1第二节基因的奥秘

1、第二节 基因的奥秘基因是有什么物质组成的？1928，1944学生返校上体育课连续发生猝死！戴口罩跑步惹的祸还是体质差造成？【文/观察者网 陈聪】疫情趋缓，多个省份都相继迎来了返校复课，但是在校期间，学生的口罩防护是否到了可以松懈又成为新的争议性话题。社交网络上已经有大量文章批评上体育课仍要求学生戴口罩的做法错误，指责这是形式主义。4月30日，陕西中医药大学教授曹兰秀在接受媒体采访时却表示，戴着口罩跑步和猝死之间并没有必然的联系。曹兰秀说，“一般来说，99%的戴口罩跑步不会导致猝死。如果学生呼吸有困难，他可以自己呼吸，他是有自我意识的。他不可能戴上口罩后突然死去。”换而言之，感到呼吸不畅会及时停

2、止运动、摘掉口罩，这是人的本能反应。北京阜外医院心外科副教授孙宏涛就撰文指出了佩戴N95口罩的诸多弊端：N95口罩的密闭性很好，会导致呼吸不完全顺畅，呼出的气体有一定的数量停留在口腔与口鼻形成的空间里面，再反复吸入则会导致体内的二氧化碳水平提高而氧含量下降。前者导致体内酸碱失调，引发呼吸性酸中毒；后者则使得机体的血氧水平下降，严重的可能导致重要器官缺氧损害。学生返校上体育课连续发生猝死！戴口罩跑步惹的祸还是体质差造成？【文/观察者网 陈聪】科学与宗教、金融、传统医学、日常生活等的区别，不满足于一种解释，哪怕这种解释看起来很合理。这些解释只是一种假说，不是结论。我们要对假说进行检验，然后才能下结

3、论。即便是一种假说有证据支持，科研人员也不能结束对这个问题的思考。因为可能存在多种原因共同起作用，得到检验的假说也许只说出了问题的一部分。只要有新的迹象暗示着新的可能性，做科研的，就应该重视。36岁患者出院后猝死！是新冠导致的病毒性心肌炎吗？东京11名猝死者身上发现新冠病毒CDC：新冠病毒可致中风猝死，年轻病毒患者会因感染病毒而引起的突然中风而猝死。对于上述悲剧，一种新的假说是。，检验方法。乳糖操纵子Lactose Operonfor graduate students牛登科生命科学学院2010年10月Lactose OperonStructural geneslac z, lac y, &

4、lac aPromoterPolycistronic mRNARegulatory geneRepressorOperatorOperonInducer - lactoseiOperonRegulatoryGenepozyaDNAm-RNA-GalactosidasePermeaseTransacetylaseProteinLactose OperonInducer - lactoseAbsenceActive repressorNo expressionipozyaNo lac mRNAAbsence of lactoseActiveipozya-GalactosidasePermeaseT

5、ransacetylasePresence of lactoseInactivePresenceInactivation of repressorExpressionNegative controlIs the story complete?These two pages are copied from the PPT of an American teacher. Has your textbook told you something more?If no, are you satisfied with this theory?No lactose, no genes transcribe

6、d, no proteins produced, and then nothing to transport lactose into the cell.A dead cycleBasal transcriptionThe repressor could not entirely repress the genes. In absence of lactose, there is a low level of leaky gene expression of lactose operon genes.The negative control of lactose operon is not y

7、es or no, but more or less. In fact, in eukaryotes, there are also many genes that are transcribed and translated, at low levels, in the cells that obviously do not need them. And the reason for this is not clear, awaiting for you to discover.Do you still have any question?Why operon?Operons contain

8、 genes belonging to the same functional pathway in order to guarantee them a similar expression level. About half of the protein-coding genes are organized in operons.However, prokaryotic genomes are rather unstable and only 525% of genes belong to strings shared by at least two distantly related sp

9、ecies. The biological significance and mechanism(s) of operon formation are still under debate. At least seven different models have been proposed for operon formation.For details, see Res. Microbiol. 160: 502-512, 2009.More questions?Why negative control?That is, is there any trouble if the lactose

10、 operon genes are constitutively expressed?Waste of amino acids in useless proteinReally?More questions?The cost is associated with the process of making the lac gene products. See Genetics 178: 16531660, 2008.BioNumbersthe beginning of Quantitative BiologyBioNumbersthe beginning of Quantitative Bio

11、logyThe cost of wasteful protein expressionCells growing in rich media have higher ribosome content than cells growing in poor media. Thus, when cells are shifted from rich to poor media they have an excess of ribosomes and can absorb the cost of excess translation.On shift from poor to rich media,

12、cells have insufficient ribosomes and exhibit the cost.Since the costs are manifest only in some transitions, it is not change alone but a deficit of some specific cellular component (ribosomes are the likely candidate) that exacerbates costs.Shachrai I, Zaslaver A, Alon U, Dekel E: Cost of Unneeded

13、 Proteins in E. coli Is Reduced after Several Generations in Exponential Growth. Mol Cell 2010, 38(5):758-767.Stoebel DM, Dykhuizen DE: Waste and yet want not. Mol Cell 2010, 38(5):625-626.Why operon in C. elegan revealedWe find that transcriptional resources are initially limiting during recovery a

14、nd that recovering animals are highly sensitive to any additional decrease in transcriptional resources. We provide evidence that operons e advantageous because, by clustering growth genes into operons, fewer promoters compete for the limited transcriptional machinery, effectively increasing the concentration of transcriptional resources and accelerating recovery. From Zaslaver A, Baugh LR, Sternberg PW: Metazoan operons accelerate recovery from growth-arrested states. Cell 2011, 145(6):981-992.And something else?Left for you to discoverAnd Eames M,