The Molecular Basis of Inheritance Study Guide

The Molecular Basis of Inheritance Evidence that DNA can Transform Bacteria: ● Griffith experiment ○ Two strains of bacterium (one pathogenic one non pathogenic) ○ Killed pathogenic strain and mixed with non pathogenic, non pathogenic turned pathogenic ○ This phenomenon is called transformation Transformation is now defined as a change in genotype and phenotype due to external DNA which nters through plasmids Plasmids are double stranded DNA molecule that carries genes separate of those in a bacterial chromosome. Can be used as a vector Vector is an organism that transmits pathogens from one host to another ● Bacteriophages ○ Viruses are DNA with a protective protein ○ They take over the cell’s machinery, so must have have genetic material to get cells to do this ● Hershey and Chase experiment ○ Radioactive DNA (blue) and radioactive protein (pink) ○ Viruses exposed to cells, blue is found inside its designated cell, pink was found outside ○ This proved that DNA was genetic material, not proteins Composition of DNA: ● Nucleotide ○ Nitrogenous base (Thymine, Adenine, Cytosine, Guanine) ○ Phosphate Group (negatively charged) ○ Deoxyribose sugar (3’ at bottom, 5’ at top) ● Chargaff discovered ratios between A & T and C & G ● Watson, Crick, and Franklin discovered the double helix structure of DNA ● Watson and Crick created a model showing that the sugar - phosphate backbones run oppositely 5’ to 3’ and 3’ to 5’ DNA Replication: ● Basic concept is DNA is split into two strands, then complementary bases are added so two double stranded DNA is formed ● Different models ● 1. 2. 3. 4. 5. 6. ○ Conservative model states parent copies itself once, and then both itself and the offspring replicate again. Results in three replicated double stranded DNA and the double stranded parent ○ Semiconservative model states that parent breaks into two single strands and then each strand replicates itself. Result in two pure double stranded DNA and two mixed parent and replicated strands ○ Dispersive model states each replicated strand has parts of the parent and parts of the replication Step by Step DNA Replication Helicase unwinds the double helix at the origin of replication Primase adds RNA primer (1 to leading strand near 5’ end and multiple on lagging strand, starting near 3’ end) DNA polymerase III builds off of the RNA primer by adding complementary bases in a 5’ to 3’ (leading strand) DNA polymerase III builds off RNA primers by adding complementary base pairs in between RNA primers in same 5’ to 3’, which appears to be backwards (lagging strand) forms okazaki fragments DNA polymerase I removes the RNA primers DNA ligase joins the separate okazaki fragments together Proofreading and Repairing DNA: ● DNA polymerases do proofread the strand ● Altered nucleotides occur after replication and can result in evolutionary advancements ○ If altered phenotype survives better mutation will be passed down ● DNA repair enzymes ○ An example is a DNA cutting enzyme called a nuclease Replicating the Ends of DNA Molecules: ● DNA polymerase only goes 5’ to 3’, often times the 5’ end of DNA strands are not replicated ● Genes are preserved on this end of DNA strand by nucleotide sequences called telomeres ● They erode away instead of genes ○ Telomerase replenishes the telomeres Packing of DNA: ● A bacterium contains a nucleoid which has genetic information but is not surrounded by a membrane ● Chromatin is a culmination of protein and DNA fitting inside the nucleus ○ Heterochromatin is more condensed, occurs when cell is in interphase ○ Euchromatin is less condensed, occurs when cell is replicating and chromatin is being opened Histones are proteins that the DNA wraps around in a chromosome and are usually positively charged DNA Cloning: ● Cloning allows scientists to specify the gene that they’re working with and isolate it A plasmid is a small circular DNA that replicates separately from the rest of the bacterial chromosome ● Plasmids only hold a small number of genes, which is why they are ideal for cloning ○ Restriction enzymes cut the bacterial DNA to isolate the genes that is desired ● Cloning process ○ A plasmid is removed from a bacteria ○ Foreign DNA is inserted into plasmid, which results in formation of recombinant DNA (ligase is responsible to keeping to sources of DNA together) ○ Recombinant plasmid is inserted back into bacteria where it replicates ● Purposes of gene cloning include amplification and obviously to make copies of something Gel Electrophoresis: ● The basic idea of Gel Electrophoresis is to organize DNA fragments by size ● The procedure ○ After bacterial DNA are cut into single restriction fragments, the fragments are inserted into wells in the gel tray nearest the negative cathode ○ Smaller fragments will move quicker through the gel towards the positive cathode, while bigger fragments will be closer to the starting point and the negative cathode ■ Keep in mind that the fragments still have a sticky end and can hybridize with complementary sticky ends Polymerase Chain Reaction (PCR): ● It is essentially a new more large scale way to clone ● Three cycles of PCR, and in each cycle the DNA denatures (heat is used to separate the DNA strands), anneals (cool so primers form hydrogen bond), and elongation (DNA polymerase adds nucleotides to the 3’ end of each primer ○ Cycle 1 yields 2, Cycle 2 yields 4, and Cycle 3 yields 8 ● PCR is used to provide the DNA fragment for cloning ○ This fragment is then combined with the vector, which carries the DNA to the plasmid, by DNA ligase DNA sequencing is using the complementary base pairs to determine the gene’s complete nucleotide sequence