Introduction to Genetics BSCI223 Exam 2 Review Gene names are italicized and all lowercased Protein names are not italicized and they are capitalized Prokaryotic chromosomes are super coiled and highly compacted in order to fit into the cell DNA Nucleotides Adenine Guanine Cytosine Thymine Cytosine and guanine form 3 hydrogen bonds adenine and thymine form 2 A and G are purines C and T are pyrimidines The backbone of the DNA chain is alternating phosphates and the pentose sugar deoxyribose Phosphates connect to 3 carbon of one sugar to the 5 of the adjacent sugar DNA strands are antiparallel and complementary 10 base pairs make up one turn of the helix RNA Nucleotides Adenine Guanine Cytosine Uracil The backbone of RNA contains ribose sugar OH group on the 2 carbon and triphosphate Genome entire complement of genes in a cell or virus Chromosome main genetic element essential for life Plasmid replicate separately from the chromosome circular double stranded help antibiotic resistance Prokaryotes have no compartmentalization and can do transcription and translation simultaneously Eukaryotes have compartmentalization and transcription occurs n the nucleus and translation occurs at the ribosome Diauxic growth Response of a culture of microorganisms based on a phenotypic adaptation to the addition of a second substrate Syncytia a multinucleated mass of cytoplasm that is not separated into individual cells Palindromic sequence a nucleic acid sequence that is the same on both strands when read 5 to 3 DNA Replication A semi conservative process Replication ALWAYS proceeds from the 5 end to the 3 end Molecules are always added to the 3 end DNA polymerase catalyzes DNA synthesis adds nucleoside triphosphates to the 3 OH end only of an existing strand When a new base is added to a strand 2 phosphates are released Elongates the strand 5 3 RNA Primase makes RNA primer RNA Primer made of RNA that synthesizes DNA replication Makes primer run from the 5 end to the 3 OH end There are two primers at the origin of replication that enable the DNA polymerase to come in and extend the strand Leading strand only needs to be primed once at the original of replication It grows towards the replication fork Lagging strand needs many primers at the beginning of each Okazaki fragment It grows opposite of the replication fork Lagging strand grows until it hits the leading strands primer A nick is created DNA polymerase then takes out the primer Ligase repairs the nicks in the DNA strands Eukaryotic organisms have multiple origins of replication Transcription Central dogma DNA RNA Protein When we draw DNA and RNA we place the 5 end on the left and the 3 end on the right on the top strand Promoters found at the 5 ends of genes initiate transcription RNA polymerase recognizes promoter sequence and hydrogen bonds to the DNA moves downstream from the promoter 5 3 Adds bases to the 3 OH of growing DNA Don t need a primer to start working The bottom strand is the template strand The new RNA grows 5 to 3 Sigma factor required for initiation of transcription helps RNA polymerase bond to DNA enhances recognition of promoter Terminator the signal to stop transcription Self termination when the RNA transcribes the terminator sequence and it cause the RNA to fold and RNA polymerase loses grip of the DNA Enzyme dependent termination rho pushes between polymerase and DNA releasing the polymerase Eukaryotes have exons coding and introns noncoding The introns are spliced out Translation Ribosome small ribosomal subunit interacts with the mRNA attracts a tRNA to the site Binds to mRNA molecule because the 3 end of the 16s ribosome can form a hydrogen bond with the 5 end of mRNA Anticodon on tRNA matches with mRNA codon and proteins are RBS ribosome binding site on the mRNA where the ribosome added binds Start codon downstream from RBS AUG begins translation Stop codon ends translation UGA UAA UAG Mutations Silent mutation the change of a base pair but it doesn t change the amino acid because it codes for the same one Missense mutation change the protein sequence change a base pair and it does change the protein doesn t code for the same one Lead to changes in tertiary structure and sometimes loss of protein function Nonsense mutation the change of a base pair to make a stop codon and translation ends prematurely Loss of function of protein Frameshift insertion insertion of a base to change the entire Frameshift deletion deletion of a base to change the entire Not all mutations show phenotypic changes Sources of Mutation DNA polymerases make a mistake and add the wrong base Radiation UV light and thymine dimmers radicals that damage sequence sequence bases Chemical mutagens alfatoxin switches CG to AT and could cause missense or nonsense mutation intercalating agents get in the way of the DNA strand and cause a bubble to form and could cause an insertion or deletion Methylation marks the DNA the part of the DNA that isn t methylated is reviewed by the cell to see if there is a mutation DNA polymerases proofread replicated DNA Mutations that are not repaired by proofreading are repaired by mismatched post replication repair followed by excision repair Mutations that occur spontaneously at any time require excision repair Ames Test mutation rate of salmonella mix cells in liver extract and a chemical that is a potential mutagen Liver extract evokes metabolism Count number of colonies Gene Regulation Helps organism adapt to changing environments Allows organisms to conserve energy Allows organism to switch developmental growth processes Genes are regulated by transcription and translation Constitutive genes are always on Inducible genes that are shut off until an environmental signal turns them on Repressible genes that are generally on until an environmental signal shuts them off Inhibition the allosteric inhibitor binds to the allosteric site of the enzyme and then the substrate can t bind and no activity takes place Operon a series of genes that are all transcribed on the same mRNA and share a promoter All have similar functions Lac Operon LacI regulatory gene that makes the LacI protein It is constitually on The cell always makes LacI a repressor protein If there is no lactose in the cell LacI binds to the operator which is after the promoter and transcription will not occur Blocks RNA polymerase from moving forward When LacI is met with lactose it can no longer bind to the operator and transcription occurs Minimal media