Copying DNA

12.3 DNA Replication

Which color is the sugar?

Which color is phosphate?

If yellow is cytosine, what color is guanine?

If green is adenine, what color is thyamine?

What bond connects the phosphate and the sugar?

What bond connects the nitrogen bases?

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• DNA Replication

• Copying DNA

• The structure of DNA is perfect for the copying of DNA.

– Weak Hydrogen bonds

http://commons.wikimedia.org/wiki/File:DNA_replication_split.svg

The Replication ProcessDuring INTERPHASE, a cell must replicate its DNA before it can divide into two cells.

The Replication ProcessDuring replication, the DNA molecule separates into two strands and then produces two new complementary strands following the rules of base pairing.

Each strand of the double helix of DNA serves as a template, or model, for the new strand.

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• First, ladder separated as Helicase Enzyme breaks hydrogen bonds

• Replication Fork

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• DNA Polymerase

• Adds complementary nucleotides

• Lots of DNA polymerase

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• DNA polymerase

• Proofreads the DNA

• Ensures all bases are correctly matched

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• 1 error in every 10,000 paired nucleotides

• DNA proofreading drops the actual number of errors to 1 in a billion nucleotide pairs.

• A human cell takes a few hours to replicate the 6 billion base pairs.

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• The tip of eukaryotic chromosomes

• Hard to copy• Telomerase is a

special enzyme that adds repeating DNA sequences to the ends of chromosomes

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Eukaryotic Chromosomes:•Long strands of DNA•Located in the nucleus

•Replication• Occurs in the nucleus• Has many replication

sites

replicationProkaryotic DNA:•In a single circle•Found in the cytoplasm•Start at a single spot

Prokaryotic Replication:•One replication site•Occurs in the cytoplasm

Prokaryotic DNA ReplicationIn most prokaryotes, DNA replication does not start until regulatory proteins bind to a single starting point on the chromosome. This triggers the beginning of DNA replication.

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