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Benner and his team hypothesized that duplication of the ancestral gene occurred near the
time ______.
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更多“Benner and his team hypothesiz…”相关的问题
THE PARTY GENE
Steven Benner jokingly calls himself a dilettante (业余艺术好爱者). A biochemist at the University of Florida in Gainesville, Benner learns a wide range of disciplines, from bioinformatics to astrobiology. His aim is to gain insight into the basic chemical rules that govern how life works -- both here and, ultimately, on other planets. But although science drew his gaze to the skies, it was alcohol that brought him back down to Earth. Or, to be more exact, the enzymes that can both make and consume it.
Alcohol dehydrogenase (脱氢酶) is best known as the enzyme (酶) that breaks down alcohol in the body, and as such it has been studied exhaustively. But Benner and other researchers in the field have now turned to its evolution, and their work is providing fresh insight into the puzzle of why some creatures, such as yeast, came to make alcohol and why so many others, including ourselves, can tolerate it.
Alcohol dehydrogenase -- ADH for short -- is a blanket term applied to a large and diverse group of enzymes. In many creatures, including ourselves, they help to convert alcohols, such as ethanol, into com- pounds that other enzymes can break down and extract energy from. But in a number of microorganisms, they can help the reverse reaction, making alcohols as part of the process of extracting energy from sugars.
The stars of these alcohol-producers are the yeasts. Not only do Saccharomyces species of yeast churn out oodles of ethanol, they can also tolerate far higher concentrations of it than other microorganisms. Brewer' s yeast owes this ability to two alcohol dehydrogenases: ADH1, which makes ethanol, and ADH2, which breaks it down for use as an energy source. Yeast not only brews its own moonshine, it consumes it too —"to the last drop", as Benner says.
At first sight, this makes no sense. Making ethanol from sugar and then consuming it is energetically far more wasteful than simply consuming the sugar. Researchers have long pondered why yeast goes to all that trouble. Although it might be nice to think that there is a creature ont there whose raison d'etre is to party, evolution doesn't work that way.
Make or break
Benner and his team came across the explanation when hunting for the origins of ADH in yeast. Benner is interested in combining the study of genes and proteins with geology and palaeontology to gain insight into the history of life on Earth and present-day protein function. "Every biomolecule is better understood if we know its history as well as its structure," he says.
The ADHgenes in yeast make an intriguing subject for this approach. When yeast gained its ability to make alcohol, it must have done so as a result of a selection pressure in its environment and, what is more, this would have had a knock-on effect on other creatures. So working out when and how the ADH enzymes came to be could open a small window onto what ecosystems were like back then.
ADH genes and the proteins they make are well studied and have been isolated from many different species of yeast, so Benner' s team had plenty of useful material to work with. The goal was to reconstruct the original gene that was duplicated to give rise to ADHI and ADH2, and to ask what its function was -- did it make alcohol, or did it break it down'？
From a database of the sequences of related ADH genes in various yeasts --combined with additional ADH genes specially sequenced for this study -- Benner and his colleagues assembled an evolutionary tree of yeast ADH. This showed where the ancestral gene would have fitted in and helped the researchers work out its most likely aminoacid (氨) sequence. Inferring the past from the present isn't perfect, so they ended up with 12 slightly difterent candidate genes.
Fruitful collaboration
The group then reconstructed all 12 genes and test
A．Y
B．N
C．NG
A.committed
B.accomplished
C.endured
D.occupied
There is an obvious preference of the guest team in his _________ on that football match.
A．interpretation
B．commentary
C．directory
D．specification
A.They are helpful in improving the team spirit.
B.They are relevant to business management.
C.They are helpful in his previous work.
D.They are relevant to the job of assistant manager.
A.Work with his team leader.
B.Go to the party with the woman.
C.Stay with his aunt in his home.
D.Perform. music in a band.
A．His father's advice helped him to decide which job to take up.
B．Working in a sports team was his most important experience.
C．He learned much from his shared experience with his team members.
D．His experience as a baggage boy had a great influence on his later life.
A．exchanged
B．transmitted
C．transferred
D．removed
A.A Risky Trip Up Mount Everest
B.Pollution on Mount Everest
C.Mount Everest --- Clean-up Effort
D.Robert Hoffman and His Clean-up Team
A．His father's advice helped him to decide which job to take up.
B．Working in the sports team was his most important experience.
C．He learnt much from his shared experience with his team members.
D．His experience as a baggage boy had a great influence on his later life.
