BIO SCI 98 Study Guide - Final Guide: Open Reading Frame, Enterobacteria Phage T4, Thomas Hunt Morgan
19 Jun 2018
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Lecture 1
Understand the work that lead to the Chromosome Theory of Inheritance
-1840s = chromosomes identified in cells
-1902 = Theodor boveri and Walter Sutton
-Proposed that chromosomes are material of heredity
-Based on observations of segregation patterns of chromosomes during division
-Fit with Mendelian Laws of inheritance\
-1905 = Sex chromosomes
-Could visualive insect chromosomes
-Females = XX, Males = XY
-Identify and track chromosome responsible for gender
-1910 = Thomas Hunt Morgan
-White eye mutation
-Wild type drosophila have red eyes
-Mutant = white eyes
-Recessive trait
-Gene is on X chromosome
-White eye trait only segregated with males
-Data only makes sense if white allele is on X chromosome
-First evidence that a specific trait segregated with a specific chromosome
Understand what auxotrophs are
Auxotroph – A strain that requires a particular nutrient in order to grow because of a mutation
inactivating the enzyme that makes this nutrient.
-Prototrophs can grow on complete or minimal media. Auxotrophs cannot grow on
minimal media, unless you add something (e.g. an arginine auxotroph will not grow on
minimal media unless you add arginine to it)
Understand how Beadle and Tatum concluded “one gene, one enzyme” based on their
experiments
Understand how complementation testing works and how it was used to identify the number of
genes in a biosynthetic pathway
Understand how the order of genes in a pathway were determined using auxotrophs
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Lecture 2
Learn how to read a chart of the genetic code
Understand what codon and anticodon are
-Codon = trinucleotide sequence that codes for an amino acid
-Anticodon = triplet nucleotide sequence on tRNA that base pairs with codon on mRNA
Be able to look at a nucleotide sequence and determine whether it contains an “open reading
frame”
1) Reading frame determined by start codon
2) Scan sequence until you find the first AUG = start codon
3) Follow the sequence, 3 bases at a time, until you reach stop codon
4) That's your open reading frame
Understand the wobble rules and how to use them to identify anticodon sequences and what
codons they can recognize
1. Wobble base pairing only occurs between last (3') position of codon and first (5') position
of anticodon (the wobble position)
2. In addition to standard Watson-Crick base pairs, G can pair with U and U can pair with G
(U-G wobble rule)
3. A in the first position of anticodon converts to Inosine (I) → I in the anticodon can pair
with A, U, or G (I only occurs in the tRNA not mRNA) (I Wobble Rule)
Lecture 3
Mutation
●Know the different types of mutations, how they are caused, and what effect they have on
the protein
○Single base substitution: silent, missense, nonsense mutations (carcinogens)
○Frameshift mutations: insertion or deletion (intercalating agents)
○Deletion mutations: loss of large chunk of sequence (ionizing radiation)
○Transition mutation: A to G or G to A
○Reversion mutations: second mutation restores protein function
●Be able to read a sequence and determine what mutation occurred
●Understand how revertant mutations work and be able to determine what kind of
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find more resources at oneclass.com
revertant mutation would restore protein functionality
Rules of the Code
●Understand how the T4 Bacteriophage experiments work, the insertion/deletion
mutations, and how they led to the discovery that the code is read continuously and in
triplets
○T4 bacteriophage: virus that infects bacteria
○Plaque assay - when mixed with bacteria and plated onto agar dishes, the plate
will be confluent with growing bacteria, but not where bacteriophage is growing
■The plaques are dark regions with dead bacteria
○B gene- required for bacteriophage to infect multiple
strains of E. coli
■If mutated, will only grow on one strain
○Acridine- intercalating agent, low doses introduce
single insertion/deletion mutations
○Experiment - mutate B gene, try to grow on two E.
coli strains
■Non-functional B gene will allow it to only
grow on one strain
○Result: Mutations were almost
always catastrophic, suggesting
that frameshift mutations
occurred to completely disrupt
amino acid sequence
Cracking the Code
●Understand how cell free translation works, how to interpret data from the different
experiments performed, both the radiolabeling data and the combinatorial sequence data
A "cell free" system for synthesizing protein
Steps:
1. Lyze bacterial cells ("cell extracts")
2. Destroy endogenous mRNA with endogenous RNAses
3. Add DNase to destroy DNA
4. Add synthetic mRNA
5. Add radioactive amino acid (1 radioactive amino acid per tube, 20 tubes)
Cell extracts contain all components needed for translation
rRNA, tRNA, enzymes
Removal of host mRNA and DNA prevents any endogenous mRNA from interfering
Adding 1 radiolabeled amino acid to the mix would give radioactive readout only if that
radiolabeled amino acid was incorporated into the polypeptide
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Understand the work that lead to the chromosome theory of inheritance. Based on observations of segregation patterns of chromosomes during division. White eye trait only segregated with males. Data only makes sense if white allele is on x chromosome. First evidence that a specific trait segregated with a specific chromosome. Auxotroph a strain that requires a particular nutrient in order to grow because of a mutation inactivating the enzyme that makes this nutrient. Prototrophs can grow on complete or minimal media. Auxotrophs cannot grow on minimal media, unless you add something (e. g. an arginine auxotroph will not grow on minimal media unless you add arginine to it) Understand how beadle and tatum concluded one gene, one enzyme based on their experiments. Understand how complementation testing works and how it was used to identify the number of genes in a biosynthetic pathway. Understand how the order of genes in a pathway were determined using auxotrophs.
