BIO 101 1st Edition Lecture 21 Outline of Last Lecture I DNA as the genetic material a Transformation Experiments b Bacteriophage experiments II DNA Structure III DNA Replication Outline of Current Lecture I Transcription II Translation a Initiation b Elongation c Termination III Genetic Code a Messenger RNA b Transfer RNA c Ribsosome IV Mutations a Base pair substitutions b Base pair deletions or insertions V Split Genes and RNA Processing VI MicroRNAs and Gene Expression VII Molecular Biology of Cancer Chapter 17 From Gene to Protein Inherited DNA controls the cell s activities How It has the code for how to make enzymes and other proteins DNA does not make protein directly First the information in DNA is copied to an RNA molecule called messenger RNA mRNA The mRNA programs the making of protein This protein is called the CENTRAL DOGMA OF MOLECULAR BIOLOGY Transcription synthesis of RNA from a DNA template Information in DNA is copied into a RNA molecule mRNA is made by an enzyme called RNA polymerase BIO 101 1st Edition RNA polymerase binds to DNA at the beginning of a GENE gene has the code for how to make some particular protein at a specific place called the promoter RNA polymerase is guided the promoter by special proteins called TRANSCRIPTION FACTORS Once at the promoter RNA polymerase moves along the DNA and separates the two strands One of the two strands acts as a template to make RNA by the base pairing rules RNA nucleotides C G A U line up properly on the DNA template strand remember that RNA nucleotides include U in place of T by hydrogen bonding RNA polymerase links the lined up RNA nucleotides together to form the RNA molecule RNA is made 60 nucleotides second As RNA is made it peels off of the DNA Then 2 DNA strands come back together TRANSCRIPTION stops at a place on the DNA called a terminator At the terminator RNA polymerase releases the finished mRNA molecule and then falls off the DNA Translation synthesis of protein using mRNA information mRNA polymer of 4 different nucleotides G C U A proteins polymers of 20 different amino acids The Genetic Code How does the code work to translate from the language of nucleotides to the language of amino acids X 1 nucleotide 1 amino acid could only code for 4 amino acids X 2 nucleotides 1 amino acids of combinations of 4 things taken 2 at a time 4 2 16 could only specify 16 different amino acids BIO 101 1st Edition 3 nucleotides 1 amino acid 4 3 64 possible combinations more than enough Each 3 nucleotide code word is called a CODON codes for some particular amino acid First Codon was deciphered in 1961 by Nirenberg He made a synthetic mRNA test tube poly U Then translated it into vitro in test tube The protein that was made was composed entirely of the amino acid phenylalanine Therefore the codon UUU code for the amino acid phenylalanine Later all 64 possible combinations of nucleotides were deciphered o 61 code for amino acids o 3 don t code for any amino acid Instead they are signals to STOP translation STOP CODONS All living organism share the same genetic code Indicates that the genetic code was established very early in evolution this is an example of the unity in life How does the cell translate nucleotide codon into proteins Equipment needed for translation mRNA messenger RNA tRNA transfer RNA ribosomes 1 Messenger RNA mRNA RNA molecule that carries the coding information a series of codons that must be decoded one right after the other Translation starts at the first START CODON AUG from the 5 end of the molecule The region from the CAP a stabilizing and regulating structure to the START CODON is not translated into amino acids it is called the 5 untranslated region 5 UTR Translation ends at a STOP CODON not at the very end of the mRNA The region between the STOP CODON and the 3 end is NOT TRANSLATED and is called the 3 untranslated region 3 UTR The 3 end of the mRNA has a string of As called polyAtail acts to stabilized mRNA and regulate translation 2 Transfer RNA tRNA function as a decoder pairs the right amino acid with its CODON i e amino acids do not recognize their own codons BIO 101 1st Edition tRNA is a small RNA 80 nucleotides shaped like an L upside down and backwards L One end has a sequence of 3 nucleotides called the ANTI CODON it recognizes a particular codon on the mRNA by the base pairing rules The other end of the tRNA carries the correct amino acid the amino acid coded for by the codon that is recognized by the anti codon of the tRNA 3 Ribosome organelle that coordinates the pairing of tRNAs with their mRNA codons Ribosomes are composed of 2 subunits LARGE SUBUNIT and SMALL SUBUNIT The 2 ribosomal subunits are separate EXCEPT when translating mRNA into protein Each ribosome has one binding site for mRNA and 3 binding sites for tRNAs E site P site and A site Translation synthesis of proteins using info in mRNA Occurs in 3 stages initiation elongation termination First 2 stages require energy input from cell all stages require enzymes 1 Initiation mRNA and special tRNA initiator tRNA bind to small subunit of ribosome Requires a set of initiation factors Initiator tRNA anticodon is base paired with the START CODON on mRNA Large subunit of ribosome binds with initiator tRNA is the P site functioning ribosome 2 Elongation A tRNA with correct anticodon for the next codon after the START CODON binds in the A site with its anticodon base pairing with next codon A peptide bond forms between the 2 amino acids on the tRNAs in the P and A sites The connected amino acids stayed attached to tRNA in A site but are released from tRNA in P site BIO 101 1st Edition The ribosome moves over ONE CODON so that tRNA in P site now without an amino acid is in E site and is released the tRNA that was in A site is now in P site still holding the growing amino acid chain and the A site is over next codon Cycle is repeated until protein is complete ribosome always moving ONE CODON at a time from 5 3 3 Termination translation stops Ribosome comes to a termination codon it does not code for any amino acid so no tRNA pairs with it A release factor binds in A site this releases the protein ribosome separates into subunits ready to translate next mRNA Mutations a change in the nucleotide sequence in DNA 1 Base pair substitutions one nucleotide pair is replaced by another 2 basic kinds A missense alters a codon in a gene new codon still codes for an amino acid Depending on how different the new amino acid is and where it is