how do trna know which amino acids to pick up?

Answer 1

The amino acid that a tRNA "picks up" is based on chemical interaction between the tRNA base sequence and the amino acid. The tRNA is coded for by mitochondrial DNA. All tRNA genes are located in mitochondrial DNA and not in the chromosomal DNA!

Answer 2

pinkmarie is right. i just wanted to add a source.

for every tRNA there is a aminoacyl-tRNA-synthetase which recognizes only one tRNA. It then binds it and connects one specific amino acid. Rather dull job, but ... hey ... it works!

Answer 3

There is a specific aminoacyl-tRNA synthetase (an enzyme) that is specific for each tRNA and amino acid.

Answer 4

tRNA has a particular anti-codon which complements a particular amino acid..look at this example to understand how it happens:

First of all, let AAA-GGG-CCC-UUU be our amino-acid chain. Hypothetical, but easy to do.

REMEMBER, only DNA has the base THYMINE. RNA and proteins have URACIL instead of thymine, so therefore, Uracil pairs with Adenine outside the nucleus (ie. DNA).

So, if AAA-GGG-CCC-UUU, their complementary bases are the DNA codes.

Protein: AAA-GGG-CCC-UUU
DNA: TTT-CCC-GGG-AAA

Now, for the long way...

Let's start with DNA first:

DNA: TTT-CCC-GGG-AAA

messenger RNA comes into the nucleus to copy that code, but uses uracil to pair up with adenine.

DNA: TTT-CCC-GGG-AAA
mRNA: AAA-GGG-CCC-UUU

mRNA takes its codes to the ribosome, where transfer RNA (tRNA) makes anti-codons:

mRNA: AAA-GGG-CCC-UUU
tRNA: UUU-CCC-GGG-AAA

amino acids that are complementary to the codons of the tRNA get attached, thus forming a protein chain

tRNA: UUU-CCC-GGG-AAA
Protein: AAA-GGG-CCC-UUU