Proteins Genetic Code 4b'

Summary

This lecture delves into the translation process of the genetic code, detailing how scientists deciphered the genetic code table using various nucleotide combinations and the ribosome binding assay. It explains the universality and degeneracy of the genetic code, the role of start and stop codons, and the interaction between codons and anticodons on tRNAs. The lecture also covers the wobble hypothesis, isoaccepting tRNAs, and the process of amino acid activation and charging of tRNAs by aminoacyl-tRNA synthetases. Finally, it touches on the structure and function of ribosomes, setting the stage for a deeper exploration of translation's initiation, elongation, and termination stages in subsequent lectures.

Takeaways

• 🧬 The genetic code is deciphered through various experiments involving nucleotide combinations and ratios.
• 🔬 Scientists used different ratios of nucleotides like two U for every C to calculate the ratios and measure amino acid formation.
• 🧪 Ribosome binding assays developed by Nierenberg and Leder helped to definitively solve the genetic code for every single codon.
• 📚 The genetic code is a triplet code, with each codon made up of three nucleotides, and it is continuous and non-overlapping.
• 🌐 The genetic code is nearly universal across organisms, with a few exceptions in some organisms like mitochondria and certain protozoa.
• 🔄 The genetic code is degenerate, meaning multiple codons can code for the same amino acid, providing redundancy.
• ⏹ There are three stop codons that signal the end of protein translation and one start codon (AUG) that initiates translation.
• 🔀 The interaction between codons and anticodons on tRNAs is crucial for protein synthesis, with wobble allowing for flexibility in base pairing.
• 🔋 Amino acids are attached to their specific tRNAs through a two-step process involving aminoacyl-tRNA synthetases and ATP hydrolysis.
• 📉 Translation occurs in three stages: initiation, elongation, and termination, with ribosomes playing a central role in protein synthesis.

Q & A

What is the significance of dinucleotides, trinucleotides, and tetranucleotides in the genetic code?

Dinucleotides, trinucleotides, and tetranucleotides are significant in the genetic code because they were used in experiments to understand how different nucleotides could combine. By varying the ratios of these nucleotides, scientists could deduce the ratios of amino acids formed and thus determine which codons coded for which amino acids.

How did the ratio of U to C nucleotides affect the formation of nucleotide combinations?

By altering the ratio of U to C nucleotides, scientists could influence the likelihood of forming certain dinucleotides like UCU or CUU over others, such as all Cs. This manipulation helped them calculate the ratios and measure the amino acids that formed, aiding in decoding the genetic code.

What was the role of polynucleotides in decoding the genetic code?

Polynucleotides, such as polyU, polyG, polyC, and polyA, were used in assays to change the ratio of different nucleotides. This allowed scientists to experiment with different combinations and ratios, which was crucial in decoding the genetic code.

What technique helped scientists to definitively solve every codon in the genetic code?

The ribosome binding assay, developed by Nirenberg and Leder, was the technique that helped definitively solve every codon in the genetic code. This assay allowed for the binding of tRNA molecules to a ribosome mRNA complex in the absence of protein synthesis, enabling the synthesis of known three-nucleotide codons.

How did the ribosome binding assay work in the context of decoding the genetic code?

In the ribosome binding assay, tRNAs bound to different amino acids were introduced to a specific codon. The tRNA that matched the codon would bind to the ribosome. Unbound tRNAs would pass through a filter, while ribosomes with bound tRNAs would be caught. This allowed scientists to detect which amino acid was bound to the tRNA inside the ribosome.

What is the significance of the genetic code being nearly universal?

The near universality of the genetic code means that almost all organisms share the same code. This allows for the transfer of genes between different organisms in research and genetic engineering, as the genetic code functions similarly across species.

What does it mean for the genetic code to be degenerate?

The genetic code is degenerate because multiple codons can code for the same amino acid. This means that there is more than one way to code for each amino acid, providing redundancy in the genetic code.

What are start and stop codons, and how do they function in protein synthesis?

Start codons, such as AUG, signal the beginning of protein synthesis. Stop codons, on the other hand, signal the cell to stop translating. There are three specific codons for stop and one for start, which are crucial for controlling the process of translation.

How do codons interact with anti-codons during protein synthesis?

Codons on mRNA interact with anti-codons on tRNA through complementary base pairing. The anti-codon of the tRNA is in a three-to-five prime order and matches the five-to-three prime oriented codon on mRNA. This interaction is essential for the correct amino acid to be added to the growing polypeptide chain.

What is the role of aminoacyl-tRNA synthetases in protein synthesis?

Aminoacyl-tRNA synthetases are enzymes that attach the correct amino acid to its corresponding tRNA, ensuring that the tRNA is 'charged' with the appropriate amino acid. They recognize the tRNA's anticodon and sometimes other regions of the tRNA to perform this task accurately.

How does the process of translation occur in three stages?

Translation occurs in three stages: initiation, elongation, and termination. Initiation involves the binding of mRNA to the small ribosomal subunit, the initiation tRNA, and the large ribosomal subunit. Elongation is the process of adding amino acids to the growing polypeptide chain. Termination occurs when a stop codon is reached, signaling the end of translation.