Posted by: mrborden | March 9, 2014

Week 26 DNA replication and Protein Synthesis


F1_largeCodon-ChartMarch 10 2014
QFD: “Be glad of life because it gives you the chance to love, to work, to play, and to look up at the stars.” — Henry Van Dyke
?FD: What are the 2 nucleic acids?
Objective: BSS4. Genes are a set of instructions encoded in the DNA sequence of each organism that specify the sequence of amino acids in proteins characteristic of that organism. As a basis for understanding this concept:
a. Students know the general pathway by which ribosomes synthesize proteins, using tRNAs to translate genetic information in mRNA. b. Students know how to apply the genetic coding rules to predict the sequence of amino acids from a sequence of codons in RNA.
1) DNA replication
dna-codon-chart

Lesson Summary
So that was the basic story of how DNA becomes protein. I’m sure you don’t need to hear my French toast story again. But let’s review the steps involved in the story of the central dogma. The central dogma is a framework to describe the flow of genetic information from DNA to RNA to protein. The process of transferring genetic information from DNA to RNA is called transcription. Then the RNA code is used as the instructions for building a chain of amino acids, and that process is called translation.

When amino acids are joined together to make a protein molecule, it’s called protein synthesis. Each protein has its own set of instructions, which are encoded in sections of DNA, called genes. So the overall story of the central dogma is this: Inside the nucleus of a cell, the genes in DNA are transcribed into RNA. Once RNA leaves the nucleus, it’s translated in the cytoplasm and the process of protein synthesis begins. The end result is a fully-formed protein, just like the end result of my recipe is a plate full of yummy French toast.
1) HW transcription_translation_summary_worksheet

March 11 2014

QFD: “You can tell more about a person by what he says about others than you can by what others say about him.” — Leo Aikman
?FD: What is RNA? tRNA and mRNA?
image
Objective:
March 12 2014
QFD: If you are not fired with enthusiasm, you will be fired with enthusiasm
?FD: Name the major steps involved in making a protein
Objective:BSS4. Genes are a set of instructions encoded in the DNA sequence of each organism that specify the sequence of amino acids in proteins characteristic of that organism. As a basis for understanding this concept:
a. Students know the general pathway by which ribosomes synthesize proteins, using tRNAs to translate genetic information in mRNA. b. Students know how to apply the genetic coding rules to predict the sequence of amino acids from a sequence of codons in RNA.
Summary and Review
All three phases of transcription occur inside a cell’s nucleus. Remember, everything we’ve discussed in this lesson is related to transcription, which is only the first part of the central dogma. The purpose of transcription is to provide a copy of genetic information that can travel outside the nucleus in preparation for translation. We start with the genes in the original DNA and we end with the genes in mRNA. Just to be sure that we’ve got all the steps here, let’s walk through transcription from the top.

Transcription begins when RNA polymerase attaches to a promoter within DNA. This is called initiation. The DNA molecule splits open and allows RNA polymerase to add RNA nucleotides onto the DNA template. The DNA strand that becomes transcribed is the sense strand, and the RNA molecule built upon it is the antisense strand.
1)Proteins
Elongation is the phase in which the RNA molecule grows longer as transcription continues down the length of the gene. Termination occurs when RNA polymerase reaches the terminator and detaches from both strands. The RNA that’s produced at the end of transcription can be one of three different types. The type that we’re concerned with here, which encodes the sequence for amino acids, is messenger, or mRNA. Once the mRNA is complete, then it can leave the nucleus and continue on to the cytoplasm, where it helps with protein synthesis.
1) QUIZ

March 13 2014
QFD: “Circumstances are the rulers of the weak; they are but the instruments of the wise.” — Samuel Lover
?FD: What is an amino acid? a Protein?
Objective:BSS4. Genes are a set of instructions encoded in the DNA sequence of each organism that specify the sequence of amino acids in proteins characteristic of that organism. As a basis for understanding this concept:
a. Students know the general pathway by which ribosomes synthesize proteins, using tRNAs to translate genetic information in mRNA. b. Students know how to apply the genetic coding rules to predict the sequence of amino acids from a sequence of codons in RNA.
1) DNA LAB day 1 of 2
Lab write up
March 14 2014
QFD: “We are what we pretend to be, so we must be careful what we pretend to be.” — Kurt Vonnegut
?FD: What is transcription and how is different than translation
Objective: BSS4. Genes are a set of instructions encoded in the DNA sequence of each organism that specify the sequence of amino acids in proteins characteristic of that organism. As a basis for understanding this concept:
a. Students know the general pathway by which ribosomes synthesize proteins, using tRNAs to translate genetic information in mRNA. b. Students know how to apply the genetic coding rules to predict the sequence of amino acids from a sequence of codons in RNA.
1) DNA lab day 2 of 2
You have a flaw in your understanding, which may be the problem. A gene is NOT one codon of 3 n-bases. A gene is a series of codons along part of a DNA molecule that, together, will code for a protein. It can take thousands of codons, or more, to make a single gene for a single protein. ONE gene for ONE protein, composed of MANY codons, or nucleotide base combinations.
Now..what happens in protein synthesis?
As DNA unzips itself down the middle in the section needed for the gene for a particular protein, one mRNA molecule comes in for each 3-base codon, but it codes as an anticodon (reverse of the code.) This is called transcription. Then that mRNA molecule goes to the ribosome where tRNA molecules are stored. The matching tRNA molecule bonds with the mRNA to ‘read’ the code, but again it is in a mirror image, so the original DNA code is replicated. This is called “translation”. A single mRNA and then a single tRNA molecule codes for one amino acid in the long strand of amino acids that must be attached in exactly the right spot to correctly make a protein molecule.
Let’s try to look at this more closely.
Let’s say that we’re making part of a protein, perhaps coding for 3 amino acids in the huge chain that will be the completed protein.
On the DNA molecule, let’s say that the active side codons are:
T
T
C
G
T
G
A
C
T
The mRNA molecules reading this code would be their mirror opposites, so the first mRNA molecule would read as AAG (the mirror image of TTC). It would go to the ribosome (which is in the nucleus!) and attract its mirror image tRNA molecule, which would read UUC (uracil usually substitutes for thymine in RNA.) This replicates the first codon of the gene for this protein, and that tRNA would go and bring its corresponding amino acid and put it first in the line of the polypeptide chain that is forming on the ribosomal membrane.
The next mRNA molecule would read CAC, which is the mirror image of GTG. It then goes to the ribosome and attracts a tRNA molecule which is its mirror image, which would be GUG (uracil substituting for thymine), and that tRNA molecule would bring its corresponding amino acid to the ribosomal membrane and attach it second in line.
Then, another mRNA with the code UGA (the mirror opposite of ACT) will go out and attract a tRNA molecule with the codon ACU, which will replicate the DNA codon of ACT. The tRNA will bring the corresponding amino acid and attach it third in line in the polypeptide chain.
This process repeats until the entire protein, which may be thousands of amino acids long, is synthesized.
It takes one gene to code for one protein, but a gene is a section of DNA that may be thousands of codons long.

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