Glossary
A Site (Aminoacyl Site)
One of the three binding sites for tRNA on the ribosome. It is where the incoming tRNA carrying the next amino acid binds to the mRNA codon.
Example:
The A site is like the 'arrival gate' for new aminoacyl-tRNAs, ensuring the correct amino acid is brought into position.
ATP and GTP Hydrolysis
The breakdown of ATP (adenosine triphosphate) and GTP (guanosine triphosphate) molecules, releasing energy that powers various steps in translation, such as ribosome movement and tRNA binding.
Example:
The energy for the ribosome's precise movements and the accurate delivery of tRNAs during translation is provided by ATP and GTP hydrolysis.
Codons
Three-nucleotide sequences on mRNA that specify which amino acid should be added to the growing polypeptide chain, or signal termination.
Example:
The mRNA sequence 'AUG' is a codon that typically signals the start of translation and codes for methionine.
Elongation (Translation)
The second step of translation where amino acids are sequentially added to the growing polypeptide chain, guided by tRNA molecules matching mRNA codons.
Example:
During elongation, the ribosome moves along the mRNA, adding one amino acid at a time, like beads on a string.
Eukaryotic Translation
In eukaryotes, transcription occurs in the nucleus, and the resulting mRNA is then transported to the cytoplasm for translation, separating the two processes.
Example:
Unlike bacteria, eukaryotic translation requires mRNA to be processed and exported from the nucleus before ribosomes can begin protein synthesis.
Genetic Code
The set of rules by which information encoded in genetic material (DNA or RNA sequences) is translated into proteins (amino acid sequences). It is read in triplets of nucleotides (codons).
Example:
The universality of the genetic code allows scientists to insert a human gene into bacteria, and the bacteria will produce the human protein.
Initiation (Translation)
The first step of translation where the ribosome assembles on the mRNA at the start codon, and the initiator tRNA brings the first amino acid.
Example:
The process of initiation ensures that protein synthesis begins at the correct point on the mRNA sequence.
P Site (Peptidyl Site)
One of the three binding sites for tRNA on the ribosome during translation. It holds the tRNA carrying the growing polypeptide chain.
Example:
During elongation, the tRNA holding the nascent protein chain resides in the P site before the next amino acid is added.
Peptide Bond Formation
The chemical reaction catalyzed by the ribosome that links the carboxyl group of one amino acid to the amino group of another, forming the backbone of a polypeptide.
Example:
The ribosome's peptidyl transferase activity is crucial for peptide bond formation, creating the strong links between amino acids.
Polypeptide
A linear chain of amino acids linked together by peptide bonds. One or more polypeptides fold into a specific three-dimensional structure to form a functional protein.
Example:
Before it becomes a functional enzyme, the newly synthesized polypeptide chain must fold correctly and sometimes combine with other chains.
Prokaryotic Translation
In prokaryotes, transcription and translation occur simultaneously in the cytoplasm, allowing for rapid protein production.
Example:
Due to the lack of a nucleus, prokaryotic translation can begin on an mRNA molecule even before its transcription is complete.
Release Factor
A protein that binds to a stop codon in the A site of the ribosome, causing the hydrolysis of the bond between the polypeptide and the tRNA in the P site, leading to polypeptide release.
Example:
The binding of a release factor to a stop codon is the key event that signals the end of protein synthesis.
Retroviruses
A class of viruses that use RNA as their genetic material and replicate by reverse transcribing their RNA genome into DNA, which is then integrated into the host cell's genome.
Example:
HIV is a well-known retrovirus that targets immune cells, leading to AIDS.
Reverse Transcriptase
An enzyme produced by retroviruses that catalyzes the synthesis of DNA from an RNA template during reverse transcription.
Example:
Drugs targeting reverse transcriptase are a common treatment strategy for HIV infections, blocking the virus's ability to replicate.
Reverse Transcription
The process by which retroviruses synthesize DNA from an RNA template, a reversal of the usual flow of genetic information.
Example:
The unique ability of retroviruses to perform reverse transcription makes them challenging to treat with conventional antiviral drugs.
Ribosomes
Cellular organelles responsible for protein synthesis. They facilitate the binding of mRNA and tRNA and catalyze the formation of peptide bonds.
Example:
In a rapidly growing bacterial cell, thousands of ribosomes are actively translating mRNA into proteins to support cell division.
Simultaneous (Co-transcriptional Translation)
A characteristic of prokaryotes where ribosomes attach to and begin translating an mRNA molecule while it is still being transcribed by RNA polymerase.
Example:
The rapid response of bacteria to environmental changes is partly due to simultaneous translation, which allows for quick protein synthesis.
Start Codon
A specific mRNA codon (usually AUG) that signals the beginning of translation and codes for the first amino acid (methionine) in most proteins.
Example:
Every protein synthesis event typically begins with the ribosome recognizing the start codon AUG.
Stop Codons
Specific mRNA codons (UAA, UAG, UGA) that do not code for any amino acid but instead signal the termination of translation.
Example:
When the ribosome encounters one of the stop codons, it triggers the release of the completed protein.
Termination (Translation)
The final step of translation where the ribosome encounters a stop codon, leading to the release of the completed polypeptide chain and dissociation of the ribosomal complex.
Example:
When the ribosome reaches a 'stop' signal, termination occurs, and the newly formed protein is released.
Translation
The process by which the genetic information encoded in messenger RNA (mRNA) is decoded to synthesize a specific polypeptide chain (protein). It occurs on ribosomes.
Example:
During protein synthesis, the cell performs translation to convert the mRNA sequence for insulin into the actual insulin protein.
Translocation
The movement of the ribosome along the mRNA molecule during elongation, shifting the tRNAs from the A and P sites to the P and E sites, respectively.
Example:
After a new peptide bond is formed, translocation occurs, moving the ribosome exactly three nucleotides down the mRNA.
Universal Code
The principle that the genetic code is nearly identical across all living organisms, meaning that a given codon specifies the same amino acid in almost all species.
Example:
The universal code is strong evidence for the common ancestry of all life on Earth.
tRNA (Transfer RNA)
A type of RNA molecule that carries specific amino acids to the ribosome and matches them to the corresponding mRNA codons during translation.
Example:
A specific tRNA molecule with the anticodon UAC will bring methionine to the ribosome when it encounters the AUG codon on mRNA.