BIOLOGY 111 1st Edition Lecture 21 Outline of Last Lecture I. Transcription II. Translation III. Structural Differences between DNA and RNA IV. DNA Template Strands V. Codons Outline of Current Lecture I. RNA ProcessingII.Current Lecture- RNA Processing (eukaryotic RNAs are modified at both ends o A Cap (modified GTP) is added to the 5’ end to help the RNA in exiting the nucleus without any issues and to aid in binding to the ribosomeso A poly-A tail (A is for adenines) is added to the 3’ end to prevent degraded- Intron Splicingo When a eukaryotic transcript is modified, Intons (intervening, non-protein coding, regions) are removed and the exons (protein coding regions which are expressed) are brought together “splicing”o There are also some untranslated regions which are basically left over introns)o Intron splicing is very important and must be done before a ribosome can translate the “message” to the proteins- Translation o Ribosomes read the information encoded on the RNA three nucleotides (or codon) at a time. o Each codon specifies for a particular amino acid. Start codon is AUG – Methionine  Stop codons are UAG, UAA, UGA o Transfer RNAs (tRNAs) tRNAs are responsible for carrying amino acids to the ribosomes There are 20 different amino acids, and each have their own tRNAo Anticodon Three unpaired nucleotides that pair with the codon at the of mRNAo Aminoacyl tRNA Synthetase  An enzyme that charges tRNAs by attaching the appropriate amino acid tothem 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. It is what actually adds the amino acid according to the correct tRNA sequence  “charged DNA” is a tRNA with an attached amino acido Ribosomes have 3 sites that can hold tRNAs P site: holds the tRNA that carries the growing polypeptide chain A site: holds the rRNA that carries the next amino acid to be added to the chain E site: the exit site, discharged tRNAs leave the ribosomeo Amino end binds with the carboxyl end by a Ribozyme which makes peptide bonds in a growing polypeptide chain- Protein Elongation o Elongation indicates a growing polypeptide change, one amino acid at a timeo Elongation requires three steps  Codon recognition  Peptide bond formation  Translocation - Termination o Termination is a release factor that is signaled by a stop codon o This frees (releases) the RNA from the ribosome and all subunits go awayo If there is no release factor, there is no termination and translation continues- Mutationso Mutations are changes in the nucleotide sequence that can affect protein structure and function o Point mutations are chemical changes in one base pair of a gene (not all point mutations are bad, but some are)o Base-pair substitutions:  Silent base pair mutations show no effect on the protein or amino acid Nonsense mutations are any type of substitution that accidentally forms astop codon (“premature stopping”)  Missense mutations completely change amino acids (can be one or many)o Frameshift is the insertion or deletion which also contains nonsense and missenseo Mutations can be spontaneous (sudden change, not expected) or induced (created)o Also can be germ line (occurring in the gametes) or somatic cell (which do not necessarily carry on through generations and arise in the