what is a Transformation
a change in genotype and phenotype due to the assimilation of external DNA by a cell. Discovered by Fredrick Griffith in 1928
who identified transforming substances as DNA
Oswald Avery, Maclyn McCarty and Colin Macleod identified the transforming substance as DNA
what are Bacteriophages
viruses that infect bacteria, studies showed that the DNA part of the phages were infected instead of the protein parts. Discovered by Alfred Hershey and Martha Chase in 1952
what are Chargaff’s rules
DNA base composition varies between species
For each species, A and T base and C and G base percentages are roughly equal
DNA replication
the copying of DNA
Conservative Model
2 parental cells reassociate after acting as templates for new strands
Semiconservative model
the 2 strands of the parental molecule separate each functions as a template for synthesis of a new complementary strand
Dispersive model
each strand of both daughter molecules contain a mixture of old and newly synthesized DNA
Origin of replication
short stretches of DNA that have a specific sequence of nucleotides
Replication fork
y shaped region where the parental strands of DNA are being unwound
Helicase
an enzyme that untwists the double helix at the replication forks
Single strand binding proteins
binds to the unpaired DNA strands keeping them from re-pairing
Topoisomerase - an enzyme that relieves strain on DNA by breaking
an enzyme that relieves strain on DNA by breaking swiveling and rejoining DNA strands
Primase
the enzyme that synthesizes a strand of RNA that begins the strand of DNA called a primer
DNA polymerase III
catalyzes the synthesis of new DNA by adding nucleotides to the 3’ end of a pre-existing chain
Leading strand
DNA polymerase remains on the replication fork and continuously adds nucleotides to the new complementary strand as the fork progresses
Lagging strand
DNA elongating in the direction away from the replication fork
Okazaki fragments
the segments of the lagging strands
