Axit nucleic
Tổ chức Baccalaureate Quốc tế · IB Diploma · Biology · HL Chủ đề 2 3:57 Giọng đọc tiếng Anh · phụ đề tiếng Anh + 中文 được ghi trực tiếp
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A change in DNA can affect a protein, but not every DNA change changes the amino-acid sequence.
DNA的改变可能影响蛋白质，但并非所有DNA改变都会改变氨基酸序列。
The effect depends on the sequence and how it is used.
其效果取决于序列及其使用方式。
DNA stores information in a base sequence.
DNA 通过碱基序列存储信息。
Complementary base pairing supports copying.
互补碱基配对支持复制过程。
During gene expression, transcription makes RNA and translation uses codons to assemble an amino acid sequence.
在基因表达中，转录（transcription）生成 RNA，而翻译（translation）利用密码子组装氨基酸序列。
Transcription is the formation of RNA using a DNA template.
转录是指以 DNA 为模板形成 RNA 的过程。
Translation is the formation of a polypeptide using an mRNA sequence.
翻译是指以 mRNA 序列为模板形成多肽链的过程。
A codon comprises three bases.
一个密码子由三个碱基组成。
The genetic code is degenerate, meaning more than one codon can specify the same amino acid.
遗传密码具有简并性，即多个密码子可编码同一种氨基酸。
A substitution can therefore be silent, while insertions or deletions can shift the reading frame.
因此，碱基替换可能是沉默突变，而插入或缺失则可能导致移码突变。
In the lab: Keep DNA template, coding DNA and mRNA distinct.
在实验室中，请区分DNA模板链、编码DNA和mRNA。
State the strand used and write sequences in the required direction.
注明所使用的链，并按要求方向书写序列。
Use a codon table for mRNA, not an unexplained DNA triplet.
使用密码子表解读mRNA，而非未加说明的DNA三联体。
Known: an mRNA coding region contains 90 bases, including one stop codon.
已知：一段mRNA编码区包含90个碱基，其中包括一个终止密码子。
Codons equals bases divided by three, which is 90 divided by 3, resulting in 30.
密码子数等于碱基数除以3，即90除以3，结果为30。
A stop codon does not encode an amino acid, so the peptide contains 29 amino acids under this stated model.
由于终止密码子不编码氨基酸，因此在该模型下，该肽链含有29个氨基酸。
Your turn: A coding mRNA segment has 63 bases including a stop codon.
请作答。 一段编码mRNA片段包含63个碱基，其中包括一个终止密码子。
Find peptide length.
求肽链长度。
Pause the video and work it out.
请暂停视频，自己算一算。
Check: 63 bases make 21 codons; the stop codon adds no amino acid, so the peptide is 20 amino acids long.
核对：63 个碱基构成 21 个密码子，终止密码子不编码氨基酸，所以肽链有 20 个氨基酸。
The number of bases is not automatically the number of amino acids.
碱基数量并不自动等于氨基酸数量。
Real genes include regulatory regions and, in eukaryotes, often introns.
真实基因包含调控区域，在真核生物中通常还含有内含子。
A whole gene length is not a peptide-length calculation.
整个基因的长度不能直接用于计算多肽长度。
Not true: Each DNA base encodes one complete amino acid.
不正确。 每个DNA碱基编码一个完整的氨基酸。
Amino acids are encoded by triplets of bases (codons), not by single bases.
氨基酸是由三个碱基组成的三联体（即密码子）编码的，而不是由单个碱基编码的。
Three bases specify one amino acid, and a stop codon specifies none.
三个碱基指定一种氨基酸，而终止密码子不指定任何氨基酸。
DNA stores information in a base sequence.
DNA通过碱基序列存储信息。
A codon comprises three bases.
一个密码子由三个碱基组成。
Watch for: the number of bases is not automatically the number of amino acids.
请注意：碱基的数量并不自动等于氨基酸的数量。
An mRNA coding region has 72 bases, including one stop codon.
mRNA编码区包含72个碱基，其中包括1个终止密码子。
Find the number of amino acids.
求氨基酸的数量。
A substitution can be silent.
一种替换可以是同义突变。
The result is a peptide of 23 amino acids.
结果是一条由23个氨基酸组成的肽链。
Each base pairs with one partner only: adenine with thymine, cytosine with guanine.
每个碱基只与一个伙伴配对：腺嘌呤配胸腺嘧啶，胞嘧啶配鸟嘌呤。
The two strands run in opposite directions, so one strand is enough to rebuild the other.
两条链方向相反，因此一条链就足以重建另一条链。
An mRNA coding region has 126 bases including one stop.
一条mRNA编码区包含126个碱基，其中包括一个终止密码子。
A substitution turns codon 11 into a stop.
某次替换使第11号密码子变为终止密码子。
Compare peptide lengths, assuming translation starts at the same codon.
假设翻译起始于同一密码子，请比较肽链长度。
Originally, 126 divided by 3, minus 1 for the stop, gives 41 amino acids.
原来是 126 除以 3，再减去 1 个终止密码子，得到 41 个氨基酸。
In the new version, codon 11 is a stop and is not translated, so the peptide has 10 residues.
新版本中第 11 个密码子变成终止密码子，不被翻译成氨基酸，所以肽链只有 10 个残基。
The model excludes altered initiation, splicing and readthrough.
这个模型不考虑起始位点改变、剪接和通读。
Pause and check yourself. Explain each point on screen in your own words, then change one number in the last example and say which assumption must still hold.
暂停一下，自我检查：用自己的话解释屏幕上的每个要点，再改动最后一个例子中的一个数字，说明哪个假设仍然必须成立。