BSC 1010 Chapter Notes - Chapter 15: Archibald Garrod, Frameshift Mutation, Tata Box

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8 Feb 2017
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Chapter 15: Genes & How They Work
Archibald Garrod noted that certain disease among his patients seems to be more prevalent in particular families
Found that some disease were the product of recessive alleles
George Beadle & Edward Tatum provided definitive evidence of Garrod's findings
Deliberately created mutations in chromosomes & verified that they behave in a Mendelian fashion in crosses
Nutritional mutations: a mutation affecting a synthetic pathway for a vital compound, such as an amino acid or vitamin
Microorganisms with a nutritional mutation must be grown on medium that supplies the missing nutrient
One-gene/one-polypeptide hypothesis: states that the molecular relationship between genotype & phenotype
Central dogma of molecular biology: is an explanation of the flow of genetic information within a biological system
Information passes in one direction from the gene (DNA) to an RNA copy (transcription)
RNA copy directs the sequential assembly of a chain of amino acids into a protein (translation)
Retrovirus: an RNA virus
When a retrovirus enters a cell, a reverse transcriptase transcribes viral RNA into duplex DNA, which the cell's machinery then
replicates & transcribes as it were its own
Reverse transcriptase: a viral enzyme found in retroviruses that is capable of converting their RNA genome into a DNA copy
Template strand: the DNA strand that is used as a template in transcription
Coding strand: the strand of a DNA duplex that is the same as the RNA encoded by a
gene
Gene expression requires the participation of multiple of RNA:
Messenger RNA (mRNA): is transcribed from structural genes
Ribosomal RNA (rRNA): class od RNA molecule found, together with
characteristic proteins, in ribosomes
Transcribed from the DNA nucleus
Multiple forms found in both ribosomal units
Transfer RNA (tRNA): class of small RNAs with two functional sites
“activating enzyme” adds a specific amino acid
Other site carries the nucleotide triplet (anticodon) specific
Act to interpret information in mRNA & to help position the amino acids on the ribosomes
Small nuclear RNAs (snRNAs): a small RNA sequence that, as part of a small nuclear ribonucleoprotein complex, facilities
recognition & excision of introns by base-pairing with the 5' end of an intron or at a branch site of the same intron
SRP RNA: a cytoplasmic complex of proteins that recognizes & binds to the signal sequence of a polypeptide, & then docks with
a receptor that forms a channel in the ER membrane
In this way the polypeptide is released into the lumen of the ER
Small RNAs class of RNA that includes both;
Micro-RNA (miRNA): are very short & only recently could be detected
Small interfering RNA (siRNA): class of micro-RNAs that appear to be involved in control of gene transcription & that play a
role in protecting cells from viral attack
Codons: basic unit of the genetic code
A sequence of three adjacent nucleotides in DNA or mRNA that codes for one amino acids
the sequence of codons in a gene could be punctuated with nucleotides between the codons that are not used, like the spaces
that separate words in a sentence
o Reading frame: the correct succession of nucleotides in triplet codons that specify amino acids on translation
Is established by the first codon in the sequence as there are no spaces in the genetic code
o Frameshift mutation: a mutation in which a base is added/deleted from the DNA sequence
These changes alter the reading frame downstream of the mutation
There are 64 possible codons encoded to each particular amino acid
Stop codons: any of the three codons UAA, UAG, & UGA, that indicate the point at which mRNA translation is to be terminated
start codons: the AUG triplet, which indicates the site of the beginning of MRNA translation
also codes for the amino acid methionine
all remaining 61 codons are used, making the code degenerate
degeneracy is not uniform; some amino acids only have one codon & others have up to six
degenerate base usually occurs in position 3 of a codon
Prokaryotes have a single RNA polymerase
Exists in two forms:
Core polymerase can synthesize RNA using a DNA template, but it cannot initiate synthesize accurately
o Is composed of four subunits
Two identical α subunits
β subunit
β’ subunit
Holoenzyme can accurately initiate synthesis
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