The genetic code and protein synthesis Flashcards
the coded mRNA dependent synthesis of protein
translation
scientists who cracked the genetic code
Nirenberg and matthael
base pairing at third position is not as constrained as the other two bases
permits flexibility in codon/anticodon recognition, allowing mRNA translation with less than 64 tRNAS
wobble hypothesis
formation of aminoacyl-tRNAs
aminoacyl tRNA synthetase binds amino acid to tRNA using ATP
in prokaryotes what are the sizes of the ribosomal subunits
50S and 30S
what energy is used during translation
GTP
protein synthesis occurs in three stages
initiation
elongation
termination
binding of mRNA, ribosomal subunits and first aminoacyl-tRNA
initiation
sequential formation of all peptide bonds
elongation
stop codon recognition, release of polypeptide and dissociation of ribosome subunits
termination
three sites in the ribosome
A site
P site
E site
four steps in the formation of the prokaryotic initiation complex
IF-1 and IF-3 bind to the 30S subunit 30S subunit bind to mRNA shine-dalgarno sequence just upstream of AUG 30S slides AUG into the P site to insure that first AUG is located IF-2 and GTP bind to the 30S subunit IF-1 falls away GTP is hydrolyzed IF-2 and IF-3 fall away 50S subunit attaches to 30S subunit
blocks A site until ready for first aa-tRNA
IF-1
prevents premature binding to 50S subunit
IF-3
a purine rich mRNA sequence just upstream from the AUG start codon
shine dalgarno sequence
prokaryotes initiate translation with
N-formyl-met-tRNA
what enzyme forms peptide bonds
peptidyltransferase
how is peptide bond formed
A site amino acid amino group acts as the nucleophile and attacks the carbonyl site of P site amino acid
EF-G-GTP hydrolysis promotes
ribosome movement 5 prime to 3 prime allowing next codon into A site
what are the five things you need to complete PCR
- small amount of DNA
- dNTPS to make complementary strand
- DNA polymerase
- buffer with ATP
- DNA primers
where is the DNA polymerase from
hot springs bacteria Taq
what replaces the job of helicase
heating the DNA to 90 degrees celcius
what is the process for one run of PCR
heat to 90 degrees to break DNA strands
cool to 40 degrees to allow primers to attache
heat to 70 degrees to allow polymerase to build strands
what is the equation to tell how many molecules have been produced per so many cycles of PCR
2^n where n is the number of cycles
what is the job of EF-G
using GTP to cause a conformational change resulting in peptide translocation
what is the job of EF-Tu
delivering the next aa-tRNA to the A site
when a stop codon reaches the A site…
a release factor binds to the A site and all members of the assembly dissociate
what is different about transcription and translation in prokaryotes vs eukaryotes
in prokaryotes transcription and translation happen in the same place since there is no nucleus and translation of a protein can be occurring while transcription is still taking place
the complex formed when transcription and translation are occurring at the same time
polysome
what are the ribosomal subunits in eukaryotics
40S and 60S
acts only in prokaryotes to block binding of aminoacyl tRNA to A site in ribosome
tetracycline
acts only on prokaryotes to block the peptidyl transferase reaction on ribosome
chloramphenicol
acts only in prokaryotes to block the translocation reaction on ribosomes
erythromycin
acts only on eukaryotes to block mRNA synthesis by binding preferentially to RNA polymerase II
alpha-amanitin
the modification of a newly formed protein that is often required to finish a protein or convert it from its inactive form to its active form
post translational modification of proteins
the removal of N-terminal methionine, signal peptides; activation of precursor proteins
proteolytic cleavage
the attachment of various sugar residues to proteins
glycosylation
acylation and prenylation; allows membrane attachment/interaction; activation of Ras proteins
lipophilic modifications
activation cascades, tagging for repair/destruction, collagen
phosphorylation, methylation, hydroxylation
between cys residues to promote tertiary structure
disulfide formation
excision of peptide segments and joining flanking segments
protein splicing
a short peptide chain that directs the post translational transport of a protein to its final destination in the cell
signal peptide and protein targeting
giant protein complexes that bind protein molecules with ubiquitin tags and degrades them
proteasomes
