate of cell division. They also tell cells when to die

What do proto-oncogenes do?

They create proteins which increase the rate of cell division

What can a mutation occurring in a tumour suppressor gene or a proto-oncogene result in?

Uncontrolled cell division which can result in a cancerous tumour

List factors that are thought to contribute to the growth of tumours.

- Abnormal methylation of DNA

- Increased exposure to oestrogen

Why can abnormal methylation of DNA contribute to the growth of tumours?

Methyl groups are important in the regulation of gene expression. Too much methylation or too little methylation of cancer related genes may lead to the growth of a tumour.

What cancer can increased exposure to oestrogen increase the risk of?

Breast cancer

Why can increased exposure to oestrogen contribute to the growth of tumours?

Oestrogen increases the rate of cell division in breast tissue which increases the risk of acquired mutations. Oestrogen may also introduce mutations into the DNA of cells in breast tissue

What are some general risk factors that can affect a persons chances of getting cancer?

Their genetics and environment/lifestyle

How can genetics influence chances of getting cancer?

Certain cancers are linked to specific alleles and inheriting thid allele increases the likelihood of getting this cancer

What is the gene that massively increases chance of developing breast cancer in women?

BRCA1

How does the environment affect chances of getting cancer?

Lifestyle choices such as smoking and alcohol consumption are strongly linked to cancer risk. Occupational hazards like exposure to radiation can also contribute to cancer risk

How can cancer be detected early?

Screening

What is a benefit of screening for cancer?

If a faulty gene is detected preventative steps such as a mastectomy for women with the BRCA1 allele can be performed to significantly reduce the risk of the cancer developing

How can cancer be treated currently?

Surgery

Chemotherapy

Radiotherapy

How can surgery be used to treat cancer?

Tumours can be physically cut out of the body

Briefly describe chemotherapy.

It is a drug treatment that uses powerful chemicals to kill fast growing cells in the body

What are some issues with chemotherapy?

There are severe side-effects such as nausea, vomiting, and constipation. This is because the treatment affects healthy cells as well as the cancerous cells

Briefly describe radiotherapy.

It is a treatment that uses high doses of radiation aimed at cancer cells to shrink tumours

What are some issues with radiotherapy?

There can be bad side-effects such as fatigue, hair loss and vomiting. This is because the treatment affects healthy cells as well as the cancerous cells

What are some developing methods that can be used to treat cancer in a better way than chemotherapy and radiotherapy?

Gene therapy

Specific that target cancer cells

How can gene therapy be used to treat cancer?

It seeks to replace defective alleles for a gene with working alleles