lecture 11

Question 1

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

Answer 1

picornavirus infection causing hoof and mouth

Question 2

14 week old corgi with failure to thrive, diarrhea and vomiting the patient has very low serum immunoglobulin
What is the disease

Answer 2

canine X-linked SCID caused by a single nucleotide change resulting in a premature stop codon in the IL-2 receptor gene

Question 3

young patient is showing progressive gait difficulties and spasticity, and optic atrophy. MRI reveal abnormalities in neural white matter. What is the cause?

Answer 3

mutation in elF2B needed for translation initiation

Question 4

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?

Answer 4

mutation of ribosomal protein S19 resulting in diamond-blackfan syndrome

(mutation in small subunit of ribosome)

Question 5

conversion of nucleic acid language into protein language

Answer 5

translation

mRNA to proteins

Question 6

degeneracy of the code

Answer 6

some codons can code for same thing

Question 7

tRNA

Answer 7

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

Question 8

bacterial ribosomes

Answer 8

have two subunits

Large and small

Question 9

ribosomes read mRNA from

Answer 9

5’ to 3’

make protein from amino terminal (NH3+) to carboxy terminal (COO-) direction

Question 10

3 steps of translation

Answer 10

initiation
elongation
termination

Question 11

initiation in bacteria

Answer 11

1st step of translation mRNA to protein in bacteria

1. IF1, IF2 and IF3 complex with 30s ribosome subunit
2. IF2 binds to GTP. causes shape changes which allows mRNA and tRNA to join. IF3 is kicked off by this
3. 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

Question 12

what is Shine Dalgarno sequence

Answer 12

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

Question 13

translation uses what to make it go in bacteria

Answer 13

GTP instead of ATP

Question 14

what is different in eukaryotic translation

Answer 14

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)

Question 15

how does eukaryotes find the first initiation codon during translation? How is this different from bacteria

Answer 15

eukaryotes use scanning hypothesis

bacteria use shine- dalgarno sequence

Question 16

eukaryotic translations IFs

elF2B

Answer 16

disease: progressive gait difficulties and spasticity, optic atrophy. MRI shows abnormalities of neural white matter

Question 17

eukaryotic translations IFs

elF4E

Answer 17

bind the mRNA 5’ Cap

Question 18

eukaryotic translations IFs

elFG4

Answer 18

targeted by picornaviruses- hoof and mouth

Question 19

viral strategies to take over translation

Answer 19

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

Question 20

protein sorting and trafficking

Answer 20

• signal sequence for insertion into and out of ER
• mitochondrial import signals
• nuclear import signals
• sequestration in the cytoplasm mechanisms

Question 21

*** what is the function in translation of the Shine Dalgarno sequence in bacterial mRNA

Answer 21

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

Question 22

*** if viral RNA sequence contained an internal ribosome entry site, what eukaryotic translation protein would be dispensable for translation of the viral sequence?

Answer 22

eIF4E

(this puts 5’ cap onto mRNA in eukaryotes) if RNA has internal binding site 5’ cap is not necessary

Question 23

*** bacterial EF-G is needed for which specific step in bacterial translation?

Answer 23

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

Question 24

elongation in bacteria

Answer 24

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

Question 25

termination in bacteria translation

Answer 25

-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.