The Backbone Nucleotides combine by covalent bond between phosphates and sugars
A single strand of DNA Written as: 5’-ACTGTCAAGGTCGAT-3’ 5’ 3’
Base Pairing Hydrogen Bonds for spontaneously between specific nitrogenous bases Pairing Rule: Cytosine bonds with GuanineC-G Thymine bonds with AdenineT-A
A Double Strand of DNA 5’ 3’
How a DNA strand is written 5’ - ATAGGGCCTAGAACCTGG - 3’ 3’ - TATCCCGGATCTTGGACC - 5’ Strands are anti-parallel
Try writing one yourself 3’ - TTAAGCTATGCT - 5’ What is the complementary DNA strand?
Now draw a double strand, including bases and backbones 5’ - ATGC - 3’ 1.Does your diagram have sugars, phosphates, and nitrogen bases? 2.Are the strands anti-parallel? 3.Where are covalent bonds between nucleotides? 4.Where are the hydrogen bonds?
The Double Helix
High Resolution image of Actual DNA molecule
DNA within a Cell DNA combine with proteins called histones to create structures called chromosomes Each cell contains many chromosomes, each with a specific DNA sequence
A Nucleosome DNA strands are tightly wrapped around histone proteins to create a complex known as a nucleosome
Genes A gene is a specific sequence of DNA nucleotides The DNA sequence contains the information necessary to build a protein Each specific gene codes for a specific protein
How much DNA is there? The human genome contains 3 billion base pairs of DNA, about the same amount as frogs and sharks. But other genomes are much larger. A newt genome has about 15 billion base pairs of DNA, and a lily genome has almost 100 billion.
Unravel all the DNA in your body… …and it would stretch to the moon!
Junk DNA Only a very small percentage of your DNA (1.5%) is actually composed of coding genes, most of it is repetitive sequences or other non-coding sequences We still don’t know what the other 98.5% of DNA in our cells are for. We’ve still got a whole lot to learn