Translation

"Describe the process of translation in protein synthesis, including initiation, elongation, and termination."


Here are two definitions that mean the same thing because I'm annoying like that:

Translation is the process where the sequence of codons formed during transcription becomes the order of amino acids in a polypeptide.

Process by which the sequence of codons in mRNA dictates the sequence of amino acids in a polypeptide.


Where transcription copies the sequence of bases from the DNA string to form mRNA, translation translates these base codons to become amino acid polypeptides.


During translation, the sequence of codons on the mRNA show the amino acids which order to go in to create their polypeptide


Three Steps of translation: 

This is my incomplete Karla ramble:
 
We begin with our mRNA, hanging out in the cytoplasm. It left the nucleus after it had been transcribed and processed (Checked for errors). Here it comes into contact with ribosomal subunits. Two parts of a ribosome (subunits) surround this mRNA, a smaller one and a larger one. The smaller one fuses to the mRNA and the larger one fuses to the smaller one. the mRNA is being fed through this ribosome.

Once surrounded by ribosomes, the mRNA comes into contact with tRNA. tRNA comes bearing an amino acid complementary to the codons on the mRNA. Two tRNA enter the ribosome at a time.  The first tRNA comes in and pairs to the codons. The second tRNA enters the ribosome and receives the peptide from the first tRNA, which leaves the ribosome and makes room for another tRNA amino acid complex to enter the ribosome. Like this, the chain of amino acids grows like a tail, out of the ribosome, each tRNA pairing with a codon and giving its amino acid to the growing chain and leaving to make room for another tRNA amino acid complex to enter.

When the ribosome comes to the stop codon on the mRNA, the ribosome dissociates and falls off the mRNA molecule and is done.

The proper definition of translation:

Three steps and one pre-step to describe rRNA

0. rRNA, also called structural RNA is formed in the nucleolus. There, it join with proteins (made in the cytoplasm) to be a ribosomal subunit. it travels out to the cytoplasm to join just as protein synthesis starts. Each ribosomal sub unit contains proteins and rRNA. One of the proteins in rRNA is the enzyme that joins amino acids together with a peptide bond.

1. Initiation: mRna binds to the smaller of the two ribosomal subunits that join and surround it. 

2. Elongation: One amino acid at a time, the poly peptide begins to form and lengthen.

The ribosome has room for two tRNAs to work in it. The first tRNA goes into the ribosome bearing an amino acid. The tRNA has the anti codon to the codon on the mRNA. This first tRNA gives its peptide to the second tRNA entering the ribosome. In this way, the chain grows and forms the primary structure of the protein molecule. Secondary and tertiary structure come to be after termination.

 3. Termination of synthesis: The ribosome encounters a stop codon on the mRNA. There is no tRNA for this and the ribosome dissociates and falls off the mRNA molecule.

 a polyribosome can sometimes form on a mRNA and form several of the same polypeptides can be formed at the same time.

Transcription

Transcription:

"Describe the process of transcription in protein synthesis. Include the specific roles of DNA and mRNA."

In different contexts, when you transcribe something, you make a copy of it. This is the same in DNA transcription. A copy of a DNA strand is copied an an mRNA molecule is created.


Transcription is making an RNA molecule that is complementary to a portion of DNA. 


Remember the DNA bases- Adenine, Thymine, Guanine and Cytosine.


Again, this is only the part of transcprition that this course calls for. I know there is far more detail to the process, including a 'TATA box', which I find funny but for now, I'll include the information only relevant to my course. 

  

The process of transcription: 

During Transcription a segment of  the DNA unwinds and unzips and ONE strand of the DNA is copied from the transcription bubble. Complementary nucleotides pair with the DNA bases using the following bases: Uracil, thymine, guanine and cytosine. A strand of mRNA results.  

triplet codes

Explain what is meant by a triplet code:


DNA is a long strand of bases. A triplet code is a sequence of three bases along this strand.

 Why three? Diversity. There are four different bases. These bases need to code for all 20 amino acids.

Each triplet of bases stands for one type of amino acid. If each code were only two bases long (a doublet) the codes available would be too limited to provide codes for 20 unique amino acids. 

By having triplet codes in the four bases, we are able to provide codes for 64  different triplets. We only need 20 so some of these triplets are able to be dedicated start and stop codons.

 Codon: three letter unit of an mRNA molecule. 

All 64 codons have been discovered and 3 of  them have been determined to be stop codons.

During transcription, an amino acid is added wherever there is a triplet code.

RNA

Let's define RNA and its structure. Then, to me (and hopefully you?) protein synthesis will make more sense in one of the next posts.

RNA exists in cells to assist in protein synthesis, among other things. For now, this class focuses on just the protein synthesis aspect of RNA's job.

While DNA specifies what proteins will become, RNA helps along that journey, working with DNA and ribosomes to form proteins. There are three types of different RNA that help with this journey.

