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学生反馈开学后要迎来模拟考，为了帮助同学们更好地应对后面的考试，老师今天给大家带来一波干货福利。 Nucleic Acids 和 Protein synthesis 一直是A Level的重点章节，也是老师我常常被同学们提问的地方。下面是我为我的学生们做的一份文蓝内部复习资料，在考试期间放出来给各位同学，希望能帮助到大家！ Part 1 ：Nucleic Acids DNA is the genetic material, which carries the genetic information. Chromosome is a DNA molecule associate with the histone proteins. Gene is the small section of DNA, which can be used to make the proteins. ■ DNA - Deoxyribonucleic acids - Double helix structure with antiparallel strands。 - DNA is the polymer of DNA nucleotides (Polynucleotides) ■ RNA - Ribonucleic Acids - Made up by RNA nucleotides. - Messenger RNA: Copy the genetic information from DNA in the nucleus and bring the information to the ribosome in cytoplasm. - Transfer RNA: Carry the specific amino acid to the ribosome. - Ribosomal RNA: Form the subunits of the ribosome. l Nucleotide contains a pentose sugar, a phosphate group and a nitrogen-containing base: ■ Each nucleotide is linked to the next one by phosphodiester bonds between the phosphates of a nucleotide and pentose of another nucleotide to form the polynucleotide. ■ Commentary base pairing: purine bases pair with pyrimidine bases (A-T, G-C) - Adenine always pairs with thymine (uracil in RNA) via 2 hydrogen bonds. - Guanine always pairs with cytosine via 3 hydrogen bonds. ■ Two polynucleotide strands of the DNA is held by the hydrogen bonds between the complementary base pairing. Part 2 . DNA replication ■ Occurs during interphase before the cell division to ensure each daughter cell get correct amount of genetic material. ■ DNA replicates by semi-conservative replication: Each daughter DNA molecule contains one strand from parent DNA and one newly formed strand. ■ Process: 1. The DNA double helix structure is unwound and unzipped by helicase. 2. Both separated DNA strands are used as the template strands. 3. Free nucleotides joined with templet strand and held by the hydrogen bonds between the complementary base pairs. 4. DNA polymerase catalyses the formation of the phosphodiester bonds between DNA nucleotides. 5. Due to the new DNA strands have to formed from 5’ end to 3’ end, and the DNA is antiparallel, one daughter DNA strand is formed discontinuously. The DNA segments are connected by the DNA ligase. 6. Two identical daughter DNA molecules are formed. Part 3 ：Protein synthesis ■ Two strands of DNA: sense strand (coding strand) + antisense strand (template strand) ■ The genes are on the antisense strand ■ Transcription (occurs in the nucleus): 1. Double strands of DNA are unwound and unzipped and the antisense strand is used as the template. 2. RNA nucleotides pair up with their complementary bases on the template strand via hydrogen bonds. 3. RNA polymerase catalyse the formation of the phosphodiester bonds between the RNA nucleotides. 4. The mRNA molecules is formed, and then the hydrogen bonds between the mRNA and DNA template strand are broken. 5. The DNA rewind into the double helix structure and mRNA molecule leaves the nucleus via nuclear pore. ■ Translation: (occurs on the ribosome)： 1. The mRNA moves into the cytoplasm and attached by ribosomes to provide the binding site for tRNA. 2. tRNA will brings the specific amino acids and bind with the mRNA and ribosome via the complementary base pairing between the codon and anticodon. 3. Then, second tRNA bring another amino acids and bind with the mRNA. 4. The peptide bond form between the adjacent amino acids. 5. The first tRNA detached from the its amino acids and he ribosome moves along the mRNA molecule, and a new tRNA with the amino acids will bind with the next codon. 6. The polypeptide is formed gradually until the ribosome reach the stop codon, then the formation of the polypeptide is completely. It will fold in the secondary and tertiary structure immediately. 7. The mRNA can be read by several ribosomes at the same time to produce many polypeptide. 整理了这么多，希望能够在考试中帮到大家，如果同学们对Alevel的学习还有什么疑问，欢迎随时联系我们哦~ A-level生物知识点较多，并且考察的很深，要求学生有较高的理解，那对于那些喜欢生物学科但是学起来又有些吃力的同学来说，怎么才能学好呢？ 【文蓝国际学习中心】独家奉上CAIE考试局A-level生物分类型题库精编！ 生物精编题库中收录了CAIE生物AS与A2阶段各单元的历年高频考题，内含知识点点拨、类型题整理及答案解析，帮助大家考前巩固知识点的同时有针对性的刷题。 |
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