Chapter 16 - Nucleic Acids and Inheritance Flashcards
Frederick Griffith’s experiment
Proved the process of transformation
- transformation: change in genotype and phenotype due to the assimilation of external DNA
- used Streptococcus pneumoniae
- rough (R) type - non-pathogenic
- smooth (S) type - pathogenic (has capsule)
- mixture of heat-killed S type and living R type proved transformation
Avery
- treated mixtures of heat-killed S type and living R type of Streptococcus pneumoniae with enzymes
1) proteinase (transformation - S cells appear)
2) RNase (transformation - S cells appear)
3) DNase (no transformation - no S cells appear)
Hershey and Chase
Proved that DNA is the genetic material, not protein
- used bacteria and bacteriophage
- used radioactive isotopes to label S-35 (protein coat) and P-32 (genetic material)
1) infection
2) blending (to separate free phage outside bacteria)
3) centrifugation (heavier bacteria at the bottom and lighter phage on top - supernatant)
Results: P-32 found in pellet at the bottom - DNA is the genetic material
Meselson and Stahl
Proved semi-conservative replication of DNA
- bacteria cultured in growth medium containing heavy isotope (N-15)
- transfer of bacteria to growth medium containing light isotope (N-14)
- DNA sample centrifuged after first replication has 2 hybrid strands with 50% new strand and 50% old strand (band found in the middle) - eliminates conservative model
- DNA sample centrifuged after second replication has 4 strands - 2 that are 100% new strand (2 light bands) and 2 that are hybrid with 50% old strand and 50% new strand (2 hybrid bands)
- used stable isotope (N-15)
RNA virus examples
HIV, MERS, SARS, influenza(some are DNA virus)
Conventional DNA shape
right-handed spiral
2nm in diameter
1 full turn every 3.4nm (10 base pairs)
0.34nm distance between nucleotides
Pyramidines
Cytosine, Thymine
-single hexagon
Purines
(nitrogen containing base)
Adenine, Guanine
-1 hexagon and 1 pentagon
Complementary pairing between A-T
2 hydrogen bonds
Complementary pairing between G-C
3 hydrogen bonds
Chargaff’s rule
number of A = number of T
number of G = number of C
consistent diameter of 2nm
DNA replication models
1) Conservative
2) Semi-conservative
3) Dispersive
Replication bubble
unwound, open region of DNA helix where DNA replication occurs
- only 1 in prokaryotes
- thousands of origins of replication in eukaryotes
DNA replication template
Template strand (3' - 5') Replicated strand (5' - 3')
Enzymes involved in DNA replication
1) DNA helicase - unwinding double strand
2) Single-strand Binding Proteins (SSBP) - stabilize unwound parental strands
3) RNA primase - synthesizes RNA primers using parental DNA strand
- primer: short RNA providing 3’ OH end to initiate DNA polymerization
4) DNA polymerase III - adds new nucleotides in 3’ - 5’ direction
5) Topoisomerase - relieves strain (supercoiling) caused by unwinding, breaks - swivels - rejoins DNA ahead of rep. fork
6) DNA polymerase I - removes RNA nucleotides of primer from 5’end and replaces with DNA nucleotides
7) DNA ligase - seals gap between sugar-phosphate backbone by forming phosphodiester bonds
