transcription and translation Flashcards
gene expression
the process by which DNA directs protein synthesis, includes 2 stages:
- transcription
- translation
gene expression sequence
DNA -> transcription -> RNA (mRNA) -> translation -> protein
Beadle and Tatum
the one gene-one enzyme hypothesis
- bread mold Neurospora by changing genes, bread couldn’t grow a certain protein
- different classes of these mutants were blocked at a different step in the biochemical pathway for arginine biosynthesis
- revises to one gene- one protein/polypeptide hypothesis
RNA
single stranded, uracil, ribose sugar
transcription
synthesis of RNA using information in DNA
- produces messenger RNA (mRNA)
translation
the synthesis of a polypeptide, using information in the mRNA
- ribosomes are site of translation
transcription and translation: bacteria
both can happen at the same time
transcription and translation: eukaryotes
nucleur envelope separates the two; translation happens in cytoplasm
primary transcript
the initial RNA transcript from any gene prior to processing
central dogma
cells are governed by a cellular chain of command
triplet code
a series of non overlapping, 3 -nucleotide words
- 20 amino acids, 64 codons
template strand
provides a template for ordering the sequence of complementary nucleotides in a RNA transcript
codons
base triplets; read in 5’ to 3’ direction
- 64 codons, 61 for amino acids, 3 STOP codon’s
- redundant but not ambiguous
RNA polymerase
pries DNA strands apart and joins together RNA nucleotides
- assembles in 5’ to 3’ direction
- doesn’t need a primer
- attaches to the promoter (starting DNA sequence)
- terminator (is ending sequence)
transcription unit
stretch of DNA that is transcribed
transcription factors, TATA box and terminator in eukaryotic transcription
transcription factor: mediate the binding of RNA polymerase and the initiation of transcription
promoter has TATA box, transcription initiation complex forms (transcription factors + RNA polymerase II bound to promoter)
terminator in eukaryotes: RNA polymerase II transcribes polyadenylation signal sequence (AAUAAA) - RNA released 10-35 nucleotides after
transcription: DNA -> RNA steps
- initiation
- RNA polymerase attaches to promoter - Elongation
- RNA polymerase unwinds DNA and elongates RN transcript - Termination
- RNA polymerase detaches and RNA is made
RNA processing
both ends of primary transcript are altered, enzymes in the eukaryotic nucleus modify pre-mRNA
- introns cut out, exons spiced together
- addition of 5’ cap (5’ end) and poly A-tail (3’ end)
5’ cap and poly A-tail
- facilitates export of mRNA to cytoplasm
- protects mRNA from hydrolytic enzymes
- helps ribosomes attach to 5’ end
RNA splicing
removes introns (noncoding) and joins exons (coding)
- different segments of exons used alternative RNA splicing
- carried out by splicesomes (proteins and small RNA)
Ribozymes
RNA molecules that function as enzymes
- introns can catalyze own splicing
transfer RNA (tRNA)
helps translate mRNA message into protein
- can translate a particular mRNA code into a amino acid
- has amino acid on one end and nucleotide triplet that can base-pair with complementary codon on mRNA (anticodon)
Translation two steps: tRNA
- aminoacetyl-tRNA synthesase enzyme matches tRNA with amino acid
- tRNA anticodon matched with mRNA codon
- wobble: flexible pairing of third base of a codon
Ribosomes
facilitate coupling of tRNA anticodons with mRNA codons
- large and small subunits made of proteins and ribosomal RNAs (rRNAs)
- 3 binding sites for tRNA
