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
