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Chapter 6 Bio
Terms in this set (25)
What must a cell do before it divides?
It must accurately replicate the vast quantity of genetic information
__________ ____________ enables DNA replication
*Base-pairing enables DNA replication
*DNA synthesis begins at replication origins
*Two replication forks form at each replication origin
*DNA polymerase synthesizes DNA using a patently strand as a template
*The replication fork is asymmetrical
*DNA polymerase is self-correcting
*Short lengths of RNA act as primers for DNA synthesis
*Proteins at a replication fork cooperate to form a replication machine
*Telomerase replicates the ends of eukaryotic chromosomes
Why can DNA act as a template for its own duplication?
Because the two strands of a DNA double helix are complementary, each strand can act as a template for the synthesis of the other.
What does DNA replication produce? And what does this enable?
It produces two identical, double helical DNA molecules. This enables genetic information to be copied and passed on from a cell to its daughter and from a parent to its offspring.
DNA replication is "semiconservative" because:
Because each daughter DNA double helix is composed of one conservative strand and one newly synthesized strand.
Where does DNA synthesis begin?
At replication origins. An initiator protein binds to DNA sequences at a replication origin, pry the two DNA strands apart, breaking the hydrogen bonds between the bases. Other proteins are attracted to the replication origin to carry out DNA replication.
A DNA double helix is ________ at replication origins.
DNA molecules in the process of being replicated contain Y-shaped junctions called replication forks. Two replication forks are formed at each replication origin, they are of opposite polarities. The forks move away in opposite directions at each replication origin.
The enzyme that catalyzes the addition of nucleotides to the 3' end of a growing DNA strand, using one of the original, parental DNA strands as a template.
Synthesizing a new strand of DNA:
A new strand of DNA is synthesized in the 5' to 3' directions. DNA polymerase adds a deoxynucleotide to the 3' end of a growing DNA chain.
Short length of DNA produced on the lagging strand during DNA replication. Adjacent fragments are rapidly joined together by DNA ligase to form a continuous DNA strand.
At a replication fork, the DNA strand that is made discontinuously in short separate fragments that are later joined together to form one continuous strand.
At a replication fork, the DNA strand that is made by continuous synthesis in the 5' to 3' direction.
Why is the replication for asymmetrical?
*DNA polymerase synthesizes new DNA only in one direction
*Only the leading strand at the replication fork can be synthesized in a continuous fashion
*On the lagging strand, DNA is synthesized in a discontinuous backstitching process, producing Okazaki fragments that are later joined together by DNA ligase.
What makes DNA polymerase self-correcting?
*DNA polymerase replicates a DNA template with incredible fidelity
*Makes an error about every one in 10^7 nucleotides
*This is made possible, in part, by a proofreading process
*It contains separate sites for DNA synthesis and proofreading
The process by which DNA polymerase corrects its own errors as it moves along DNA
What are the primers for DNA synthesis? And why are they needed?
Short lengths of RNA act as primers for DNA synthesis. DNA polymerase is incapable of starting a new DNA chain from scratch. Instead, DNA synthesis is primed by an RNA polymerase called primase. Primase makes short lengths of RNA primers that are then elongated by DNA polymerase. These primers are subsequently erased and replaced with DNA.
An RNA polymerase that used DNA as a template to produce an RNA fragment that serves as a primer for DNA synthesis. Primase can start a new polynucleotide chain by joining together two nucleotide triphosphates without the need for a base-paired 3' end as a starting point.
Enzyme that reseals nicks that arise in the backbone of a DNA molecule. In the lab, can be used to join together two DNA molecules.
Multiple enzymes are required to synthesize Okazaki fragments on the lagging DNA strand:
*In eukaryotes, RNA primers (10 nucleotides long) are made at intervals of ~200 nucleotides on the lagging strand
*Primers are removed/degraded by a nuclease
*The gaps are filled by a repair polymerase
*The completed fragments are joined together by DNA ligase
Proteins at a replication fork cooperate to form a multienzyme replication machine that copies both DNA strands as it moves along the double helix:
*DNA helicase-unwinds the double helix
*DNA topoisomerase-relieves the torsional stress/tension by generating temporary nicks in the DNA
*Circular protein clamp-allow the polymerase to slide on single-stranded DNA
*Clamp loader-allow the protein to clamp to the lagging strand
*Single-stranded DNA binding protein-keep the DNA strands apart
What happens if there isn't any topoisomerase in DNA synthesis?
The DNA cannot rotate rapidly, and the torsional stress builds up.
Enzyme that elongates telomeres, synthesizing the repetitive nucleotide sequence found at the ends of eukaryotic chromosomes.
What would happen without a special mechanism to replicate the ends of linear chromosomes?
DNA would be lost during each round of cell division
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