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Overview Transcription Detail Another Transcription Animation
Part I: TRANSCRIPTION- the building of mRNA, tRNA, and rRNA (takes place in the NUCLEUS) Initiation: RNA polymerase binds to the gene’s promoter on the template strand of DNA(a specific sequence of the DNA that acts as a “start signal” for transcription) RNA polymerase unwinds and separates the two strands of the DNA. Elongation: RNA polymerase adds and then links complementary RNA nucleotides as it “reads” the gene” on the template strand. Termination: A “stop” signal on the DNA tells the RNA polymerase to detach from the DNA and release the RNA molecule
DNA coding strand nucleotides (usually ~5,000 nucleotides): ATT CGC ACC TAA mRNA UAA GCG UGG AUU
RNA Processing Before leaving the nucleus…….. 1.A cap (methyl-guanine or mG) is added by enzymes to the starting end of the mRNA molecule 2.A poly-A tail is added to the end of the mRNA 3.The molecule is spliced. Introns are removed (non-coding nucleotides) and exons remain.
Translation The assembly of a protein (occurs on the ribosome in the cytoplasm) Translation Detail 1.mRNA leaves the nucleus through the nuclear pore and forms a functional ribosome with two ribosomal subunits, and a tRNA 2.Initiation: The mRNA “start” codon AUG is oriented in a region of the ribosome called the P site where the tRNA molecule carrying methionine can bind to the start codon.
Translation- cont. 3. The codon in the area of the ribosome called the A site is ready to receive the next tRNA. 4.Elongation: Both the A site and the P site are holding tRNA molecules- each carrying a specific amino acid. A peptide bond forms between the adjacent amino acids 5.The tRNA in the P site detaches and leaves its amino acid behind 6.The tRNA in the A site moves to the P site. The tRNA carrying the amino acid specified by the codon in the A site arrives. 7.Termination: Steps 4-6 are repeated until a stop codon is reached.
Translation animation One more Translation animation
If a segment of DNA is: TAC AAA GTA ACT The mRNA strand would be: AUG UUU CAU UGA This would code for the following amino acids : MetPhe His Stop
Types of Mutations Point Mutations- a change of one or just a few nucleotides in a gene Substitution- one nucleotide is replaced by another. sometimes called a “missense” mutation Insertion – an extra nucleotide is added. Deletion- a nucleotide is omitted.
Frame shift mutations are caused by deletions and insertions Original Strand AUG AAU GCG GAC UAA Start - Asparagine - alanine –aspartate –stop Ex. Deletion AUG -AU GCG GAC UAA becomes AUG AUG CGG ACU AA Start -methionine -arginine- threonine-
Ex. Insertion AUG AAU GCG GGAC UAA becomes AUG AAU GCG GGA CUA A Start- Asparagine- alanine - glycine- Leucine -