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12 Cards in this Set
- Front
- Back
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DNA replication requires DNA Polymerase |
DNA Polymerase - catalysed step by step addition of deoxyribonucleotide units to DNA - New DNA assembled on template DNA - Requires primmer (with free 3’-OH) to begin synthesis - New DBA grows at 3’ (synthesis is 5’ to 3’)
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DNA Replication |
DNA template Primase RNA primer DNA Polymerase Newly synthesised DNA |
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Strands in DNA replication |
Second (anti parallel) strand of DNA is synthesised in fragments called OKAZAKI FRAGMENTS in a 5’ to 3’ direction. Fragments are joined together by ligase |
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Types of RNA and RNA Polymerases |
mRNA Template for protein synthesis RNA polymerase 2 [Pol 2] ATP dependent tRNA Carries activated amino acids to ribosomes RNA polymerase 3 [Pol 3] rRNA Major component of Ribosomes RNA polymerase 1 [Pol 1]
All require template DNA, ribonucleotides and a divalent metal ion (Mg+) |
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RNA Synthesis Steps |
Initiation RNA polymerase 2 and transcription factors assemble at promoter; RNA synthesis begins Elongation RNA polymerase 2 moves alone template strand as a RNA molecule grows in a 5’ to 3’ direction Termination RNA molecule completed and stabilised by modifications |
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Initiation step |
Pol 2 bunds to a specific region of DNA - the PROMOTER TATA box [-25] CAAT box [-75] GC box |
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Other RNA Pols and their Specific Promoters |
Pol 1 : UPE (upstream Promoter Element) and rInr Pol 3 : type 1 5sRNA type 2 tRNA |
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How does RNA Polymerase read DNA |
RNA Polymerase must unwind the DNA to allow the template strand to be read [unwound DNA usually 17bp open] |
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What is Required for Initation? |
Transcription Factors are also required, assembled in a complex with “mediator” Phosphorylation of Pol 2 allows it to move along the template |
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Elongation Step |
RNA molecule grows 5’ to 3’ (new nucleotides added to 3’) |
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Termination and Modification Step |
Modifications provide stability to RNA molecule Requires 5’ cap and a Poly A Tail |
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Translation [Synthesis of Protein] |
m |
