BIOSC 0100 Lecture Notes - Lecture 3: Srb, Metabolic Pathway, Gene Expression

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6 Feb 2017
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The Central Dogma
In the late 1930s, biologists already knew two things:
-Genes are made of DNA
-Genes carry hereditary information
Gene expression is the process of translating the information in DNA into functioning molecules within
the cell
Beadle & Tatum:
-One gene, one enzyme hypothesis: by destroying genes they destroy that specific function
-Oserved that defets i partiular gees resulted i the old’s iaility to produe speifi
compounds
-Proposed that each gene contains the information needed to make an enzyme
Srb & Horowitz (1944)
-Knew that organisms synthesized arginine in a metabolic pathway made of several steps
-Stopped an enzyme at a metabolic pathway (arg 2) blocking the gene
Genes contain the information for all of the proteins in an organism not just enzymes one gene, one
polypeptide
Messenger RNA (mRNA) was found to carry information from DNE to the site of protein synthesis the
enzyme RNA polymerase (ends in ase = protein)
Gene expression occurs via two processes: transcription and translation
Transcription is the process by which the hereditary information goes from DNA to RNA (nucleotide to
nucleotide)
Translation is the process by which the information is used to synthesize proteins (nucleotide to amino
acid)
The genetic code is a triplet code, with a three base sequence called a codon specifying a single amino
acid
AUG (Methionine) is the start codon which signals the start of protein synthesis
Three stop codons (termination codons) that signal the end of the protein coding sequence: UAA, UAG,
UGA
Genetic code:
-Redundant all amino acids expcept Met and Trp have more than one codon
-Unambiguous A single codon never signals for more than one amino acids
-Universal all have the same
-Conservative the first two bases of the codons are almost always identical
Using the genetic code to predict an amino acid sequence
-Bottom strand is a template strand
-Top strand is the coding strand
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