A-level生物知識點學(xué)習(xí)筆記，帶你鞏固DNA部分重要考點

 

　　脫氧核糖核酸（英文DeoxyriboNucleic Acid，縮寫為DNA）是生物細(xì)胞內(nèi)含有的四種生物大分子之一核酸的一種。DNA攜帶有合成RNA和蛋白質(zhì)所必需的遺傳信息，是生物體發(fā)育和正常運作必不可少的生物大分子。在A-level生物知識點學(xué)習(xí)中，Nucleic Acids和Protein synthesis是我們學(xué)習(xí)和考察的重點章節(jié)，今天A加未來小編就帶大家解析一下這部分中的一些重點內(nèi)容，希望對大家有所幫助。

　　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.

　　以上就是A加未來小編關(guān)于A-level生物知識點中有關(guān)DNA和RNA部分的一些重點內(nèi)容的總結(jié)和分析，希望能夠幫助同學(xué)們更好的做好知識點的復(fù)習(xí)和鞏固。更多A-level學(xué)習(xí)問題，歡迎隨時咨詢我們。

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