8a) DNA and Genomics table_9744_2018

Genetics and Inheritance (9744) DNA replication, transcription, translation & mutations 2018 Prepared by: Mrs Selvamani Nair Raffles Institution (Yr 5-6) 1 Nucleic acid RNA (mRNA, tRNA & rRNA) DNA Pentose (five carbon) sugar Ribose Deoxyribose Nitrogenous bases Purines (2 rings) Adenine & Guanine Adenine & Guanine Pyrimidines (1 ring) Cytosine & Uracil Cytosine & Thymine Complementary base pairing occurs between Adenine & Uracil ( 2 H bonds) Cytosine & Guanine ( 3 H bonds) Adenine & Thymine ( 2 H bonds) Cytosine & Guanine ( 3 H bonds) Structure Single Stranded Double Stranded Found in (location) Cytoplasm, Nucleus Nucleus Structure of a nucleotide (a nucleoside + phosphate group = nuceloside monophosphate) Structure of RNA and DNA Evidence for semi-conservative replication Nitrogenous base: attached to C1 Phosphate group: attached to C5 OH group attached to C3: involved in phosphodiester bond formation If H is attached to C2  deoxyribose sugar If OH is attached to C2  ribose sugar In DNA * A:T = 1:1 and C:G = 1:1 * (A+G) = (C+T) i.e. no.of purines = no.of pyrimidines * Purines: 2 rings (baby’s are pure & go googooGAGA) * Pyrimidines: 1 ring (CUT food on dinner plate) * Constant width between sugar phosphate backbone = 2nm * 2 strands are anti-parallel: one strand runs in the 5’ to 3’ direction, while the other strand runs in the 3’ to 5’ direction DNA is said to have directionality * 1complete turn of the double helix has 10 base pairs and spans a distance of 3.4nm * 1 DNA molecule is made up of 2 strands of DNA 3 hypotheses for DNA replication mechanism: 1) Semi-conservative replication both strands separate by the breaking of hydrogen bonds and each strand acts as a template for the synthesis of a new strand through complementary base pairing. Thus each DNA molecule formed is a hybrid consisting of 1 original strand and 1 newly synthesized strand. 2) Conservative replication 2 parental strands re-associate after acting as templates, thus restoring the original double helix. The other DNA molecule consists of 2 newly synthesized strands. 3) Dispersive replication Parental DNA molecule is fragmented and dispersed. Daughter molecules are madeup of a mixture of old and newly synthesized parts. (a) A stock of parental E. coli were grown for many generations in 15N medium as the only source of nitrogen until 15N wa s incorporated into the nitrogenous bases of all bacterial DNA. (b) The E.coli containing 15N-15N were then transferred into a medium containing only 14N. The transferred E.