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Long-term smoking can damage the body ability to fight skin cancer

Posted by star on 2019-03-22 00:19:06

Smoking may weaken the body's immune response to melanoma, according to a study published in the journal Cancer Research. The scientists found that long-term smokers had a 40 percent lower survival rate than non-smokers with melanoma. Among 156 patients with the most genetic markers of immune cells, smokers were about 4.5 times less likely to survive cancer than never-smokers.
The researchers found the drop in survival was most pronounced among smokers in the group with the highest number of immune-cell markers, suggesting that smoking may have a direct effect on the rapid proliferation of cancer cells.
Scientists believe that smoking may have an effect on the body's immune system, altering its ability to fight skin cancer. Smokers can still boost the immune response to try to destroy melanoma, but it seems to be less effective than nonsmokers, and smokers are less likely to survive cancer. Therefore, people diagnosed with melanoma should be strongly advised to quit smoking.
Dr Julie sharp, director of health information at cancer research UK, said: "taken together, these results suggest that smoking may reduce the survival rate of melanoma patients, so it is particularly important for their health to stop smoking."

The structural basis for pre-and post-transfer editing has been elucidated for the bacterial IIe-tRNA synthetase. The Rossman-fold domain of this enzyme has a polypeptide with it. This insert, which is approximately 200 residues long, it called connective polypeptide 1 (CP1). Three different kinds of experiments show that CP1 forms the editing domain. First, mutations that alter residues in CP1 block the editing function. Second, the CP1 fragment hydrolyzes Val-tRNAwithout the assistance of any other part of the synthetase. Third, structural studies performed by Shigeyuki Yokoyama and coworkers in 1998 show that valine binds to both the Rossman-fold and the CP1 domain in IIe-tRNA synthetase from the gram-negative bacterial Thermus thermophilus, whereas isoleucine binds to only the former. The double-sieve model predicts this binding difference between the two amino acids. The Rossman-fold domain acts as the coarse sieve that accommodates both amino acids, whereas CP1 (the editing site) acts as the fine sieve that accommodates only valine.
Ile-tRNA synthetase’s aminoacylation and editing sites are more than 25 Á apart, raising the issue of how the 3’-end of a misacylated tRNA moves from the aminoacylation to the editing site. Structural studies performed by Thomas Steitz and his coworkers show that when Ile-tRNA synthetase forms a complex with tRNAIIe and mupirocin ( an antibiotic inhibitor that binds to the aminoacylation site ), the 3'-terminal of tRNAIIe is located in the CP1 domain. This observation suggests that when valine attaches to tRNAIIe, the tRNA’s acceptor stem flips from the aminoacylation site to editing site while the rest of the RNA molecule remains in place.
CP1 also catalyzes the hydrolysis of valyl-AMP that is mistakenly formed at Ile-tRNA synthetase’s aminoacylation site. Many, but probably not all of the CP1 residues that participate in editing Val-tRNAIIe al......

Selenocysteine and pyrrolysine are building blocks for polypeptides

Posted by star on 2019-03-22 00:08:47

By the mid-1980s, there was general agreement that the protein synthetic machinery uses just 20 amino acid building blocks to make proteins. Many modified amino acids were known to be present in proteins but these were formed by modifying amino acid residues after the polypeptide chain was formed. Therefore, it was a great surprise when selenocysteine (Sec) was identified as the 21st amino acid. This rare amino acid, an analog of cysteine in which the element selenium replaces sulfur, is present in a few proteins, mostly oxidoreductases, from eukaryotes, bacteria, and archaeons.
The bacterial pathway for selenocysteyl-tRNASec formation, which was elucidated largely through the efforts of August Böck and coworkers beginning in 1986. The three steps in this pathway are as follows: (1) Selenophosphate synthetase catalyzes the synthesis of selenophosphate from ATP and selenide, (2) Ser-tRNA synthetase attaches a séryl group to tRNASec, and (3) Selenocysteine synthase catalyzes a pyridoxal phosphate- dependent conversion of selenophosphate and Ser-tRNASec to selenocystcyl- tRNASec. The tRNASec species contains up to 100 nucleotides, making it the longest known tRNA. It also has other unusual features. For example, it has one more nucleotide base pair in its acceptor arm than most other tRNAs and an extended D-arm. Because of these unique features, selenocysteyl- tRNASec is not recognized by elongation factor 1A (EF1A) (see Chapter 20), and requires its own special elongation factor.
A second unusual amino acid building block, pyrrolysine, was independently discovered by Joseph A. Krzycki and coworkers and Michael K. Chan and coworkers in 2002. Although details of the pathway for pyrrolysine -tRNA formation must still be worked out preliminary data suggest that lysine is first attached to a special tRNA and then modified. Thus far, pyrrolysine has only been observed in archaeons tha......

Several research groups initiated programs to determine tRNA's tertiary structure in the late 1960s. Progress was quite slow at first because of the difficulty in obtaining crystals that were satisfactory for x-ray diffraction analysis. Finally, in 1974 two independent research groups, one led by Alexander Rich and the other by Aaron Klug, obtained crystals of yeast tRNAphe that were suitable for x-ray diffraction analysis. The crystal structure showed that the cloverleaf folds into an L-shape. The D and anticodon arms stack to form one section of the L, while the acceptor and Т?С arms ?tасk to form the other section.
The tRNA molecule's tertiary structure is stabilized by complex interactions. Helical regions in the acceptor, anticodon, D, and Т?С arms are usually stabilized by Watson-Crick base pairing as well as by non-Watson- -Crick base pairing such as the G : U pair in the tRNAphe acceptor arm. Non-helical regions of the tRNA molecule are stabilized by hydrogenbonding interactions between two or three bases that are not usually considered to be complementary to one another and by hydrogenbonding interactions that involve the 2'-hydroxyl group in ribose. 2'-Hydroxyl interactions are especially interesting because they cannot occur in DNA molecules. Different tRNAs have a similar folding pattern, ensuring that various components of the protein synthetic machinery will be able to recognize the tRNA after an amino acid has been attached to it. However, tRNAs also must have unique features that can be recognized by aminoacyl-tRNA synthetases.

New ways to detect cancer

Posted by star on 2019-03-17 19:30:35

    Researchers in the United States have developed a new way to detect cancer cells. With a new blood test, they can determine a patient's condition by identifying the pieces of DNA characteristic of cancer cells released into the blood after they have been cleaved. The technique is sensitive and accurate enough to detect individual "outliers" in hundreds of millions of healthy blood cells.
    The mortality rate of cancer is extremely high. It is particularly important to detect the early signs of cancer. However, the high cost of money and time actually makes ordinary people feel inconvenient. A simple blood test that can pick up signs of cancer proliferation is a quick fix for many people. Scientists believe that tumors need blood to grow, and that blood may contain information left behind by cancer cells. "It's a liquid-like biopsy that avoids pain and is a better way for doctors to monitor the development of cancer cells than a conventional imaging scan," said Dr. Robert Haber, director of the cancer center at Massachusetts general hospital, who was involved in the test.

    This idea has encountered many difficulties in practical operation. It is generally believed that in both cases, the proliferation of cancer cells is at a mild stage. Therefore, the amount of DNA samples is small compared with the amount of DNA in normal blood. Therefore, it is very difficult to find the mutated DNA. In addition to DNA mutations, scientists think they can be detected through epigenetics. Scientists believe that different tissues leave different methylation modifications on DNA, and analyzing the degree of DNA methylation modification can infer the source of DNA. They tested this idea and effectively detected circulating tumor DNA by analyzing methyl......

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