Medicine Notes > Oxford Medicine Notes > Biochemistry Notes

Translation Notes

This is a sample of our (approximately) 7 page long Translation notes, which we sell as part of the Biochemistry Notes collection, a First package written at Oxford in 2014 that contains (approximately) 216 pages of notes across 33 different documents.

Learn more about our Biochemistry Notes

The original file is a 'Word (Docx)' whilst this sample is a 'PDF' representation of said file. This means that the formatting here may have errors. The original document you'll receive on purchase should have more polished formatting.

Translation Revision

The following is a plain text extract of the PDF sample above, taken from our Biochemistry Notes. This text version has had its formatting removed so pay attention to its contents alone rather than its presentation. The version you download will have its original formatting intact and so will be much prettier to look at.

MRNA TRANSLATION
-Mature mRNA has a modified 5' end which has a methylated guanosine residue attached by a 5' to 5' triphosphate linkage- this is attached to a cap binding proteinit also has a modified 3' end which has a poly A tail and this is bound to a poly A binding protein
-these modifications protect from premature degradation, nuclear cytoplasmic export and the poly A tail facilitates in translation initiation
-There are also a 5'untranslated region and a 3'untranslated region- these regions contain regulatory elements that control how much mRNA is translated
-in between these untranslated regions- there is a coding region- which contains the sequence of nucleotides that specifies the sequence of amino acids in the polypeptide Genetic code
-the mRNA is used as a template to translate the information into protein
-the sequence of 3 consecutive nucleotides on the mRNA strand, CODON codes for one amino acid- GENETIC CODE
-Each CODON codes for one amino acid
-there are four different nucleotides on the mRNA- therefore there are 64 possible combinations of 3 nucleotides- this means that the Genetic code is- REDUNDANTsome amino acids are coded by more than one triplet
-examples - AUG-codes for methionine and is the start codon from which translation begins
-UAA,UAG,UGA- are stop codons that are not recognised by tRNA molecules but proteins instead- these proteins force the termination of translation
-in theory, RNA sequence can be translated in any one of the 3 different reading frames- this depends on where the decoding process begins- different reading frames have a different sequence of codons-different sequence of amino acids-however only one of these three reading frames codes for the required protein- the genetic protein on the mRNA strand is read in non overlapping triplets from a fixed starting point- start codon AUG- Open reading frame consists of start codons that contains exclusively triplets that encode for amino acids
-deletion or insertation of a single or two nucleotides changes the sequence from that point onwards- frame shift mutations

Mutations and the genetic code a) If a single nucleotide is changed
-Mis-sense mutation: the B globlin mRNA contains codon GAG-codes for Glutamic acid but when there is a substitution reaction a new codon is formed- GUG and this codes for valine- this leads to Sickle cell disease
-Nonsense mutation: E.g- B globin mRNA contains the codon- UGG however if the codon is changed to UGA it codes for a stop codon-causes Ribosomes to stop translation at the wrong place and a shortened protein with aberrant function or regulation is produced Surveillance mechanism: nonsense mediated decay
-

When splicing completes the exon-exon junctions are marked by the deposition of exon junction proteins
- These proteins serve as markers in indentifying faulty mRNA that contain premature stop codon- introduced due to a mutation in a gene or through mis-splicing
- The presence of a Exon junction protein down stream of a stop codon identifies the mRNA as faulty and induces its degradation b) If single nucleotide is deleted
-if a number of nucleotides in an open reading frame are deleted/inserted and this number is not a multiple of 3- reading frame from that position onwards is changedresults in incorporation of incorrect amino acids into the polypeptide chain
-E.g- Huntingtons disease Transfer RNA-tRNA
-small RNA molecules- 80 nucleotides long- base pairing occurs to form a clover leaf shape
-anticodon- three consecutive nucleotides that pairs with complementary codon in the mrna molecule
-single stranded 3' region at the end of the molecule which is wher the amino acid that matches the codon is attached to the Trna at the carboxy end
-as there are 64 possible codons fromed from the 4 nucleotides- it would require 61 codons (3 stop codons)- however there are less than 45 t-RNAs- some of the t-RNAs can recognise more than one codon- these t-RNA differ in their third base- Trna molecules are constructed so they base pair with the first two bases of the codon and can tolerate mismatch with the third (wobble)- wobble base pairings mean less Trna molecules are needed.

****************************End Of Sample*****************************

Buy the full version of these notes or essay plans and more in our Biochemistry Notes.