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| transcription |
the synthesis of RNA using a DNA template (DNA -> RNA) |
| translation |
synthesis of a polypeptide under the direction of mRNA (MRNA -> proteins) |
| 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 |
| 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 |
| RNA is always synthesized in what direction? |
5' -> 3' |
| 3 phases of transcription of RNA |
1. Initiation <br /> 2. transcription elongation<br /> 3. Termination |
| 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 |
| 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 |
| 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) |
| 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 /> |
| Why are pre-mRNA modifications made? |
to facilitate transport of mRNA out of nucleus <br /> and to slow degradation of MRNA into cytoplasm |
| Other pre-mRNA modifications |
introns removed from Pre-mRNA transcript<br /> Exons - covalently linked to form mature mRNA |
| Why have introns? |
if one or more introns is not removed, a new mRNA transcript (and protein) can be synthesized |
| How could 4 nucleotides encode 20 amino acids? |
4^3 = 64 (<20) |
| Codon |
a three nucleotide sequence in mRNA that specifies which amino acid will be added to a growing polypeptide |
| 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 |
| 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 |
| Ribosome |
- coordinates the pairing of trna with mrna - composed of two subunits (Lg and sm |
| 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) |
| three stages of translation |
initiation, elongation +translocation, termination |
| 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) |
| 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 |
| 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 |
| 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 |
| Missense (point mutation) |
point mutation resultin in a new amino acid in the protein |
| nonsense |
point mutation resulting in the early stop in the amino acid sequence, <br /> - results in a truncated protein , always harmful effects |
| 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 |
| Insertions and deletions results |
- more harmful than base pair substitutions because can have potential effet on reading frame <br /> can cause frameshift in mRNA |
