Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
82 Cards in this Set
- Front
- Back
|
in what direction is RNA synthesized?
|
5' to 3'
|
|
|
in what direction is a template strand of DNA read during transcription?
|
3' to 5'
|
|
|
in what direction is protein synthesized?
|
N-terminus to C-terminus
|
|
|
in what direction is the mRNA strand read during translation?
|
5' to 3'
|
|
|
what is referred to when someone mentions degeneracy of the genetic code?
|
several codons can encode the same amino acid
|
|
|
what is the "wobble nucleotide" in an RNA codon?
|
3' nucleotide of the codon
|
|
|
what is the "wobble nucleotide" in a tRNA anticodon?
|
5' nucleotide of the anticodon
|
|
|
what is the scanning model of translational initiation?
|
that the 40s subunit of the ribosome, along with some initiation factors, bind to the 5' cap on the mRNA and scan down until a start codon is found before starting translation
|
|
|
what is the codon that all eukaryotic proteins start with?
|
AUG - Methionine
|
|
|
what are the three stop-codons?
|
UAA
UAG UGA |
|
|
why don't all proteins have a methionine at the N-terminus?
|
the methionine can be cleaved during post-translational modification
|
|
|
what does eIF mean?
|
eukaryotic initiation factor
|
|
|
what does eEF mean?
|
eukaryotic elongation factor
|
|
|
where is an amino acid attached to a tRNA?
|
3' end
on the free 3' hydroxyl of adenine (in a terminal -CCA sequence) |
|
|
what happens to an amino acid if it is altered after attachment to the tRNA?
|
it will be placed in the protein, because the tRNA cannot discriminate what is attached to it
|
|
|
what is the first step in the formation of an aminoacyl-tRNA?
|
amino acid adenylation
ATP + AA -> AMP-AA + PPi |
|
|
where is energy stored for the transfer of an amino acid from tRNA?
|
phosphoanhydride bond between AMP and AA (released when AMP is cleaved from AA)
|
|
|
what is the function of aminoacyl-tRNA synthetases?
|
to activate an amino acid by attaching it to a tRNA
AMP-AA + tRNA -> AMP + tRNA-AA |
|
|
wear in the cell does translation occur?
|
cytosol
|
|
|
where are charged tRNAs stored until they find a ribosome?
|
cytosol
|
|
|
what is the kozac consensus sequence?
|
-xxxxRxxAUGRxxxxxxx-
where R is any purine (A or G) at the +4 and -3 positions |
|
|
what is the function of eIF2?
|
ternary complex formation
|
|
|
what are the components of the ternary complex?
|
eIF2
met-tRNA GTP |
|
|
why is the ternary complex important?
|
one must be present to start EVERY protein
|
|
|
what happens when eIF2 is phosphorylated by an eIF2 kinase?
|
eIF2B cannot exchange GTP for GDP on eIF2 as efficiently, and so the rate of translation is decreased
|
|
|
what is the function of eIF2B (GEF)?
|
to exhange GTP for GDP on eIF2 after the previous GTP has been used to start a round of translation
|
|
|
what is eIF4F?
|
complex of initiation factors eIF4A, eIF4E and eIF4G
|
|
|
what is the function of eIF4A?
|
in eIF4F complex, acts as an ATP-dependent helicase, resolving secondary 5' structures of the mRNA
|
|
|
what is the function of eIF4E?
|
in eIF4F complex, physically recognizes the cap sequence as long as it is on the scaffold of eIF4G
|
|
|
what is the function of eIF4G?
|
acts as a scaffold for the assembly of eIF4E and eIF4A in the eIF4F complex
absolutely necessary for eIF4E to recognize cap structure |
|
|
what does PHAS mean?
|
proteins of heat and stability
aka 4EBP |
|
|
what is the function of 4EBP?
|
binds to eIF4E, preventing its interaction with eIF4G, and thereby inhibiting translation
|
|
|
from where does the energy needed to form the 80S ribosomal complex come?
|
hydrolysis of the GTP on eIF-2
|
|
|
what is the effect of phosphorylation of 4EBP?
|
releases eIF4E, so that it can recognize the cap sequence and initiate translation
|
|
|
what is necessary to bring in an initial met-tRNA?
|
eIF2
|
|
|
what must happen to eIF2 between rounds of protein translation?
|
recycling
(exchange of GTP for GDP) |
|
|
how does eIF2 know with which met-tRNA complexes it should interact?
|
initiation met-tRNA is different from internal met-tRNA
|
|
|
what is the function of eEF-1alpha?
|
binds aminoacyltRNA and GTP
|
|
|
what is the function of eEF-1betagamma?
|
assists in the exchange of GTP and GDP in eEF-1alpha
|
|
|
what is the function of eEF-2?
|
translocates mRNA through the ribosome, using GTP hydrolysis for then energy
|
|
|
what must every amino acid be bound to when brought to a ribosome?
|
eEF-1alpha
|
|
|
what provides the energy to transfer amino acids from eEF-1 to a protein?
|
hydrolysis of the GTP which is also bound to eEF-1alpha
|
|
|
what enzyme (functional unit of a ribosome) catalyzes the transfer of the peptide in the P-site to the amino acid in the A-site of a ribosome?
|
peptidyltransferase
(reaction is called transpeptidation) |
|
|
where is the peptidyltransferase activity of a ribosome?
|
in the 60S subunit
|
|
|
what is regenerated by translocation?
