MCAT Anatomy CH 3,4 - Anatomy and Physiology (1)
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| transcription | the synthesis of RNA using a DNA template (DNA -> RNA)
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| translation | synthesis of a polypeptide under the direction of mRNA (MRNA -> proteins)
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| Structure of RNA vs DNA | Rna<br /> - single stranded, ribose sugar, U replaces T & pairs with A <br /><br /> DNA <br /> - Double stranded, deoxyribose sugar (mising O), ATGC, A&T, C&G
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| RNA Polymerase & 3 key features | catalyses the transcription of RNA from DNA<br /> Key Features<br /> - pries two DNA strands apart<br /> - synthesizes RNA in 5' -> 3' direction<br /> - doesn't need a primer to begin synthesis
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| RNA is always synthesized in what direction? | 5' -> 3'
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| 3 phases of transcription of RNA | 1. Initiation <br /> 2. transcription elongation<br /> 3. Termination
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| Initiation phase of TRANSCRIPTION (3 steps) | 1. transcription factors bind to promoter on DNA<br /> 2. RNA polymerase binds <br /> 3. RNA synthesis begins at the start point downstream from the TATA box
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| Transcription Elongation TRANSCRIPTION (4 key points) | 1. Only one DNA strand is copied by RNA polymerase <br /> 2.RNA polymerase adds the complementary base pair on RNA <br /> 3. RNA polymerase moves in 5'->3' direction <br /> 4. Synthesizes RNA at rate of 60 nucleotides /sec
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| Transcription termination TRANSCRIPTION (3 key points) | 1. termination sequence causes the RNA transcript to be released <br /> 2. In prokaryotes mRNA is immediately translated <br />3. in Eukaryotes, pre-mRNA transcript is modified before leaving nucleus (us)
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| Pre-mRNA Modifications after Transctipsions (where does it happen, what modifications) | Pre-mRNA mdifications in the nucleus before transportation into the cytoplasm. <br /> Modifications include: <br /> - 5' cap structure (capped with modified Guanine nucleotide)<br /> - 3' polyA tail (50=250 atenine nucleotides added <br />
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| Why are pre-mRNA modifications made? | to facilitate transport of mRNA out of nucleus <br /> and to slow degradation of MRNA into cytoplasm
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| Other pre-mRNA modifications | introns removed from Pre-mRNA transcript<br /> Exons - covalently linked to form mature mRNA
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| Why have introns? | if one or more introns is not removed, a new mRNA transcript (and protein) can be synthesized
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| How could 4 nucleotides encode 20 amino acids? | 4^3 = 64 (<20)
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| Codon | a three nucleotide sequence in mRNA that specifies which amino acid will be added to a growing polypeptide
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| Codon chart info (start codon, stop codon, how many codons code for each amino acid? ) | - AUG = start codon & methionine<br /> - UAA, UAG, UGA = stop codon<br /> each amino acid has 4-6 codons
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| Functions and Structure of T-RNa | - carries an amino acid to the ribosome<br /> - binds a codon on mRNA<br /> -one head has an amino acid attachment site, oter has anticodon region which base pairs with MRNA
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| Ribosome | - coordinates the pairing of trna with mrna - composed of two subunits (Lg and sm
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| Each Ribosome has 3 sites | EPA - <br /> E - exit site<br /> P - (tRNA + growing polypeptide) <br /> A - (tRNA and the next amino acid to be added)
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| three stages of translation | initiation, elongation +translocation, termination
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| Initiation of Translation (3 steps) | 1. small ribosomal subunit binds mRNA at the AUG<br /> 2. met-TRNA binds mRNa at the Aug site <br /> - the large ribosomal subunit binds<br /> NOTE: the met-RNA is in the P-site (middle)
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| Translational Ellongation + Translocation (4 steps) | 1. tRNA binds to A site<br /> 2. Peptide bond formation between 2 amino acids <br /> 3. the tRNA in the A site moves to the P site<br /> - the tRNA in the P site moves to the E-site and is released
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| Translational Termination | Stop codons (do not code for an amino acid)<br / >- release factor binds to stop codon and breaks the bond between the tRna and the polypeptide
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| point mutation (def & 2 categories) | one base pair change in a gene<br /> Categories include: <br /> - base pair substitution<br /> - base pair insertions or deletions
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| Missense (point mutation) | point mutation resultin in a new amino acid in the protein
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| nonsense | point mutation resulting in the early stop in the amino acid sequence, <br /> - results in a truncated protein , always harmful effects
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| Base pair substitution & its results | the replacement of one base pair with another<br /> can result in:<br /> - little or no change in protein <br /> - less active or inactive protein (rare)<br /> - improved protein (very, very rare)<br /> sickle-cell
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| Insertions and deletions results | - more harmful than base pair substitutions because can have potential effet on reading frame <br /> can cause frameshift in mRNA
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