BIOL 152 Bulluck Lecture 1 Gene The gene states the characteristics of an organism Region of DNA whose final product is either a polypeptide or an RNA molecule Proteins Proteins are the link between genotype and phenotype Gene expression Process by which DNA directs protein synthesis Two stages of gene expression o Transcription occurs inside the nucleus o Translation occurs in the cytosol of the cell One gene one enzyme hypothesis A flaw with this hypothesis is that not all proteins are enzymes so this lead the hypothesis of one gene one enzyme to be inaccurate One gene one protein hypothesis A flaw with this hypothesis is that proteins are made up of more than one polypeptide so specifying one gene to one protein is inaccurate Proteins also comprise of beta and alpha structures that give it a dynamic function for genes to specify a single protein One gene one polypeptide hypothesis This is the best hypothesis but still isn t technically true because it has been recently discovered that one gene doesn t necessarily define one polypeptide but also codes for certain RNA molecules involved in protein synthesis 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 Three differences between DNA and RNA 1 Double helix in DNA vs Single stranded in RNA 2 Thymine is in DNA vs Uracil takes the place of Thymine in RNA 3 Deoxyribose structure lacks an oxygen vs Ribose structure has oxygen Transcription in Prokaryotes 1 Initiation begins at the Promoter region 2 Elongation occurs with the help of RNA polymerase RNA polymerase pries DNA strands apart and joins RNA nucleotides RNA polymerase doesn t need primer RNA polymerase processed in a 5 to 3 direction 3 Termination RNA polymerase falls off after reaching stop codon The mRNA is ready for use and will processed to translation without any modification to mRNA Transcription in Eukaryotes 1 Initiation Promoter starts initiation o Promoter binds after seeking the TATA box which are repeating codes of TATATA that signal transcription factors to bind to the region to start initiation o Transcription errors lead to diseases o Transcription factors make up a huge part of DNA 10 o This region where initiation begins is called the Transcription Initiation Complex o Prokaryotes don t have transcription factors 2 Elongation RNA polymerase copies 40 nucleotides sec Single genes can be transcribed simultaneously RNA polymerase unwinds DNA and adds nucleotides to growing mRNA strand 3 Termination Terminator sequence tells the RNA polymerase to stop In eukaryotes the mRNA strand goes through modification before beginning translation o Polyadenylation signal sequence RNA Splicing Introns non coding regions Exons expressed regions or regions that exit Splicesomes protein complex made up of snRNAs small nuclear RNA that make up snRNPs small nuclear RNA protein complex Together they make the splicesome Importance of Introns Alternative RNA splicing 1 gene can encode more than 1 polypeptide The genes protein products RNA Processing after Transcription In eukaryotic cells there are enzymes that alter both ends of primary transcript mRNA o 5 prime cap is attached to mRNA o 3 prime poly A tail is attached to mRNA o Prokaryotes don t have a nuclear membrane so their mRNA is ready for translation unlike eukaryotes Function of these modification in eukaryotes o Seem to facilitate exiting nucleus o Protect mRNA from hydrolytic enzymes o Ribosome attachment Why need an RNA intermediate Protects DNA blueprint Allows copies of protein to be made simultaneously this makes it more efficient Many RNA transcripts can be made from one gene Codons Codon are series of non overlapping three nucleotide words that provide the genetic instructions for a polypeptide found in mRNA Evolution of the genetic code It is nearly universal Translation in Prokaryotes and Eukaryotes mRNA is translated into protein Interpreter is the tRNA translational RNA Site of translation is at the ribosome Transfer RNA Transcribed from DNA Translation 1 Initiation mRNA binds to small subunit tRNA binds to mRNA start codon AUG Large subunit then binds to the small subunit finally making a ribosomal site for translation to occur 2 Elongation Moves from the Active site to Polypeptide site where the chain of polypeptides are formed Then the empty tRNA that has already translated its codons to a protein moves to the Exit site where it leaves 3 Termination Stop codon is a release factor that adds water this begins hydrolysis which breaks the subunits apart Post translation Spontaneous folding secondary and tertiary The polypeptide chain go into Chaperonin cells that protects the chain and folds the chain properly During post translational modifications o Sugars phosphates lipids etc can be added o Removes few Amino Acids from the N terminus o Cleaving of the polypeptide chains can occur o The original chain may join with other polypeptide chains to make complex proteins Polyribosomes Are an array of ribosomes that consequently translate mRNA in a chain to make polypeptide chains faster Types of Point Mutations Substitutions Often have the least effect on an organism leads to Missense or Nonsense mutations Insertions and Deletions Almost always disastrous causes Frameshift mutations Point mutations If occurs in germ cells can cause hereditary disease Change in a single nucleotide can lead to abnormal proteins General DNA and RNA Overview Francis Crick named the dogma DNA RNA Protein DNA polymerase moves 5 to 3 direction RNA polymerase moves 3 to 5 along template strand DNA and RNA are polymers of nucleotides Proteins are polymers of amino acids Genes are hundreds to thousands of nucleotides long DNA and RNA have two different chemical languages mRNA is complementary not identical to DNA template Diseases are necessarily not in the genes but in the switches that regulate genes