1. Review Where and in what form in prokaryotic DNA found

2. Review Where is eukaryotic DNA found3. Infer What could be the result of damaged DNA

being replicated

CH 12 DNA12.3 DNA Replication

Copying the Code

Base pairing in the double helix explained how DNA could be copied

Each strand has all the information Complementary strands

Each strand could be used to make the other.

The Replication Process

Replication Process of a cell duplicating it’s DNA

Ensures that each resulting cell has the same complete set of DNA molecules.

DNA molecule separates into two strands Produces two new complementary strands

following base pairing rules Each strand is a template.

Two strands of the double helix separate, or “unzip,” allowing two replication forks to form.

New bases are added following the rules of base pairing.

Produces two DNA molecules identical to each other and to the original molecule

Each molecule had one original strand.

The Role of Enzymes

DNA polymerase Joins individual nucleotides to produce a new strand

of DNA Proofreads DNA molecule.

Telomeres

Tips of chromosomes Particularly difficult to copy DNA is lost during each replication Telomerase

Special enzyme that some cells have that can rebuild the telomeres.

Replication in Living Cells

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

Have a single, circular DNA molecule in the cytoplasm.

Prokaryotic DNA Replication

Replication starts until regulatory proteins bind to a single starting point on the chromosome.

Eukaryotic DNA Replication

Replication may begin at dozens or even hundreds of places on the DNA molecule, proceeding in both directions until each chromosome is completely copied.

Two copies of DNA remain closely associated until the cell enters prophase of mitosis

Chromosomes condense, and the two chromatids in each chromosome become clearly visible.