Each set of three nitrogen bases that codes for an amino acid is known as a codon; the functions of proteins are contradicted by the characteristics of the amino acids that make up them, in particular the sequence of amino acids in a protein determines the function of that protein as the amino acids are linked through peptide bonds.
Amino acids are the structural units that make up proteins; they join together to form short polymer chains called peptides or longer chains called either polypeptides or proteins.
The mRNA molecule moves through the nuclear membrane pores to attach to ribosomes in the cytoplasm; a number of ribosome’s then attach to the mRNA strand and each ribosome produces one polypeptide…
Transfer RNA (or know as tRNA) molecules are found in the cytoplasm and carry amino acids on one end, the other end of a tRNA molecule has a complementary triplet of bases to the codons of mRNA; these tRNA triplets are called anti-codons.
The anti-codon of the tRNA attaches to the codon of the mRNA, the binding of two tRNA anti-codons allows two amino acids at the opposite ends of the tRNA molecules to come together then these amino acids join together by forming a peptide bond.
The tRNA molecules then detach from the mRNA and move off to pick up more amino acids, another tRNA molecule (with its specific amino acid) then moves in and its anti-codon attaches to the codon of the mRNA and more peptide bonds join the amino acids; this process continues until a stop codon on the mRNA dictates that the polypeptide synthesis is finished, this then results in the base sequences of the mRNA being translated into amino acid sequences in polypeptides.
A codon is a three base sequence (three nitrogen bases in a row) on mRNA; a codons function is to call for a specific amino acid to be brought to the growing polypeptide.
An anticodon is a three base sequence on tRNA, it matches the codon and that's how the right amino acid is put onto the polypeptide next however the tRNA must fit its anticodon onto the mRNA codon; each tRNA can only bring one kind of amino acid.
There are 61 codons that specify the amino acids used in proteins and 3 codons known as stop codons which signal the termination of growth of the polypeptide chain which mean there are 64 in total; there are 64 codons because there are four bases and three bases per codon.
Code is a triplet code because there are three different unique amino acid codes that make up that codon by following a certain sequence, the amino acids then combine into three to form a DNA or RNA strand (hence the name triplet).
Start and stop codons: A start codon is the message that starts a certain protein being synthesized from a certain sequence and stop codons are the messages that tell the cell that the protein is made and that it should stop adding more amino acids to the polypeptide.
Degeneracy is basically things that are different structurally but create the same results; some codons (3 nucleotides that code for an amino acid during translation) may code for the same amino acid for example argentine, multiple codons can code for that specific amino acid but for polypeptides, however changing those specific codons may give the same result.
If argenine was coded with CGU and was changed to CGC both these results may still produce the amino acid argentine which means the polypeptide didn't change however the genetic code did change this is known as the wobble effect.
If base sequences are changed this can result in mutations; these mutations can be caused by radiation, viruses, transposons and mutagenic chemicals as well as errors that occur during meiosis or DNA replication, these mutations can also be caused by the organism itself by cellular processes.
Task 3
Protein biosynthesis:
Protein biosynthesis is the process in where cells build or manufacture proteins; the term is sometimes used to refer only to protein translation but more often it refers to a multi-step process which begins with amino acid synthesis and transcription of nuclear DNA into messenger RNA which is then used as for translation.
Protein synthesis takes place in two stages, stage one is transcription; this is where the DNA helix is untwisted by the enzyme DNA helixase, then the DNA is split into two as the hydrogen bonds are broken between the complementary base pairs then a mRNA strand is made with complementary pairs, this is similar to DNA replication however this mRNA strand leaves the nucleus through the nuclear pores.
This diagram explains how transcription
featured in the above paragraph
takes place...
The second step of protein synthesis is translation; this occurs in the cytoplasm and requires ribosome’s, for this to take place a small ribosomal subunit attaches to the bottom of the mRNA strand and then a large ribosomal subunit attaches to the top of the mRNA.
Now this has taken place the synthesis can begin; in order for it to start the first codon (base triplet) must be methionine which is known as AUG and then the anti codons on a tRNA with an amino acid comes into the large ribosome unit and matches itself with a codon.
The first anti codon must be UAC because it is complementary to AUG, then the next anti codon comes along but before the tRNA leaves the ribosome polmerase it creates a peptide bond between the amino acids.
Then the tRNA leaves the ribosome which leaves the amino acid behind, this process repeats itself until it reaches a stop codon and then the amino acid chain or which is known as a polypeptide is released into the cytoplasm as a protein when the ribosome and mRNA separate.
This diagram explains how translation featured in the above paragraphs takes place...
The cistron DNA (A section of DNA that contains the genetic code for a single polypeptide) is transcribed into a variety of RNA intermediates, proteins can often be synthesized directly from genes by translating mRNA.
For synthesis of protein to take place a succession of tRNA molecules charged with appropriate amino acids have to be brought together with an mRNA molecule and matched up, this is done by base pairing through their anti codons with each of its successive codons.
The amino acids then have to be linked together to extend the growing protein chain and then the tRNAs are relieved of their excess which are released.
This processes is carried out by a multimolecular process (like a machine), the ribosome is formed of two main chains of RNA which are called ribosomal RNA (rRNA) and also more than 50 different proteins.
This molecular juggernaut (large force) latches onto the end of an mRNA molecule and then moves along it, as this takes place it captures loaded tRNA molecules and attach together the amino acids they carry to form a new protein chain.
DNA is transcribed to mRNA which is then translated (decoded) into protein, the protein biosynthesis takes place in the ribosome; a series of ribosome’s (poly ribosome) can simultaneously translate the same mRNA molecule.
tRNA brings specific amino acid to ribosome and mRNA carries the genetic information to protein, the codons that encode the same amino acid often differ slightly but only by their third base; the joining of the third base is less stringent than the other two, because of this differentiation one tRNA can pair with multiple mRNA codons.
There are signal sequences before the main coding sequence at the translation initiation sites, amino acid activation is catalyzed by amino acyl-tRNA synthetase and pairs it to its corresponding tRNA; anti codon in the tRNA molecule forms base pairs with the appropriate codon on the mRNA.
In the initiation step initiation factors are involved; the initiation factor is the protein that promotes the association of ribosome’s with messenger RNA, in the elongation step incorporation of an amino acid into a protein takes place as a result of this a polypeptide chain is grown then the termination stage is the last stage in protein biosynthesis.
This diagram represents the
basic process of Bio – synthesis
of proteins…
Basically protein synthesis is simply the method that takes place in order to produce proteins; a protein is simply a long chain of amino acids linked together by bonds which have been previously produced and formed from the two stages of protein synthesis known as transcription and translation, the research carried out on protein synthesis shows that protein synthesis is a highly important process that is required for correct bodily functioning and not just physically but mentally as well.
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*Class Notes
