Cell Biology Chapter 17 Flashcards
Cells must be able to accurately do what? Without it what would result? Cells must also repair damage to what?
accurately reproduce, or replicate, their genetic material at each cell division; unaccurate replication, the genetic material of resulting cells would be damaged with errors; their genetic material
New DNA molecules are derived from what and what is it called?
derived from when the parent molecule and the other strand is newly synthesized; semiconservative replication
Replication is very similar in what? What are replication forks?
in Prokaryotes and eukaryotes; formed where replication begins and then proceeds in bidirectional fashion away from the origin
At each origin of replication what happens? What is the origin of replication?
two replication forks synthesize DNA in opposite directions forming a “replication bubble”; the site where DNA replication initiates by several groups of initiator proteins. Consist of AT-rich regions
The sequence varies among what? Replication origins of multicellular eukaryotes are generally what and more what?
bacterial species but contains recognizable similar sequences, called consensus sequences; generally larger and more variable in sequence but also contain regions that are AT-rich
In E. Coli how many enzymes bind and to what and what does it initiate? Binding to part of the what sequence results in what?
3 enzymes bind to oriC (origen of replication) and initiate replication; part of the oriC sequence results in unwinding of DNA
To stabilize the single strands of DNA what binds? DNA helicase unwinds what?
SSB (single stranded binding protein) binds to the unwound regions; unwinds the DNA strands as replication proceeds
DNA polymerase is a what? Incoming nucleotides are added to what?
an enzyme that can copy DNA molecules; added to 3’ hydroxyl end of the growing DNA chain, so elongation occurs in the 5’ to 3’ direction
DNA is synthesized in which direction, but the 2 strands of the double helix are oriented where? The lagging strand is synthesized in what?
5’ to 3’ direction, oriented in opposite directions; in discontinuous fragments called Okazaki fragments
The leading strand is synthesized as what? DNA synthesis from the lagging strand is synthesized in what? These are then joined by what to form what?
as a continuous chain; synthesized in Okazaki fragments; joined by DNA ligase to form a continuous new 3’ to 5’ DNA strand
About how many nucleotides incorporated during DNA replication is incorrect? How are the mistakes usually fixed? Almost all DNA polymerases have a what?
1 of every 100,000 nucleotides; fixed by proofreading mechanism; have a 3’ -> 5’ exonuclease activity
Exonucleases degrade what? The exonuclease activity of DNA polymerase allows it to remove what?
degrade nucleic acids from the ends of the molecules; remove incorrectly base-paired nucleotides and incorporate the correct base
DNA polymerase can add nucleotides only to what? Cells contain an enzyme called what that synthesizes what?
only to the 3’ end of an existing nucleotide chain; contain an enzyme called primase that synthesizes short chains of RNA using DNA as a template
After the RNA primer is made, DNA polymerase adds what? For the leading strand what is needed? For the lagging strand a series of what are needed?
deoxynucleotides to the 3’ ends of the primer; just one primer is needed; a series of primers are needed to initiate each Okazaki fragment
When DNA chain reaches the next Okazaki fragment the RNA is what? Then, adjacent fragments are joined together by what?
degraded and replaced with DNA; DNA ligase
During DNA replication, the two strands of the double helix must unwind at each what? 3 classes of proteins facilitate the what?
each replication fork; the unwinding;
DNA helicases: The DNA double helix is what? Helicases breaks the what between what of the what?
unwound ahead of the replication fork by helicase; the hydrogen bonds between nitrogeneous bases of the nucleotides of the DNA duplex as they go
Single-stranded DNA binding proteins: Once strand separation has begun, molecules of SSB move how and attach to what? They keep the DNA how?
move in quickly and attach to the exposed single strand; unwound and accessible to the replication machinery
Topisomerases: The unwinding of the helix would create too much what?
supercoiling if not for topisomerases
What proteins are involved in replication? What is a replisome?
DNA helicase, DNA topoisomerase, SSBs, primase, DNA polymerase, and DNA ligase; proteins that are closely associated in a large complex
As the replisome moves along the DNA, it must accomadate what? A key element of the replisome is what?
for the fact that DNA is being produced on both leading and lagging strands; the folding of the lagging strand template into a loop
What is the trombone model? What is a sliding clamp protein?
model for how the replisome works; attaches to a DNA polymerase catalytic subunit allows the polymerase to “process” along the DNA without falling off
The leading and lagging strand differ regarding how?
how long the sliding clamp and associated polymerase remain attached
It can remain associated with the what? On the lagging strand as each Okazaki fragment is completed, the polymerase what?
with the leading strand throughout replication; detaches and the sliding clamp must be reloaded