|
open A-site
active eEF-2 |
|
|
what protein is required for termination of translation?
|
eukaryotic chain release factor (eRF)
|
|
|
what happens when a protein reaches a stop codon (termination)?
|
polypeptide is transferred by peptidyltransferase to water and is thereby released from the tRNA and ribosome
|
|
|
where is selenocysteine found?
|
several peroxidases
several dehydrogenases most importantly, glutathione reductase |
|
|
what codon is recognized by the specific ser-tRNA?
|
UGA
|
|
|
what unique/specific molecules must be present for use of selenocysteine?
|
specific ser-tRNA
specific tRNA synthetase specific eEF |
|
|
what determines if a UGA (usually a stop codon) can be read as a selenocysteine codon?
|
hairpin loop in 3' untranslated region
(if present, selenocysteine can be incorporated, if absent it cannot) |
|
|
what recognizes the hairpin loop for a selenocysteine to be incorporated?
|
selenocysteine-specific translation factor (not eEF1)
|
|
|
what is the major way to control translation?
|
phosphorylate eIF2-alpha subunit
|
|
|
what is HCR?
|
heme-controlled repressor
(aka heme-controlled inhibitor or HCI) an eIF-2 kinase |
|
|
how does HCR (HIR) work?
|
in the presence of high concentrations of heme, HCR is inactive
in the the absence or trace amounts of heme, HCR phosphorylates eIF-2 and thereby inhibits translation |
|
|
where is heme-controlled repression utilized?
|
reticulocytes
(immature red blood cells) |
|
|
what is the main target of heme-controlled repression?
|
inhibit translation of globin
(so that the red blood cell is not making excess globin without heme present) |
|
|
why is ER stress bad?
|
stress in the endoplasmic reticulum could cause misfolded proteins, non-recognition of misfolded proteins, and non-functional proteins
|
|
|
what is PEK (PERK)?
(aka GCN2) |
RNA-dependent protein kinase-like endoplasmic reticulum kinase
an eIF-2 kinase induced by stress on the endoplasmic reticulum |
|
|
what is the effect of ER stress?
|
PEK (PERK) is induced ->
eIF2 is phosphorylated -> General Translation is inhibited |
|
|
what is PKR?
|
protein kinase RNA-activated
an eIF-2 kinase which is induced by double-stranded viral RNA |
|
|
what are the effects of viral infection?
|
induces PKR
induces 2',5'-adenylate synthetase --activates RNaseL |
|
|
what is RNaseL?
|
ribonuclease L
an enzyme, activated by pppA, which degrades mRNA (esp. in response to viral infection) |
|
|
what binds to eIF-4E, rendering the eIF-4E inactive?
|
4E-BP
|
|
|
what are mitogenic factors?
|
chemical substances that encourage a cell to commence cell division
|
|
|
what are the effects of mitogenic factors on 4E-BP?
|
induce phosphorylation of 4E-BP, causing it to dissociate from eIF-4E
|
|
|
which mitogenic factors induce the phosphorylation of 4E-BP and eIF-4E?
|
insulin
IL-2 PDGF EGF angiotensin II |
|
|
what effect do mitogenic factors have on eIF-4E?
|
induce phosphorylation of eIF-4E, making it bind the cap more avidly
|
|
|
what is required for translation of picorna virus RNAs?
|
40S ribosome coming into contact with IRES
eIF-4G |
|
|
what is an IRES?
|
internal ribosome entry site
a nucleotide sequence that allows for translation initiation in the middle of a messenger RNA |
|
|
what is an iron response element?
|
secondary structure in the mRNA (hairpin loop) that is recognized by iron response binding proteins as a site to regulate the translation of the protein
|
|
|
what is the iron response element binding protein (IRBP) for ferritin and transferrin?
|
iron-deficient form of aconitase
(aconitase is the iron-dependent enzyme of the TCA cycle) |
|
|
where is the iron response element found in ferritin mRNA?
|
5' untranslated region
|
|
|
where is the iron response element found in transferrin receptor mRNA?
|
3' untranslated region
|
|
|
in iron starvation conditions, what happens to ferritin mRNA?
|
iron-deprived aconitase is bound to the IRE, and translation of ferritin is blocked
|
|
|
in iron starvation conditions, what happens to transferrin receptor mRNA?
|
iron-deprived cytosolic aconitase binds to the IRE in the 3' untranslated region, the mRNA becomes stable, and transferrin receptor is made
|
|
|
in excess iron conditions, what happens to ferritin mRNA?
|
iron binds to aconitase, causing it to release the ferritin mRNA and allowing ferritin to be made
|
|
|
in excess iron conditions, what happens to transferrin receptor mRNA?
|
iron binds to aconitase, causing it to release the transferrin mRNA and allowing the mRNA to be degraded
(transferrin receptor is not made) |
|
|
what is the function of ferritin?
|
binds and stores intracellular iron, so that it cannot become toxic to the cell
|
|
|
what is the function of transferrin receptor?
|
binds transferrin so that cells can take up iron
|
|
|
what is dipthamide?
|
a naturally occurring modification to a histidine residue in eEF2
(it is recognized by diphtheria toxin) |
|
|
what is the significance of diphthamide in eEF-2?
|
the diphtheria toxin recognizes this residue and poly-ADP ribosylates the enzyme at that point; the poly-ADP ribosylation renders the enzyme non-functional, translocation stops, and the cell dies
|
