Gene expression Flashcards
Mutation definition
Change in the DNA base sequence
When in the cell cycle are mutations most likely to occur?
Interphase - DNA replication
Name 2 mutagens
- High energy radiation e.g. UV
- Chemicals e.g. asbestos
What are the 5 types of mutation?
- Deletion/addition
- Substitution
- Inversion
- Duplication
- Translocation
Translocation mutation definition
Sequence of bases moves from one location on the genome to another
What is a frame-shift mutation?
All triplet codes change from the point of mutation
What are the 3 types of substitution mutation?
- Mis-sense mutation: base change leads to a new amino acid produced
- Silent mutation: degenerate
- Nonsense: base change leads to a stop
How does a cell differentiate?
Certain genes for specific proteins are expressed
Stem cell definition
Unspecialised cell which can keep dividing and differentiate into specialised cells
What are the 4 types of stem cell?
- Totipotent - can divide and differentiate into ANY type of cell
- Pluripotent - MOST
- Multipotent - LIMITED
- Unipotent - ONE
When are the different stem cell types present in an organisms lifetime?
Totipotent: first 4 days of embryo
Pluripotent: after 4 days (embryo)
Multipotent: mature mammals
Unipotent: mature mammals
How can stem cells be used in the treatment of disease?
Can be transplanted to divide and differentiate into the cell type required
What are the advantages and disadvantages of adult stem cells?
Advantages: no ethical issues, less chance of rejection
Disadvantages: multipotent, difficult to isolate
What are the advantages and disadvantages of embryonic stem cells?
Advantages: Pluripotent, easy to isolate
Disadvantages: unethical?, high chance of rejection
What are induced pluripotent stem cells?
Normal cells which were removed and had factors added to them to make them pluripotent
What are the advantages of induced pluripotent stem cells?
• No ethical issues
• Can differentiate into most cell types
• Less chance of rejection
How do transcription factors cause transcription?
Proteins which bind to a promotor of a gene which stimulates RNA polymerase to transcribe the gene and produce mRNA
What are the 2 types of transcription factor?
- Activators - activate transcription
- Recessors - inhibit transcription
How does oestrogen act as a transcription factor?
Lipid so crosses phospholipid bilayer by diffusion and binds to complementary protein receptor in cytoplasm. Receptor-oestrogen complex binds to promotor which stimulates RNA polymerase etc.
How can oestrogen cause cancer?
Can cause breast cells to divide more so more likely that mutations occur when DNA replicates so can produce tumours
How does siRNA prevent translation?
- siRNA has specific complementary base sequence to target mRNA
- Binds to RISC protein which acts as an enzyme
- One of siRNA strands becomes single-stranded
- siRNA binds to mRNA molecule by complementary base pairing
- mRNA destroyed
- Can’t be used in translation
How is miRNA different to siRNA?
Not fully complementary to one mRNA so targets more than one type of mRNA
What is the difference between benign and malignant tumours?
Cells in benign tumours can’t metastasise whilst in malignant tumours they can
What do tumour suppressor genes do?
Code for proteins which prevent cell division
What do proto-oncogenes do?
Code for proteins which stimulate cell division
How can mutations of tumour suppressor genes cause cancer?
Changes DNA base sequence, amino acid sequence, tertiary structure which stops production of proteins which prevent cell division –> uncontrolled cell division
How can mutations of proto-oncogenes cause cancer?
Changes DNA base sequence changes amino acid sequence changes tertiary structure –> become oncogenes which produce more proteins which stimulate cell division –> uncontrolled cell division
Epigenetics definition
Heritable changes in gene function without a change in DNA base sequence
How does the methylation of DNA affect gene expression?
Methyl groups added to DNA so transcription factors can’t bind to promotor. RNA polymerase not activated so gene is not transcribed
How does acetylation of histone proteins affect gene expression?
Addition of acetyl groups makes chromatin less condensed so transcription factors can bind to the promotor. RNA polymerase is activated so gene is transcribed
The DNA of which cells needs to be methylated/acetylated in order for offspring to ‘inherit’ their parents environmental effects?
Gametes
How can the methylation of a tumour suppressor gene lead to cancer?
Methyl groups added to tumour suppressor gene so transcription factor can’t bind to the promotor so no transcription so no proteins which prevent cell division –> uncontrolled cell division
How can the demethylation of a proto-oncogene lead to cancer?
Methyl groups removed from proto-oncogene so transcription factor can bind to promotor so more transcription and more proteins which stimulate cell division –> uncontrolled cell division
