Question

2. Describe the experimental protocol used by Weinberg and colleagues in their 1979 landmark paper "Passage of phenotypes of chemically transformed cells by transfection of DNA and Chromatin". Define the terms shown in bold and describe how the cells were "chemically transformed". Why was this paper so important considering the recent work at the time) on tumor viruses? Also, briefly describe the importance of subsequent experiments using transfection of human tumor cell DNA 3. A requisite characteristic for many identified oncogenes is that they are constitutively expressed/activated. Define this term and identify two mechanisms by which oncogenes may be constitutively activated (hint: may be by either structural changes (translocation/point mutation) or regulatory changes (proviral integration, gene amplification)]. In your answer. describe how one of these changes impacted the mye oncogene. Finally, name two general classes of proteins that oncogenes encode that allow them to be tumorigenic.

Answer 1

Ans 2

Transformation is the genetic alteration of a cell resulting from the direct uptake and incorporation of exogenous DNA from its surroundings through the cell membrane.

Many method for transformation of cells (1) biological (2) chemically (3) physical transformation

In biological transformation it's based on virus which use as a vector to induce DNA, physical method like electroporation, microinjection etc

Chemical transformation method based on calcium phosphate based , liposome based in this liposome based method DNA present inside lipid layered vesicles and it hydrophobic in nature so it will bind to plasmamembrane of cells and DNA goes inside the cells.

Transfection is very important in genetic engineering

Transformation of human tumor cell DNA used to make cell lines (immortal cells) which is immortal in nature means cells live after infinite cell division. Normal cells is mortal it die after some cell division becouse of loosing telomere , but in tumor cell telomerase activity present which protect telomere shortening.

Immortal cells or transformed cells by tumor DNA use for production of many biological products eg. Hormones, recombinant proteins, enzymes etc. And it live after so many passage of cell line. So it's very important research now a days to make transformed cells using tumor DNA eg. Vero cell line is transformed cell line and most frequently use in animal biotechnology

Ans 3.

Constitutively active gene means gene transcription and translation are always on.

Oncogenes: expert positive effect of cell growth when activated by mutation or amplification to a hyper functioning form.

This Oncogenes may be structural genes or regulatory genes

Structural gene converted to Oncogenes by mutation and also inherited and regulatory gene converted to Oncogenes by amplification of gene, inhibition of transcription of gene, and duplication, inversion and also viral infection may cause change in regulatory gene

Transposomal elements also play important role in cancer

Myc is a family of regulator genes ( regulatory gene)  and oncogenes that code for transcription factors. The Myc family consists of three related human genes: c-myc, l-myc, and n-myc.

The transcription factor c-Myc strongly stimulates cell proliferation but also regulates apoptosis, senescence, cell competition and cell differentiation, and its elevated activity is a hallmark for human tumorigenesis.

Oncogenic protein : p53, ras GTPase

p53 gene , also known as TP53 or tumor protein is a gene that codes for a protein that regulates the cell cycle and hence functions as a tumor suppression. It is very important for cells in multicellular organisms to suppress cancer.

If any mutation present in p53 gene sequence it lead to activate cell growth and loose it's tumor suppressor activity

Ras is a family of related proteins which is expressed in all animal cell lineages and organs. All Ras protein family members belong to a class of protein called small GTPase, and are involved in transmitting signals within cells (cellular signal transduction). Ras is the prototypical member of the Ras superfamily of proteins. RAS gene family A family of genes that make proteins involved in cell signaling pathways that control cell growth and cell death. Mutated (changed) forms of the RAS gene may be found in some types of cancer. These changes may cause cancer cells to grow and spread in the body.

So any type of mutation in RAS gene it lead to cause cancer becouse cell cycle irregulation in absence of RAS protein or mutated RAS protein and lead to cell growth and tumor

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