ZOOHCC - 501: Molecular Biology (Theory)
Unit 4: Translation
Ribosomes
Ribosomes are molecular machines found in all living cells and play a central role in protein synthesis. They are composed of ribosomal RNA (rRNA) and ribosomal proteins, which together form two ribosomal subunits, the small subunit and the large subunit, which together form the complete ribosome. increase.
The main function of the ribosome is to read the genetic information encoded in messenger RNA (mRNA) and use this information to synthesize proteins. Ribosomes do this by binding to mRNA and moving it along in a process known as translation. As ribosomes move along the mRNA, they read the genetic code and use transfer RNA (tRNA) molecules to deliver the correct amino acids to the growing protein chain. Ribosomes are found in both prokaryotic and eukaryotic cells, but there are some differences in the structure of these two cell types. Prokaryotic ribosomes have a small size of 70S, while eukaryotic ribosomes have a large size of 80S. The difference in size is due to the presence of additional rRNA and rprotein in eukaryotic ribosomes.
Depending on their function, ribosomes are also found in different locations within the cell. Free ribosomes reside in the cytoplasm and synthesize proteins that remain in the cytoplasm, whereas ribosomes bound to the endoplasmic reticulum (ER) are involved in the synthesis of proteins that are secreted or inserted into the plasma membrane. In addition to their role in protein synthesis, ribosomes are also important targets for antibiotics. Many antibiotics work by targeting the ribosome and interfering with its function, preventing the bacterium from producing proteins and ultimately killing the bacterium.
In summary, ribosomes are essential molecular machines found in all living cells and are responsible for protein synthesis. They are composed of rRNA and rprotein and vary in size and location depending on function. Ribosome structure and function are highly conserved in all organisms and are critical for proper cell function.
Ribosomes are molecular machines responsible for protein synthesis in all living cells, including prokaryotes. In prokaryotes, the ribosome is composed of two subunits, a small (30S) subunit and a large (50S) subunit, which together form a complete 70S-sized ribosome.
Ribosome structure and assembly in prokaryotes can be divided into three main stages: transcription, translation, and assembly.
Transcription:
The first step in ribosome synthesis is the transcription of genes encoding ribosomal RNA (rRNA) and ribosomal protein (r-protein) in the nucleoid region of bacterial cells. The rRNA and rprotein genes are transcribed by RNA polymerase to form precursor rRNA (pre-rRNA) transcripts. translation:
After transcription, the pre-rRNA transcript undergoes several post-transcriptional modifications and processing steps to form the mature 16S, 23S and 5S rRNAs required for ribosome assembly. These rRNAs then associate with rproteins to form the small and large subunits of the ribosome.
The small subunit (30S) of the ribosome is composed of one 16S rRNA molecule and approximately 21 rproteins, and the large subunit (50S) is composed of two rRNA molecules (23S and 5S) and approximately 34 rproteins. increase.
Assembly
The final step in ribosome synthesis is the assembly of the two ribosomal subunits into a complete ribosome. The small and large subunits assemble on mRNA molecules during translation initiation to form functional 70S ribosomes. During assembly, several chaperones and assembly factors assist in the folding, modification, and processing of rRNA and rprotein so that they associate correctly with each other to form stable ribosomal subunits. Some of these assembly factors include ribosome biogenesis GTPases, ribosome assembly chaperones, and RNA helicases.
In summary, ribosome synthesis in prokaryotes is a complex process involving transcription and processing of rRNA and rprotein genes, followed by assembly of ribosomal subunits and their binding to functional ribosomes. This process requires the coordination of many different factors and is tightly regulated to ensure efficient and precise synthesis of proteins within the bacterial cell.
Ribosomes are molecular machines responsible for protein synthesis in all living cells. They are composed of ribosomal RNA (rRNA) and ribosomal protein (r-protein), which together form two ribosomal subunits, the small subunit (30S) and the large subunit (50S), which together form a full-sized ribosome. 70S in prokaryotes and 80S in eukaryotes.
The ribosome structure can be broken down into three major components: rRNA, rprotein, and functional sites.
rRNA:
The rRNA molecule is the major structural component of the ribosome and makes up the bulk of the ribosome. They provide a scaffold for ribosome assembly and structural support for the functional sites of the ribosome. In prokaryotes, the small subunit contains a single 16S rRNA molecule and the large subunit contains two rRNA molecules, a large 23S and a small 5S. These rRNAs fold into complex secondary and tertiary structures that are essential for their function in protein synthesis.
protein:
The r protein is involved in stabilizing rRNA and maintaining the overall structure of the ribosome. In prokaryotes, the small subunit contains approximately 21 r-proteins and the large subunit contains approximately 34 r-proteins. These proteins are organized into specific domains such as the head, body and stalk regions within the ribosome, giving the ribosome its unique shape and stability. Functional location:
Ribosomes contain several functional sites essential for protein synthesis, such as the A site (aminoacyl-tRNA binding site), P site (peptidyl-tRNA binding site), and E site (exit site). These sites are within the ribosomal RNA and interact with tRNA molecules and mRNA during translation.
The A site allows incoming aminoacyl-tRNAs to bind to the ribosome, whereas the P site retains the growing polypeptide chain. At the E site, the empty tRNA leaves the ribosome after releasing an amino acid.
In summary, the ribosome is a complex molecular machine composed of rRNA and rprotein that work together to translate mRNA into protein. Ribosome structure is highly conserved in all organisms and is essential for ribosome function in protein synthesis. The structure of the ribosome provides scaffolding for the functional sites of the ribosome, allowing it to synthesize proteins accurately and efficiently.
