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Lecture 10

BSC 108 Lecture 10: Biology Chapter 10 Notes

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Biological Sciences
BSC 108
Christina Yates

Biology Chapter 10 Notes The History of DNA • 1890s: Nucleic acids known to be in cells • 1940s: Genes (inheritance units) were known to be… ➢ On chromosomes and ➢ Chromosomes were known to be made of protein and nucleic acid • 1950s: DNA known as the molecule of inheritance • Even though its chemical makeup was known, its structure wasn’t understood. • The big question: How does DNA transmit information from one generation to the next? What Came Next? • A discovery that began a new era in biology • Figuring out the 3D arrangement of DNA that gives it unique properties • James Watson, Frances Crick, Maurice Wilkins, Rosalind Franklin • Watson and Crick determined that DNA is a double helix. DNA: Structure and Replication • DNA ➢ Has the capacity to store genetic information ➢ Can be copied and passed from generation to generation DNA and RNA Structure • DNA and RNA are nucleic acids ➢ They consist of chemical units called nucleotides ➢ The nucleotides are joined by a sugar-phosphate backbone • The four nucleotides found in DNA ➢ Differ in their nitrogenous bases ➢ Are thymine (T), cytosine (C), adenine (A), and guanine (G) • RNA has uracil (U) in place of thymine (T) • The model of DNA is like a rope ladder twisted into a spiral DNA Replication • When a cell or whole organism reproduces, a complete set of genetic instructions must pass from one generation to the next. • Watson and Crick’s model for DNA suggested that DNA replicates by a template mechanism. • DNA replication ➢ Begins at specific sites on a double helix ➢ Proceeds in both directions Replication • It sounds easy – it is complex • Dozens of enzymes ➢ To make the covalent bonds ➢ To keep the DNA unzipped, etc • The process is fast and quite accurate • Only about 1 in 1 billion bases is incorrectly paired ➢ Mutations DNA Damaging • DNA can be damaged by ultraviolet light ➢ The enzymes and proteins involved in replication can repair the damage The Flow of Genetic Information from DNA  RNA  Protein • DNA functions as the inherited directions for a cell or organism ➢ How are these directions carried out? • An organism’s genotype, its genetic makeup, is the sequence of nucleotide bases in DNA. ➢ The phenotype is the organism’s specific traits, which arise from the actions of a wide variety of proteins • DNA specifies the synthesis of proteins in two stages: ➢ Transcription ➢ Translation • In eukaryotic cells, ➢ Transcription occurs in the nucleus ➢ Translation occurs in the cytoplasm Review: DNA  RNA  Protein • The flow of genetic information in a cell • A mutation ➢ Is any change in the nucleotide sequence of DNA • Mutations may result from ➢ Errors in DNA replication ➢ Physical or chemical agents called mutagens • Although mutations can be harmful, ➢ They are the source of the rich diversity of genes in the living world ➢ They contribute to the process of evolution by natural selection • Mutations can be good, bad or result in no change depending on: ➢ The type of change ➢ Where the change in DNA occurs ➢ If the change is detected and fixed before replication ➢ How it affects the organism and its survival • Mutations are the basis of cancer, many genetic diseases and evolution Unique Viral Characteristics • They are energy-less • They contain either DNA or RNA but not both • Replication is only by taking control of the host cell’s synthetic machinery Viruses: Genes in Packages • Viruses sit on the fence between life and nonlife ➢ They exhibit some, but not all, characteristics of living organisms ➢ Protein coat covers DNA/RNA • Must enter and exit the cell Plant Viruses • Viruses that infect plants ➢ Can stunt growth and diminish plant yields ➢ Can spread throughout the entire plant Animal Viruses • Viruses that infect animals are common causes of disease • AIDS is one of the most significant health challenges facing the world today ➢ Infection by HIV can cause AIDS Aids Is • Acquired immune deficiency syndrome • The disease caused by HIV infection • Treated with the drug AZT HIV • HIV is a retrovirus ➢ A retrovirus is an RNA virus that reproduces by means of a DNA molecule ➢ It copies its RNA to DNA using reverse transcriptase. Emerging Viruses • Many new viruses have emerged in recent years: • How do new viruses arrive? ➢ Mutation of existing viruses ➢ Spread to new host species • A lot of the new viruses come out of Asia because it is so densely populated • Ebola virus • West Nile virus New Pandemic: Swine Flu • CDC Recommendations: ➢ Influenza is thought to spread mainly person-to-person through coughing or sneezing of infected people ➢ Cover your nose or mouth with a tissue when you cough or sneeze. Throw the tissue in the trash after you use it ➢ Wash your hands often with soap and water, especially after you cough or sneeze. Key Terms • Molecular biology: the study of the molecular basis of heredity; molecular genetics. • Nucleotide: an organic monomer
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