前導(dǎo)鏈的合成方向與復(fù)制叉的移動(dòng)方向相反,通過不連續(xù)地5'→3'方向聚合生成新的DNA鏈。
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"Don't Drink Alone" Gets New Meaning
In what may be bad news for bars and pubs, an European research group has found that people drinking alcohol outside of meals have a significantly higher risk of cancer in the mouth and neck than do those who drink with food. Luigino Dal Maso and his colleagues studied the drinking patterns of l,500 patients from four cancer studies and another 3,500 adults who had never had cancer.
After the researchers accounted for the amount of alcohol consumed, they found that individuals who downed a significant share of their alcohol outside of meals faced at least a 50 t0 80 percent risk of cancer in the oral cavity(口腔) , pharynx (咽 ) , and esophagus(食管) , when compared with people who drank only at meals. Consuming alcohol without food also increased by at least 20 percent the likelihood of laryngeal cancer(喉癌). "Roughly 95 percent of cancers at these four sites traced too smoking or drinking by study volunteers, " Dal Maso says. The discouraging news his team reports, is that drinking with meals didn't eliminate cancer risk at any of the sites.
For their new analysis, the European scientists divided people in the study into four groups,based on how many drinks they reported having in an average week. The lowest-intake group included people who averaged up t0 20 drinks a week. The highest group reported downing at least 56 cups of alcohol weekly for an average of eight or more per day. Cancer risks for the mouth and neck sites rose steadily with consumption even for people who reported drinking only with meals. For instance, com-pared with people in the lowest-consumption group, participants who drank 21 t0 34 alcohol cups a week at least doubled their cancer risk for all sites other than the larynx. If people in these consump-tion groups took some of those drinks outside meals, those in the higher consumption group at least quadrupled(四倍) their risk for oral cavity and esophageal cancers.
People in the highest-consumption group who drank only with meals had lo times the risk of oral cancer, 7 times the risk of pharyngeal cancer, and 16 times the risk of esophageal cancer compared with those who averaged 20 0r fewer drinks a week with meals. In contrast, laryngeal cancer risk the high-intake, with-meals-only group was only triple that in the low-intake consumers who drank with meals.
"Alcohol can inflame(使發(fā)炎) tissues. Over time, that inflammation can trigger cancer. " Dal Maso says. He suspects that food reduced cancer risk either by partially covering digestive-tract (消化道) tissues or by scrubbing alcohol off those tissues. He speculates that the reason laryngeal risks were dramatically lower for all study participants traces to the tissue's lower exposure to alcohol
Who are more likely to develop cancer in the mouth and neck?
A.People who drink alcohol outside of meals
B.People who drink alcohol at meals
C.People who never drink alcohol
D.People who drink alcohol only at bars and pubs
W: What is all this glass doing on the floor?
M:________
A.Look at the window and you’ 11 see.
B.I’11 clean it.
C.I’11 call the repair man.
D.Can ’ t you find out?