Chapter 7 Flashcards
(34 cards)
forward mutation
a mutation that changes a wild-type allele of a gene to a different allele
reverse mutation/ reversion
cause a novel allele to revert back to wild type
substitution
occurs when a base at a certain position in one strand of the DNA molecule is replaced by one of the three other bases
transitions
one purine replaces the other purine; pyrimidine replaces the other
transversions
purine changes to pyrimidine and vice cersa
deletion
occurs when a block of one or more nucleotide pairs is lost from a DNA molecule
insertion
the addition of one or more nucleotide pairs
point mutations
affect one or just a few base pairs in the DNA and this alter only one gene at a time
What did Salvador Luria and Max Delbruck devise an experiment for?
Designed a fluctuation test to show that bacterial resistance arises from mutations that exist before exposure to bacteriophages.
replica plating
demonstrate more directly that mutations conferring bacterial resistance occur before the cells encounter the bactericide that selects for their resistance
How are mutations created?
By two different events:
- Damaged by chemical reactions of radiation
- Mistakes can occur when DNA is copied during replication
depurination
DNA alteration in which the hydrolysis of a purine base, either A or G, from the deoxyribose-phosphate backbone occurs.
thymine-thymine dimers
causes adjacent thymine residues to become chemically linked
mutagen
any physical or chemical agent that raises the frequency of mutations above the spontaneous rate
base analogs
similar in chemical structure to the normal nitrogenous bases that the replication machinery can incorporate them into DNA
intercalators
: flat, planar molecules that can sandwich themselves between successive base pairs and disrupt the machinery for replication, generating deletions, or insertions of a single base pair
base excision repair
particularly important in the removal of uracil from DNA
homologous recombination
can be used to repair most double-strand breaks accurately through complementary base pairing.
non-homologous end-joining (NHEJ)
bind the DNA ends at the site of the breakage and protect the ends from nucleases.
methyl-directed mismatch repair
backup repair system that easily recognize the incorrectly matched base pair because the improper base pairing distorts the double helix, resulting in abnormal bulges and hollows.
auxotroph
a nutritional mutant microorganism that requires supplementation with substances not needed by wild-type strains
prototroph
an organism that does NOT require the addition of a substance
proteins
polymers composed of amino acids
dipeptide
A pair of amino acids connected together
