lecture 11 Flashcards
cattle suffer from pyrexia, anorexia, shivering and have shown reduced milk production. they are smaking their lips. grinding their teeth, drooling and seem lame with blisters in their mouth and feet. You find that the level of elFG4 is reduced.
What is the problem
picornavirus infection causing hoof and mouth
14 week old corgi with failure to thrive, diarrhea and vomiting the patient has very low serum immunoglobulin
What is the disease
canine X-linked SCID caused by a single nucleotide change resulting in a premature stop codon in the IL-2 receptor gene
young patient is showing progressive gait difficulties and spasticity, and optic atrophy. MRI reveal abnormalities in neural white matter. What is the cause?
mutation in elF2B needed for translation initiation
patient is experiencing bone marrow failure caused by proapoptotic hematopoiesis and shows a snub nose, wide spaced eyes and abnormal digits. What is cause of the problem?
mutation of ribosomal protein S19 resulting in diamond-blackfan syndrome
(mutation in small subunit of ribosome)
conversion of nucleic acid language into protein language
translation
mRNA to proteins
degeneracy of the code
some codons can code for same thing
tRNA
see mRNA and transfer to protein language
5’ end is phosphorylated is usually a G residue
3’ end is usually CCA with a OH
anticodon loop where the tRNA reads the mRNA
(3’ X’Y’Z’5’) gets matched to codon of mRNA(5’ XYZ 3’)
each tRNA is attached to an amino acid at its 3’ end
ribosome help tRNA line up with mRNA
bacterial ribosomes
have two subunits
Large and small
ribosomes read mRNA from
5’ to 3’
make protein from amino terminal (NH3+) to carboxy terminal (COO-) direction
3 steps of translation
initiation
elongation
termination
initiation in bacteria
1st step of translation mRNA to protein in bacteria
- IF1, IF2 and IF3 complex with 30s ribosome subunit
- IF2 binds to GTP. causes shape changes which allows mRNA and tRNA to join. IF3 is kicked off by this
- release of IF3 allows 50s subunit to bind. GTP bound to IF2 is hydrolyzed resulting in release of IF1 and IF2
mRNA in bacterial has Shine Dalgarno Sequence that base pairs with ribosomal 16sRNA to position the mRNA at the correct place for translational initiation
what is Shine Dalgarno sequence
mRNA in bacterial that basepairs with ribosomal 16sRNA to position the mRNA at the correct place for translational initiation
found in initiation step of translation in bacteria
translation uses what to make it go in bacteria
GTP instead of ATP
what is different in eukaryotic translation
ribosomes bigger
first amino acid is Met, not N-formyl Met
initiation factor elF4E binds the mRNA 5’ cap slides until it find AUG then starts
finding initiation codon is different- scanning hypothesis instead of Shine-Dalgarno sequence
consensus AUG is GCCA/GCCAUGG
mRNA are moncistronic (1 mRNA can only make 1 protein) vs polycistronic (mRNA can make many different proteins)
how does eukaryotes find the first initiation codon during translation? How is this different from bacteria
eukaryotes use scanning hypothesis
bacteria use shine- dalgarno sequence
eukaryotic translations IFs
elF2B
disease: progressive gait difficulties and spasticity, optic atrophy. MRI shows abnormalities of neural white matter
eukaryotic translations IFs
elF4E
bind the mRNA 5’ Cap
eukaryotic translations IFs
elFG4
targeted by picornaviruses- hoof and mouth
viral strategies to take over translation
internal ribosome entry sites
- proteolysis of elF4G (hoof and mouth)
- removal of 5’ CAP from cellular mRNA
- CAP snatching
- protein covalent attachment at 5’ RNA end to protect viral mRNA
protein sorting and trafficking
- signal sequence for insertion into and out of ER
- mitochondrial import signals
- nuclear import signals
- sequestration in the cytoplasm mechanisms
*** what is the function in translation of the Shine Dalgarno sequence in bacterial mRNA
ensures that the mRNA enters the ribosome correctly, so it may be read 5’ to 3’ and so that the start condon may be found and start translation
*** if viral RNA sequence contained an internal ribosome entry site, what eukaryotic translation protein would be dispensable for translation of the viral sequence?
eIF4E
(this puts 5’ cap onto mRNA in eukaryotes) if RNA has internal binding site 5’ cap is not necessary
*** bacterial EF-G is needed for which specific step in bacterial translation?
moves the growing polypeptide chain attached to a tRNA from A site to the Psite. Also moves mRNA 3 nucleotides
- fMet attached to tRNA goes to Psite
- Ef-Tu finds next tRNA and puts in A site
- peptide bond forms polypeptide chain and P leaves
- EF-G moves tRNA from A to P and mRNA moves over 3 nucleotides
repeats
elongation in bacteria
1st animo acid has N-formyl Met. binds to P site
-Ef-Tu uses GTP to add next tRNA at site A
-N-formyl Met (peptide bond) attaches to nucleotide attached to the A site-
old tRNA gets kicked out of P site
-A site tRNA moves to P by EF-G. (mRNA moved three nucleotides over)
-process repeats
termination in bacteria translation
-termination sequences (UAA, UGA or UAG) activate peptidyl transferase to hydrolyze the peptide from the tRNA in the P site and releases peptide chain from ribosome.
