Protein Synthesis Flashcards
Name the three characteristics of the genetic code.
specific, universal, and degenerate
aminoacyl tRNA and charging
hydrolysis of 2 ATP equivalents to charge
Name the 3 steps of translation.
initiation, elongation, and termination
process similar in prokaryotes and eukaryotes except translation in prokaryotes is co-transcriptional
Describe the formation of the pre-initiation complex.
eIF2 and eIF4 complexes bind
Kozak sequence
a sequence recognized tby the ribosome to know where to start translation
in sequences that flank it, ATF are the preferred baces
initiation complex
once eIF2 finds the correct site, it will hydrolyze its GTP into GDP and then initiates after ejecting the initiation factors
Describe the process of elongation
kinetic proofreading - if eIF1alpha sits for long enough without forming the base pairs, the wrong tRNA is released and another one enters
describe the process where EF1alpha is recycled
Describe the initiation process in prokaryotes.
ribosomes are smaller, bacterial mRNA not capped, ATP uis not required
uses the Shine-Dalgarno sequence
Describe the termination process in eukaryotes.
when there is a stop codon, a release factor binds to terminate translation.
polysome
when many ribosomes are translating at the same time on an mRNA, approximately 100 nucleotides apart
streptomycin
binds to 30S subunit of prokaryotic ribosomes distorting their structure and interfering with initiation
tetracycline
binds to the 30S subunit of prokaryotic ribosomes and inhibits binding of aminoacyl-tRNAs to the A site
puromycin
aminoacyl-tRNA analog and becomes incorporated into the polypeptide chain inhibiting elongation
erythromycin and clarithromycin
bind to the P site of the 50S subunit of prokaryotic ribosomes and inhibits translocation
chloramphenicol
interferes with the 50S ribosomal subunit of prokaryotes inhibiting peptidyl transferase activity
high levels are toxic in humans because it also inhibits human mitochondrial protein synthesis
diphtheria toxin
inactivates EF-2 by catalyzing ADP-ribosylation preventing transliocation
even a little bit can be lethal to humans
ricin
removes an adenine from eukaryotic 28S rRNA and inhibits ribosome function
chaperone-assisted protein folding
help unfold stuck proteins and uses ATP as a source of energy to help overcome kinetic barriers
enzyme-mediated modifications
addition of hydrophobic lipid groups for membrane localization
addition of cofactor for enzyme activity
addition of small chemical groups (mostly reversible)
non-enzyme mediated modification
glycation - the addition of sugar
proteostasis
the maintenance of the proteosome of the cell, correct combinations of all the different proteins are improtant for function
on-pathway intermediates are partially folded proteins
two reasons for degradation of intracellular proteins
removal of uneeded proteins in response to physiologic demand
removal of proteins damaged by mutation, oxidation, and other modifications
lysosome degradation
mainly deal with things that come fromt he outside of the cells
fusion with endocytic tissues, degradation of proteins through directy targeting, autophagy of organelles and protein aggregates
chaperone mediated autophagy (CMA)
use LAMP2A channel
microautophagy
when lysosomes engulf molecules in bulk or slective ly through hsc70 interactions
microautophagy of organelles
phagophore formation int he ER
ubiquitin proteosome system
polyubiquitination targets protein for degradation
only one E1 that actis with a few dozen E2s, each one with a few dozen E3s
amplifcation of signal to specific proteins
cytoplasmic mis-folded protein response
fold, hold or degrade
chaperones are the first linke of defense, failure to fold leads to targeting for degradation
accuulation forms aggregates that can lead to amyloid
four types of conditions that can lead to protein aggregation
mutations in proteins or in the quality control system
defects in translation and assembly into protein complexes
environmental stress: heat, oxidative stress
aging: increased oxidative stress and reduced capacity to remove misfolded proteins
