Translation of proteins.pdf

Translation of proteins DNA → RNA → Polypeptide  After this chapter you will be able to... Identify the simple backbone structure of all amino acids (note: do not memorize all individual amino acids) Explain the primary, secondary, tertiary, and quaternary structure of polypepti...

Translation of proteins DNA → RNA → Polypeptide  After this chapter you will be able to... Identify the simple backbone structure of all amino acids (note: do not memorize all individual amino acids) Explain the primary, secondary, tertiary, and quaternary structure of polypeptides Explain what is meant by the genetic code being “degenerate” and “universal” Apply the genetic code table correctly to translate DNA or RNA sequences Explain the wobble position in a codon and what this means Explain the reading frame and be able to find it in a sequence Explain the process of translation including roles of tRNA, ribosome sites in bacteria Explain mutation types: missense, nonsense, silent, frameshift Predict the most likely outcome of mutations including whether mutation is in a coding or non-coding part of a gene Amino Acid structure and bonding No, you do not need to memorize the a.a. N-terminus C-terminus Levels of protein structure Tertiary –interactions among side chains Primary – Quaternary Secondary – sequence of –interactions between H-bond amino acids 2 or more separate interactions polypeptides among backbone The process of translation What’s needed? Large & small ribosomal subunits mRNA sequence tRNA “adapters” Amino acids (building blocks) Initiation factors Note directionality The Genetic Code Explain the following ○ Codon ○ Degenerate ○ Synonymous ○ Universal Why a three letter code? Why not two letter code? The Genetic Code Mutations Silent Missense Nonsense Frameshift Degeneracy and the Wobble hypothesis  How does a cell read the RNA sequence? 3 bases at a time (codon) Nonoverlapping → Starting signal is the initiation (start) codon Open reading frame (ORF) +1 +2 +3 Where you start 5’THECATANDRATATEONEHAT-3’ reading matters! Change the THE|CAT|AND|RAT|ATE|ONE|HAT reading frame, change the T|HEC|ATA|NDR|ATA|TEO|NEH|AT whole message! TH|ECA|TAN|DRA|TAT|EON|EHA|T +1 +2 +3 5’THECATANDRATATEONEHAT-3’ 5’THECATANDRATATEONEHAT-3’ Frameshift THE|CAT|AND|RAT|ATE|ONE|HAT mutations – THE|CAT|ANA|TEO|NEH|AT change all codons after the mutation The role of tRNA - adapter Each amino acid (aa) is carried by a specific tRNA tRNA with aa attached is called “charged” Base pairs with mRNA codon Elongation in bacteria Eukaryotic initiation 5’ cap required mRNA forms loop with interaction between 5’ & 3’ poly(A) tail Termination of Translation Stop codons - no tRNA pairs with stop codon Instead, a release factor protein enters the A site Question 3 What functional impacts does the difference in cell structure make with respect to translation in bacteria vs. eukaryotes? [Hint: think about timing] Mutations & effects on polypeptide products - summary Consider the following types and/or locations of mutations and what effect (if any) these will have on a protein product: 1. Single base change in the coding sequence of a gene (point mutation) a. Nucleotide level: Transition vs. transversion, insertion/deletion b. Amino acid level: missense, nonsense, silent 2. Addition or deletion of nucleotide(s) in a gene a. Frameshift (applies to both nucleotide and aa sequence) 3. Mutation in a noncoding sequence of a gene (promoter, etc.) a. Up mutation vs. down mutation - how much transcription 4. Mutation in somatic vs. germ cells Summary of molecular genetics unit of semester Series of experiments revealed DNA is the hereditary material for all cellular life Bacteria reproduce asexually but can trade DNA in many ways Series of experiments and modeling revealed the structure of DNA and RNA; this structure (complementary bases, antiparallel) informs us of everything else! Structure of DNA suggested three models of DNA replication - experiments reveals semiconservative model fit best Structure of DNA can be read (one strand at a time) to build new RNA strands Most RNA transcripts are modified before taking final form mRNA is read to build polypeptides; tRNA & rRNA have crucial functions in translation; tRNA is adapter that allows conversion from nucleic acid to amino acid Any gene (or noncoding region) can be mutated in many ways at the DNA level; this change is carried through to RNA and possibly polypeptide Mutations may have many effects: change of protein structure/function, change amount of protein, no change at all