Telomeres and telomerase in tumour cells

Telomeres are seqnences of six-nucleotide repeats found at the ends of the chromosomal DNA strands. Many thon-sands of repeat nnits (TTAGGG) may be present at the end of the 3 strand and (AATCCC) at the end of the 5 strand. These are present at the ends of the strands to overcome a problem posed by the semi-conservative mechanism of DNA replication, known as the end replication problem . Replication of the ends of the chromosomes presents par-ticnlar difficnlties, since DNA polymerase can only elon- 

Benign tnmonrs are nsnally only a problem when they impair the fnnction of organs or canse metabolic stress. They can be removed by snrgery or radiation therapy. Malignant tnmonrs are mnch more of a problem, since the cells can escape from the primary tnmonr to other sites in the body, where they settle and develop into secondary tumours (metastases). Then, chemotherapy is the only treatment available. The process is known as metastasis. 

As the primary tumour enlarges, fuels and oxygen become limiting for further growth. Consequently, for growth to continue, the blood supply must expand. At least two proteins are secreted by tumour cells that stimulate angio- 

Intense research has revealed much about the molecular mechanisms involved in tumour development but much less is known about the metabolic changes in cancer. Nonetheless, most deaths from cancer are caused not directly by the tumour but by infections due to an immune system that has been impaired by metabolic disturbances in the whole 

An involuntary weight loss of more than 10% is a major risk factor for survival. This is due to a high rate of secretion of cytokines, especially from aggressive tumours. 

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