DNA DNA ReplicationReplication

DNA ReplicationDNA Replication• Definition: The DNA

within the nucleus is Replicated

• Before a cell can go through mitosis or meiosis the DNA MUST be replicated, or the new cells would have only HALF the amount of DNA

How Does it How Does it Replicate?Replicate?

1. An enzyme begins replication by breaking the hydrogen bonds between the nitrogenous bases (“unzipping”)

2. The free-floating nucleotides attach to the nitrogen bases using another enzyme

How Does it How Does it Replicate?…Replicate?…

3. The strand continues to “unzip” until the entire strand has become “unzipped” and replicated

4. Each new strand formed is a complement of the original (parent) strand

DNA ReplicationDNA Replication

Proofreading New DNAProofreading New DNA• Initially about 1 in 10,000 mistakes

in base pairing during replication!

• Enzymes proofread and correct these mistakes

• The new error rate for DNA that has been proofread is 1 in 1 billion base pairing errors

Semiconservative Model of Semiconservative Model of ReplicationReplication

• Idea presented by Watson & CrickIdea presented by Watson & Crick• TheThe two strands of the parental molecule

separate, and each acts as a template for a new complementary strand

• New DNA consists of 1 original and 1 new strand of DNA

Original DNA

DNA Template

New DNA

What's The Big Deal?What's The Big Deal?• DNA achieves its goals by

producing proteins

• All living things contain proteins (muscles, skin, and bones)

• Everything that you do depends on proteins called enzymes

• These enzymes are important because they control chemical reactions that control life

ProteinsProteins•Proteins control cell functions

and chemical reactions•Made up of amino acids – so we

call them “polymers” of amino acids

•A group of nucleotides in each gene carry information for making a string of amino acids that make up a protein