Trabajillopillo

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12.3 DNA Replication


Lesson Objectives
Summarize the events of DNA replication.


Compare DNA replication in prokaryotes with that of eukaryotes.
LessonSummary
Copying the Code Each strand of the double helix has all the information needed to reconstruct the other half by the mechanism of base pairing. Because each strand can be used to make the otherstrand, the strands are said to be complementary. DNA copies itself through the process of replication:


The two strands of the double helix unzip, forming replication forks.


New bases areadded, following the rules of base pairing (A with T and G with C).


Each new DNA molecule has one original strand and one new strand.


DNA polymerase is an enzyme that joins individualnucleotides to produce a new strand of DNA.


During replication, DNA may be lost from the tips of chromosomes, which are called telomeres.

Replication in Living Cells The cells of most prokaryoteshave a single, circular DNA molecule in the cytoplasm. Eukaryotic cells have much more DNA. Nearly all of it is contained in chromosomes, which are in the nucleus.


Replication in mostprokaryotic cells starts from a single point and proceeds in two directions until the entire chromosome is copied.


In eukaryotic cells, replication may begin at dozens or even hundreds of places on theDNA molecule, proceeding in both directions until each chromosome is completely copied.

Copying the Code
1. Why are the strands of a DNA molecule said to be complementary?
Because they fit eachother following the Chargaff’s rule
2. What is the first step in eukaryotic DNA replication?
Unzip strands

3. If the base sequence on a separated DNA strand is CGTAGG, what will the base sequenceon its complementary strand be?
GCATCC.
4. What enzyme joins individual nucleotides to produce the new strand of DNA?
DNA polymerase.




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5. What enzyme...