Overview Transcription Detail Another Transcription Animation

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Overview Transcription Detail Another Transcription Animation

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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 : - PowerPoint PPT Presentation

Transcript of Overview Transcription Detail Another Transcription Animation

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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

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DNA coding strand nucleotides (usually ~5,000 nucleotides):

ATT CGC ACC TAAmRNAUAA GCG UGG AUU

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RNA ProcessingBefore 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.

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TranslationThe assembly of a protein (occurs on the ribosome in the cytoplasm)Translation Detail1. 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.

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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.

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If a segment of DNA is: TAC AAA GTA ACTThe mRNA strand would be: AUG UUU CAU UGAThis would code for the following amino acids: Met Phe His Stop

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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.

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Frame shift mutations are caused by deletions and insertions Original Strand AUG AAU GCG GAC UAAStart - Asparagine - alanine –aspartate –stop Ex. Deletion

AUG -AU GCG GAC UAA becomes AUG AUG CGG ACU AA Start -methionine -arginine- threonine-

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