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12.5 Gene Expression: Translation -- Part 1
The events that occur during each stage are examined.
The sequence of codons in the mRNA is read by a ribosome, which connects the sequence of amino acids dictated by the mRNA into a polypeptide.
TransferRNA is a molecule that transfers amino acids to ribosomes.
A tRNA molecule is a single-stranded nucleic acid that doubles back on itself to create regions.
A space-filling model shows the molecule's actual three-dimensional shape, but the structure of the molecule is drawn as a flat cloverleaf.
The molecule's characteristic loops are caused by the formation of base pairs between the nucleotides.
There are three loops that hold the molecule at the ribosome.
An appropriate amino acid is attached at the 3' end of the molecule.
Leucine is the specific amino acid for this codon and anticodon.
There is at least one tRNA molecule for each of the 20 Page.
The 3' end contains the amino acid.
A tRNA that has the anticodon 5' AAG 3' bind to the codon 5' CUU 3' carries the leucine.
Most cells have around 40 different tRNA molecules.
Some tRNAs can pair with more than one codon.
The A-U/G-C configuration rule is followed in the first two positions.
The third position can change.
There are as many as four different codons in the third nucleotide.
The wobble effect helps make sure that the resulting sequence of amino acids is correct despite the changes in the DNA base sequence.
This is one of the reasons that the genetic code is not perfect.
The task is carried out by a group of enzymes.
Just as a key fits a lock, each enzyme has a recognition site for a particular amino acid to be joined to a specific tRNA.
The correct anticodon is attached to the leucine-tRNA by the leucine-tRNA synthesizer.
This is an energy-requiring process.
The large pool of charged tRNAs that exist in the cytoplasm can now be accessed by a ribosome, once the amino acid-tRNA complex is formed.
The ribosome is the site of synthesis.
The ribosome is well-suited to its function in the cell.
RRNA is produced from a template in the nucleus of a nucleus.
One of the ribosomal subunits is larger than the other.
The subunits move through the nuclear envelope into the cytoplasm, where they join together at the start of translation.
Once translation begins, ribosomes can stay in the cytoplasm or become attached to the reticulum.
There is a side view of a ribosome.
A view of a ribosome.
The growing polypeptide is carried by the tRNA to the A site.
The A site is once again accessible to a new tRNA after the new tRNA moves over one binding site.
The ribosome reaches the codon.
A number of ribosomes translate the same molecule.
Thousands of ribosomes are found in both prokaryotic and eukaryotic cells.
There are three binding sites for tRNA molecule in ribosomes.
The large ribosomal subunit has an activity from a ribozyme.
This bond is created many times to produce a polypeptide, which folds into its three-dimensional shape.
When a ribosome moves down an mRNA molecule, the polypeptide increases in size.
The polypeptide folds into its normal shape once translation is complete.
Section 3.4 states that a polypeptide twists and bends into a shape based on the makeup of its amino acids.
The process of folding begins when the polypeptide emerges from the ribosome.
The ER and the cytoplasm have chaperones that ensure that folding proceeds as it should.
Multiple ribosomes attach and translate the same mRNA at the same time.
One ribosome can attach to another ribosome if the first ribosome has been translated.
The efficiency of translation is greatly increased by the entire complex of ribosomes.
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