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Why are there 48 (humans) different tRNAs for 61 codons and only 20 aminoacyl-tRNA-synthases coupling these 48 (humans) tRNAs?

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Keith Leannon
Keith LeannonLv2
28 Sep 2019

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Related questions

A single base substitution in the anticodon loop of one of thetRNAs for glutamic acid (tRNAglu) can hypothetically generate amutant tRNA that is able to suppress translational termination bycausing insertion of a glutamic acid residue at certain terminationcodons. Such mutant tRNAs are in fact encountered in nature and arereferred to as suppressor tRNAs. Assume that there are two tRNAgenes for glutamic acid (so that this hypothetical mutation wouldnot be lethal) and that one of these tRNAs acquires a single basemutation in its anticodon loop. Assume also that this tRNA has a Uresidue at the wobble position (and can therefore base pair withboth Glu codons) and that the mutation does NOT occur at thiswobble position.

A) What is the nucleotide sequence of the wildtype anticodon oftRNAglu (5’?3’ polarity) and what is the mutant sequence that wouldhave the properties described above?

Wt sequence:

Mutant sequence:

B) At which stop codons would the mutant tRNAglu be able tosuppress translational termination? (assume that G-U base pairingis possible at the wobble position)


C) Mutations of the sort described above are rarely encountered innature, due in part to the existence of a key step in the chain ofevents that helps ensure translational fidelity. What is this stepand how might it prevent suppressor tRNAs from being able toincorporate amino acids at stop codons?

1- Elongation Factor Tu and GTP allow tRNAs to enter the A site and form the appropriate codon/anticodon binding. Elongation Factor _______ regenenerates Tu.

2- When a stop codon arrives in the A site, _________ or 2 bind to it and cause the release of the polypeptide.

3- There are 61 sense codons and 3 stop codons, but only 20 amino acids - thus the code is _______.

4- The idea that genes encodes proteins was first put forth by __________ in 1908 but not widely accepted until the 1940’s following the work of Beadle and Tatum.

5- In tRNA ________ (with an amino acid), a single ATP is required.

QUESTION 16

What is the function of tRNA molecules?

The A-P-E sites of the ribosome are made out of tRNA molecules

tRNAs transfer the ribosome onto the 5' cap of an mRNA molecule

tRNAs catalyze the formation of new peptide bonds

tRNAs form covalent bonds between the ribosome and the mRNA

tRNAs bring amino acids to specific codons

QUESTION 17

What's the difference between primary and secondary active transport?

Only primary active transport requires energy

Only in primary active transport does a solute move against its concentration gradient

Primary active transport can only move a single ion, while secondary transport moves two ions simultaneously

Primary transport is used for larger solutes, while secondary transport is used for smaller molecules

Primary transport uses ATP-powered pumps, while secondary transport uses energy indirectly

QUESTION 18

When do beta cells release insulin into your bloodstream?

When you are very hungry

When blood sugar levels are high

When high levels of glycogen initiate the relase of insulin-containing vesicles

When a G-coupled receptor on the beta cells binds to insulin

When adrenaline binds to a beta cell receptor tyrosine kinase

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