Molecular biology Session 1 Nucleic acids DNA Genes

Molecular biology Session 1 Nucleic acids, DNA, Genes presented by Ali Barzegar 23/Apr/2020

1) Titles 1) 2) 3) 4) 5) 6) Nucleic acids Gene, genome Chromosome Replication Transcription Translation ﺯیﺴﺖ ﺷﻨﺎﺳی ﺳﻠﻮﻟی ﻭ ﻣﻮﻟکﻮﻟی : ﻣﻨﺒﻊ ﺩکﺘﺮ ﻣﻬﺪﻭی

Nucleic acids: Composed of pentose, phosphate group and organic base Pentose: ribose in RNA and deoxy ribose in DNA Organic base: -Pyrimidine: uracil (U), cytosine (C), Thymine (T) -Purine: adenine (A), guanine (G) U is present in RNA, T is present in DNA (sometimes in RNA) Ali barzegar (alibar 647@yahoo. com) 3

Nucleosides: binding of base and sugar (1’-1 , 1’-9) without phosphate, b-N-Glucoside bond Nucleotides (Nt): Binding of nucleosides and phosphate (AMP, GMP, CMP, TMP, UMP) Oligonucleotides: Binding of nucleotides (attachment of 5’ end of one nucleotide to 3’ end of another nucleotide by phosphodiester bond) (4 bp) Kbp=1000 bp RNA= nt Ali barzegar (alibar 647@yahoo. com) 4

DNA: double helix oligonucleotide chains nucleotide sequence. of two antiparallel with complementary The opposite strands are held together by a regular base pairing between two strands: A with T by two hydrogen bonds G with C by three hydrogen bonds This base pair is a consequence of the size, shape, and chemical composition Ali barzegar (alibar 647@yahoo. com) 5

Different forms of DNA 1) B DNA: right-handed, each turn 34 Ao and containing 10 base pairs, the stacked bases are 3. 4 nm apart, containing major and minor grooves 2) A DNA: right-handed, 28 Ao each turn, with 11 base pairs, 2. 54 Ao each bp apart, created in non aqueous situation and DNA-RNA hybrids 3) Z DNA: left-handed, zigzag, each turn 45. 6 Ao, 3. 8 Ao each bp apart, immunogenic form, act in regulation of gene expression. Created when cations existed in the medium Ali barzegar (alibar 647@yahoo. com) 6

DNA supercoils: overturning or underturning of ccc. DNA -Negative supercoils: is created by turning of cc. DNA in opposite direction of double helical turn -Positive supercoils: is created by turning of cc. DNA in direction of double helical DNA Supercoils roles: 1) Easily opening of double helix during replication 2) Protect of DNA from nuclease damages 3) Providing intermediate structure for producing other DNA structures Ali barzegar (alibar 647@yahoo. com) 7

DNA supercoil structures: 1) Linking number: number of helical turns of two DNA strands 2) Twisting number: frequency of the turns of the helix 3) Writhe (W): Number of supercoils L=T+W ﻣﻘﺎﺩیﺮ B DNA کیﻠﻮ ﺑﺎﺯ ﺍﺯ ﻧﻮ 4 ﻣﺎﺭپیچی ﺣﻠﻘﻮی ﺑﻪ ﻃﻮﻝ DNA ﺩﺭ یک ﻣﻮﻟکﻮﻝ : ﺳﻮﺍﻝ ﺭﺍ ﻣﺤﺎﺳﺒﻪ کﻨیﺪ W ﻭ L, T Bp=base pair 4 kbp=4000 bp 4000/10=400=T 400/20=20=w L=400 + (-20)= 380. ﺩﻭﺭ ﻣﺎﺭپیچ یک ﺳﻮپﺮکﻮیﻞ ﻣﻨﻔی ﻭﺟﻮﺩ ﺩﺍﺭﺩ 20 ﺑﻪ ﺍﺯﺍی ﻫﺮ B DNA ﺩﺭ : ﺭﺍﻫﻨﻤﺎیی Ali barzegar (alibar 647@yahoo. com) 9