Transcription and Translation. Transcription and Translation. Gene- a section of DNA that codes for a protein. Genes have three parts: promoter, coding region, and termination site (stop codon). Transcription and translation both have three steps: initiation, elongation, and termination. .
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Transcription and Translation • Gene- a section of DNA that codes for a protein. • Genes have three parts: promoter, coding region, and termination site (stop codon). • Transcription and translation both have three steps: initiation, elongation, and termination.
Transcription • The process of making a mRNA strand from a DNA template using base pairing rules. Occurs in the nucleus. • Initiation- RNA polymerase binds to the promoter. • Elongation- RNA polymerase makes a copy of the coding region using base pairing rules. The bond that forms between adjacent RNA nucleotides is a phosphodiester bond. • Termination- RNA polymerase makes mRNA until it reaches the termination site where it stops.
mRNA Processing • G-capping: a methylated guanine is added to the 5’ end of the mRNA, this cap acts as a signal to allow the mRNA to exit the nucleus. • Poly- A tail: A tail made of many adenines is added to the 3’ end of the mRNA. This tail protects the 3’ end of the mRNA from being degraded. • Intron Removal: Introns are sections of the message that do not contain code for the desired protein. Exons are sections that do contain the code. Introns must be removed to translate the correct protein.
Translation • The process of making a protein from a mRNA message. Uses (transfer) tRNA as a translator to convert the nucleic acid message into the amino acid sequence. Occurs in the cytoplasm. • Initiation- The ribosome binds to the start codon (AUG) and begins translation. • Elongation- The ribosome elongates the amino acid chain each time a tRNA base pairs a new anti-codon to the mRNA codons. The growing polypeptide is removed from the P site tRNA and attached to the amino acid in the A site tRNA. The bond that is formed between adjacent amino acids is a peptide bond. • Termination- Once the ribosome reaches the stop codon (UAG, UAA, UGA) the ribosome terminates translation and the protein is released into the cytoplasm.
Marshall Nirenberg cracked the code that Francis Crick discovered in the central dogma. Nirenberg allowed us to de-code the nucleic acid to protein message and begin to understand the structure and function of genes and proteins. Nirenberg discovered 64 codons that code for 20 amino acids. This means that the genetic code is degenerate, meaning that some amino acids are coded for my multiple codons.
Practice- Transcription and Translation • DNA TAC GGC TAC TCC CGC ATA GAT • mRNA • tRNA • Protein • DNA TAC AAT GTT CAG GGT CGA AAG • mRNA • tRNA • Protein
Mutations • Substitution (point mutations)- the exchange of one base for another. CGT→ CAT • Missense- codes for a different amino acid • Nonsense- codes for a stop codon • Silent- codes for the same amino acid using a different codon • Wobble- Substitutions in the 1st codon position are the most dangerous. Because of a phenomena called wobble substitutions in the 2ndis less dangerous and in the third position is the least dangerous. This is a result of the degenerate genetic code. • Frameshift- a mutation that results in a shift in the codon reading frame. • Insertions- Addition of 1 of more nucleotides. Shifts the reading frame downstream • Deletion- Deletion of one or more nucleotides. Shifts the reading frame upstream • Large Scale Mutations- whole chunks of the chromosome can be inverted, duplicated, inserted, and deleted which usually has a drastic affect on the organism. This also can benefit the organism and drive human evolution as shown by the duplications of hemoglobin genes and by the fusion of chimp chromosome 2p and 2q into the human chromosome 2.
Practice- Identify the type of Mutation • Wild type DNA TAC GGC TAC TCC CGC ATA GAT • Mutant DNA TAC GGC GAC TCC CGC ATA GAT • Mutant mRNA • Mutant tRNA • Mutant Protein • Wild type DNA TAC AAT GTT CAG GGT CGA AAG • Mutant DNA TAC AAT GTT CAG TGG TCG AAA • Mutant mRNA • Mutant tRNA • Mutant Protein
Links https://www.youtube.com/watch?v=itsb2SqR-R0 https://www.youtube.com/watch?v=WsofH466lqk https://www.youtube.com/watch?v=zFVH9SqtJCM https://www.youtube.com/watch?v=YjWuVrzvZYA https://www.youtube.com/watch?v=5bLEDd-PSTQ https://www.youtube.com/watch?v=FN9JA-EpujE https://www.youtube.com/watch?v=qxXRKVompI8 http://www.pbs.org/wgbh/aso/tryit/dna/shockwave.html http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/Mutations.html http://evolution.berkeley.edu/evolibrary/article/mutations_03 http://www.evolutionpages.com/chromosome_2.htm