Recording-2025-02-13T18:51:10.238Z

Gene Expression Overview

• Gene expression refers to the process by which information from a gene is used to synthesize functional gene products, primarily proteins. It follows the flow of genetic information from DNA to RNA to protein, commonly referred to as the central dogma of molecular biology.

• DNA serves as a template for all biological functions, encoding the instructions for traits that arise through the proteins synthesized.

Stages of Gene Expression

• The flow of genetic information can be summarized in the following sequence:

  1. DNA (template)

  2. RNA (intermediate)

  3. Protein (functional product)

• This process occurs in the various cellular compartments:

  • In eukaryotic cells, transcription occurs in the nucleus, while translation occurs in the cytoplasm at ribosomes.

Transcription

• Definition: The process of synthesizing RNA from a DNA template.

• Initiation: This stage begins when RNA polymerase binds to a specific region of DNA known as the promoter, which contains a TATA box that signals the transcription machinery.

• Elongation: RNA polymerase moves along the DNA template strand, adding complementary RNA nucleotides following base pairing rules (A-U and C-G). The growing RNA strand is formed in the 5' to 3' direction.

• Termination: Transcription ends when RNA polymerase reaches a termination sequence, resulting in the release of the newly formed messenger RNA (mRNA) strand.

RNA Processing in Eukaryotes

• After transcription, pre-mRNA undergoes modifications before it can be translated:

  • Capping: A 5' cap is added for protection.

  • Polyadenylation: A poly-A tail is added to the 3' end for stability.

  • Intron Splicing: Introns are non-coding sequences that are removed. Exons, which code for the final amino acid sequence, are joined together by spliceosomes.

Translation

• Definition: The synthesis of polypeptides from mRNA at ribosomes in the cytoplasm.

• The genetic code in mRNA is read in triplet codons (three nitrogenous bases) to translate the information into an amino acid sequence.

• Initiation: The ribosome assembles around the mRNA, and the start codon (AUG) signals the beginning of translation, with the first transfer RNA (tRNA) bringing methionine.

• Elongation: Additional tRNAs bring amino acids, and peptide bonds form between successive amino acids. The ribosome moves along the mRNA, reading the next codons.

• Termination: Translation concludes when one of the three stop codons is reached, prompting the release of the completed polypeptide chain and disassembly of the translation complex.

Comparisons of Eukaryotic and Prokaryotic Gene Expression

• In eukaryotic cells, transcription occurs in the nucleus, and processing is required to generate mature mRNA before translation begins in the cytoplasm.

• In prokaryotes, transcription and translation occur simultaneously in the cytoplasm, as they lack a defined nucleus and do not undergo mRNA processing like eukaryotes.

The Genetic Code

• The genetic code consists of 64 codons that correspond to the 20 amino acids, with most amino acids being encoded by multiple codons.

• Start and stop codons play crucial roles in initiating and terminating the translation process, respectively.

Conclusion

• Understanding the processes of transcription and translation provides insight into how genes express traits through protein synthesis. The intricate steps involved ensure the accurate and efficient translation of genetic information into functional proteins crucial for cellular and organismal functions.