Lecture 3H

Lecture 3H - #3 Structure and function of genes RNAs and...

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#3 Structure and function of genes, RNAs, and proteins 1. Gene structure and function 2. RNA structure and function 3. Protein structure and function 4. The “central dogma” 5. Mutations
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1. Gene structure and function - A gene is the entire DNA sequences required to encode a functional polypeptide (protein) or RNA (tRNA, rRNA, miRNA etc). - Cistron is an old name for gene. -A pseudogene is DNA sequence that looks like a gene but is not transcribed, pseudogenes are most likely dead genes.
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Gene structure terminator gene Transcribed region DNA promoter mRNA protein regulatory elements (enhancer, silencer, operator, etc) intron intron
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1. Promoter a sequence that determines transcription (RNA synthesis) initiation, it is always at the 5’ end (of the strand that is identical to RNA) of the transcribed region. Promoters are usually 10 2 bp long, they contain specific sequences (usually 5-10 bp long each) that allow RNA polymerase and transcription factors to bind to. One of such sequences is called TATA box. 2. Transcription regulatory sequences Sequences that are not promoter but can also regulate transcription. e.g. operator (prokaryote), enhancers, silencers (eukaryote) 3. Transcribed sequence the sequence that is actually copied into RNA, including 5'UTR,amino acid coding sequence (and introns for eukaryotic genes), and 3'UTR 4. Terminator transcription termination sequence, it is always at the 3’ end of the transcribed region Basic gene structure
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1. Prokaryotic genes are polycistronic —one promoter direct the synthesis of a mRNA that can encode more than one proteins Eukaryotic genes are monocistronic —one promoter direct the synthesis of a mRNA that encodes only one protein. 2. Eularyotic (but not prokaryotic) genes go through post- transcriptional RNA processing, to add CAP, polyA tail, and to remove introns Introns are non-coding sequences of a gene that are transcribed into RNA, but later cut off and never get translated into protein. Exons are the regions of a gene that are translated into protein Procaryotic and eukaryotic genes
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Gene function The major function of a gene is to direct synthesis of RNA (transcription) and protein (translation)
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RNA is a single strand polyribonucleotide composed of 4 ribonucleotides: A, C, G, and U. RNA uses ribose instead of deoxyribose 2. RNA structure and function
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RNA and DNA RNA DNA ssDNA is stable in alkaline solution, but RNA is not. Why? The 2’-OH group makes RNA unstable in alkali, because it can attack the phosphodiester bonds of the RNA chain and break RNA into small pieces or nucleotide monomers RNA DNA
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DNA RNA sugar Deoxyribose ( 2 -H ) Ribose ( 2 –OH ) base A, C, G, T A, C, G, U structure double strand single strand size large (kb-Mb) Small (bp-kb) type DNA mRNA, tRNA, rRNA, snRNA Stability in alkaline Stable (ds DNA denatured at high pH but it is not hydrolyzed) Unstable (Hydrolyzed to nucleotides) Comparison between RNA and DNA
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1. Secondary structure The secondary structures are stem-loops and hairpins, which are
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