Ch 17 Protein Synthesis Flashcards
transcription
the synthesis of RNA from DNA (RNA then processed into mRNA)
translation
the synthesis of a amino acids/polypeptide from mRNA
ribosomes re: (protein synthesis)
molecular complexes that facilitate the orderly linking of amino acids into polypeptide chains
Primary transcripts
initial RNA from any gene
central dogma of biology
DNA -> RNA -> Protein
genetic code
language of genes, codons being translated to amino acids
codon, triplet code
genetic instructions for a polypeptide chain are written in the DNA as a series of nonoverlapping three nucleotide “words” (codons) in mRNA. codon codes for specific amino acid
template strand vs coding strand
codons are complementary to the template strand of DNA which provides the pattern; product will match the coding (non template) strand of the DNA
reading frame
nucleotides must be read in the correct groupings to code properly for amino acids
promoter
DNA sequence where RNA polymerase attaches and initiates transcription
terminator
DNA sequence that signals the end of transcription
RNA polymerase
enzyme, pries two strands of DNA apart and elongates the RNA polynucleotide
transcription factors
collection of proteins that help guide the binding of RNA polymerase
transcription initiation complex
entire complex of transcription factors and RNA pol II bound to the promotor
downstream and upstream (transcription)
direction of transcription is downstream, other direction is upstream
RNA processing definition
enzymes in the eukaryotic nucleus modify pre-mRNA in specific ways before the genetic message is dispatched to the cytoplasm
Poly-A tail
50-250 adenine nucleotides added to the 3’ end of mRNA
RNA splicing
stage of RNA processing where RNA goes through a spliceosome, introns are removed and exons are reconnected
introns, exons
introns are non-coding segments of nucleotides, exons will eventually be EXpressed
spliceosome
large complex made of proteins and small RNAs, splices exons from introns
alternative RNA splicing
a single gene can encode more than one kind of polypeptide because of the presence of introns
domains (proteins)
structural and functional regions of a protein (ex: active site, binding site)
tRNA
transfer RNA transfers amino acid from the cytoplasmic pool of amino acids to a growing polypeptide in a ribosome
anticodon
nucleotide triplet on the tRNA that can base pair with the complementary mRNA codon
aminoacyl-tRNA synthetases
a family of 20 enzymes (one for each amino acid) which ensure tRNA matches with appropriate codon
stages of translation
initiation, elongation, termination
signal peptide
sequence of ~20 amino acids which marks the polypeptide at the N-terminus for secretion (removed by an enzyme after ribosome lands on ER)
signal recognition particle (SRP)
recognizes the signal peptide and escorts ribosome to the ER in protein synthesis
Polyribosomes/polysomes
Multiple ribosomes which translate a single mRNA at the same time
Mutations
changes to the genetic information of a cell, ultimate source of new genes/evolution
Point mutations
small scale mutation, changes in a single nucleotide pair of a gene
Nucleotide-pair substitution
the replacement of one nucleotide and its partner with another pair of nucleotides
Silent mutation
substitution, no observable effect on phenotype, can occur outside genes
Missense mutation
substitution, changes one amino acid to another, most common substitution
Nonsense mutation
substitution, changes a codon for an amino acid into a stop codon, most lead to non functional protein
insertion and deletion (mutation)
additions or losses of nucleotide pairs in a gene. can alter reading frame, more disastrous than substitutions
Frameshift mutation
whenever the number of nucleotides inserted or deleted is not a multiple of three
Mutagens
physical and chemical agents which interact with DNA in ways that cause mutations
Gene editing
altering genes in a specific, predictable way
CRISPER-Cas9 system
Gene editing technique, Cas9 is a nuclease that cuts double stranded DNA molecules, will cut any sequence for which it is directed
transcription initiation
During initiation, RNA polymerase pries the two strands of DNA apart. Transcription factors attach to the DNA at the promotor region of the gene (TATA or CAAT). The RNA can then attach to the gene at the promotor region, along with the transcription factors, forming the transcription initiation complex.
transcription elongation
During elongation, RNA pol adds complementary nucleotides one at a time to the 3’ end of RNA. RNA then peels away, and the double helix reforms.
transcription termination
In the last stage, termination, the RNA pol II reaches the terminator (aauaaa). Polymerization stops
translation initiation
requires initiation factors to bind mRNA, two subunits of the ribosome, first amino acid with its attached tRNA. Ribosome scans for “start” codon AUG which establishes reading frame.
translation elongation
requires elongation factors, three steps:
a. Codon recognition – anticodon of appropriate tRNA base pairs with complementary mRNA codon in A site
b. Peptide bond formation – rRNA molecule removes polypeptide from tRNA and forms peptide bond between carboxyl end of growing polypeptide in the P site and amino of new amino acid in the A site.
c. Translocation – ribosome translocates the tRNA in the A site to the P site, and the empty tRNA in the P site is moved to the E site & released
translation termination
requires release factor, ribosome reaches a stop codon (terminators are UAA, UAG, UGA), release factor promotes hydrolysis of the bond between the tRNA and the P site, frees polypeptide from the ribosome
genetic code
a universal set of rules. The same codons will correlate with the same amino acid and therefore the same protein in every organism - so a gene from one organism can build the same protein in a different organism.
ingredients & roles of translation
mRNA – instructions for building
tRNA – transfer an amino acid from the cytoplasmic pool of amino acids to a growing polypeptide. anticodon on one end, amino acid on other end
Ribosomes – makes polypeptides, made up of two subunits, contain ribosomal RNA (rRNA). “grooves”:
A site – arrival site
P site – placeholder site
E site – exit site
What happens during RNA processing?
RNA is processed into mRNA. A 5’ cap is added to the beginning and a poly-A tail is added to the 3’ end to protect the mRNA from degradation and export it from the nucleus. Before entering the cytoplasm, the RNA goes through the spliceosome to remove the introns and join the exons together.
