BLG 143 Study Guide - Final Guide: Aminoacyl Trna Synthetase, Aminoacyl-Trna, Transfer Rna

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16.4 Structure and Function of Transfer RNA

➢ Was a mystery until researches added radioactive amino acid leucine to an in vitro

protein synthesis system

➢ Some of the leucine attached to tRNA molecules

➢ An input of energy, in the form of ATP, is required to attach an amino acid to a tRNA

➢ Enzymes called aminoacyl tRNA synthetases catalyze the addition of amino acids to

tRNAs  charging a tRNA

➢ For each 0 amino acids, there’s a different aminoacyl tRNA synthetase and one or

more tRNAs

Aminoacyl tRNA  combination of a tRNA molecule covalently linked to an amino acid

➢ Tightly attached to tRNA makes it possible for the enzyme and substrate ti interact

in a very specific way

➢ Amino acids are transferred from aminoacyl tRNAs to proteins, to the growing end

of a new polypeptide

➢ tRNAs act as the interpreter in the translation process

What tRNAs Look Like

• Primary structure: sequence of nucleotides

• Sequence are relatively short, 75-85 nucleotides in length

• Secondary structure: CCA sequence at the ’ end offered a binding site for amino

acids, while a triplet on the loop at the far end could serve as anticodon  set of 3

ribonucleotides that forms base pairs with the mRNA codon

• Tertiary structure: folds into an L-shaped molecule; anticodon at one end, CCA

sequence and attached amino acid at other end; maintains a precise physical

distance between the anticodon and amino acid; this separation is key to the

positioning of the amino acid and the anticodon in the ribosome

• All of the tRNAs in a cell have the same structure, shaped like an upside-down L;

they vary at the anticodon and attached amino acid

How Many tRNAs are there?

Crick proposed the wobble hypothesis:

• Inside ribosome, certain bases in 3rd position of tRNA anticodons can bin to bases in

3rd position of a codon in a manner that doesn’t match the normal base pairing

• That’d allow a limited flexibility or wobble in base pairing

• A nonstandard base like U-G is acceptable in the 3rd position of a codon as long as it

doesn’t change the amino acid that the codon specifies

• A wobble in the 3rd position of a codon allows just 40 or so tRNAs to bind to all 61

mRNAs codons

16.5 Structure and Function of Ribosomes

Protein synthesis occurs when the sequence of bases in an RNA message is translated into a

sequence of amino acids in a polypeptide.

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Document Summary

Was a mystery until researches added radioactive amino acid leucine to an in vitro protein synthesis system trnas charging a trna. Some of the leucine attached to trna molecules. An input of energy, in the form of atp, is required to attach an amino acid to a trna. Enzymes called aminoacyl trna synthetases catalyze the addition of amino acids to. For each (cid:884)0 amino acids, there"s a different aminoacyl trna synthetase and one or. Aminoacyl trna combination of a trna molecule covalently linked to an amino acid more trnas. Tightly attached to trna makes it possible for the enzyme and substrate ti interact in a very specific way. Amino acids are transferred from aminoacyl trnas to proteins, to the growing end of a new polypeptide. Trnas act as the interpreter in the translation process. Inside ribosome, certain bases in 3rd position of trna anticodons can bin to bases in.

Related Questions

The energy for protein synthesis comes from which of the following?

	a.	The ATP used in the synthesis of aminoacyl-AMP molecules that are then converted to aminoacyl-tRNAs
	b.	The GTP that is bound to initiation factors used in the initiation and translocation phases of translation
	c.	The high energy C-N bond of the amino acid
	d.	a, b, and c
	e.	a and b

The enzymatic process of "charging" a molecule of tRNA is similar to other enzyme catalyzed reactions. Which of the following correctly describes such similarities?

	a.	Formation of an acyl-adenylate intermediate coupled to the hydrolysis of pyrophosphate in fatty acid activation is similar to reactions involved in the "charging" of tRNA.
	b.	Proofreading and correcting abilities that prevent incorporation of the wrong molecule are analogous to the action of DNA polymerase.
	c.	The aminoacyl-tRNA synthetase is a relatively non-specific enzyme (i.e., it can activate many different amino acids) and, in this respect, is similar to ribonucleotide reductase.
	d.	a and b.
	e.	b and c.

What are some of the longterm consequences of a mutation in the aminoacyl tRNA synthetase?

What end of the transfer RNA has the amino acid associated with it?

What is the importance of the leader sequence in the messenger RNA? What does the leader sequence do regarding translation? What is itâs role in transcription after the RNA has been created

What is the alternative name for charging the amino acid? What does this name signify?

Is the entire mRNA used to create a polypeptide? Why or why not?

I just came across this abstract:

Aminoacyl-tRNA synthetases (aaRSs) are responsible for creatingthe pool of correctly charged aminoacyl-tRNAs that are necessaryfor the translation of genetic information (mRNA) by the ribosome.Each aaRS belongs to either one of only two classes with twodifferent mechanisms of aminoacylation, making use of either the29OH (Class I) or the 39OH (Class II) of the terminal A76 of thetRNA and approaching the tRNA either from the minor groove (29OH)or the major groove (39OH). Here, an asymmetric pattern typical ofdifferentiation is uncovered in the partition of the codonrepertoire, as defined by the mechanism of aminoacylation of eachcorresponding tRNA. This pattern can be reproduced in a uniquecascade of successive binary decisions that progressively reducescodon ambiguity. The deduced order of differentiation is manifestlydriven by the reduction of translation errors. A simple rule can bedefined, decoding each codon sequence in its binary class, therebyproviding both the code and the key to decode it. Assuming that thepartition into two mechanisms of tRNA aminoacylation is a relicthat dates back to the invention of the genetic code in the RNAWorld, a model for the assignment of amino acids in the codon tablecan be derived. The model implies that the stop codon was alwaysthere, as the codon whose tRNA cannot be charged with any aminoacid, and makes the prediction of an ultimate differentiation step,which is found to correspond to the codon assignment of the 22ndamino acid pyrrolysine in archaebacteria.

Granted, this is a few years old, but I often find myself havingto admit that "I don't know" when at the root of discussions onevolution. That is, once abiogenesis has occurred, we can go on andexplain the rich diversity of life, but sadly we really don't knowmuch before that critical step. Generally, those satisfied with"magic" as an answer posit their myths and fables, whereas I'drather try to actually find out what happened. Sadly, as theabstract shows, you actually need a level of education tounderstand papers such as this that is generally well beyond thosewho would deny the reality of evolution.

Does anyone have a collection of papers on abiogenesis that aremore accessible and understandable to laypeople?

BLG 143 Study Guide - Final Guide: Aminoacyl Trna Synthetase, Aminoacyl-Trna, Transfer Rna

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