Bio Lecture 1.docx - Bio Lecture 1 Molecular Biology...

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Bio Lecture 1 Molecular Biology Transcription, Translation and Mutation DNA and RNA runs 5’ to 3’ Sugar phosphate backbone covalently bonded to nitrogenous bases DNA consists of a pentose sugar (deoxyribose), nitrogenous base ( Adenine / Guanine /Thyamine/ Cytosine ) and a Phosphate (PO4 3- or simply P) group. The parent molecules which take part in synthesis of this gigantic DNA molecule are Nucleoside triphosphase (dNTPs). Each nucleotide in RNA contains a ribose sugar , with carbons numbered 1' through 5'. A base is attached to the 1' position, in general, adenine (A), cytosine (C), guanine (G), or uracil (U). Adenine and guanine are purines, cytosine and uracil are pyrimidines . Hydrogen bonds form between nitrogenous bases 2 DNA strands are reverse complementary to each other C binds to G -3 hydrogen bonds A binds to T- 2 hydrogen bonds RNA is most commonly single stranded but not always Secondary structures are formed between hydrogen bonds between nitrogenous bases 1
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A pairs with T (or U) C pairs with G The two strands of DNA are REVERSE COMPLEMENT Strand 1: 5’ ATGCCGACT 3’ Revision Fig 5.25 Central dogma DNA- information (that is copied exactly) DNA is relatively inert Transcription- copies the information of DNA into mRNA Gene (segment of DNA): area on a chromosome (piece of DNA) that produces a functional product i.e protein A gene is the entire DNA sequence required for synthesis of a functional protein or RNA molecule . In addition to the coding regions (exons), a gene includes transcription- control regions and sometimes introns Do all genes produce proteins: NO (excpetion to the dogma) Gene can produce an RNA molecule (RNA itself has a function) Transcription- occurs in the nucleus Translation- occurs in the cytoplasm Reverse transcription: enzyme reverse transcriptase RNA polymerase: splits the DNA double helix, produces newly made RNA (5’ to 3’ direction) Produced using the template strand of the DNA Non-template strand of DNA Dna is eventually rewinded to double strand Downstream: 3’ end 2
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Direction of transcription is downstream (5 to 3’) Specific differences in eukaryotic transcription -sequence of TATA Box: helps recognise the start of transcription includes general transcription factors that bind at the promoter of the TATA box prokaryotes begin with RNA polymerase initially There are multiple RNA being produced on a single gene Prokaryotes- transcription and translation all occur in the cytosol of the cell Eukaryotic specific difference- splicing Introns are removed, exons are spliced and glued together to form one continuous stretch of RNA (coding segment/open reading frame), this coding sequence codes Spliceosome- recognises the boundary between exons and introns Contains protein and RNA recognises small RNA’s Remove introns and degrades them UTR- untranslated regions; originate from first and last exons Modulate the stability of mature mRNA or regulate translation -not translated, one at the 3’ end and one at the 5’ end Modifications of pre-mRNA
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