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BIO 1113 Chpt 15

DNA and the gene: Synthesis and Repair

TermDefinition
What did the Hershey-Chase experiment figure out? Designed experiment with radioactive macromolecules ( protein and DNA) to test whether genes were made out of protein or DNA. In the end, DNA was the only macromolecule found on the inside of the capsid, proving genes were made out of DNA.
How is double helical DNA molecule stabilized? 1. Complementary base pairing 2. Interactions between the stacked base pairs inside the helix.
What were the 3 alternative hypothesis about how DNA replication works? 1. Dispersive - parental double helix fragmented into and then replaced and put back into sequence 2. Conservative- Both strands of DNA molecule replicated 3. Semiconservative- Parental strands separated and used as a template for a daughter strand
What did the Meselson experiment discover? use radioactive molecules to determine densities of the dna molecules. If conservative, first line would have two bands. If dispersive, 1 intermediate line on 2nd tube, if semi, 2 lines.
DNA Polymerase builds deoxynucleotide monomers into DNA. Also begins DNA synthesis
DNA Polymerase III Enzyme that copies chromosome before cell division; also adds nucleotides in the 5'-3' direction following RNA primer signal.
Can synthesis work in multiple directions? No; can only work in one direction: 5'-3'; but proceeds bidirectionally
What end will nucleotides be added to? the 3' end of a growing DNA chain
DNA Helicase Separates DNA strands by breaking the hydrogen bonds that hold nucleotides together.
Top Reduce strain and release positive supercoiling that can form ahead of the replication fork
SSB proteins (single-stranded bonded proteins) protect the two strands from cleavage; stabilize the two strands which will prevent them from snapping back together
RNA Primer sequence of RNA nucleotides; DNA Polymerase III
Template Strand runs in the 3'-5' direction, but DNA polymerase III builds new strand in the 5'-3' direction.
Primase Creates the RNA primer.
Leading Strand Moves in same direction as replication fork; synthesized continuously
Lagging Moves in opposite direction of replication fork; replication is discontinuous
Which strand in discontinous? The lagging Strand. Moves in opposite direction of replication fork, so needs multiple rna primers.
Which protein removes the RNA primer and replaces it with DNA Material DNA Pol. I;
Okazaki fragments Fragments that are forms on the lagging strand due to the discontinuity of the strand.
Exonuclease Activity Proofreading reading strand. Will go back and look for mistakes in the sequence (has both 3'-5' and 5'-3' nuclease activity.
DNA ligase Enzyme that seals the nix formed between okazaki fragments
Which polymerase is resposible for DNA repair in a strand? DNA polymerase I
topoisomerase Enzyme that relieves torsional strain and supercoiling built up whe helicase seperates the two strands. Is found ahead of the DNA fork.
Exonuclease Removes all RNA primers from both strands of DNA
Telomerase TTAGGG; uses RNA template to repeat sequences and then allows RNA primer to be built, Because of the repeat sequence, the last strands of actual DNA will be replicated; protects from being trimmed.
Exonuclease active site The site where incorrect base pairs go to wait for the removal of an incorrect site.
Mismatch Pair Enzyme that scans the DNA strand to search for mistakes. It will prompt polymerase to come in and correct the mistake.
Proofreadingin DNA Enzyme that will make sure nucleotide matches before movingon. If it is not correct, it will move into the exonuclease site.
What can UV rays do to the genes? Can cause covalent bond to form between adjacent pyrmadine bases within the same DNA strand.
Why can't a thymine dimer (thymine-thymine) be recognized as a template for DNA synthesis by standard DNA polymerases? Because it creates a kink in the sugar phosphate backbone of DNA.
Nucleotide excision repair Enzymes will cut nucleotides around the thymine-thymine error and remove it. It will then be repaired.
xeroderma pigmentosum (XP) why? an extreme sensitivity to sunlight; happens because proteins involved in excision repair process are damages are unable to fulfill repair.
Created by: CarmTay
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