Proteins are vital substances for any organism. They participate in all metabolic processes of the cell, are structural components of organs and tissues, work as signaling molecules. In the process of protein synthesis, many enzymes, as well as organelles of the cell and nucleus, are directly involved.
Stages of protein synthesis: biological chemistry
The mechanism for constructing a protein molecule is very complex and requires a large number of factors. Peptides are composed of several amino acid molecules, and their number varies in a very large range.
The proper functioning of the protein depends on the conformation of the molecule, as well as on the amount of amino acids and their correct sequence in the peptide. Information about this sequence is stored in DNA, and its violation due to mutations and other factors can lead to the shutdown of vital proteins and cell death.
The following stages of protein synthesis in the cell are distinguished:
1. Transcription.
2. Broadcast.
Stage One: Transcription
In the process of protein synthesis, nucleic acid molecules are directly involved . DNA as a repository of all genetic information encodes, using its structural nucleotides, the sequence of the future peptide. Starting from the start codon (triplet) and ending with the terminal one, the protein information is read onto another nucleic acid - RNA. This single-stranded molecule is transported through the pores in the nucleus into the cytoplasm of the cell.
If in eukaryotes the transcription process is coupled with the participation of the nucleus, then in prokaryotes its absence simplifies the synthesis of the peptide. The RNA that forms on the bacterial chromosome is immediately processed and attached to the ribosomes.
Enzymes play a crucial role in the formation and synthesis of RNA on a DNA template. In the process of protein synthesis, molecules such as transcription factors, or TF , are directly involved. These are a number of proteins that contribute to the process of reading information from deoxyribonucleic acid.
Stage Two: Broadcast
When RNA enters the cell cytoplasm from the nucleus, information on the composition of the peptide must be read by special structures. In the process of protein synthesis, ribosomes are directly involved - non-membrane, small in diameter structures, consisting of two subunits: large and small. RNA is placed between these subunits, after which reading of the information begins.
Codon after codon is the construction of a long protein molecule like a gun. This is explained as follows: in the interribosomal space, only two codons are placed at once. When one of them has been read, the amino acid joins the peptide and in the form of a kind of tail falls out of the ribosome through a special hole. This happens as the sleeve falls out of the gun after firing.
In the process of protein synthesis, proteins of the IF group, or initiation factors, are directly involved. With their help, the synthesis of the polypeptide begins with the start codon, which in the vast majority of cases is methionine.
It is worth mentioning that amino acids are delivered to the ribosomes by special carriers called tRNAs, or transport RNAs. These molecules have the shape of a clover leaf, at the end of which the amino acid is attached, as well as ATP and a special protein - aminoacyl-tRNA synthetase. The whole complex allows for the energy delivery of the structural component of the protein to the ribosome and attach via peptide bond.
What are nucleotides?
Nucleic acids are a group of organic compounds that are polymers. They consist of purine (adenine, guanine) and pyrimidine (thymine, cytosine, uracil) bases. The sequence of these nucleotides determines the information that is stored in DNA or RNA. This information is read on the ribosomes with the formation of proteins, and for simplicity, the nucleotides are divided into triplets. Each triplet encodes its own amino acid, which tRNA delivers to the ribosomes.
Synthesis of mitochondrial proteins
Mitochondria and plastids have a distinctive feature - they have their own circular DNA, similar to the bacterial chromosome of bacteria. With this nucleic acid, organelles can work autonomously, synthesizing most of their structural proteins.
However, information on factor proteins, which are necessary for the transcription and translation process, is not stored on mitochondrial DNA. These peptides are assembled on ribosomes using nuclei rather than mitochondria. Therefore, two-membrane structures are not completely autonomous.
How did mitochondria and plastids get their own DNA? These organelles are believed to be descendants of bacteria. They lost independence within the cell, but brought with them ring nucleic acid. This is also hinted at by the similarity of mitochondrial DNA with a similar prokaryotic molecule.
Conclusion
All stages of protein synthesis are interconnected, and their task is to build peptide molecules using information stored in nucleic acids. Direct participants in the process are structures such as the nucleus and ribosomes, as well as some specialized proteins.
In prokaryotes, the process of synthesis of peptides proceeds noticeably faster due to the fact that they lack a nucleus. RNA, which is transcribed on a bacterial DNA matrix, immediately binds to the ribosomes, after which translation also proceeds simultaneously.