BOLOGY 107 Lecture 29 Outline of Last Lecture I Gene Expression a Transcription cont b RNA Processing c Translation Outline of Current Lecture II Gene Expression a Translation cont b Protein targeting c Polyribosomes III Mutations a What they are b How they arise Current Lecture Gene Expression 1 Translation cont a tRNA i Cloverleaf structure when modeled in 2D l shaped in 3D ii Anticodon base pair for codons on mRNA iii Amino acid attachment site 3 opposite of anticodon b Activation i tRNA syntetase binds tRNA to amino acid match 1 Uses one ATP 2 Specific enzyme for each amino acid c Ribosome i Consists of protein and RNA 1 rRNA acts as catalyst protein holds structure 2 Large subunit and small subunit ii 3 binding sites 1 A site aminoacyl new tRNA enters binds to mRNA 2 P site peptidyl amino acids are bound to each other most recent still attached to tRNA 3 E site exit empty tRNA leaves the complex These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute a Each site aligns with a codon on the mRNA d Initiation i Small subunit of the ribosome attaches to mRNA 1 Eukaryotes bind at 5 cap bacteria specific sequence ii Small subunit lines up with the start codon start tRNA methylanine binds to the codon iii Large subunit attaches with start tRNA in P site 1 Uses GTP e Elongation i Codon recognition 1 Aminoacyl tRNA loaded into A site a Anticodons sampled similar to DNA synthesis b Uses GTP for loading factor ii Peptide bond formation 1 A site acid bonded to P site peptide chain a Transfers polypeptide to A site iii Translocation 1 Complex shifts by one condon a Uses one GTP 2 Empty tRNA in E site tRNA connected to the polypeptide in P site A site open for tRNA a Empty tRNA leaves new tRNA enters cycle begins again f Termination i Protein release factor RF binds to stop codon in A site ii Bond connecting peptide to P site tRNA is hydrolyzed tRNA releases polypeptide iii Ribosome dissociates releases mRNA 1 Uses GTP iv Protein folds into secondary and tertiary structures as it exits the ribosome top 2 Protein targeting a Signal sequence targets protein to endomembrane system i Specific sequence found in first amino acids of new protein ii Recognized by signal recognition proteins SRP iii Entire ribosome dragged to rough endoplasmic reticulum 1 Injects protein through ER membrane 2 Signal peptide removed from protein during processing 3 Polyribosomes polysomes a Multiple ribosomes translate the same mRNA i Once one ribosome clears the start codon another can attach and start processing ii Allows for rapid translation b Linked transcription and translation i Bacteria do not have a separation for transcription and translation 1 Multiple RNA polymerases can transcribe the same gene 2 Polysomes attach to each mRNA start translating 3 Exponential protein synthesis Mutations 4 What they are a Change in DNA sequence b Mutations classified by effect on protein i Silent no change 1 Same amino acid is coded for in the new codon as in the old ii Missense changes amino acid iii Nonsense mutation premature termination 1 New codon codes for a stop rather than an acid iv Framshift insertion or deletion of bases 1 Number added or deleted is not divisible by three changes all subsequent codons shifts reading frame 2 Usually results in premature termination v Entire codon shift insertion or deletion of entire codon 1 Number added or deleted is divisible by three removes or adds an amino acid 2 Subsequent codons are read the same 3 Can still be detrimental one amino acid can change the whole proteins shape 5 How they arise a Error in DNA replication i UV light ii Ionizing radiation iii Chemical mutagens 1 While there are mechanisms to correct these errors the correction mechanisms can have an error End of Exam 3
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