The Replication of DNA

DNA Replication

DNA replication happens in all living organisms

This is done before mitosis and meiosis× During Interphase

DNA replication is the process of copying one DNA helix into two identical helices

× Old strands of DNA become templates for the production of new strands

× This type of replication is called semiconservative replication

× Semiconservative replication is when new strands are made up of one old strand and one new strand

× The old strand is acting as a template to produce a new complementary strand

× Dna Replication uses base pairing to pair nucleotides× The old strand is read and the new

strand is built by pairing with the old strand’s nitrogenous bases

× Replication begins at thousands of sites along the DNA strand called origins of replication

× Look like bubbles in the DNA strand

× Hydrogen bonds between the bases are broken and the paired bases separate

DNA does not do this all on its own. Enzymes are used at each stage of this process.

Enzymes involved in DNA replication:

× DNA helicase- breaks down the hydrogen bonds that hold the nucleotides together (unzips the DNA)

× DNA Primase- begins replication by adding a primer of a few nucleotides

× DNA polymerase- place new DNA nucleotides in position and causes nucleotides to bond

Note me: More to the story

Replication goes in a particular direction – always from the 5’ to the 3’ end.

So, one new strand moves forward through the DNA molecule. (Leading Strand)

Note me: More to the story

The other strand works backwards. It is made in chunks, and then these chunks are attached to each other as they get longer. (Lagging Strand)× The multiple chunks of DNA found in the

lagging strand are called Okazaki fragments

Polymerase also follows along checking for any errors in replication (mutations)

Enzymes involved in DNA replication:

DNA ligase- seals breaks in the sugar-phosphate strands

Final Result: Two Identical DNA molecules

These ideas are used to treat forms of cancer× Chemotherapeutic drugs stop

replication× Some chemotherapeutic drugs

have things that are similar to the four nucleotides only when they are used by the cancer cells to replicate they fail and the cancer cell is unable to replicate causing the cancer cells to die off

Why is this important?

× DNA is the instruction manual for all the proteins that our body creates and depends on

× The DNA needs to be replicated accurately in order to create actively functioning proteins

× Proteins carry functions within cells that influence the way our body works (ex. Transport proteins inside cell membranes)

Why is this important?

× If the amino acid chain is produced in the wrong order it can cause a faulty gene or mutations× A gene mutation is a change in

the sequence of bases that make up the gene

Overall Summary1. Helicase unwinds the DNA strand

2. Primase begins the replication by adding a few nucleotides to the open strand

3. DNA Polymerase works its way down the strand, continuing the work that Primase started. It can only move from 5’ to 3’.a. Replication occurs continuously in the

5’ to 3’ direction (leading strand) and discontinuously in a 3’ to 5’ direction on the other side (lagging strand).

Overall SummaryThe lagging strand is is made in short, unconnected segments, known as “Okazaki fragments”

4. Ligase moves along these fragments and connects them to create a continuous strand.

5. DNA polymerase enzymes continuously move along the new strands and check for errors.

Vocabulary

Try to simplify in your own words:× Semi-conservative Replication× Helicase× Primase× Polymerase× Ligase× Okazaki Fragment× Leading Strand× Lagging Strand