(1902) , Determined that DNA is involved in protein production; alkptonuria - lack enzyme necessary to catalzye breakdown of homgentisic acid, turning urine black when exposed to air
Beadle & Tatum
(1941) provided definitive evidence that Garrod was correct about how DNA acts to specify enzymes; experimented on gene alterations of bread mold (Neurospora crassa); each mutant examined had a defect in a single enzyme, caused by a mutation at a single site on a chromosome
mutation causing cells to be unable to grow on minimal medium; growth only occurs if the medium is supplemented with additional nutrients
(Beadle & Tatum) each gene encodes the structure of one enzyme
central dogma of molecular biology
the nature of information flow in cells described by Francis Crick: DNA is transcribed to make mRNA, which is translated to make a protein
when DNA is produced to make RNA by making an exact copy of the DNA
mRNA is produced from nucleic acid to the protein
can convert their RNA genome into a DNA copy, using the viral enzyme reverse transcriptase
the strand copied from DNA to RNA
strand of DNA not used as a template
intermediate form of the information in DNA that can be transported out of the eukaryotic nucleus to the cytoplasm for ribosomal processing
found in both ribosomal subunits; critical to the function of the ribosome
intermediary adapter molecule between mRNA and amino acids; act to interpret information in mRNA and to help position the amino acids on the ribosome
a specific sequence of three adjacent bases on a strand of DNA or RNA that provides genetic code information for a particular amino acid
Crick and Brenner
concluded that the genetic code is read as a triplet of nucleotides continuously, no punctuation
the way a cell's mRNA-translating machinery groups the mRNA nucleotides into codons
shift the reading frame of the genetic message
Determined the first match of matching each codon to its amino acid. UUU coded for the amino acid phenylalanine. He created an artificial mRNA molecule entirely of uracil and added it to the test tube of amino acids, ribosomes, and other compounds for protein synthesis.
AUG; the codon that begins all RNA; also encodes the amino acid methionine
UAG, UAA, or UGA; the codon that ends all RNA.
some amino acids are specified by more than one codon
RNA polymerase in prokaryotes
core polymerase: can synthesize RNA using a DNA template, but cannot accurately initiate synthesis; holoenzyme: can accurately initiate synthesis
forms a recognition and binding site for the RNA polymerase and actual start site
The location on a chromosome where transcription begins.
region from promotor to terminator
region containing the RNA polymerase, DNA template, and growing RNA transcript
RNA polymerase I
Eukaryotic RNA polymerase that transcribes the genes for the large ribosomol RNAs
RNA polymerase II
in eukaryotes, this type of polymerase transcribes the mRNAs and small nuclear RNAs
RNA polymerase III
Eukaryotes; transcribes tRNA and some other small RNAs. Each has a specific promoter sequence it recognizes.
RNA polymerase II primary promotor element; similar to prokaryote -10 sequence; allows for tissue specific and developmental time-specific gene expression
proteins necessary to get the RNA pol II to a promotor and to initiate gene expression forming initiation complex
An initial RNA transcript; also called pre-mRNA when transcribed from a protein-coding gene.
The final product that results when the pre-mRNA in eukaryotes undergoes processing events before it exits the nucleus
when pre-mRNA is modified the 5 primed end is synthesized first; it is a modified form of a guanine nucleotide; methylated; protection from degradation and involved in translation initiation
3' poly-A tail
series of adenine residues added after the cleavage by poly-A polymerase; protects from degradation
An enzyme that splices introns out of RNA.
sequence of a eukaryotic gene's DNA that is not translated into a protein
expressed sequence of DNA; codes for a protein, expressed sequence of DNA; codes for a protein
primary transcript is cut and put back together to produce mature mRNA; occurs in nucleus prior to export of mRNA to the cytoplasm
small nuclear ribonucleoproteins; recognize the splice sites in the pre-mRNA; located in the nucleus and are composed of proteins and RNA; forms splicosome
hypothesis - The variation in the patterns by which RNA may produce diverse sets of exons from a single gene.
A process which selects which exons will be retained as part of the mature mRNA that will be used during translation; allows for the possibility that a single gene can produce more than one type of protein
joins each amino acid to the correct tRNA
the 3' end of the tRNA molecule.
One of three loops on a tRNA which contains the 3 nucleotides that allow it to align specifically with mRNA. Contains the anticodon
The reaction catalyzed by the enzymes whose product is an amino acid joined to a tRNA.
(peptidyl) binds to the tRNA attached to the growing peptide chain
(aminoacyl) binds to the tRNA carrying the next amino acid to be added
(exit) binds the tRNA that carried the previous amino acid added
An enzyme in the ribosome responsible for peptide bond formation during translation.
a complex of protein factors, mRNA, met-tRNA, and the small and large ribosomal subunit which is required to start translation
A specific tRNA that recognizes the start codon AUG in mRNA and binds to it; shown as tRNA^fMet
ribosome-binding sequence (RBS)
conserved sequence in the 5' end of mRNA that is complimentary to the 3' end of a small subunit rRNA
initiating amino acid is methionine, not N-formylmethionine; initiation complex contains several subunits, not just one; lack RBS
(EF-Tu) binds to the charged tRNA and to GTP; hydrolyzes GTP and dissociates from the ribosome
matching tRNA anticodon with mRNA codon; peptide bond formation; translocation of the ribosome
the ability of tRNAs to "wobble" in the ribosome, so they can read more than one codon in the mRNA
signal recognition particle
binds to the signal sequence and the ribosomal subunits and transports the complex to the ER
prokaryotic gene expression
lack introns; several genes may be transcribed into a single mRNA molecule; transcription and translation are coupled - no membrane bounded nucleus; initiation begins at AUG codon preceded by special sequence that binds ribosome; no modification of mRNA after transcription
eukaryotic gene expression
contain introns; one gene per mRNA molecule; transcription in nucleus, translation in cytoplasm; initiation begins at AUG codon preceded by 5' cap (methylated GTP) that binds the ribosome; many modifications while mRNA is in nucleus: introns are removed and exons are spliced together; a 5' cap and poly-A tail is added
Mutation that alters a single base; deletion or addition or substitution of a base
base substitution mutation
Substitution of one base pair for another in DNA; can or cannot alter amino acid code
When base substitution changes an amino acid in a protein; transition - no change in type of base (ex. purine to purine); transition - change in type of base (ex. purine to pyrimadine)
When base substitution changes codon into a stop codon; premature stop resulting in truncated protein
Point mutations may lead to chromosomal changes
Loss of a portion of a chromosome (ex. Chri-du-chat syndrome)
change to a chromosome in which part of the chromosome is repeated
Segment of a chromosome is broken in two places and reversed; no necessary affect on phenotype
Piece of chromosome breaks off and joins another chromosome; cause problems during meiosis