Protein Synthesis

Definition

Protein synthesis is the biological process through which cells generate proteins based on the genetic instructions encoded in DNA. This process involves two main stages: transcription, where the DNA sequence is transcribed into messenger RNA (mRNA), and translation, where the mRNA is translated into a polypeptide chain at the ribosome. Understanding how protein synthesis operates is essential for grasping how cells produce the molecules necessary for various functions, including structure, signaling, and catalysis.

5 Must Know Facts For Your Next Test

1. Protein synthesis occurs in two primary locations within the cell: transcription takes place in the nucleus, while translation occurs in the cytoplasm.
2. In eukaryotic cells, mRNA undergoes processing (like splicing and the addition of a 5' cap and poly-A tail) before it exits the nucleus for translation.
3. The genetic code consists of codons, sequences of three nucleotides on mRNA that correspond to specific amino acids, guiding the assembly of proteins during translation.
4. Ribosomes can be found either free-floating in the cytoplasm or attached to the endoplasmic reticulum (ER), with those on the ER involved in synthesizing proteins destined for secretion or membrane insertion.
5. Post-translational modifications, such as phosphorylation or glycosylation, can occur after translation to help regulate protein function and activity.

Review Questions

• How do transcription and translation work together to facilitate protein synthesis?
  • Transcription and translation are two critical steps that work in concert to ensure proper protein synthesis. In transcription, the DNA sequence of a gene is copied into mRNA within the nucleus. The mRNA then travels to the cytoplasm where translation occurs; ribosomes read the mRNA codons and assemble corresponding amino acids into a polypeptide chain, ultimately forming a functional protein.
• Discuss the role of ribosomes in protein synthesis and how their location affects protein destination.
  • Ribosomes play a crucial role in protein synthesis by translating mRNA sequences into polypeptides. Their location determines the fate of the synthesized proteins: free ribosomes produce proteins that typically function within the cytosol, while ribosomes attached to the endoplasmic reticulum synthesize proteins meant for secretion or incorporation into membranes. This compartmentalization ensures that proteins are correctly sorted based on their function.
• Evaluate how errors in protein synthesis can lead to diseases and what mechanisms are in place to correct these errors.
  • Errors during protein synthesis can result in dysfunctional proteins that contribute to various diseases, such as cystic fibrosis caused by a mutation affecting CFTR protein production. Cellular mechanisms like proofreading during transcription and chaperone proteins assist in correcting mistakes by ensuring proper folding and assembly. Furthermore, cells can degrade misfolded proteins through pathways like ubiquitin-proteasome system, maintaining proteostasis and preventing cellular dysfunction.

Related terms

Transcription: The first step of protein synthesis where a specific segment of DNA is copied into mRNA by RNA polymerase.

Translation:

The process following transcription where ribosomes read the mRNA sequence to assemble amino acids into a polypeptide chain.

Ribosome: The cellular machinery composed of ribosomal RNA and proteins that facilitates the translation of mRNA into proteins.