bio ch16

the molecular basis of inheritance

much of the evidence for DNA as the genetic material came from the study of what

viruses that infect bacteria

what is the term for the viruses that are widely used in molecular genetics research

bacteriophages (or phages)

what is a virus

DNA (sometimes RNA) enclosed by a protective coat, often simply protein

what is DNA

a polymer of nucleotides, each consisting of a nitrogenous base, a sugar, and a phosphate group

what are the possible nitrogenous bases

• adenine (A)

• thymine (T)

• guanine (G)

• cytosine (C)

what is the term for the structure DNA takes

the double helix

what are Chargaff’s rules

• the base composition of DNA varies between species

• in any species, the number of A and T bases is equal, and the number of G and C bases is equal

how do the nucleotide base structures pair

A pairs only with T, and G pairs only with C

in DNA replication, what happens to the parent molecule in relation to base pairs

the parent molecule unwinds, and the two new daughter strands are built based on base-pairing rules; the new strands that are formed are complementary to the template strands

what was predicted by Watson & Crick’s semiconservative model of replication

it predicts that when a double helix replicates, each daughter molecule will have one old strand (derived or “conserved” from the parent molecule” and one newly made strand

what were the models competing withe the semiconservative model, and what did they propse

• the conservative model: said that the two parent strands rejoined after replication

• the dispersive model: each strand is a mix of old and new

what were the hypothesized results under the conservative model (first and second replication)

• first replication: one new helix would be made completely of the “old” bases, and the second new helix would be made completely of the “new” bases

• second replication: the “old” base helix makes one “old” helix and one “new” helix, and the “new” base helix makes two “new” base helixes

• by the second replication, you have three “new” helixes and one "“old” helix

what were the hypothesized results under the semiconservative model (first and second replication)

what were the hypothesized results under the dispersive model (first and second replication)

where does replication begin

sites called origins of replication, where the two DNA strands are separated, opening up a replication “bubble”

how many origins of replication might a eukaryotic chromosome have

hundreds or even thousands

in what direction does replication proceed from the origin of replication

replication proceeds in both directions from each origin, until the entire molecule is copied

what is at the end of each replication bubble

a replication fork, a Y-shaped region where new DNA strands are elongated

what are helicases

enzymes that untwist the double helix at the replication forks

what binds to and stabilizes single-strand DNA

single-strand binding proteins

what does topoisomerase do

it relieves the strain of twisting of the double helix by breaking, swiveling, and rejoining DNA strands