Gene expression is the mechanism at the molecular level by which agene is able to express itself in the phenotype of an organism. The mechanism of gene expression involves biochemical genetics. It consists of synthesis of specific RNAs, (i.e., transcription) polypeptides, structural proteins, proteinous biochemicals or enzymes (i.e., translation) which control the structure or functioning of specific traits.
Gene expression in eukaryotes is much more complex than in prokaryotes. The differences are follows:
1. Transcription Enzyme: One RNA polymerase for all RNA’s
2. Enhancer: Transcription enhancers are not required.
3. Primary transcript: Directly function as mRNA.
4. mRNA: Polycistronic
5. Location of transcription: Cytoplasm (Nucleoid region)
6. Coupling of transcription and translation: Occurs
7. Translation initiation factors: Three represented as IF-1, IF-2, IF-3
8. Exit of deactylated tRNA: From E site of ribosomes
Eukaryotic Gene Expression:
1. Transcription Enzyme: At least three (RNA polymerase I for rRNA, RNA polymerase II for hnRNA, RNA polymerase III for tRNA, 5SRNA and snRNA)
2. Enhancer: Alongwith promoter region, enhancers are also required.
3. Primary transcript: It is hnRNA that contains both introns and exons. Processing removes introns and produces functional mRNA.
4. mRNA: Monocistronic
5. Location of transcription: Nucleus
6. Coupling of transcription and translation:
7. Translation initiation factors: Nine represented as eIF where e donates eukaryotes. These are eIF2, eIF3, eIFIA, eIF4B, eIF4E, eIF4G, eIF5 & eIF6.
8. Exit of deactylated tRNA: From P site as E site is absent in eukaryotic ribosomes.