My_Ch17_lecture_protein_rev(2009030423560928) - Chapter 17...

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Chapter 17: Protein Synthesis Purpose —to understand that DNA codes for proteins; to know the basic steps of protein synthesis (transcription, translation), and the types of point mutations (AP Major What you MUST know in Ch 17: Codons Transcription vs. Translation (summary) Introns vs. Exons Ribozymes Point mutations DNA codes for proteins. This is the primary function of DNA . One gene-one polypeptide hypothesis (Beadle & Tatum, 1941, originally “1 gene-1 enzyme”) o A gene codes for 1 specific polypeptide (protein) o Traits are the end products of the metabolic processes regulated by enzymes (& proteins)—what you see is the result of the proteins that you are made of. o This is what AP wants you to know, but… Time and science move rapidly beyond AP-land. Recent evidence suggests that this 1-gene 1- protein concept may not be strictly true; in fact one gene may code for many different RNA’s, regulators and eventual proteins 3 steps in protein synthesis : 1. transcription : RNA made from DNA template (DNA RNA) 2. RNA processing : mRNA introns deleted, ends added 3. translation : amino acid chains formed (RNA protein)
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3 types of RNA are made in transcription (not just mRNA!): Messenger RNA (mRNA) o Single strand of RNA that provides the template used for the amino acid sequence that makes up a specific polypeptide o A triplet sequence of nucleotides on mRNA is a codon , which codes for 1 amino acid (GCA = alanine) o Since there are 20 amino acids, and a possible 64 codon combinations, there is redundancy in the genetic code (for example, 4 possible codons code for alanine). This allows for the possibility of the correct protein to be made if there is a point mutation (1-base change). o mRNA is the form of RNA that carries the DNA code out of the nucleus for translation Transfer RNA (tRNA) o Short 3-dimensional RNA molecule that brings amino acids to the mRNA template. o
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This note was uploaded on 09/29/2011 for the course BIO 020.152 taught by Professor Pearlman during the Fall '08 term at Johns Hopkins.

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My_Ch17_lecture_protein_rev(2009030423560928) - Chapter 17...

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