From Gene to Protein Flashcards
how did archibald garrod propose the gene / protein relationship?
-suggested that genes and phenotypes are directly related
-enzyme presence / absence was due to a genetic defect
what experiments did beadle and tanum perform?
-created genetic mutants out of bread mold
-non mutants grew on minimal medium & synthesized necessary nutrients on their own
-when mutants were exposed to an additional nutrient, they developed a mutation to synthesize that nutrient
what experiments did srb and horrowitz perform?
-found a pathway for arginine production that involved precursor amino acids as well as a 4 step process that needed an enzyme at each step
-if an enzyme at one precursor step was not present, the process could not continue unless the next product was artificially added in
-tldr - further evidence for the “one gene = one enzyme” hypothesis
what is the one gene - one enzyme hypothesis ? (also called one gene - one polypeptide)
-the idea that a gene dictates the production of a specific polypeptide or enzyme
how does a gene become a polypeptide?
-DNA strand stays in the nucleus
-DNA is read 5’ to 3’
-DNA template strand is read and forms a mRNA non-template strand
what is RNA, what does it do, and how does it differ from DNA?
-RNA is a transcribed message / code read from DNA
-RNA is translated into a protein in the cell cytoplasm
-RNA contains a uracil base instead of a thymine base, and is single stranded as opposed to DNAs double strand
what are transcription and translation?
-transcription = creates RNA strand from DNA in nucleus
-translation = creates polypeptide from RNA strand in cytoplasm, more specifically ribosomes
how does transcription and translation differ in prokaryotes / eukaryotes?
prokaryotes = can perform transcr. and transl. at the same time in the cytoplasm
eukaryotes = transcription occurs in nucleus, mRNA must then be modified before being translated in cytoplasm
how do genes code for proteins? what is the triplet code system / codon?
-genes code for proteins by containing a sequence of 3 nucleotides called the “triplet code system”
-mRNA with the 3 nucleotides is a “codon”
-1 codon = 1 amino acid
how many codons are there and what kinds are there?
-64 possible codons
-1 start codon (AUG) and 3 stop codons (UAA, UAG, UGA)
-20 possible amino acids that the codons can correspond to
what does genetic code being universal and unambiguous mean?
-genetic code is the same across all organisms: CCG will always translate into proline in all organisms
-unambiguous = CCG only codes for proline and nothing else
what are the three stages of DNA transcription?
-initiation
-elongation
-termination
what occurs during DNA transcription?
-mRNA is transcribed from DNA by reading a “transcription unit”: a sequence of DNA that creates a single RNA molecule
what occurs during transcription initiation?
-RNA polymerase opens up the DNA to begin the process
-reads DNA 3’ to 5’, forms a strand of mRNA that is 5’ to 3’
-forms a pre-mRNA strand
what is the promoter region and what does it contain?
promoter region = the initiation site for RNA synthesis. contains a binding site called the TATA box
what is a transcription factor?
-transcription factors are proteins that attach to the TATA box
-this enables RNA poly. to attach and begin transcription
what occurs during transcription elongation?
-DNA bases are continuously added to the pre-mRNA strand, transcribed according to the template strand
-formed 5’ to 3’
what occurs in transcription termination?
-RNA poly. transcribes a termination sequence - AAUAAA that releases the pre-mRNA strand
what occurs during RNA processing in eukaryotes?
-a 5’ cap is added to the front of the pre-mRNA as well as a poly-A tail
-these work to protect the strand from being degraded by cellular enzymes
what occurs during RNA splicing in eukaryotes?
-introns [non necessary info] are removed by a protein complex called a spliceosome
-exons [necessary info] are spliced together
what are the key players in RNA translation?
-ribosomes
-tRNA
-mRNA
-enzymes
what is tRNA and what does it contain?
-tRNA = translation RNA, carries amino acids to a ribosome to add them to a polypeptide chain
-tRNA contains an anticodon that is opposite to the mRNA codon
how do the correct amino acids get joined to a tRNA molecule?
-through an enzyme called aminoacyl-tRNA synthetase
what are the three sites of a ribosome?
A Site = holds tRNA that has the next amino acid in a chain
P Site = holds tRNA that carries the growing chain
E Site = exit site, where discharged tRNAs leave the ribosome
what are the three stages of translation?
-initiation
-elongation
-termination
what occurs during translational initiation?
-tRNA brings in first anticodon amino acid, and top unit of the ribosome binds with the small subunit
what occurs during translational elongation?
-amino acids are added to the A site one by one, and the P site polypeptide chain begins to grow
what occurs during translational termination?
-when the ribosome reads a stop codon in the mRNA, a release factor binds in the A Site and the ribosome breaks apart
what post translational processing can occur?
-the resulting polypeptide chain can be modified after being completed
-the type of ribosome the mRNA is read through can impact where it goes (ex - free floating or an attached ribosome)
why can prokaryotes transcribe and translate at the same time?
-their cells lack a nuclear envelope, thus the mRNA does not need to leave to join with a ribosome. similarly, eukaryotes need to undergo mRNA processing after transcription
what is a polyribosome?
several ribosomes translating a single mRNA
what are mutations?
-a permanent change in the DNA
-are heritable, and can create new genes that code for different proteins
what are base pair substitutions?
when one nucleotide (and therefore its corresponding one as well) are replaced with another pair of nucleotides
what are the types of base pair substitutions?
silent = substitution has no effect on the protein that is coded
missense = substitution changes what amino acid is coded for. can have little or serious effects
nonsense = substitution changes an amino acid into a stop codon
what are base pair insertions / deletions?
-when nucleotide pairs are added or removed in a gene due to a mutation
what is a base pair frameshift?
-when a base pair mutation alters the reading order of nucleotides to no longer be a pair of 3
what are mutagens?
physical or chemical agents that can cause mutations
what is the dogma definition of a gene?
a gene is a region of DNA whos final product is either a polypeptide or an RNA molecule
