Replication, Transcription and Translation (2.7)
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NOTES HLNOTES SL HL Replication: see Topic 7.1HL Transcription see Topic 7.2HL Translation see Topic 7.3 |
For Gene Mutation see Genes (3.1)
For Polymerase chain Reaction: See Biotechnology (3.5)
Meselson & Stahl Experiment
How does DNA replicate? This was a fundamental question that needed to be answered even after Watson and Crick discovered the structure of DNA. Three competing theories at the time:
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The Experiment:
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DNA Replication
DNA replication= makes a copy of DNA (each chromosome) which makes the sister chromatids (3.1)
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HL Extension: 7.1 DNA Structure & Replication
Protein SYnthesis Overview
Protein synthesis is the conversion of DNA into messanger RNA (mRNA) then into protein. It occurs in two stages:
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Transcription
Transcription is the conversion of DNA to messenger RNA (mRNA). DNA is a rather delicate molecule, and since is carries the organisms code generation to generation, it is important to protect it from unnecessary degradation, so in Eukaryotic cells, the DNA never leaves the nucleus! (exception is during mitosis/ meiosis when the nucleus disintegrates.) Hence transcription occurs in the nucleus.
- Because DNA never leaves the nucleus, messenger RNA acts as its message to the rest of the cell.
- Note: RNA nucleotides contain ribose sugar and uracil replaces thymine as a nucleic base
- RNA polymerase acts like DNA polymerase III and helicase in replication combined.
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HL Extension: 7.2 Transcription and Gene Expression
Translation
Start and stop:
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Translation is taking the mRNA sequence and turning it in to an amino acid sequence.
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HL Extension: 7.3 Translation
Interpreting the Genetic Code:
Codon ChartsChart 1: first codon base starts on the left hand side, 2nd base on the top, thrid base found in the box that joins the two. Example: CAA = gln
Chart 2: First base of codon found in the middle of the chart, work your way to the perimeter of the cicle using the codon. Example: UCA = Serine
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Scientists have figured out which mRNA codon works with what tRNA and therefore we can determine which amino acid every codon will place. (see figures on the left)
NOTE: The charts to the left deal with mRNA codons NOT tRNA anticodons Every gene begins with AUG (Start) and ends with one of three STOP codons (UAA, UAG, UGA), which do not code for an amino acid. Example: TACTTGTGAATGCGCATT (coding DNA strand) AUGAACACUUACGCGUAA (mRNA strand) Steps:
Answer: our amino acid sequence for the given DNA code would be read: met- asp - the- tyr - ala- Stop This amino acid chain is then folded based on the chemistry of the amino acids which gives the protein its 3D shape. |