Small Ribosomal Subunit (40S):
Large Ribosomal Subunit (60S):
Protein synthesis occurs in two main steps: transcription and translation.
Ribosomes are involved in translation, which is the process of synthesizing proteins from mRNA.
Translation Steps:
RNA molecules that are part of the ribosome structure.
Three main types of rRNA in eukaryotes:
rRNA molecules provide a scaffold for ribosomal proteins and contribute to the catalytic activity of the ribosome.
Ribosomes are synthesized through a complex process known as ribosome biogenesis.
Ribosome biogenesis involves the production and assembly of ribosomal RNA and ribosomal proteins.
Steps in Ribosome Biogenesis:
Apart from protein synthesis, ribosomes have additional functions:
Ribosomes have a dynamic nature, allowing for diverse cellular functions beyond protein synthesis.
Antibiotics target bacterial ribosomes, exploiting differences from eukaryotic ribosomes.
Different binding sites and protein structures between bacterial and eukaryotic ribosomes make antibiotics selective.
Some examples of antibiotics and their mode of action:
Riboswitches are regulatory elements found in bacterial mRNA.
They are made up of a folded RNA sequence that can change its structure upon binding to specific molecules.
Types of riboswitches and their functions:
Riboswitches offer a unique mechanism for gene regulation through direct binding of ligands to mRNA.
In eukaryotes, translation initiation is a complex process involving multiple factors:
Translation initiation ensures accurate and efficient protein synthesis.
Example: Upstream Open Reading Frames (uORFs) regulate the translation of main open reading frames (ORFs) by affecting ribosome scanning efficiency.
Ribosome slippage and frameshifting are rare events, but they play important roles in gene expression regulation.
Ribosome slippage:
Frameshifting:
These mechanisms allow for the production of multiple proteins from a single mRNA.
Ribosome profiling (or Ribo-seq) is a technique used to study translation at a genome-wide scale.
It involves mapping the position of ribosomes along mRNA molecules.
Steps in ribosome profiling:
Ribosome profiling has revolutionized our understanding of translation and gene expression.
Ribosomes are not uniform in structure and composition; they exist in multiple forms.
Different ribosome populations have unique functions in specific cellular contexts.
Examples of ribosome heterogeneity:
Ribosome heterogeneity allows for specialization and fine-tuning of protein synthesis.
After completing translation, ribosomes need to be recycled for future rounds of protein synthesis.
Steps in ribosome recycling:
Quality control mechanisms monitor ribosome fidelity, eliminating any error-prone or aberrant complexes.
Ribosome-targeting diseases result from dysregulation or malfunction of ribosomes.
Therapeutic approaches for ribosomal disorders are being explored.
Examples of ribosome-targeting diseases:
Potential therapeutic approaches include restoring ribosome function or compensating for ribosome dysfunction using targeted therapies.
Transfer RNA (tRNA) functions as an adapter molecule during translation.
tRNA carries amino acids to the ribosome and matches them with their corresponding codons on mRNA.
Key features of tRNA:
tRNA plays a crucial role in accurate and efficient protein synthesis.
Initiation factors are proteins that assist in the initiation phase of translation.
They help assemble ribosomes at the start codon of mRNA.
Examples of initiation factors:
Initiation factors ensure proper start codon recognition and initiation of protein synthesis.
Elongation factors are proteins that facilitate the elongation phase of translation.
They help coordinate the addition of amino acids to the growing polypeptide chain.
Examples of elongation factors:
Elongation factors ensure accurate and efficient addition of amino acids to the growing polypeptide chain.
Termination is the final phase of translation when protein synthesis is completed.
It occurs when a stop codon is reached on mRNA.
Key components of termination:
Termination ensures the accurate and timely completion of protein synthesis.
Ribosome profiling can provide insights into translation efficiency and transcriptome-wide protein synthesis.
It involves measuring the density of ribosomes along mRNA molecules.
Ribosome profiling allows for:
Understanding translation efficiency can shed light on gene expression regulation and protein synthesis.
Translation is a critical step that can regulate gene expression post-transcriptionally.
Mechanisms for translational control:
Translational regulation allows cells to fine-tune protein levels in response to various stimuli.
Co-translational protein folding is the process by which nascent polypeptide chains fold into their functional structures during translation.
Factors influencing co-translational protein folding:
Co-translational protein folding ensures the correct conformation and functionality of newly synthesized proteins.
Codon bias refers to the preference for certain codons encoding the same amino acid in different organisms or genes.
Codon usage can impact translation efficiency and protein expression levels.
Factors influencing codon bias:
Codon bias plays a role in fine-tuning translation and protein synthesis.
Translational control plays a crucial role in organismal development and is dysregulated in many diseases.
Examples of translational control in development:
Dysregulated translational control is associated with various diseases, including cancer, neurodegenerative disorders, and metabolic diseases.