Ribosome

Definition

A ribosome is a complex molecular machine found within all living cells that serves as the site of protein synthesis. It reads the genetic code carried by messenger RNA (mRNA) and translates it into polypeptide chains, which then fold into functional proteins. Ribosomes can be found freely floating in the cytoplasm or attached to the endoplasmic reticulum, playing a crucial role in cellular function and gene expression.

5 Must Know Facts For Your Next Test

1. Ribosomes consist of two subunits, a larger and a smaller one, each made up of ribosomal RNA (rRNA) and proteins.
2. In eukaryotic cells, ribosomes can be found either free in the cytoplasm or bound to the endoplasmic reticulum, known as rough ER, which is involved in synthesizing proteins for export or for use in membranes.
3. Ribosomes can be classified as either prokaryotic or eukaryotic based on their size and structure, with prokaryotic ribosomes being smaller than those found in eukaryotes.
4. During translation, ribosomes facilitate the formation of peptide bonds between amino acids, creating polypeptides according to the sequence encoded in mRNA.
5. Ribosomes play a vital role in gene expression by determining which proteins are produced based on the mRNA they translate, influencing cellular function and overall organismal development.

Review Questions

• How do ribosomes contribute to the process of translating genetic information into functional proteins?
  • Ribosomes play a key role in translating genetic information by reading the sequence of codons on the mRNA. Each codon corresponds to a specific amino acid, and ribosomes facilitate the matching of these codons with appropriate transfer RNA (tRNA) molecules that carry the corresponding amino acids. As the ribosome moves along the mRNA strand, it catalyzes the formation of peptide bonds between amino acids, assembling them into a polypeptide chain that eventually folds into a functional protein.
• Discuss the differences between prokaryotic and eukaryotic ribosomes and their implications for protein synthesis.
  • Prokaryotic and eukaryotic ribosomes differ in size and structure; prokaryotic ribosomes are 70S (composed of 50S and 30S subunits), while eukaryotic ribosomes are larger at 80S (composed of 60S and 40S subunits). These differences affect how proteins are synthesized; for example, antibiotics that target bacterial ribosomes can inhibit protein synthesis in bacteria without affecting eukaryotic cells. This specificity is crucial for developing treatments that kill bacteria while leaving human cells unharmed.
• Evaluate how mutations in mRNA can affect ribosome function and protein synthesis.
  • Mutations in mRNA can lead to changes in the sequence of codons that ribosomes read during translation. Depending on the nature of the mutation, this can result in missense mutations, where an incorrect amino acid is incorporated into a protein, or nonsense mutations, which create premature stop codons leading to truncated proteins. Such alterations can severely impact protein function, potentially leading to diseases or cellular dysfunction due to improper folding or loss of biological activity.

Related terms

mRNA: Messenger RNA (mRNA) is a type of RNA that carries genetic information from DNA to the ribosome, where it serves as a template for protein synthesis.

tRNA: Transfer RNA (tRNA) is a type of RNA that brings amino acids to the ribosome during protein synthesis, matching them with the corresponding codons on the mRNA.

polypeptide: A polypeptide is a chain of amino acids linked by peptide bonds that fold into a functional protein once synthesized by the ribosome.