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Summary Chapter 11 - DNA Replication
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Chapter 11 of Genetics by Brooker.
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Chapter 11 DNA ReplicationDNA replication: the original DNA strand are used as templates for the synthesis of new
DNA strands.
11.1 Structural overview of DNA replication
Existing DNA strands act as templates for the synthesis of new strands. DNA
replication relies on the complementarity of DNA strands, based on the AT/GC rule. During
the replication process, the two complementary strands of DNA come apart and serve as
template strands, for the synthesis of two new strands of DNA. The two newly made strands
are referred to as the daughter strands. DNA is replicated in such a way that both copies
retain the same information - the same base sequence - as in the original molecule.
11.2 Bacterial DNA replication: the formation of two replication
forks at the origin of replication.
Bacterial chromosomes contain a single origin of replication. The site on the bacterial
chromosome where DNA synthesis begins is known as the origin of replication. The
synthesis of new daughter strands is initiated within the origin and proceeds in both
directions, or bidirectionally, around the bacterial chromosome. This means that two
replication forks move in opposite directions outward from the origin. A replication fork is the
site where the parental DNA strands have separated and new daughter strands are being
made.
Replication is initiated by the binding of DnaA protein to the origin of replication.
Three types of DNA sequences are found within oriC (origin of Chromosomal replication): an
AT-rich region, DnaA box sequences and GATC methylation sites. DNA replication begins
with the binding of DnaA protein to sequences within the origin of replication known as DnaA
boxes. Following separation of the AT-rich region, the DnaA proteins, with the help of DnaC
proteins, recruit the enzyme DNA helicase to this site. This initiates the replication of the
bacterial chromosome in both directions, bidirectional replication.
11.3 Bacterial DNA replication: synthesis of new DNA strands.
Several proteins are required for DNA replication at the replication fork.
Unwinding of the helix:
- Topoisomerase II/ DNA gyrase: travels in front of DNA helicase and alleviates
positive supercoiling.
- Single-strand binding proteins: bind to the strands of parental DNA and prevent them
from re-forming a double helix
Synthesis of RNA primers via primase:
- Primase: synthesizes short strands of RNA (RNA primers)
- These primers start the process of DNA replication.
- Leading strand is a single primer made
- Lagging strand multiple primers are made.
Synthesis of DNA via DNA polymerase:
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