Topic 8 - Control of Gene Expression

AQA GCE A-Level Biology - Topic 8 - Control of Gene Expression

[3.8.1] What is a mutation?

A spontaneous change in the base sequence.

[3.8.1] What is a substitution mutation?

A base is replaced by another.

[3.8.1] What is a deletion mutation?

A base is deleted from the base sequence, resulting in a frame shift.

[3.8.1] What is an addition mutation?

A base is added to the base sequence.

[3.8.1] What is a duplication mutation?

One or more bases are repeated.

[3.8.1] What is an inversion mutation?

A sequence of bases is reversed.

[3.8.1] What is a translocation mutation?

A sequence of bases is moved from one location in the genome to another. It could be movement within a chromosome, or movement to another chromosome.

[3.8.1] How can a mutagenic agent acting as a base increase the rate of mutation?

Base analogs can substitute for a base during DNA replication, changing the base sequence in the new DNA.

• For example, 5-bromouracil can substitute for thymine.

[3.8.1] How can a mutagenic agent altering bases increase the rate of mutation?

Some chemicals can delete or alter bases.

• For example, alkylating agents can add an alkyl group to guanine so that it pairs with thymine.

[3.8.1] How can a mutagenic agent changing the structure of DNA increase the rate of mutation?

Some radiation can change the structure of DNA.

• For example, UV radiation can cause adjacent thymine bases to pair up.

[3.8.2.1] What are stem cells?

Unspecialised cells that can develop into other types of cell.

[3.8.2.1] What are totipotent cells?

Cells which can mature into any type of body cells.

[3.8.2.1] During development, totipotent cells only translate part of their DNA. What is the result of this?

Cell specialisation.

[3.8.2.1] What are pluripotent cells?

Cells that can differentiate into any body cell except placental cells. They are found in the bone marrow.

[3.8.2.1] What are multipotent cells?

Cells that can differentiate into a few types of cell.

[3.8.2.1] What are unipotent cells?

Cells that can differentiate into one type of cell.

[3.8.2.1] What are cardiomyocytes?

Heart muscle cells that make up tissue in the heart, derived from unipotent stem cells. These typically are able to replace old or damaged cardiomyocytes.

[3.8.2.1] How can clones be produced from plants?

• A plant tissue culture is taken, placed in a culture medium.

• Calluses can be cultured to form plantlets which will be planted in the soil.

  • As such, thousands of genetically identical plants (clones) are created.

[3.8.2.1] What are embryonic stem cells?

Totipotent cells which exist for the first few weeks after fertilisation.

[3.8.2.1] What are adult stem cells?

Multipotent cells that exist in the bone marrow.

[3.8.2.1] What are induced pluripotent (iPS) stem cells?

Specialised adult body cells that are ‘reprogrammed’ to become pluripotent.

• They are made to express a series of transcription factors that are normally associated with pluripotent stem cells, causing them to express the genes linked to it.

  • It is often introduced by infection with a GMO virus.

[3.8.2.1] What are the ethical issues surrounding embryonic stem cells?

• Some people believe it is wrong to destroy embryos as life begins at fertilisation.

• Some people have less objections around stem cells obtained from unfertilised egg cells but many people believe that only adult stem cells should be used.

[3.8.2.1] What are the benefits of stem cell treatments?