About how many cells are our bodies made of? TRILLIONS! How many of those cells contain your DNA? All of them! All of your cells contain a complete copy of your genome (DNA)!

Your life started as just 1 cell Your life started as just 1 cell. How do we come from 1 cell & end up as trillions? That single cell divided over & over again as you grew. Every single cell needs copies of your DNA. HOW DOES THAT HAPPEN?

DNA Replication

DNA Replication The process of copying DNA Because DNA is double stranded, we can separate the 2 strands & create a new strand using 1 strand as a template. Our end product is 2 identical double stranded DNA molecules. The 2 strands are called complementary.

During DNA Replication… The DNA is unwound & unzipped (the 2 strands separate). Each original DNA strand is used as a template (model) to make a new DNA strand with base pairing.

Remember – Enzymes Enzymes are catalysts that speed up chemical reactions. Forming & breaking chemical bonds takes energy. Enzymes lower the amount of energy needed to make & break chemical bonds.

Enzymes in DNA Replication DNA replication could not occur without enzymes. There are several enzymes involved in this process.

Enzymes Used in DNA Replication Helicase unzips/separates the 2 DNA strands by breaking the hydrogen bonds between the nitrogenous bases. DNA Polymerase adds new nucleotides to the new DNA strand. DNA Polymerase also “proofreads” the new DNA to check for errors. The strands are rewound when the process is finished.

The Semi-Conservative Method of Replication When replication is complete, each DNA molecule is made of 1 old strand & 1 new strand.

Chromosome Arrangement in Prokaryotic Cells (Bacteria) Prokaryotic cells have 1 circular chromosome that is free-floating in the cytoplasm. Prokaryotic cells do not have a nucleus. When prokaryotic cells copy their DNA, the process begins at 1 point in the chromosome & moves around the circle in both directions until complete.

Chromosome Arrangement in Eukaryotic Cells Eukaryotic cells have many chromosomes & DNA replication begins at hundreds of places & continues in both directions until each chromosome is completely copied.

The point in the DNA where the 2 strands are separating & replication is occurring is called the replication fork.

DNA Polymerase DNA Polymerase only works in 1 direction (5’ to 3’). One strand is read & synthesized continuously while the other is synthesized in fragments.

DNA Polymerase makes the new strand from 5’ to 3’. If DNA polymerase continues in this direction (away from the replication fork), what will happen? It will run out of DNA! Once DNA polymerase gets to the end, it loops back around & starts another fragment.