Lecture 22, 11/2 (Maybruck 7); Translation + Transcription regulation

Audio for lecture on 11/2 can be heard here.

• • Slide 1 (handout 10/29/07)
• RNA are the work horse of the DNA, they are responsible for construction of proteins. The mRNA has the blueprint of the nucleotide sequence associated with the gene. (main difference between DNA and RNA is uracil (in RNA) instead of thymine which is found in DNA)
• tRNA (transfer RNA) – single stranded nucleotide sequence (characteristic of all RNA). It has specific areas that are complementary to each other where it folds on itself forming hairpin loops. On a hairpin loop there is a span RNA nucleotides (3) that are referred to as anticodon. This is the compliment to the codon.
• On a gene there are 3 consecutive bases that code for a specific amino acid. The gene is coding for a protein. That protein consists of a bunch of amino acids all linked together. With every three nucleotides in DNA will code for a protein. The three nucleotides link together is referred to as a triplet. In RNA this is called a codon. . . . You have a triplet that is coding for a specific amino acid within mRNA that grouping of three nucleotides is referred to as a codon.
• Anticodon also codes for a specific amino acid. The tRNA knows which amino acid to bring over due to complimentary binding between the codon and anticodon.
• The function of the tRNA is to bring the amino acid over to the mRNA which is within the ribosome.
• • Slide 2
• Ribosomal RNA – involved in being part of protein synthesis
• • Slide 3 bacterial genetics: Transcription
• RNA polymerase only reads one strand which is the 3’ to 5’ strand. The strand that it reads is referred to as the template strand.
• RNA polymerase begins transcribing when it sees a certain pair of sequences. RNA polymerase binds to promotor region (which is made up of a couple different nucleotide sequences) and begins transcribing.
• Continues to transcribe until it gets to the termination DNA sequence → end transcription.
• • slide 1 of bacterial genetics: details of translation and transcription regulation (handout from 11/2/07)
• • slide 2
• you want genes to be selectively expressed. If all genes were expressed at the same time there would be energy lost by the bacteria.
• You can regulate gene expression during replication, transcription and translation.
• mRNA codons specifying for amino acids
• genetic code – a way of translating the nucleotide sequence of a gene into the correct amino acids (amino acids make protein and in turn exhibit a trait).
• 20 amino acids and 64 codons
• • this means codon usage will be redundant in formation of a particular amino acids
• • slide 3 translation – protein synthesis
• translation is happening on a ribosome
• in prokaryotes it is referred to as a 70s ribosome. The “s” stands for Svedberg units. “S” units measures the sedimentation rate of a particle during centrifugation. The larger the particles the larger their “S” value.
• Characteristic of a ribosome – there are spots in it for tRNA (settles within the 50s) and mRNA (settles within the 30s)
• There is an “E” site an “A” site and a “P” site
• 3 stages in translation – initiation, elongation, termination.
• • slide 4 translation
• initiation (formation of a protein – the adding together of amino acids) – starts with one codon – methionine (always first amino acid that is translated).
• There are different tRNA’s with different amino acids that try to get into the slots. The only ones that get in are the ones with anticodons that will bind to the codons. For example an AUG looks to bind with UAC.
• CUG (codes for lucine) looking to bind with something that has an anticodon for lucine.
• Ribosome is mixture of protein and RNA
• • slide 5 translation
• elongation
• dipeptide strand - peptide strand of two amino acids bound together (the beginning of the building of the protein)
• the ribosome moves down the mRNA and moves in 5’ to 3’ direction.
• As it (ribosome) is moving in 5’ to 3’ direction (elongation) the dipeptide moves from both tRNA’s to just one tRNA. It is moving to the one located in the “A site” of the ribosome. The tRNA in the “A site” then moves to the “p site”. The one in the “a site” (bare of amino acids) moves to “e site”. Once in “e site” it is released into the surrounding. Now tRNA that was in “a site” is in the “p site” and has two amino acids associated with it (a dipeptide).
• this process made a polypeptide strand that has two amino acids in it.
• A site – where the new tRNA’s with amino acids are going to be added
• P site is where elongation is occurring
• E site is where tRNA is being discarded
• Protein synthesis: termination
• Stop codon stops translation
• • slide 6 regulation of protein synthesis at the level of transcription
• operon – grouping of genes right next to each other. Also are working towards expressing one particular phenotype
• Transcription regulation in the operon is handled by two general processes: induction or repression
• • inducible regulated operon – regulates transcription – transciption is off. This means that transcription must be induced to get going.
• • repressible regulated operon – (always on) to turn this off it needs a molecule to repress it.
• Examples
• • Catabolic (breaking something down) operons – are usually inducible. Example → glucose.
• • anabolic operons – associated with repressible regulated operons. molecule has to be present to turn transcription off.