BIS 010 Week 3 Notes
BIS 010 Week 3 Notes BIS 010 021
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This 11 page Class Notes was uploaded by AlexandraRita Notetaker on Wednesday April 20, 2016. The Class Notes belongs to BIS 010 021 at University of California - Davis taught by Debello in Spring 2016. Since its upload, it has received 117 views. For similar materials see General Biology in Biology at University of California - Davis.
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Date Created: 04/20/16
Day 5 (April 12 )-‐ Viral Hijacking Research on HIV Zika Virus • Flavivirus: closely related to yellow fever, dengue and west nile viruses • (+) ssRNA virus • Infects skin cells and dendritic cells • In US, fewer than 1000 cases/year: 1/316,000 Autoimmune and neurological associated disorders spread by Aedes mosquitoes • one large protein, >3000 aa • cleaved into smaller functional proteins by a viral protease • (+)ssRNA serves as mRNA to make polypeptide • dsRNA made, (-‐) strand serves as template for more genome copies Viruses mediate evolution • endogenous retroviruses • retroviruses -‐ insert genetic material into host DNA • "endogenous” = from within • riddled with copying mistakes • remain a silent, hobbled passenger in the genome • viral genomes become part of host genome many remain dormant and are not pathogenic We are actually part virus: • = 8% of our total DNA • the human genome about 100,000 copies of dead viruses in our genome • one virus carries a protein called syncytin expressed in the placenta • in all placental mammals, syncytin is key for drawing nutrients into the embryo’s bloodstream 2 DNA-‐ The Narrative Life for DNA • Heredity • Mendel (1866) • DNA = heredity • Watson and Crick (1953) Human Genome (2001) • Your own DNA sequence -‐ now. A brief History of DNA • Principles"of"inheritance" using "pea" plant "traits" • Why "peas" as"a"model&system?" -‐ Control"fertilization,"easily"defined"traits" • Characteristic"patterns"of"trait"inheritance:"traits"were" NOT"blended" • Laws"of "trait"segregation:""" -‐ independent "assortment"" -‐ Dominant "versus"recessive"traits" -‐ Homozygous "versus"heterozygous" -‐ Alleles "as" multiple "forms" of "genes” Candidate polymers • Lipids • Carbohydrates • Proteins • Nucleic acids 3 The Discovery of DNA Joanna Fredrich Miescher circa 1870 • Worked in a hospital with white blood cells. • When he added salt and a alkaline solution he precipitated a substance high in phosphorous. He postulated that it was the storehouse for the phosphorous atom. Phoebus Levene circa 1900s • Discovered that Miescher’s substance • DNA building blocks called nucleotides contained protein and DNA. -‐ deoxyribose sugar, a phosphate group, and one of four nitrogen bases -‐adenine (A), thymine (T), guanine (G), and cytosine (C). • Components are linked together: phosphate – sugar – base DNA 4 Transformation-‐ dead to living bacteria 1928 Griffin: • Virulence and appearance of Streptococcus & pneumoniae could be transferred to a non-‐virulent strain 1944: DNA transforms • 1st experiment: Avery and colleagues used a process&of&elimina3on to identify the transforming agent. • Identical extracts from heat-‐treated S cells were treated to • destroy protein -‐ hydrolytic enzymes • destroy RNA – RNA nucleases • destroy DNA -‐ DNA nucleases • DNA is necessary for transformation. • 2nd experiment: • They chemically isolated DNA and showed that it possessed t he same transforming ability as the heat-‐treated extract. The structure of DNA 1953 How can you determine the Structure of DNA? • Rosalind Franklins X-‐ray diffraction images of DNA: -‐ The X pattern was a tell tale sign of a very regular helical structure and provided the basic dimensions. • Hydration Experiments: Phosphate groups on the outside and the basis on the inside. 5 How do the helices fit together? How are bases arranged? -‐ Franklins experiment were critical -‐ Watson and crick put evidence together -‐ Had to agree with Chargaff’s rules: A=T C=G End of Notes Day 5 6 Notes day 6 (April 14 )-‐ The Code th Base Pairs The Secondary Structure of DNA 7 Implications from DNA structure • The possible permutations of 4 nucleotides in a polymer become VERY large as the polymer lengthens. Human genome has over 3 billion base pairs! • Each strand is complementary to the other, each has the information needed to construct the other. • Once separated, each strand can serve as template to direct the formation of the other strand • The nucleotide bases pair through hydrogen bonds. A pairs with T. G pairs with C. In a helix strand these bonds compliment each other. Central dogma -‐ “breaking” the code • DNA: self-‐replicating genetic material encodes the blueprint; capable of variation • RNA: convert information in DNA into proteins • Proteins: Catalysts and workhorses 8 What is an Enzyme? • The enzyme is not modified by the reaction • An enzyme is a biomolecule that acts as a catalyst, increasing the rate at which a chemical reaction occurs • Enzymes can speed up reactions dramatically Properties of enzymes • Enzymes are highly specific • A single enzyme can catalyze the same reaction many ^mes • Enzymes are typically regulated (they are not always working) DNA is copied by an enzyme • Arthur Kornberg: reconstituted replication in cell free systems to define the necessary components • Protein does the work of DNA replication: DNA polymerase • Complex system: many proteins required • Sequences on the DNA specify where replication is initiated: origin DNA is copied by an enzyme DNA Polymerase Challenges: 1.) Speed – need to copy the whole genome for each cell division 2.) Accuracy – errors will become mutations 9 DNA is copied by an enzyme • DNA Polymerase • Speed: Can add about 50 nucleotides per second!!! Accuracy: Only one error every 10^8 base pairs!!! Mechanism of DNA replication DNA polymerase • can only add nucleotides to 3'-‐OH end of an existing strand; a primer is necessary • DNA polymerase primers are RNA molecules • can only work in a 5’ – 3’ direction • Needs a template DNA strand to copy Mechanism of DNA replication • Replication “fork” • The strand growing toward the fork grows continuously in 5'—>3' direction (leading strand) as the replication fork advances • The strand growing away from fork (lagging strand) grows discontinuously as Okazaki fragments End of Notes Day 6 10 11
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