Gene Expression Flashcards
Topic 8 revision
What is a stem cell?
Undifferentiated cells, that can divide indefinitely and turn into other specific cell types
Name & define three types of stem cells
- Totipotent= can develop into any cell type including placenta & embryo
- Pluripotent= can develop into any cell type excluding the placenta & embryo
- Multipotent= can develop into a few different types of cell
What happens to totipotent cells during embryonic development?
Certain parts of DNA are selectively translated so that only some genes are ‘switched on’, in order to differentiate the cell into a specific type & form tissue that make up foetus
Give a unique feature of pluripotent cells & use of this feature
Can divide in unlimited no. & so can be used to repair or replace damaged tissues
What is a unipotent cell? (give example)
Cell that can only develop into 1 type of cell. This happens at end of spescialisation when cell can only propagate its own type.
(e.g. cardiomyocytes - heart cells)
Uses of stem cells
Medical therapies (e.g. bone marrow transplant, treating blood disorders)
Drug testing on artificially grown tissue
Research (e.g. on formation of organs & embryos)
How are induced pluripotent stem cells produced?
From mature, fully specialised (somatic) cells. Cell regains capacity to differentiate through use of proteins, especially transcription factors.
What is a transcription factor?
Protein that controls transcription of genes so that only certain parts of DNA are expressed (e.g. to allow a cell to specialise)
How do transcription factors work?
- Move from cytoplasm into nucleus.
- Bind to promoter region upstream of target gene.
- Makes it easier or more difficult for RNA polymerase to bind to gene. This increases or decreases rate of transcription.
Give example of hormone that affects transcription & explain how it works
- Steroid hormone oestrogen diffuses through cell membrane
- Forms hormone-receptor complex with ER a receptor in cytoplasm
- Complex enters nucleus & acts as transcription factor to facilitate binding of RNA polymerase
Describe process of RNA interference, including organisms in which it occurs.
RNA molecules act to inhibit gene expression, usually by destroying mRNA so that it cannot be translated.
Occurs in eukaryotes & some prokaryotes.
Characteristics of benign tumours
- Slow growth
- Defined by clear boundary due to cell adhesion molecules.
- Cells retain function & normal shape.
- Don’t spread easily
- Easy to treat
Characteristics of malignant tumours
- Rapid, uncontrollable growth.
- Ill-defined boundary
- Cells do not retain function & often die
- Spreads quickly & easily (metastasis)
- Difficult to treat
Role of tumour-suppressor genes
Code for proteins that control cell division; especially stopping cell cycle when damage is detected.
(Also involved in programming apoptosis i.e. ‘self-destruction’ of cells)
How can oestrogen be involved in developing breast cancer?
Oestrogen is an activator of RNA polymerase. So in areas of high oestrogen concentration, such as adipose tissue in breasts, cell division can become uncontrolled.
Epigenetics meaning
Heritable change in gene function without change to the base sequence of DNA
How does increased methylation of DNA affect gene transcription?
Involves addition of a CH3 group to cytosine bases which are next to guanine.
Prevents transcription factors from binding. Therefore gene transcription is suppressed.
How does decreased acetylation of DNA affect gene transcription?
Positively-charged histones bind to negatively-charged DNA. Decreasing acetylation in creases positive charge of histones. Binding becomes too tight and prevents transcription factors from accessing the DNA. Therefore gene transcription is suppressed.
Application of epigenetics
Treatment of various diseases.
Development of ways to reverse epigenetic changes.
Describe role of proto-oncogenes
Control cell division; in particular, code for proteins that stimulate cell division.
How can proto-oncogenes be involved in developing cancer
Mutation in the gene could turn it into permanently activated oncogene. Decreased methylation or increased acetylation can cause excess transcription.
Results in controlled cell division and formation of a tumour.
How can abnormal methylation of genes cause cancer?
Hyper-methylation of tumour-suppressor genes or oncogenes can impair their function and cause the cell to divide uncontrollably.
Explain how tumour-suppressor genes can be involved in developing cancer
Mutation in gene could code for non-functional protein. Increased methylation or decreased acetylation could prevent transcription
Cells will divide uncontrollably resulting in tumour