1. mRNA: messenger RNA carries a coded sequence of bases to ribosomes. 
2. tRNA: transfer RNA carries or -escorts- amino acids to the ribosomes during protein synthesis.
3. rRNA: ribosomal RNA is found in the ribosomes.



RNA is a polynucleotide, a chain of nucleotides with paired bases, like DNA is. There are some differences however.

1. RNA is not a double helix like DNA is. DNA is purposely a double helix with paired bases. That's how it rolls (and replicates, semiconservatively). RNA sometimes pairs with other bases but it's not on purpose and it's when the strand doubles back in itself to form a hairpin type structure.

2. DNA's  bases are: Adenine, Guanine, Thymine, Cytosine.
    RNA's bases are: Adenine, Guanine, Uracil, Cytosine.

3. Instead of Deoxyribose sugars, RNA uses Ribose 5-carbon sugar.

For now, this is all I have to say for the structure of RNA. There is more on RNA codons but for the amount of sense it is making to me right now, it deserves its own posting ;)

DNA as hereditary material.

 

 

 

DNA is the hereditary material. It must: 

(3 points)

1. Replicate with high accuracy so that a copy may be passed to ech daughter cell. DNA must also be transmitted from one generation to the next through eggs and sperm.

2. Undergo mutations to provide genetic variability for evolutionary change.

3. Store information to control both the development and the metabolic activities of the cell and organism. 

DNA replication.

So DNA carries your genetic information, is made of a double helix with hydrogen-bonded nitrogenous bases, a 5-carbon sugar and a phosphate group... how do they come to be? how does EVERY DNA molecule come to be an exact replica of the one before?

DNA makes a copy of itself in the nucleus before cells divide to ensure continuity of hereditary traits

The textbook I have been assigned (Inquiry into Life by Sylvia S. Mader 8th edition) shows us three steps to DNA replication (I know there are a few more, and much more detail, but for the purposes of this course, we learn the 3 simple steps)



1. Unwinding: The two strands that make DNA unwind and 'unzip' to become two phosphate-sugar strands (temporarily) thanks to the enzyme DNA Helicase.

Oh man... anyhow, Helicase causes the hydrogen bonds to break. We now have two separate strands with single bases.


2. Complementary bases pair with the free nucleotides. Free floating nucleotides are always floating in the nucleus. They now pair with the nucleotides that have been unzipped.


3. Joining: DNA Polymerase joins the paired nucleotides and they are sealed together form two new strands of DNA.


So there are now two newish strands of DNA. Each helix that has just been created contains one strand of the old (parental) helix and one strand of the new (daughter) helix. In this way, DNA replication is known to be semiconservative. 

In this way, the double helix of DNA is handy- the old strand is used as a template during replication to ensure accuracy.

Loved this video... the process is easy to understand and it's cute. A bit more information than is needed in my class at present but who cares? ;) it's a good video. 

Important terms from my flashcards:

1. DNA Polymerase~ an enzyme that joins nucleotides to their complementary bases during DNA replication


2. DNA Helicase~ An enzyme that causes the DNA molecule to unzip and unwind.

3. Semiconservative: DNA replication is known as semiconservative because the parental strand is conserved when it separates to join with new nucleotides forming daughter strands and a new helix.

DNA part 1.

What do we know about DNA? We know that DNA evidence is used to help convict criminals, prove who the father is on Jerry Springer and in other trashy daytime TV shows but not many of us really know how DNA works, what its structure is or what it actually does....


To be simplistic about it, DNA is short for Deoxyribonucleic acid. It is the genetic material that specifies protein synthesis in cells. It holds our genes and therefore dictates every part of us.




Before I describe the structure of DNA, I want to clarify what a nucleotide is, since DNA is made up of nucleotides. If you were wearing a necklace of beads, the necklace as a whole would be DNA and a nucleotide is the bead as a singular part of the necklace.

A nucleotide is made from a phosphate (an acid), a pentose (5 carbon) sugar (Deoxyribose sugar) and a nitrogenous base.  The nitrogenous base can take up hydrogen atoms (hence the term 'base')

 Nulcleic acid is synthesized (made) by condensation synthesis.


Structure of DNA

DNA is a polymer of nucleotides all bonded together in a string and fused in the middle to a second string of nucleotides. All these nucleotides are bound together in the middle of the double helix with hydrogen bonding holding the bases together.

DNA looks like a twisted ladder- otherwise known as the double helix. The sides of the ladder are made of sugar-phosphate-sugar-phosphate.

DNA has 2 strands of polynucleotides bound together with hydrogen bonding. They twist around each other in a double helix structure.

The nitrogenous bases in DNA are paired together in complementary pairs.
There are four bases, divided into two categories.

There are the purines: Adenine (A) and Guanine (G)
There are the pyrimidines: Thymine (T) and Cytosine (C) 

Each base has a complimentary pairing with one other base:
Adenine pairs with Thymine.
Guanine pairs with Cytosine.

The bases are bound together with hydrogen bonding.