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Overview Transcription Detail Another Transcription Animation

Overview Transcription Detail Another Transcription Animation. Part I: TRANSCRIPTION- the building of mRNA, tRNA , and rRNA (takes place in the NUCLEUS) Initiation :

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Overview Transcription Detail Another Transcription Animation

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  1. Overview Transcription Detail Another Transcription Animation

  2. 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

  3. DNA coding strand nucleotides (usually ~5,000 nucleotides): ATT CGC ACC TAA mRNA UAA GCG UGG AUU

  4. RNA Processing • Before leaving the nucleus…….. • A cap (methyl-guanine or mG) is added by enzymes to the starting end of the mRNA molecule • A poly-A tail is added to the end of the mRNA • The molecule is spliced. Introns are removed (non-coding nucleotides) and exons remain.

  5. Translation The assembly of a protein (occurs on the ribosome in the cytoplasm) Translation Detail mRNA leaves the nucleus through the nuclear pore and forms a functional ribosome with two ribosomal subunits, and a tRNA 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.

  6. Translation- cont. • 3. The codon in the area of the ribosome called the A site is ready to receive the next tRNA. • 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 • The tRNA in the P site detaches and leaves its amino acid behind • 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. • Termination: Steps 4-6 are repeated until a stop codon is reached.

  7. Translation animation One more Translation animation

  8. 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: Met Phe His Stop

  9. 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.

  10. 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-

  11. Ex. Insertion AUG AAU GCG GGAC UAA becomes AUG AAU GCG GGA CUA A Start- Asparagine- alanine - glycine- Leucine -

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