Chapter 22 Flashcards
Stem cells
What can small interfering (siRNA) do?
Knockdown proteins
- experimental technique by which the expression of one or more of an organism’s genes are reduced
Explain the concept ‘epigenetic memory’
Epigenetic memory describes the mechanisms by which an epigenetic status (cell type specific modification of the chromatin) is maintained while cells proliferate
Provide at least two examples of molecular mechanisms involving histone and DNA modifications that contribute to epigenetic memory
- Maintenance of DNA methylation by DNA-methylases which methylate CpGs on the newly synthesized DNA strand at sites which are marked by methylation on the parent strand.
- A self-propagating histone modification (reader-writer-complex which spreads a particular histone modification) leads to manifestation of an epigenetic signal which gets diluted upon cell division but is then capable of being re-manifested
- Action of histone modifying enzymes directed to active sites via transcription factors, non-coding RNAs or remaining histone modifications to rebuild epigenetic signature of the parent cell
- Recycling of histone variants during cell division
List at least four different mechanisms by which transcription factors can be activated
- Changing the amount of transcription factor (e.g. gene expression, mRNA degradation or protein synthesis)
- Post-translational modification
- Ligand binding
- Dimerization with activator or dissociation from inhibitor
- Protein stabilization leading to less degradation
- Localization (e.g. release from a compartment such as membrane or nuclei translocation)
Provide a reason that two cell lines will not bind to the same site
The two different cell lines have common but also a variety of different transcription factors expressed
How do co-factors bind to enhancers?
Co-regulators cannot directly bind to DNA but need to be recruited by transcription factors.
How can a point mutation convert a proto-oncogene into an oncogene?
A point mutation may produce a hyperactive protein when the mutation occurs within a protein-coding sequence (e.g. constitutively active Ras).
How can a deletion convert a proto-oncogene into an oncogene?
A deletion may produce a receptor without the extracellular domain that is active independently of ligand binding. A gene amplification event can lead to extra gene copies and thereby overproduction of a cancer critical gene
How can a gene amplification event convert a proto-oncogene into an oncogene
In the presence of excessive stimulation of a mitogenic pathways, activated Arf sequester MDM2 preventing its interaction with p53. Stabilized p53 translocates to the nucleus and activates transcriptions of the gene encoding p21. This protein binds cyclin-dependent kinases and thereby block cell cycle progression
What is a proto-oncogene?
A normal gene which, when altered by mutation, becomes an oncogene that can contribute to cancer
Explain oncogene dependency and its use in cancer treatment
Although tumours are heterogeneous populations of cells, they are often clonal descendants of a single abnormal cell that initially experienced an advantageous change such as an oncogenenic mutation.
Once a cancer cell has undergone an oncogenic mutation, it will often undergo further mutations, epigenetic changes, and physiological adaptions.
Despite the complexity of acquired capabilities/hallmarks, the cells often remain dependent on the hyperactivity of the initial oncogene and thereby sensitive to drugs targeting this protein
Explain how β-catenin and gene transcription are inactive in the absence of a Wnt ligand
In the absence of a Wnt ligand, β-catenin interacts with the axin/APC degradation complex. Within this complex, β-catenin is target for ubiquitylation by the β-TrCP E3 ubiquitin ligase when phosphorylated by the CK1 and GSK3 kinases. Ubiquitylated β-catenin is then degraded by the proteasome. In the absence of β-catenin, the co-repressor Groucho binds LEF1/TCF and block transcription.
What can CRISPR/Cas9 be used for?
o The Crispr/Cas9 system can be used to make DNA double strand breaks at unique sites in the genome. This can be followed by insertion of a gene encoding a green fluorescent protein (GFP) next to a gene encoding a signalling protein of interest (by homologous recombination). This will lead to stable expression of a GFP-tagged signalling protein that can be followed by live-cell imaging.
What is characteristic of stem cells?
They can divide for the entire lifetime of an organism
Name the 4 major cell types in the epithelial tissue in the small intestine and briefly describe their function.
Absorptive cells – function in nutrients uptake.
Goblet cells – secrete mucus which lines the epithelium as a protective coat.
Paneth cells – part of the innate immunesystem, secrete proteins which kill bacteria.
Enteroendocrine cells – regulate the growth, proliferation and digestive activities of cells both in and outside the gut through secretion of peptide hormones.
