I just finished reading
Chapter 9: Evidence of Biological Information for this Sunday. You should all
be happy to know that it is relatively short! When you are reading through this
week’s material, I suggest that you read it once maybe straight through trying
to get the general gist of what is being said. Strobel tries to emphasize the
point that the molecule holding our genetic information, DNA, is extremely
complex and would require an intelligent source to create diversity for the molecules that make up our
cells. He examines the way a molecule might be developed gradually, such as
self-organization. However, go back and do some research because I believe it
is important that you understand how DNA functions, at least to a basic degree,
so that you can be amazed at its complexity! On Sunday I will be prefacing our
conversation with a DNA 101 session. I want to throw out there that genetics is
a quickly growing topic. Our knowledge base has exploded since the discovery of
the structure of DNA in 1953 and more recently grown with the completion of the
Human Genome Project in 2003. So if you feel like this is foreign and new to
you, it’s ok! It’s kind of new to everyone!
Here are some resources to
help as you read.
Broad
overview of DNA components and structure
> http://www.ornl.gov/sci/techresources/Human_Genome/project/info.shtml
(down to the horizontal line only)
Feel
free to look at everything, but specifically:
-Cells
and DNA; ii. What is DNA?; iv. What is a gene?; What is a chromosome?
-How Genes Work: i What are proteins and what do they do?; ii. How do genes direct the production of proteins?; iii. Can genes be turned on and off in the cells?
See
“Flow of Information” and “Genetic Code”
> OR A VIDEO--http://www.youtube.com/watch?v=-ygpqVr7_xs (The Central Dogma)
http://www.youtube.com/watch?v=D3fOXt4MrOM&NR=1&feature=endscreen
(DNA to proteins)
And for some laughs……http://www.youtube.com/watch?v=_Q2Ba2cFAew
(Central Dogma Song)
When we talk about DNA,
we are talking about a double helical structure which is similar to a ladder
twisted to resemble a spiral staircase.
http://www.mhhe.com/biosci/esp/2001_gbio/folder_structure/ge/m4/s1/assets/images/gem4s1_1.jpg
(DNA structure)
http://www.sciohio.org/Image84.jpg
(twisted ladder)
The sides of this ladder are
made up of two components, a sugar and a phosphate, that alternate to make a
sturdy backbone. The rungs of this ladder are formed by specialized pieces known
as nitrogenous bases. There are four nitrogenous bases: A, C, T, and G also
known as adenine, cytosine, thymine, and guanine, respectively. These four
letters function to as the information source for the proteins necessary to the
cell. These letters are independently arranged along the length of the
sugar-phosphate side rails. However, in pairing up to form a complete rung,
only specific interactions may take place. (A goes with T; C goes with G). The
interaction between the bases (hydrogen bonds) knits together the two strands
of DNA to form the double helix.
So
DNA acts as the holder of all our genetic information and resides in the
nucleus of the cell. But how is
this information extracted so that it can be put to use?
http://www.bio.miami.edu/~cmallery/150/gene/central.dogma2.jpg
This takes us to a little thing
known as the Central Dogma. The Central Dogma describes the process of moving
from DNA to proteins.
Our journey starts with the
need for a particular protein. When this happens, a complex of proteins
assembles on the stretch of DNA that corresponds to the protein in need. The
DNA is unzipped so that a single strand (a backbone with attached bases) can
act as a template for creating a new strand, known as messenger RNA, or simply
mRNA. Messenger RNA closely resembles DNA. It has a sugar phosphate backbone
with attached nitrogenous bases. The most notable difference is a substitution
of U (uracil) for T (thymine). Then, units known as nucleotides (which consist
of a sugar+phophate+nitrogenous base) are fit like puzzle pieces to the
matching template on DNA. Once the stretch of DNA is paired in a complementary
fashion , the mRNA is released. This mRNA will be processed and then leaves the
nucleus so that it may proceed to the factory-like unit known as the ribosome.
The ribosome is the site of
protein synthesis. The process of creating mRNA is known as transcription. The
next phase where mRNA is used to manufacture proteins is known as translation.
Back to the story…mRNA moves
out of the nucleus and travels through the interior of the cell until it
encounters the ribosome. As the ribosome pulls the mRNA through its subunits,
proteins are made in an intricate process involving a three-letter code. These
three letter codes, known as codons, correspond to one of twenty amino acids.
There are 64 codons that are used in building proteins. How is this done, you ask?
http://hyperphysics.phy-astr.gsu.edu/hbase/organic/imgorg/translation2.gif
There are special players
known as transfer RNA, or tRNA. Transfer RNA is responsible for matching the
right amino acid to each codon. They do this through a structure known as the
anticodon. Each tRNA has a three letter anticodon that can be matched (again,
kind of like a puzzle piece) to its complementary codon. So in the depths of
the ribosome, tRNAs are matching up and moving out, leaving behind their amino
acids on a growing peptide chain. Once all the amino acids are assembled, a
protein is released.
Viola!
Through the complexity of DNA we have arrived at a protein.
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