2017_Molecular-Techniques_STQ_MS

2017 Molecular Techniques STQ MS2017 / H2 / AJC PRELIM / P2 Q21Recently, scientists discovered the presence of a population of bone-marrow derived stem cells that have the ability to form heart muscles cells when transferred to the heart. The stem cells were removed from the bone marrow and cultured so that they divided by mitosis. It was proposed that these stem cells resembled embryonic stem cells. (a)(i)Describe two similarities between these bone-marrow derived stem cells and embryonic stem cells.Unspecialised cell with no specific structure and function; Ability to self-renew via mitosis Ability to differentiate into specialised cell types under suitable conditionsExhibit pluripotency: ability to differentiate into almost any cell types except cell of extra-embryonic membranal cells[2](ii)Describe how the rate of mitosis is controlled. External growth factors serve as ligands that bind to receptors of cell surface membrane;fully- activated receptor activates relay protein which activates a series protein kinases in the phosphorylation cascade;Cellular response is the switching on genes that code for transcription factors which will bind to promoter of cyclin genes/ genes that promote or slow down cell cycle;Increase transcription and translation of proteins that promote or slow down cell division/ M,S, G1 cyclins/CDKs which control checkpoints in cell cycle;G1 checkpoint checks that cell size is adequate/ There is sufficient nutrients are available to support daughter cells/ Growth factors (Extracellular signal proteins that stimulate a cell to grow or divide) are present.G2 checkpoint checks that cell size is adequate/ DNA replication is complete and successful/ there is no DNA damage.Metaphase (M) checkpoint checks that chromosomes are under bipolar tension (in other words, properly attached to kinetochore microtubules originating from the two different poles of the cell)/ chromosomes are aligned at the metaphase plate.Cell cycle checkpoints prevent premature progression of the cell cycle/ E.g. prevent the segregation of chromosomes before DNA replication is completed.Provides time for cell machinery to be repaired should there be any damage/ E.g. To repair incorrectly replicated DNA sequence.Tumour suppressor genes code for proteins that preventing the stimulating activity of cellular proto-oncogenes or oncogenes/ activating DNA repairing genes /activating apoptosis (programmed cell death), preventing uncontrolled cell division. [4](iii)State an advantage of using bone marrow derived stem cells rather than heart stem cells for the treatment of heart diseases.Idea of bone marrow stem cells are easier to isolate / extract by direct aspiration from the bone marrow in the spinal cord ORIdea of isolation/ extraction of bone marrow stem cells are less less risky/ may puncture major blood vessels in removing heart stem cells. [1](c)Troponin is a protein that is integral to muscle contraction in heart muscles. Fig. 2.1 shows p