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 Processing II 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 ribosomes o A poly A tail A is for adenines is added to the 3 end to prevent degraded Intron Splicing o 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 tRNA o Anticodon Three unpaired nucleotides that pair with the codon at the of mRNA o Aminoacyl tRNA Synthetase An enzyme that charges tRNAs by attaching the appropriate amino acid to them 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 acid o 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 ribosome o 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 time o 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 away o If there is no release factor there is no termination and translation continues Mutations o 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 a stop 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 missense o 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 environment