Biological Processes of mRNA and Translation

Overview of Alternate mRNAs

• One gene can code for many proteins due to variability in exons included in the mRNA.
• All introns get removed, but some exons may also be removed.
• Introns appear blue in diagrams, while exons appear purple.

Key Processes in Protein Synthesis

• DNA Replication and Transcription both occur in the nucleus.
• Translation happens in the ribosomes, located in the cytoplasm.
• After mRNA is formed in the nucleus, it leaves to the cytoplasm for translation.
• The lifespan of mRNA in the cytoplasm can be influenced by its poly-A tail.

The Central Dogma of Molecular Biology

• The flow of genetic information: DNA → RNA → Protein
• Transcription: converting DNA to mRNA, followed by translation into proteins.

Structure of Ribosomes

• Ribosomes consist of two subunits: large and small.
• They have three main sites: A (Aminoacyl), P (Peptidyl), and E (Exit).
• Peptide bonds form between amino acids during the translation process.
  • Peptide bond formation: Involves dehydration synthesis, leading to the formation of polypeptides.

Amino Acids and Peptides

• Amino acids are the building blocks of proteins; a chain of amino acids forms a polypeptide.
• A dipeptide consists of two linked amino acids; a polypeptide consists of multiple amino acids.
• Disulfide bridges: Formed between cysteine residues as a result of oxidation, stabilizing protein structure.

Understanding Codons

• Codons are triplet sequences in mRNA that specify amino acids (64 possible combinations from 4 bases).
  • Example: AUG is the start codon, signaling the beginning of translation (methionine).
• Each tRNA carries a specific amino acid corresponding to its anticodon, which pairs with the mRNA codon.
• The tRNA anticodon for AUG (methionine) is UAC.

Redundancy and Wobble in Codons

• There is redundancy in the genetic code; multiple codons can code for the same amino acid.
• Wobble hypothesis: The third base in the codon/anticodon pair is less stringent, allowing for flexibility in binding.

Stop Codons

• Stop codons signal termination of translation; they do not have corresponding tRNAs, halting the process.
• Example stop codons include UAA, UAG, and UGA.

Transcription and Translation Summary

• Transcription: DNA is transcribed into mRNA within the nucleus, where RNA polymerase binds to promoter regions.
• Translation: mRNA binds to ribosomes in the cytoplasm, where tRNAs bring amino acids to form proteins based on codons in mRNA.
• The peptidyl transferase activity of ribosomes forms peptide bonds during elongation of the polypeptide chain.

Factors Influencing Translation

• The length of the mRNA and the poly-A tail affects how long it can be translated.
• The presence of tRNAs and their ability to recognize codons increases the efficiency of translation.
• Potential applications of synthetic tRNAs for unnatural amino acids in research and biotechnology.