在PTE中,无论是Summarise Spoken Text 还是 Re-tell Lecture的考题大都是从真实的讲座或者演讲中截取的,中间经常经常夹杂很多不同的环境音.很多同学都反映有时未必是听不懂,而是听不到. 鉴于此,墨尔本文波雅思PTE专门为大家总结了真实讲座的PTE练习音频,相比新闻音频来说,整体更加接近PTE考试的真题,内容方面,我们也会为大家提供考试中存在的近似题,最近我们会持续更新,敬请期待!
So DNA and RNA are the two types of nucleic acids that you’re most likely to encounter and in a lot of ways they’re very similar. But there are a few differences that you should be aware of. The first one is that RNA contains uracil, which is a pyrimidine and it contains that in place of Thymine. So the U binds with the A in RNA, whereas Thymine and adenine what bind in DNA. Secondly RNA usually exits in single stranded form, whereas DNA U tend to find in a double helix with complementary antiparallel strands. Partly because of this, RNA is capable of fitting through nuclear pores, and therefore is often found in the cytoplasm. And so a lot of times when you are looking at transcription and translation, the translation step will occur in the cytoplasm because the RNA is capable of moving out of the nucleus into the cytoplasm, whereas DNA you are likely to find sequestered within a nucleus in most healthy cells. And lastly something that is so fundamental that I actually forgot and put it last on the list is that RNA is ribonucleic acid, whereas DNA is deoxyribonucleic acid. And what that means is that the sugar that forms the part of the nucleotide. In RNA, this sugar is ribose. It’s that pentose sugar that it uses is ribose instead of deoxyribose, and the difference between these is that there is an OH group on carbon two of the ribose, whereas deoxyribose does not have that. These are the four main distinctions that you’re looking at when you’re comparing RNA and DNA. And otherwise they are very very similar in structure.
