What Is DNA Transcription?

Transcription is the process by which genetic information flows from DNA to RNA. That is, using a determined one of the double-stranded DNA (template strand for transcription and coding strand not for transcription) as a template, using four ribonucleotides A, U, C, and G as raw materials, and catalyzed by RNA polymerase The process of RNA synthesis. As the first step in protein biosynthesis, a gene is read and copied into mRNA during transcription, that is, a specific DNA fragment serves as a template for genetic information, and a DNA-dependent RNA polymerase serves as a catalyst. The principle is to synthesize precursor mRNA. RNA polymerase forms a dynamic complex with a series of components to complete the process of transcription initiation, extension, and termination. The codons carried by the generated mRNA can enter the ribosome to achieve protein synthesis. Transcription uses only one strand of DNA as a template, and the single strand selected as the template is called the template strand, also known as the nonsense strand; the other single strand is called the non-template strand, which is the coding strand. The RNA generated by the coding strand and transcription The sequence T becomes consistent with other sequences except U, so it is also called the sense strand. Transcribed regions on DNA are called transcription units.

Transcription (transcription) refers to the process of synthesizing RNA under the action of RNA polymerase using DNA as a template, ATP, UTP, GTP, and CTP as raw materials. Prokaryotic cells have only one type of RNA polymerase; eukaryotic cells have three types: RNA polymerase I, RNA polymerase II, and RNA polymerase III. The single strand of the DNA double-strand as a transcription template is called the templatestrand or antisense strand, and the other strand is called the coding strand or sense strand (Figure 2- 6). There are many genes on a DNA molecule, and not all the coding regions of a gene are on the same single strand, so the template or coding strand is relative to the transcription of a certain gene. RNA transcription of prokaryotic cells: RNA polymerase holoenzyme (a2B') of prokaryotic cells is a core enzyme composed of 4 polypeptide chains plus a sigma factor. The transcription process can be divided into three stages: beginning, extension and termination. Start: The factor recognizes the promoter on the DNA molecule and binds to it, and the DNA double strand is partially unraveled, RNA synthesis begins, and the factor is separated from the core enzyme. Extension: RNA polymerase moves forward along the template strand, making the RNA strand continuously synthesized and extended. Termination: Prokaryotic cell transcription termination is divided into two types: factor and p factor. Since prokaryotic cells do not have a nuclear membrane and the synthetic RNA requires almost no complex processing and modification, the two processes of transcription and translation of prokaryotic cells can be performed almost simultaneously ^[1]

During transcription, the cell uses the principle of base complementation to generate a

DNA: 5'-ATCGAATCG-3 '(this is a non-template strand)

3'-TAGCTTAGC-5 '(this is the template chain)

Transcribed mRNA: 5'-AUCGAAUCG-3 '

It can be seen that only T of the non-template chain is changed to U, so the non-template chain is also called a sense chain. This too

Using the RNA strand as a template,

Post-processing of mRNA precursors

Original transcripts of prokaryotic mRNA (except for individual

The transcription of eukaryotic RNA is basically the same as that of prokaryotic RNA. However, the process is much more complicated, mainly due to the following differences:

Some eukaryotic RNAs are transcribed in the nucleus, while protein synthesis is performed in the cytoplasm. And the genetic information system of mitochondria and chloroplasts of eukaryotes is called the second genetic information system of eukaryotic cells, or extranuclear genes and their expression systems. This is because research has found that in addition to DNA in mitochondria and chloroplasts, there are also RNA (mRNA, tRNA, RNA), ribosomes, and amino acid activating enzymes. These two organelles have the function of independent transcription and translation. In other words, both mitochondria and chloroplasts have systems that transcribe RNA and translate proteins by themselves.

M One mRNA molecule of eukaryote generally contains only one gene, and one mRNA molecule of prokaryote usually contains multiple genes. Except for a few lower eukaryotes, one mRNA molecule generally contains only one gene, encoding one

The regulation and control of transcription is an important link in the regulation and control of gene expression. Promote gene transcription

Transcription can be

In eukaryotic cells, RNA polymerases usually cannot perform transcription alone, but need to cooperate with other transcription factors. Some auxiliary transcription factors are helicases.

Factors that affect transcription in trans can be collectively referred to as transcription factors (TF). RNA polymerase is a trans-acting protein factor. Transcription factors corresponding to RNA polymerases , , and are called TF, TF, and TF, respectively. TF has been the most studied. Table 19-2 lists the basic TFII required for eukaryotic gene transcription.

Table 19-2 Basic transcription factors of RNA polymerase II

Transcription factor	Molecular weight (kD)	Features
TBP	30	Combined with TATA box
TF-B	33	Mediates RNA polymerase II binding
TF-F	30,74	Helicase
TF-E	34,37	ATPase
TF-H	62,89	Helicase
TF-A	12,19,35	Stable TF-D binding
TF-I	120	Promote the binding of TF-D

It was previously thought that the protein factor that binds to the TATA box is TFII-D. Later, it was discovered that TFII-D actually includes two types of components: The protein that binds to the TATA box is TBP (TATAbox binding protein), which is the only transcription that can recognize and bind the TATA box Factors are required for the transcription of all three RNA polymerases; others are called TBP-associated factors (TAF) and include at least 8 factors that can tightly bind to TBP. Before transcription, TFII-D binds to the TATA box; then TFII-B binds to the TBP-DNA complex with its C-terminus, and its N-terminus can bind affinity to RNA polymerase II, followed by TF composed of two subunits -F is added to the assembly, TFII-F can form a complex with RNA polymerase, and it also has a DNA helicase activity that depends on the energy supplied by ATP, which can unravel the DNA double helix in front and play a role in the extension of the transcription chain. In this way, the promoter sequence is combined with TFII-D, B, F and RNA polymerase II to form a "minimum" pre-initiation complex (PIC) with transcriptional function basis, which can transcribe mRNA . TF-H is a multi-subunit protein complex, which has a DNA helicase activity that depends on the energy supplied by ATP, and plays a role in the extension of the transcription chain; TF-E is a tetramer composed of two subunits, which is not directly related to DNA The combination may be related to TF-B, which can increase the activity of ATPase; the addition of TF-E and TF-H forms a complete transcription complex, which can be extended by transcription to generate long-chain RNA, and TF-A can stabilize TF-D The combination with the TATA box improves the transcription efficiency, but it is not necessarily required for the transcription complex ^[1] .