Biology Higher HL Nucleic Acids – Chapter 7 DNA structure and replication Hershey-Chase experiment (DNA is a genetic material) 1 Nucleosomes help to supercoil the DNA 2 Rosalind Franklin’s investigation of DNA structure through X-Ray diffraction Watson and Crick – semi conservative model for replication of DNA 1 https://www.bing.com/images/search?q=hershey+and+chase+experiment&view=detailv2&&id=A8B2F8F7E3AF073B2DAC67AF5 AAF28F221B0EB82&selectedIndex=0&ccid=aVJyzSQi&simid=608044487145424814&thid=OIP.aVJyzSQim923_43R5znnGAEsDt& ajaxhist=0 2 https://www.bing.com/images/search?q=nucleosomes+to+supercoil&view=detailv2&id=098B58D9FA7BAEDCE94164A2699AB6 5CAE5B7B9E&selectedindex=1&ccid=Ml6P7hDH&simid=608030068943618824&thid=OIP.M325e8fee10c7f487d92fba768cd3fec 7o0&mode=overlay&first=1 3 ^ DNA structure suggested a mechanism for DNA replication DNA polymerases can only add nucleotides to the 3’ end of a primer - Replication occurs in a 5’ to 3' direction DNA replication is continuous on the leading strand and discontinuous on the lagging strand - Two strands in a double helix structure in an antiparallel fashion, Okasaki fragments DNA replication is carried out by a complex system of enzymes 4 3 https://www.bing.com/images/search?q=Watson+and+Crick+semi+conservative&view=detailv2&id=5EA0CEB783E16782BF2E87 D2A13B7AD90A52665C&selectedindex=2&ccid=%2BAcL610K&simid=608025868458724676&thid=OIP.Mf8070beb5d0a09b7278 83c0d0662b2c1o0&mode=overlay&first=1 4 https://www.bing.com/images/search?q=dna+replication&view=detailv2&&id=A7864EE96E49A211DC8FD8E9D80D45E401A7AB C1&selectedIndex=0&ccid=5FoQUza6&simid=608003208221822215&thid=OIP.5FoQUza6fVOq6TvGmLAiZwEsDK&ajaxhist=0 Helicase unwinds the DNA at the replication fork Topoisomerase releases the strain that develops ahead of the helicase Single stranded binding proteins keep the strands apart long enough for the template strand to be copied RNA primer starts the replication of the DNA – lagging strand = more than one, leading = just one, it is a necessary enzyme as it initiates the activity of DNA polymerase DNA primase creates one RNA primer on the leading strand and many on the lagging strand DNA polymerase links the deoxyribonucleic monophosphate to the 3’ end of the growing strand DNA ligase connects the gaps between the Okasaki fragments Some regions of DNA do not code for proteins but have other important functions - All according to a genetic code Most of the eukaryotic genome is non-coding DNA profiling: tandem repeats, a short nucleotide sequence that shows variations between individuals in terms of the number of times the sequence is repeated. Transcription and gene expression Promoter – non-coding DNA with a function, the binding site of RNA polymerase (catalyses the formation of the covalent bond between nucleotides during the synthesis of RNA) Transcription occurs in a 5’ to 3’ direction Nucleosomes help to regulate transcription in eukaryotes - Histone proteins Acetyl group Methyl group Amino acid lysine on histone tails can have acetyl groups added or removed Eukaryotic cells modify mRNA after transcription Post-transcriptional modification: 5 5 https://www.bing.com/images/search?q=post+transcriptional+modification+diagram&view=detailv2&id=5B2E66792314A3034A Splicing of mRNA increases the number of different proteins an organism can produce - Occurs in genes with multiple exons The proteins translated from alternatively spliced mRNA’s will differ in their amino acid sequence and possibly their biological function Gene expression is regulated by proteins that bind to specific base sequences in DNA EG: absorption and metabolism of lactose by E.Coli 6 The environment of a cell and of an organism has an impact on gene expression EG: production of skin pigmentation during exposure to sunlight in humans/Siamese cats Translation Initiation of translation involves the assembly of the components that carry out the process Synthesis of the polypeptide involves a repeated cycle of events Disassembly of the components follows termination of translation 54C7FC1C6ED6F3239A81BB&ccid=nsFzSaD7&simid=608002439416580973&thid=OIP.nsFzSaD7rk389ECn6F94NAEsD2&mode=o verlay&first=1 6 https://www.bing.com/images/search?q=Lac+Operon+Diagram&view=detailv2&id=C70801E5A128B3B82B3149D7867E3CCC454 B655F&selectedindex=2&ccid=A8vxJFc7&simid=608017596361476167&thid=OIP.M03cbf124573ba734e7c82e7c44be7dacH0& mode=overlay&first=1 7 Free ribosomes synthesize proteins for use primarily within the cell (synthesized in the cytoplasm or the endoplasmic reticulum) Bound ribosomes synthesize proteins primarily for secretion or for use in lysosomes (must be sorted to end up in the right place, bound to the rough endoplasmic reticulum) Translation can occur immediately after transcription in prokaryotes due to the absence of a nuclear membrane The sequence and number of amino acids in the polypeptide is the primary structure The secondary structure is the formation of alpha helices and beta pleated sheets stabilized by hydrogen bonding The tertiary structure is the further folding of the polypeptide stabilized by interactions between the R groups The quaternary structure exists in proteins with more than one polypeptide chain 7 https://www.bing.com/images/search?q=translation&view=detailv2&&id=4EFD7B3A0A19B152E0993DA5C9FE70A090A76531&s electedIndex=0&ccid=WkeZZc5N&simid=608025164088544126&thid=OIP.M5a479965ce4d8a49195e1686a9b76448H0&ajaxhist =0
