Question

RECALL What are two major similarities between protein synthesis in bacteria and in eukaryotes? What are two major differences?

Short answer

Similarities: Use of genetic code and stages of protein synthesis. Differences: Location of transcription and complexity of ribosomes.

Step-by-step solution

Identify Similarity #1

Both bacteria and eukaryotes use the genetic code to translate mRNA sequences into amino acids and synthesize proteins. The process involves ribosomes reading the mRNA and tRNAs bringing the correct amino acids.

Identify Similarity #2

In both bacteria and eukaryotes, protein synthesis involves three main stages: initiation, elongation, and termination. During these stages, ribosomes assemble on the mRNA strand, elongate the amino acid chain by adding one amino acid at a time, and release the completed protein.

Identify Difference #1

One major difference is that in eukaryotes, transcription occurs in the nucleus, and mRNA must be transported to the cytoplasm for translation. In contrast, in bacteria, both transcription and translation occur simultaneously in the cytoplasm.

Identify Difference #2

Another major difference is the complexity of the ribosomes. Eukaryotic ribosomes are larger (80S, composed of 40S and 60S subunits) compared to bacterial ribosomes (70S, composed of 30S and 50S subunits). This difference affects the initiation and regulation of translation.

Key concepts

genetic code

The genetic code is the set of rules by which information encoded in DNA or RNA sequences is translated into proteins by living cells. Each triplet of nucleotides, called a codon, corresponds to a specific amino acid. This code is universal across most organisms, meaning the same codon specifies the same amino acid in bacteria and eukaryotes. Understanding the genetic code is essential for grasping how proteins are constructed from genetic instructions.

ribosomes

Ribosomes are the molecular machines responsible for synthesizing proteins. They read the sequence of mRNA and facilitate the addition of corresponding amino acids. Ribosomes are composed of rRNA and proteins and are found in both prokaryotic and eukaryotic cells. In bacteria, ribosomes are slightly smaller (70S) compared to those in eukaryotes (80S). Despite these size differences, their core functions are remarkably similar across different types of cells.

initiation

Initiation is the first step of protein synthesis. It involves the assembly of the ribosome on the mRNA template and the recruitment of the first tRNA molecule. In eukaryotes, this process is more complex due to additional factors. The ribosome binds to the mRNA's 5’ cap and scans for the start codon. In contrast, bacterial ribosomes directly recognize the start codon on the mRNA without a 5' cap. Despite these differences, both systems ensure that protein synthesis starts at the correct position on the mRNA.

elongation

Elongation is the process during which amino acids are sequentially added to the growing polypeptide chain. In this stage, the ribosome moves along the mRNA, and tRNAs bring in amino acids corresponding to each codon. The ribosome facilitates the formation of peptide bonds between amino acids, ensuring the protein is built according to the mRNA sequence. This process continues until a stop codon is encountered.

termination

Termination is the final stage of protein synthesis. It occurs when the ribosome encounters a stop codon on the mRNA. Stop codons do not code for any amino acids and signal the ribosome to release the newly synthesized protein. Release factors help disassemble the ribosomal complex and free the mRNA and the complete polypeptide. This step ensures that the protein synthesis process is properly concluded, allowing the protein to undergo folding and modifications.

transcription

Transcription is the process of copying a segment of DNA into RNA. In eukaryotes, transcription takes place in the nucleus where DNA resides. The RNA produced, typically mRNA, then undergoes processing before being transported to the cytoplasm for translation. In bacteria, transcription and translation are coupled processes occurring simultaneously in the cytoplasm. This rapid succession allows bacteria to adapt quickly to environmental changes.

translation

Translation is the process by which the sequence of an mRNA molecule dictates the sequence of amino acids in a protein. This process occurs at the ribosome and involves converting genetic information into functional proteins. Translation in eukaryotes happens in the cytoplasm where ribosomes read the processed mRNA. In bacteria, translation begins while the mRNA is still being transcribed from DNA, ensuring swift protein production. The accuracy and efficiency of translation are critical for cellular function and health.