3.8 The Control Of Gene Expression Flashcards
What is inversion mutation?
A section of bases detach from the DNA sequence but rejoin inverted (back to front) = different as coded in this region
E.g TTC = CTT
What is translocation mutation?
A section of bases on one chromosome detached and attached onto a different chromosome which causes sig. alterations e.g to phenotype
What is duplication mutation?
Section of bases are duplicated in the DNA sequence
What is a stem cell?
Undifferentiated cells that can continually divide and become specialised into any cell type
What are totipotent stem cells?
•can divide and produce any type of body cell
•during development they only translate part of their DNA causing cell specialisation
•occur for limited time in early mammalian embryos
What are pluripotent stem cells? (Problems with its use in research?)
•can divide into most cell types
•found in embryo
•being used in research to treat disease
Issues:
•continually divide to create tumours
•ethically is it right to make a therapeutic clone and then destroy embryo?
What are multipotent stem cells?
•can differentiate into a limited no. of cells
•found in e.g bone marrow in adults
What are unipotent stem cells?
•can only differentiate into one type of cell e.g formation of cardiomyocytes
What is an induced pluripotent stem cell? (IPS) (advantages?)
A pluripotent stem cell produced from an adult somatic (body) cell that are unipotent by using appropriate protein transcription factors that will switch on the genes switched off to make the cell specialised
Ad:
•repair and replace damaged tissues
•less risk of rejection
•don’t have to destroy embryos= unethical
How are plant stem cells different?
•plants retain many totipotent cells
•this allows for tissue cultures = cloned plants can form from a few cells
•meristems in the tip of roots/shoots
What is a transcription factor?
Molecules that can move from the cytoplasm to the DNA and bind to a specific gene (promoter region), leading to or blocking mRNA production (activate or inhibit RNA polymerase)
What is the control of transcription?
•transcription factor protein will bind to the promoter region (from cytoplasm to DNA) which will stimulate RNA polymerase to transcribe the gene (form mRNA)
•when a gene is not being expressed,site in the transcription factor that binds to DNA is blocked by an inhibitor which prevents transcription
What is the role of oestrogen in initiating transcription?
1.oestrogen diffuses through the cell membrane (lipid soluble)
2.oestrogen diffuses through the nuclear membrane
3.oestrogen attaches to oestrogen receptors (ERalpha) which was initially inhibited as part of a protein complex and activates ERalpha
4.ERalpha changes shape (complementary) and leaves the protein complex to bind to the promoter region of DNA and RNA polymerase is activated which will begin transcription of a gene
What is meant by epigenetics?
heritable change in the gene function without changing the DNA base sequence = can be caused by changes in the environment and can inhibit transcription
What is methylation of DNA?
methyl groups are attached to DNA which will cause chromatin structure to be very tightly coiled so transcriptional factors cannot bind and transcription will be inhibited
What is acetylation of histones?
acetyl groups binds to histones which causes DNA chromatin structure to be more loosely packed so transcriptional factors can bind to DNA
How can abnormal methylation lead to cancer?
•tumour suppressor genes could become hypermethylated (more methyl groups added to DNA) so transcription of this gene is inhibited (these genes won’t produce the proteins that slow cell division/cell death during DNA copying error)
•oncogenes could be hypomethylated (less methyl groups) so gene is permanently switched on (continual triggering of mitosis)
What occurs during RNA interference?
•
•RNA dependent RNA polymerases (RDRs) catalyse formation of double stranded RNA (dsRNA)
•dsRNA is hydrolysed to siRNA which will form a protein complex
•this protein complex will bind to mRNA via complementary base pairing
•mRNA will be cut up into pieces so it cannot be translated to make the gene product
What is a benign tumour?
•grow large but slow rate
•produce adhesion molecules so stick together and to specific tissues (localised)
•often in capsule so compact and easy removal
What is a malignant tumour?
•cancerous and grow large rapidly/cell can become unspecialised again
•metastasis can occur= tumour can break off and spread to form secondary tumours
•can grow projections and develop own blood supply
How can mutation in proto-oncogenes cause cancer?
•oncogenes (mutated) can form protein that is involved in initiation of DNA replication
•mutation can result in process permanently activated to make cells divide continually
How can mutation in tumour suppressor gene cause cancer?
•tumour suppressor genes produce proteins that slow down cell division and cause cell death if DNA copying error
•mutation will prevent protein production so cell division continues/mutated cells not destroyed
How can increased oestrogen concentration cause cancer?
•oestrogen can activate gene by initiating transcription = could permanently turn proto-oncogene on and activate continual cell division
•excess of oestrogen in breast tissue after menopause causing tumour growth
What is occurring in the methods used to sequence genomes?
•continually being improved
•now automated