DNA, RNA, and Protein The Whole Story
They didn t always know DNA was the Genetic Material. But they did know that the genetic material needed to do four things.
The Master Molecule Contains Information Transmits information to the ribosomes Replicates Makes Mistakes (Mutations)
The unique characteristics of an organism are encoded in DNA
After scientists discovered that DNA was the Genetic Material, it then became the task to figure out what it looked like.
They knew that DNA was made up of nucleotides which are composed of
Sugar Nitrogen Base Phosphate
They also knew that there were four nitrogen bases
Adenine Thymine Guanine Cytosine
Chargaff s Rule Thymine - Adenine Cytosine - Guanine
Rosalind Franklin took X-ray photographs of DNA that Suggested...?
DNA was Helical
Watson and Crick Using these, and other experiment s s data, Watson and Crick put together the Model of DNA. They called the shape... A Double Helix
The Double Helix Two spiraled strands of nucleotides whose bases face each other
From here it was rather easy to figure out how DNA replicated itself
Using Chargaff s Rule, A Hydrogen Bonds with T and C Hydrogen Bonds with G and the model, they determined...
During DNA replication, the molecule uncoils and unzips down the middle. As the base pairs separate, complimentary nucleotides are added by DNA polymerase, and the molecules recoils.
If We Have a DNA strand of... A T C G A T C G G C T A
First they seperate... A T C G A T C G G C T A
First they seperate... A T C G A T C G G C T A
First they seperate... A C A C G T T G T G C A
Then new nucleotides are put in.. A T T C G A T C G G C T T A
Then new nucleotides are put in.. A T T C G G A T C G G G C T T A
Then new nucleotides are put in.. A T T C G G A T T C C G G G C T T A
Then new nucleotides are put in.. A T T C G G A T A T C G C G G G C T T A
Then new nucleotides are put in.. A T T C G C G A T A T C G C G G C G C T T A
Until you have two complete strands. A T A T C G C G A T A T C G C G G C G C T A T A
Each time DNA replicates we get two new strands that are exactly like the original. Unless,
there is a mispairing, such as A with C. Then DNA Repair (enzymes and polymerases) come along and fix the DNA. Recognize the mistake Remove what is wrong Replace with what is right
Some Mutations don t get fixed It could be Harmful -Cause the organism not to grow or to die -Cause cancers It could be Beneficial -Creates variation in a species and the variation could be good.
Now we know how to make more DNA. Is this all we need to know for life?
No, Our bodies use Protein for its Life Processes Since, the information of how the proteins are arranged (and thus, its function) is stored in DNA There must be some connection must exist between the two. Which is...
ribonucleic acid
DNA vs. RNA double- stranded contains deoxyribose contains thymine single- stranded contains ribose contains uracil
Two Steps 1. DNA to mrna Transcription 2. mrna to Protein Translation
DNA uncoils RNA polymerase reads DNA template and matches up RNA nucleotides RNA strand splits off and DNA rejoins Transcription DNA to mrna
Before it goes out of the nucleus, RNA Processing
Introns and Exons Introns get spliced out of chain Exons are left and get sent out of the nucleus
Transposons Genes that jump around on the chromosome Changes expression of trait
The Genetic Code How can only four nucleotides code for 20 different amino acids? The nucleotides in mrna are read in groups of three Called a codon
AAACACGGU becomes AAA-CAC CAC-GGU
Each codon codes for a specific amino acid
So, AAA-CAC CAC-GGU becomes Lysine-Histidine Histidine-Glycine
How, You Ask?
Translation RNA to Protein mrna exits nucleus and enters cytoplasm
Ribosomes attatch to mrna and attract a trna The trna contains an anticodon - three nucleotides that base-pair to a specific codon in mrna The trna is connected to an amino acid
The ribosome binds another trna, joins the two amino acids with a Peptide Bond, cuts the bond it had with its trna,and releases that trna to bind with another amino acid
The ribosome advances along the mrna, binding new trna molecules and amino acids until it reaches a stop codon.
The result is an amino acid chain, otherwise know as a Protein
Gene Expression is controlled by Promoters - promote RNA polymerase to bind Repressors - represses the making of genes by binding to the site that RNA polymerase binds to, thus the polymerase can t
Gene Expression is controlled by Inducers - bind to the repressor and take it away, so the RNA polymerase can bind to it an do its thing
And that is the Jist of it. Reading Resource - Chapter 12 pages 324-343
Rest of this Hour Internet Demo and Decoding Practice
Tomorrow
http://www.pbs.org/wgbh/aso/try it/dna/shockwave.html