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Unit 5: DNA

Last updated

May 14, 2022
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- 4.15: Bioluminescence
- 5.1: Transformation in Bacteria

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5.1: Transformation in Bacteria
This page explains bacterial reproduction and genetic recombination mechanisms, including transformation, conjugation, and transduction. It highlights the historical significance of transformation in identifying DNA as genetic material. The text further explores the implications of these processes in biotechnology and medicine, particularly regarding the spread of antibiotic resistance.
5.2: The Hershey - Chase Experiments
This page discusses the 1952 experiment by A. D. Hershey and Martha Chase, which used the T2 DNA virus to demonstrate that genes are composed of DNA. By labeling DNA with radioactive phosphorus and proteins with radioactive sulfur, they showed that only the DNA entered E. coli cells, while the protein coat remained outside. This confirmed that genetic information is carried by DNA, as it directed the production of new virus particles.
5.3: The Double Helix of DNA
This page discusses the 1953 discovery of the double helix structure of DNA by Francis Crick and James D. Watson, which confirmed DNA as the physical basis of genes. This work illustrated DNA's role in replication and genetic transmission, leading to their Nobel Prize win in 1962.
5.4: Base Pairing in DNA and RNA
This page explains the rules of base pairing in DNA, where adenine pairs with thymine and cytosine pairs with guanine, enabling the double helix structure through hydrogen bonds. This pairing adheres to Chargaff's rule, ensuring the quantity of A equals T and C equals G, though ratios can differ across organisms. The rules derive their name from Watson and Crick, who identified the structural basis for these pairings.
5.5: DNA Replication
This page examines the regulation of DNA replication in eukaryotic cells, emphasizing the control mechanisms during the G2 phase. It describes positive control through the Origin Recognition Complex (ORC) and licensing factors (Cdc-6 and Cdt-1) essential for replication preparation. Additionally, a negative control system prevents re-replication until post-mitosis. This dual mechanism ensures genomic integrity during cell division.
5.6: The Meselson - Stahl Experiment
This page explains semiconservative DNA replication, where the two strands of DNA separate to serve as templates for new strands. Proposed by Watson and Crick and validated by the Meselson-Stahl experiment, this process ensures each daughter DNA molecule consists of one old and one new strand, resulting in an "immortal strand" passed through generations. This mechanism is observed in both bacteria such as E. coli and eukaryotic organisms during chromosome replication.
5.7: Restriction Enzymes
This page discusses restriction enzymes, which are bacterial DNA-cutting enzymes that enable precise DNA cleavage, facilitating sequencing and producing uniform fragments for analysis. The development of recombinant DNA technology relies on these enzymes and DNA ligase, revolutionizing genetics and biotechnology, particularly in the production of therapeutic proteins like insulin.
5.8: DNA Sequencing by the Dideoxy Method
This page discusses the DNA sequencing process, detailing the preparation of a single strand of template DNA and the use of nucleotides and dideoxynucleotides with fluorescent tags. This method allows for the detection of nucleotides during DNA synthesis by polymerase I. An example DNA sequence from the lysU gene of E. coli is also included, featuring 455 nucleotides.
5.9: Genome Sizes
This page discusses the genome of organisms, highlighting that diploid species inherit genes from both parents and showcasing the diversity in genome sizes. It presents the C value paradox, underlining the lack of correlation between genome size and complexity. It notes that not all genes are crucial for survival, with examples from Mycoplasma genitalium and humans.
5.10: The Human Genome Projects
In February 2001, IHGSC and Celera Genomics reported preliminary findings on the human genome, estimating 30,000 to 38,000 protein-encoding genes, fewer than earlier predictions, and highlighting unique human genes. They acknowledged incomplete genome sequencing with many gaps and extensive repetitive DNA.
5.11: The Human and Chimpanzee Genomes
This page outlines that humans and chimpanzees share 98.8% of their genomes, with the FOXP2 gene being a key difference due to 5 nucleotide variations related to language. While coding differences are minimal, gene insertions, deletions, and duplications, particularly in non-coding regions, play a significant role in gene regulation and may explain the distinct traits, such as language capabilities, observed in humans.
5.12: Pyrosequencing
This page discusses efforts by scientists to sequence genomes of different organisms to better understand evolution, microbial diversity, and human disease genetics. While traditional DNA sequencing is common, innovations like pyrosequencing offer faster and more cost-effective alternatives. Pyrosequencing works by fragmenting DNA, replicating it on beads, and using light emissions to identify sequences, achieving the capability to process 20 million base pairs in six hours.
5.13: DNA Repair
This page outlines the importance of DNA repair mechanisms in living cells, detailing 130 genes involved in repair processes that counteract damage from various sources, including radiation and chemicals. Key repair pathways include direct reversal, Base Excision Repair (BER), Nucleotide Excision Repair (NER), and Mismatch Repair (MMR), with specific enzymes for each.
5.14: Harlequin Chromosomes
This page discusses the behavior of chromosomes during mitosis in eukaryotes, highlighting that while most align randomly, some stem cells, particularly in skeletal muscle, may preferentially segregate immortal strands to maintain original DNA and reduce mutations. It also mentions that certain chromosomes may show preferential segregation while others distribute randomly, indicating variability in this process across different cell types.
5.15: Metagenomics - Exploring the Microbial World
This page explores advancements in metagenomics focused on unexplored microbial ecosystems, utilizing DNA sequencing technologies for microbial analysis. It highlights techniques like 16S rDNA and shotgun sequencing to uncover diverse organisms and their functions, including antibiotic resistance and enzyme production.

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