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考博英语试题答题练习:obesityandCancer

发表时间:2015/5/7 10:23:03 来源:互联网 点击关注微信:关注中大网校微信

OVERWEIGHT women are more likely to develop breast cancer than lean ones.Why has been a mystery.

But it is now less mysterious thanks to the work of Kevin Gardner, a researcher at America'sNational Cancer Institute in Bethesda, Maryland.

Dr Gardner and his colleagues have found that processing calories affects the activity ofBRCA1, a gene that encodes a well-known tumour-suppression protein.

Mutations of this gene are strongpredictors of breast and ovarian cancer―so strong that the gene's DNA sequence is thesubject of litigation in America about whether natural gene sequences can be patented, andthus the market in tests for these mutations cornered.

Dr Gardner's discovery is that a substance called C-terminal binding protein helpsregulate BRCA1.

Since the activity of CtBP is, itself, governed by the processing of calorie-rich molecules,the more of those molecules the body processes, the more at risk of cancer it becomes.

Previous work has shown that CtBP senses the amount of energy in a cell by binding to asmall molecule called NADH.

This chemical is a by-product of metabolism, and cells that are processing an excessiveamount of energy for storage have a superabundance of it compared with the amount of arelated molecule called NAD+.

As the ratio of NAD+ to NADH falls, CtBP combines with NADH.

This changes CtBP's shape and enables it to form complexes with several other proteins.

These complexes control the activity of DNA by shutting off certain genes.

Dr Gardner and his team report in the latest issue of Nature Structural & MolecularBiology that one of the genes so controlled is BRCA1.

The protein encoded by BRCA1 is involved in DNA repair.

Cells that lack a working version of it gradually accumulate genetic changes.

Though most of these changes either have little impact or will lead to the cell's death, somemay promote the formation or progression of tumours.

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