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8.4 & 8.5 Protein Synthesis. Introduction - Transcription. Ever play skee ball at an arcade before? If you have, then you realize the need to exchange quarters for tokens before you can use them. Just like converting quarters to tokens, DNA must convert to RNA before proteins can be made.
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Introduction - Transcription • Ever play skee ball at an arcade before? • If you have, then you realize the need to exchange quarters for tokens before you can use them. • Just like converting quarters to tokens, DNA must convert to RNA before proteins can be made.
Transcription • Transcription – Process of copying a sequence of DNA to produce a complementary strand of RNA.
Central Dogma Involves three processes: • Replication – DNA replicates • Transcription – DNA converts to RNA • Translation – RNA interpreted for proteins • Pg 225, Figure 4.1 • Francis Crick
RNA • RNA stands for ribonucleic acid • Like DNA, RNA is also a chain of nucleotides, each made of a sugar, phosphate group, and nitrogen containing base.
RNA Polymerase • Just like DNA polymerase binds nucleotides to make new DNA… • RNA polymerase binds nucleotides together to make new RNA!!!
Transcription • 1) RNA polymerase and other proteins begin to unwind DNA • 2) RNA polymerase uses one strand of DNA as a template to string together a complementary strand of RNA nucleotides. The RNA strand hangs freely as DNA zips back together. • 3) The RNA strand detaches from the DNA once the entire gene has been transcribed. • Pg 227, figure 4.2
Types of RNA • Messenger RNA (mRNA) – Intermediate message that is translated to form a protein. • Ribosomal RNA (rRNA) – Forms part of ribosome (the cell’s protein factory). • Transfer RNA (tRNA) – Brings amino acids from the cytoplasm to ribosome to help make the growing protein.
Translation • Translation – The process that converts, or translates, an mRNA message into a polypeptide. • One or more polypeptides make up a protein.
Introduction - Translation • Ever hear of a translator? • Translators translate language (for example, Spanish to English) • In translation, the RNA’s message is translated to make amino acids. • Amino acids are the building blocks of protein.
Codons • Codon – A three nucleotide sequence that codes for an amino acid. • Example: AUG, CUU, AGCall of these are codons
mRNA • mRNA stands for “messenger RNA” • mRNA carries instructions of DNA from the nucleus to the cytoplasm as well as reads sets of codons.
Stop & Start Codons • Start Codon – AUG; signals the start of translation. • Stop Codons – UAA, UAG, UGA; signals the end of an amino acid chain.
Protein Synthesis • In protein synthesis, tRNA translates mRNA to create three-piece codons. • Proteins are synthesized as a result when the STOP codon is reached in the translation.
