CHAPTER 11_DNA Replication and Recombination Flashcards
how many base pairs exist within the human genome
3 Billion
which experiment grew E. coli cells for many generations in a medium that had ^15NH4Cl (ammonium chloride) as the only nitrogen source
Meselson-Stahl experiment
Samples are forced by centrifugation through a density gradient of a heavy metal salt, such as cesium chloride. Molecules of DNA will reach equilibrium when their density equals the density of the gradient medium
sedimentation equilibrium centrifugation (buoyant density gradient centrifugation)
J. Herbert Taylor, Philip Woods, and Walter Hughes presented evidence that semiconservative replication also occurs in eukaryotic organisms. They experimented with root tips of the broad bean _______
Vicia faba
J. Herbert Taylor, Philip Woods, and Walter Hughes were able to monitor the process of replication by labeling DNA with _____, a radioactive precursor of DNA, and by performing ______
^3H-thymidine
autoradiography
______ is a common technique that, when applied cytologically, pinpoint the location of a radioisotope in a cell
Autoradiography
a chemical derived from the crocus plant that poisons the spindle fibers
Colchicine
_______ creates two replication forks that migrate farther and farther apart as replication proceeds
Bidirectional replication
These forks eventually merge, as semiconservative replication of the entire chromosome is completed, at a termination region, called ___
ter
two major requirements for in vitro DNA synthesis under the direction of DNA polymerase I:
- All 4 deoxyribonucleoside triphosphates (dNTPs)
- Template DNA
a mutant strain of E. coli that was deficient in polymerase I activity. The mutation was designated ____
polA1
Although none of the three polymerases can initiate DNA synthesis on a template, all 3 can elongate an existing DNA strand, called a _____
primer
polymerase I is present in greater amounts than is polymerase III, and it is also much more stable
Its 3′ to 5′ exonuclease activity also provides a proofreading function that is activated when it inserts an incorrect nucleotide
_____ is believed to be responsible for removing the primer, as well as for the synthesis that fills gaps produced after this removal.
DNA Pol I
_____, which imparts the catalytic function to the holoenzyme
core enzyme
pairs with the core enzyme and facilitates the function of a critical component of the holoenzyme, called the sliding DNA clamp
sliding clamp loader
oriC, it consists of ____ DNA base pairs and is characterized by five repeating sequences of 9 base pairs, and three repeating sequences of 13 base pairs, called ________
245
9mers and 13mers
initiator protein, called ___________, is responsible for initiating replication by binding to a region of 9mers.
DnaA (because it is encoded by the dnaA gene)
_____ (made up of multiple copies of the DnaB polypeptide). —– is assembled as a hexamer of subunits around one of the exposed single-stranded DNA molecules. The —- subsequently recruits the holoenzyme to bind to the newly formed replication fork to formally initiate replication, and it then proceeds to move along the ssDNA, opening up the helix as it progresses.
DNA helicase
Helicases require energy supplied by the hydrolysis of ATP
base pairing must be inhibited until it can serve as a template for synthesis. This is accomplished by proteins that bind specifically to single strands of DNA, appropriately called _____
single-stranded binding proteins (SSBs)
supercoiling can be relaxed by ______, a member of a larger group of enzymes referred to as DNA topoisomerases
DNA gyrase
Together, the DNA, the polymerase complex, and associated enzymes make up an array of molecules that initiate DNA synthesis and are part of what we have previously
called the ______
replisome
Synthesis of the RNA is directed by a form of RNA polymerase called ______, which is recruited to the replication fork by DNA helicase, and which does not require a free 3′ end to initiate synthesis
primase
DNA Pol I removes the primers and replaces the missing nucleotides. Joining the fragments is the work of another enzyme, _______, which is capable of catalyzing the formation of the phosphodiester bond that seals the nick between the discontinuously synthesized strands
DNA ligase
After the synthesis of ____nucleotides, the monomer of the enzyme on the lagging strand will encounter a completed Okazaki fragment
1000 to 2000
This process, called ______, increases the fidelity of synthesis by a factor of about 100
proofreading
Many other mutations interrupt or seriously impair some aspect of replication, such as the ligase-deficient and the proofreading-deficient mutations mentioned previously. Because such mutations are lethal ones, genetic analysis frequently uses _____, which are expressed under one condition but not under a different condition.
conditional mutations
ex. temperature-sensitive mutation
This method allows one to eliminate a particular gene in a specific organ instead of the whole animal
conditional knockout approaches
Eukaryotic replication origins not only act as sites of replication initiation, but also control the timing of DNA replication. These regulatory functions are carried out by a complex of more than 20 proteins, called the ______, which assembles at replication origins
prereplication complex (pre-RC)
In the early G1 phase of the cell cycle, replication origins are recognized by a six protein complex known as an ______, which
tags the origin as a site of initiation of replication
origin recognition complex (ORC)
_____, a term that refers to the strength of the association between the enzyme and its substrate
processivity
The assembly of new nucleosomes is carried out by ______ that move along with the replication fork
chromatin assembly factors (CAFs)
Telomeric sequence in humans
5’ - TTAGGG - 3’
