Biology 120 Notes (Last Part of BIO Notes 22) Discussing Translation

Ribosomes

• ==Ribosomes== are made up of ribosomal RNA and various proteins.
• Each ribosome contains a ==large subunit== and ==small subunit==.
• The large subunit “…is composed of two RNA strands. One is an orange strand and the other is yellow.”
• The small subunit “…is in charge of information flow during protein synthesis.”
• The website that I got the definition for the small and large subunits is linked here: https://pdb101.rcsb.org/motm/10#:~:text=The%20large%20subunit%20is%20composed%20of%20two%20RNA,gluing%20the%20RNA%20strands%20into%20their%20proper%20shape. )
• rRNA is produced in the nucleus.
• Large and small subunits exist in the cytoplasm separately until translation begins.
• Each ribosome has a binding site for mRNA and three binding sites for tRNA.
• Multiple ribosomes can attach to one mRNA simultaneously.

Translation

• ==Translation occurs in three steps: initiation, elongation, and termination.==

• mRNA and tRNA unite in order to make proteins.

  Initiation

• ==Initiation== occurs when all the products of translation are brought together and is the first step of translation.

• The products that come from translation are ribosomal units, mRNA, and initiator RNA.

• ==Initiator RNA== is usually a form of ==methionine==.

• Methionine "…is an amino acid found in many proteins including the proteins in food and those found in the tissues and organs of your body."

• (The website that I found the definition for methionine for is linked here: https://www.healthline.com/nutrition/methionine#what-it-is )

  Elongation

• ==Elongation== is the process of polypeptide formation and is the second step on translation.

• A tRNA arrives at the A site.

• The ribosome confirms that its ==anticodon== matches the codon on the mRNA.

• “Anticodons are sequences of nucleotides that are complementary to codons. They are found in tRNA’s and allow the tRNA’s to bring the correct amino acid in line with an mRNA during protein production.”

• (The link that the information about the term “anticodon” comes from the website attached here: https://biologydictionary.net/anticodon/ )

• The ==polypeptide== is transferred to the tRNA at the A site via peptide bond.

• A polypeptide is “a molecular chain of amino acids.”

• (The link for the website that the definition for the term “polypeptide” is attached here: https://www.merriam-webster.com/dictionary/polypeptide )

• After the amino acid is added to the polypeptide, the ribosome moves forward.

• The tRNA in the P site moves to the E site and exits the ribosome.

• The polypeptide-bearing tRNA is now in the P site and the A site is ready to receive the next RNA.

• Elongation continues until a ==stop codon== is reached.

• "A stop codon is a genetic code that signals the end of protein manufacturing inside the cell…"

• (The link on the information obtained for the term “stop codon” is attached here: https://biologydictionary.net/stop-codon/ )

  Termination

• ==Termination== is the last step of translation and ends the process of protein synthesis.

• The ribosome transcribes the mRNA molecule until it finds a ==termination codon== on the RNA.

• A termination codon is a "trinucleotide sequence (UAA, UGA, UAG) that specifies the end of translation or transcription."

• (The link for the information obtained on the term “termination codon” is attached here: https://medical-dictionary.thefreedictionary.com/termination+codon )

• (The link for more information and the information used in these notes on translation and termination is located here. https://www.thoughtco.com/protein-synthesis-translation-373400 )

• The polypeptide is freed and begins to form into its secondary or tertiary structure.

• The ribosomal subunits dissociate and are returned to the cytoplasm.

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