DNA – The Molecule of Life Hidden in all life is a unique code This code is in the form of a chemical, called DNA DeoxyriboNucleic Acid

WE STUDY DNA FOR MANY REASONS SUCH AS…. WHY DO WE STUDY DNA? WHY IS IT IMPORTANT??????? WE STUDY DNA FOR MANY REASONS SUCH AS…. CENTRAL IMPORTANCE TO ALL LIFE ON EARTH MEDICAL BENEFITS SUCH AS CURES FOR DISEASES OR RISKS FOR GENETIC DISEASES.

Where is DNA found in the cell? One chromosomes enlarged Genes are pieces of DNA that code for a characteristic e.g. Eye colour Chromosomes in the cell nucleus Chromosome uncoiled to show DNA

DNA – The Molecule of Life A photo of DNA from an electron microscope What does DNA look like? A photo of DNA from an electron microscope

DNA – The Molecule of Life What is DNA made up of ? What results if a DNA molecule like this is broken down?

DNA – The Molecule of Life Watson and Crick discovered that DNA has 2 strands twisted together called a double helix. (like a twisted ladder) DNA is found to be made of three types of molecules:

DNA – The Molecule of Life Sugar This is a special type of sugar called deoxyribose

DNA – The Molecule of Life Phosphate

DNA – The Molecule of Life Base NITROGENOUS BASE

DNA – The Molecule of Life SUMMARY: DNA is made of three types of molecules 1. Sugar 2. Phosphate 3. Nitrogenous Base

and a base joined to the side A SINGLE NUCLEOTIDE These three molecules are bonded in a special way to form the monomers of the DNA molecule called NUCLEOTIDES Consists of a Sugar and a base joined to the side a Phosphate joined to

In the DNA molecule, nucleotides link together to form long chains called polynucleotide chains. (poly=many)

There are four different bases. These make up the “steps of the ladder” The sugar and phosphates are the same throughout the DNA molecule but …

The four bases are either single or doubled ringed A single ringed base A double ringed base

There are two types of single ringed bases (PYRIMIDINES) Thymine C Cytosine

There are two types of double ringed bases (PURINES) Adenine G Guanine

Four different nucleotides therefore occur in the DNA molecule G

The polynucleotide chain now with the four different bases G

The DNA molecule consists of TWO chains The sugar and phosphates form the backbone of DNA (the “side of the ladder”) The DNA molecule consists of TWO chains

It is arranged in the opposite direction to the first chain What do you notice about the second chain? The 2 DNA strands are ANTIPARALLEL to each other

But how are the bases arranged to link the two chains?

always links to a one ringed base When bases combine .. A two ringed base always links to a one ringed base

Adenine always joins to Thymine Guanine always joins to Cytosine Chargaff’s Rule: Adenine Thymine Adenine always joins to Thymine A T Guanine Cytosine Guanine always joins to Cytosine G C

look at how the bases link with each other to join the two chains of the DNA molecule Complimentary rule: DNA made of 2 strands of nucleotides bonded in a specific way C A G C T A T G

A The DNA molecule has many nucleotides To see this clearly we need to simplify a nucleotide Sugar Base A Phosphate

Which nucleotide will link to A ? Try to determine which nucleotide will link to the form the second DNA chain G C A T C G T A T A A T G C Which nucleotide will link to A ? Remember A joins to T and G to C C G T A A T

Two Sugar-Phosphate backbones As the bases link to each other, the DNA molecule is twisted into a double helix (looks like a twister ladder) Inter-linking bases- Two Sugar-Phosphate backbones

Genetic diversity Different arrangements of NUCLEOTIDES in DNA provide the key to DIVERSITY among life: We all have different codes that make us unique!!!!

As soon as you walk in 5-10 minutes to finish DNA strand from Friday (supplies found on counter) Make sure it is colored as instructed on whiteboard Everyone needs their notebook – please get it

DNA UNIT 3 DNA Replication

DNA replication How DNA is copied

DNA Replication occurs during the S Phase of Interphase DNA Replicates in the cell’s nucleus

DNA replication When a cell divides, the DNA needs to be copied so that each new cell has the same DNA as the parent cell

DNA replication The two chains separate Enzyme Helicase Breaks the Hydrogen Bonds New strands form complimentary to parent strands Called Semi-Conservative because each New DNA has a strand from the parent The two chains separate

The 2 DNA strands open forming Replication Forks (Y-shaped area) Parental DNA Molecule 3’ 5’

An enzyme (HELICASE) unzips T A A T G C A closer view of DNA replication looking at part of a strand A T C G T A T A A T An enzyme (HELICASE) unzips the DNA molecule G C C G T A A T

T G C A T A Single Strand binding proteins keep the two strands separated G DNA Strands separate A C T T A G C T A

T A T A A T A T G C G C A T A T C G C G T A T A T A T A A T A T G C G DNA POLYMERASE ADDS NEW NUCLEOTIDES to form the new side of the DNA chain A T A T C G C G T A T A T A T A A T A T G C G C C G C G T A T A A T A T