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30 Cards in this Set
- Front
- Back
Frederick Griffith
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Investigated 2 strain of strep:
1. pathogenic 2. harmless -injected mice with pathogenic = mouse died -injected with harmless = no effect -injected with dead pathogenic cells = no effect -infected with harmless & dead pathogenic = dead Conclusion : some sort of transformation occured |
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Avery, McCarthy, and Macleod
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Tested Griffith's theory that either DNA, protein, or RNA was the transforming agent
-only when they allowed DNA to be active, did the transformation occur *DNA is the transforming agent |
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Erwin Chargaff
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"Chargaff's Rules"
-DNA from one species to another has different composition (order and amt. of adenine, guanine, cytosine, and thymine) -the amount of the 4 nitrogenous bases are not all equal but are always present in a characteristic ratio |
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Hershey Chase
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infected E.coli with T2 bacteriophages in order to determine whether or not DNA or proteins were the transforming agent
Conclusion : DNA is transforming agent |
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Pauling
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had the idea that DNA was a 3-stranded helical molecule
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Wilkins & Franklin
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-took a picture of DNA that led to the realization that DNA was a double helix
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Watson & Crick
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discovered that DNA was a double helix based off of Franklin's photo
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purine and pyrimidines
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bairs pairs are always purine (long) + pyrimidine (short)
Purines: Adenine and guanine Pyrimidines: thymine and cytosine AT : double bond GC : triple bond |
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Semiconservative Model
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The Meselson-Stahl experiment tested 3 models
1. conservative 2. semi conservative (accepted) -2 strand of parental molecule separate and each functions as a template for a new complementary strand 3. dispersive |
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DNA Replication:: Prokaryotes vs. Eukaryotes
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-Prokaryotes – single chromosome; no nucleus; 5 million base pairs; can quickly replicate – 1 hr.
-Eukaryotes - human – 46 DNA molecules in nucleus; 6 billion base pairs ( 900 AP bio books); very few errors; few hours to replicate |
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Synthesis of leading and lagging strands during DNA replication
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1. DNA polymerase elongates DNA strands in 5’ – 3’ direction.
2. Leading strand – elongates continuously. 3. Lagging strand – adds short segments - Okazaki fragments 4. Ligase connects the Okazaki fragments |
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Priming DNA synthesis with RNA
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-DNA polymerase cannot initiate the reaction.
-Primer - a short segment of RNA synthesized by the enzyme primase. -Each primer is eventually replaced by DNA |
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Summary of DNA Replication
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1. Helicase unwinds DNA.
2. Proteins stabilize the unwound strand. 3. Leading strand synthesized continuously by DNA polymerase. 4. Lagging strand – Primase adds RNA primer, Okazaki fragments added. 5. Another DNA polymerase replaces RNA primer with DNA. 6. DNA ligase joins the Okazaki fragment to the growing strand. |
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DNA Structure and Features
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-bases are on interior (hydrophobic)
-double helix -sugar phosphate backbone on outside -hydrogen bonds between bases -covalent bonds hold nucleotides together -"right-handed" : curves up to the right -anti-parallel : strands oriented in opposite directions -1 full turn approx. every 10 base pairs -van der wahl interactions hold molecules together |
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The two strands of DNA are antiparallel
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The 5’ to 3’ direction of one strand runs counter to the other strand.
The numbers are assigned to the Carbons of the sugar. |
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helicase
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unwinds DNA to begin replication
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topoisomerase
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relieves the tension before the fork
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DNA polymerase III
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elongates DNA strands in 5’ – 3’ direction
-the leading strand is synthesized continuously by DNA polymerase |
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Leading strand vs. Lagging strand
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leading - DNA is synthesized continuously by DNA polymerase
lagging - DNA can only be synthesized from 5 prime to 3 prime so DNA is added on in fragments (Okazaki fragments) |
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ligase
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connects the Okazaki fragments
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primase
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coordinates the rate of repplication between leading and lagging strands
-DNA polymerase cannot initiate the reaction. -primase adds a short segment of RNA (primer) and DNA polymerase takes over from there -Each primer is eventually replaced by DNA |
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DNA polymerase 1
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replaces primer with DNA
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telomere and telomerase
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the end of strands of DNA with repeating sequences with no genes
-protects the end of the chromosome from deterioration -During cell division, enzymes that duplicate the chromosome and its DNA cannot continue their duplication all the way to the end of the chromosome -If cells divided without telomeres, they would lose the ends of their chromosomes, and the necessary information they contain -The telomeres are disposable buffers blocking the ends of the chromosomes and are consumed during cell division and replenished by an enzyme, the telomerase reverse transcriptase -telomerase adds RNA that acts like a template for DNA where the telomere is |
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Chargaff's Rules
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-DNA composition varies from one species to another
And anyone species the amount of four nitrogenous bases are not all equal but are present in a characteristic ratio - molecular diversity |
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Three stages of transcription
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Initiation
Elongation Termination |
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Initiation
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After all and a polymerase binds to the promoter, the DNA strands unwind, and the enzyme initiates RNA synthesis of the start point on the template strand
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Elongation
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Polymerase moves downstream unwinding DNA and elongating RNA. The DNA strands then reform a double helix. A single gene can have several polymerases following each other
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Termination
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Terminator sequence stops transcription
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Initiation
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1. eukaryotic promoters: include a TATA box about 25 nucleotides upstream from the transcriptional start point.
2. transcription factor recognizes the TATA box and binds to DNA before RNA polymerase II 3. additional transcriptional factors join the polymerase on the DNA forming the transcription initiation complex. DNA unwinds and RNA synthesis begins on the template strand |
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the roles of snRNPs and splicosomes in mRNA splicing
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1. pre-mRNA combines with snRNPs and other proteins to form a spliceosome
2. within spliceosome, base pairs match up at ends of intron 3. RNA transcript is cut to release intron and eons are spliced together |