Lecture Two: DNA and RNA - Genetic Material

LECTURE TWO  IV- Evidences that DNA and RNA are the genetic material 1-Prokaryotes 2-Eukarotic evidence A-Transformation experiment Recombinant DNA research B-Hershy-Chase experiment C-Experiments with RNA-viruses  1-Prokaryotic experiment The initial e...

LECTURE TWO  IV- Evidences that DNA and RNA are the genetic material 1-Prokaryotes 2-Eukarotic evidence A-Transformation experiment Recombinant DNA research B-Hershy-Chase experiment C-Experiments with RNA-viruses  1-Prokaryotic experiment The initial evidence was derived from studies of viruses and bacteria. Microorganisms are ideal for this experimantion. Why? A-Transformation experiment Identification of the transformation substance RNA destroy Destroy protein Destroy DNA Destroy lipid Destroy carbohydrate B-Hershy-Chase experiment C- Experiment with RNA-virus  2-Eukaryotic evidence DNA recombination research  II-Organization of genetic material Molecular structure and packing of: 1-prokaryotic chromosomes 2-eukaryotic chromosomes A-structure and organization of prokaryotic chromosomes 1-Structure of prokaryotic chromosome Prokaryotes have single circular DNA molecule known as bacterial chromosome located in the dark central nucleoid area. Bacterial chromosome containing the essential genes necessary for growth and reproduction. Plasmids is smaller circles of double stranded DNA, from 1000 bp(small) to 250 kb (large), have their origin of replication and carry additional genes such as resistance to antibiotic. The integrated plasmid is known as episome Prokaryotic chromosome structure  2-Organization of prokaryotic chromosome The DNA molecule is extremely long relative to the cell size, thus its necessary to be compacted by a process called supercoiling. Topoisomerases introduce additional turns into the double DNA strand to wind up on itself and become more compacted (positive supercoiling) and also remove it by creating a turn in opposite directions (negative supercoiling) Organization of E.coli chromosome Negative and positive supercoiling Differences between pro and eukarotes chromosomes Eukaryotic DNA  Classification of introns Despite splicing of all intron-containing RNA molecules is superficially similar, different types of introns were identified through the examination of intron structure. At least four distinct classes of introns have been identified: 1. Spliceosomal introns: introns in nuclear protein-coding genes that are removed by spliceosomes 2. tRNA introns: introns in nuclear and archaeal transfer RNA genes that are removed by proteins 3. Self-splicing group I introns that are removed by RNA catalysis 4. Self-splicing group II introns that are removed by RNA catalysis Group I intron Group II intron B-structure and organization of eukaryotic chromosomes It is much more complex than in prokaryotes due to: 1-greater amount of DNA per chromosomes 2-presence of large amount of proteins associated with DNA Chromosome morphology Different shapers of eukaryotic chromosomes  Chromosome identification By grouping metaphase chromosomes depending on size and shape, it is possible to identify them. The process become much simpler by the development of banding pattern Although there are several banding pattern e.g. G, Q, R and C, G-banding is the most common Different banding pattern techniques  High resolution (prometaphase) banding It is achieved with R or G banding in prophase or prometaphase Prometaphase reveals 550 to 850 bands or even more exceed 450 in metaphase Fluorescence In Situ Hybridization (FISH)  Fluorescence In Situ Hybridization (FISH) A process which paints chromosomes or portions of chromosomes with fluorescent probes to: 1-examine the presence or absence of particular DNA sequence. 2-evaluate the number of or organization of chromosome or chromosomal region. The used probes are divided into three types: locus-specific, satellite DNA and chromosome paint probe.  Probe types Probe types are locus-specific, satellite DNA and chromosome paint probe FISH