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Bio Exam II
Gene expression
| Term | Definition |
|---|---|
| Flow of genetic info | - Crick (1956) - DNA to RNA to Protein - In cells it's unidirectional (goes in one direction) |
| Originally "1-gene, 1-enzymes" | - not all proteins are enzymes -revised to : 1 gene- 1 protein but not all proteins are single polypeptides - revised to 1 gene- 1 polypeptide * still not 100% accurate |
| Processes | - Transcription: DNA to RNA - Translation: RNA to polypeptide ( ribosomes use info in RNA to make polypeptide) |
| RNA composition and types | - ribonucleic acid - DNA: deoxyribose; ATCG, double strand - RNA: ribose; AUCG; single strand |
| Ribose | - contains an -OH where DNA only has an -H ( DNA is more stable) |
| Uracil | - pyrimidine base - used instead of thymine in RNA - same structure as thymine minus on methyl group (-CH3) - Complementary to adenine |
| 3 types of RNA | - mRNA: Messenger; encodes AA sequence - rRNA: ribosomal; part of ribosome structure - tRNA: transfer; carries AA's to ribosome during translation |
| The genetic code | - order of amino acids - mechanisms for A,U,C,G - reads 3 bases @ a time - Crick figured it out |
| Codons | - 3 bases= 1 amino acid - 4 bases (AUCG) so there are 64 possible combos |
| The genetic code | -Unambiguous: each codon codes for 1 AA - degenerate: several codons coding for same AA |
| Genetic Codon | - 1 start codon: AUG: starts translation - 3 stop codons: UAA,UGA,UAG: stops translation |
| Reading Time | - codons must be grouped correctly - mutations can result in frame shift ( deletion specifically) |
| Genetic Code is mostly universal | - minor exceptions in some microbes and mitochondria - generally the same across viruses, & cellular life |
| Transcription (1st part of gene expression) | - synthesis of RNA complementary to DNA - 3 stages |
| Transcription Initiation | - DNA is template for RNA synthesis & reads on 3'-5' direction - one strand in transcribed (template strand) ; other strand not transcribed - RNA synthesized in 5'-3' direction |
| Components of Transcription initiation | - Promoter: specific DNA sequence on transcribed strand (promoter region not transcribed) - RNA polymerase: makes new RNA strand; binds promoter; unwinds helix; begins transcription |
| RNA synthesis | ex. Non Transcribed Strand: 5' A-T-G-A-C-T 3' Transcribed "template" Strand: 3' T-A-C-T-G-A 5' RNA: 5' A-U-G-A-C-U 3' |
| Transcription Elongation | - RNA synthesis; anti- parallel to template strand - Uses RNA nucleotide triphosphate |
| Transcription Termination | - specific DNA sequence signals RNA polymerase to stop (not a stop codon) - RNA transcription stops & polymerase falls off - results in completed RNA strand |
| mRNA modification | - only in eukarytoes - transcription to pre-mRNA; not useful for protein synthesis - Add 5' Cap to get out nucleus - Add ploy-A-tail to get out nucleus; provide protection; and ribosome recruitment |
| RNA Splicing | - exons: coding region in pre-mRNA - introns: non-coding region in pre-mRNA - splicing: process of removing introns from pre-mRNA - occurs in nucleus |
| Translation | -mRNA to polypeptide - occurs in ribosomes (cytoplasm or surface of ER) |
| Components | - tRNA; small RNA mol; single strand about 80 nucleotides - 3D structure, intramolecular base-pairing |
| tRNA function | - binds specific AA - brings AA into ribosome - binds correct codon to mRNA - AA can be added to polypeptide |
| Anti Codon | - 3 specific bases on loop of tRNA - complementary to codon on mRNA |
| Many different tRNA's | - all general same shape - each w/ different anti-codon, carries diff. AA - made by aminoacyl-tRNA synthetases |
| Ribosomes | - carries out translation - protein + rRNA |
| rRNA | - ribosomal RNA - transcribed from DNA- not translated into protein |
| Ribosome function | - works as a large enzyme complex - catalyzes reaction b/w mRNA, charged tRNAs, & polypeptides |
| Translation Initiation | - small ribosomal subunit binds mRNA and tRNA- met - moves along mRNA until reaches AUG - initiation factors bring in large subunit (translation initiation complex) |
| Translation Elongation | -repeating cycle - peptide bond formation -translocation - each cycle adds single AA |
| Translation Termination | - stop codon not recognized by tRNA's - recognized by release factors (proteins)- bind to stop codon A site - cannot form new peptide bond - polypeptide released |
| Translation Termination results in... | - release of polypeptide from p-site - release of mRNA - release of last tRNA - dissociation of ribosomal subunits |
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tennadeleta.
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