Why the insulin gene can only be expressed in insulin B cells

Macroscopically, it is the result of cell differentiation, that is, different cells express their respective proteins.

Microscopically speaking, insulin gene transcription is a very complex network regulatory process, with the participation of as many as 40 transcription factors, and it is precisely in the process of differentiation that pancreatic islet B cells can express transcription factors involved in the transcription regulation of insulin genes, so insulin is mostly expressed in insulin B cells, in addition, there are also a small amount of expression in the pituitary gland, retina, placenta and mouse seminal vesicles.

The emergence of insulin B cells is the result of cell differentiation, and the essence of cell differentiation is the selective expression of genes, that is, the expression of insulin genes makes insulin B cells produce.

In fact, different cells express mRNA differently, and the translated proteins are of course different. The more basic question is to ask why different cells transcribe different mRNAs or express different genes. This is related to the differentiation of cells during embryonic development, which is a very complex problem.

Due to the location information at the time of embryonic development, the influence of surrounding cells, etc., the cells will selectively express a certain gene, which eventually leads to cell differentiation.

Tube This is a fact... You can only admit it ... If you are the one who discovered this fact, you can choose to secrete insulin from pancreatic islet A cells! B cells secrete glucagon--

However, I personally think that this is a good reflection of the division of labor and cooperation of various organs and tissues in the human body

The control gene for insulin synthesis is on the short arm of chromosome 11. If the gene is normal, the insulin structure produced is normal; If there is a genetic mutation, the insulin produced is structurally abnormal, and it is called mutated insulin. In the nucleus of the cell, the DNA of the insulin gene region on the short arm of chromosome 11 is transcribed to the mRNA, and the mRNA moves from the nucleus to the endoplasmic reticulum of the cytoplasm and is translated into proinsulin, which is composed of 105 amino acid residues.

Proinsulin undergoes proteolysis to remove its propeptide to produce a long peptide chain composed of 86 amino acids. Proinsulin enters the Golgi apparatus with the microbubbles in the cytoplasm, and through the action of proteolytic enzymes, the three arginine-linked chains are cut off, and the chain is broken to form a non-effective C-peptide, and at the same time insulin is generated, which is secreted outside the cell and enters the blood circulation.

The human insulin gene is located on chromosome 11, 8416 bp in length, contains 3 exons and 2 introns, after transcription and translation, the signal peptide and c-peptide are removed, and finally the B and A peptides are folded through two disulfide bonds to form functional insulin, you can search for the reference sequence of human insulin on NCBI.

Nucleus, ribose, endoplasm, gol, cell membrane are required. The process is guidance, synthesis, primary processing, processing, and secretion.

In the nucleus of B cells, the insulin gene is transcribed into mRNA, which moves from the nucleus to the endoplasmic reticulum of the cytoplasm, where it is translated into a long peptide by ribosomes. Proinsulin enters the Golgi apparatus with microvesicles in the cytoplasm, where it is processed and secreted outside the B cell.

Since insulin is a protein, it needs the organelles needed for the protein synthesis process. There is the nucleus, endoplasmic reticulum, Golgi apparatus, ribosomes, tRNA and mRNA (these two days are not part of the structure).

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Insulin is a protein hormone composed of 51 amino acids, and its polypeptide chain is synthesized in the ribosomes of the endoplasmic reticulum, which processes the polypeptide chain and transports it to the Golgi apparatus, which is related to the processing and transport of proteins, so the synthesis and secretion of insulin require the participation of these organelles. The general process is as follows: in the nucleus, the gene completes transcription to form mRNA, and the mRNA is transferred to the cytoplasm, which directs the synthesis of polypeptide chains in the ribosomes of the endoplasmic reticulum (the first long chain macromolecule is called proinsulin); The proinsulin can cross the endoplasmic reticulum membrane and enter the endoplasmic reticulum, where it is processed to become proinsulin. The proinsulin is then transported to the Golgi apparatus and continues to be processed into mature insulin, which is transported by the vesicles secreted by the Golgi apparatus to the cell membrane and secreted outside the cell.

Insulin is made up of two protein molecules tightly bound together to form a complete functional unit.

The answer to this question is d

A: It should be that the two segments of the gene encode the two peptide chains A and B respectively, rather than the two DNA single strands encoding the two peptide chains A and B respectively.

B: After heating in a boiling water bath, the peptide chains that make up insulin are denatured (higher order structure changes), but do not break (primary structure remains unchanged).

I've done this question, and the choice d is the concept, insulin needs the ...... of protease processing

Pick D. The action of protease can only make the protein partially and incompletely broken, and the mechanism of action is that only peptidase can fully break the peptide bond.

A error. For a gene, only one strand is the coding strand and the other strand is not involved. The insulin gene is one of the strands that transcribes a long mRNA that translates a long peptide chain, which is then processed, and the long peptide chain is cut into two strands, which make up insulin.

In other words, both peptide chains A and B are encoded by the same single strand of DNA in the insulin gene.

b。When heated in a boiling water bath, the protein is denatured at high temperature, and the structure becomes very loose, which can be understood as "fully stretched peptide chain". But to say "break", it requires the action of enzymes. Under the action of high temperature and high pressure, the peptide chain may also be broken.

c。The function of protein is related to the structure, that is, the type of amino acids, the number, the arrangement, the spatial folding of the peptide chain, and the most important of which is the spatial structure of the protein.

(2011 Beijing Volume) 4The two peptide chains of insulin, A and B, are encoded by a gene. The following statement about insulin is correct.

a.The two DNA strands of the insulin gene encode two peptide chains, A and B, respectively.

b.After heating in a boiling water bath, the peptide chains that make up insulin are fully stretched and broken.

c.The function of insulin depends on the sequence of amino acids and is independent of the spatial structure.

d.The polypeptide chain synthesized by ribosomes is formed by proteases to form insulin.

Answer] D [Analysis] From genes to peptide chains, it is a process of transcription and translation. DNA is transcribed to produce messenger RNA (mRNA), which then enters the cytoplasm and binds to ribosomes to synthesize peptide chains based on the genetic information on the mRNA. Therefore, the single chain of the gene cannot encode the peptide chain alone, and it can only be said that the number, type and folding method of the amino acids of the gene control peptide chain are wrong; Peptide chain breakage should have the effect of enzymes, and the water bath will not break the peptide chain, B is wrong; Differences in spatial structure affect the function of proteins, c wrong.

It is wrong to say that in the double strands of genes, each chain encodes a different peptide chain. The two strands of DNA are complementary, and only one of them can be transcribed when transcribed, and insulin is no exception.

B: Thermal denaturation of proteins does not result in peptide chain breaks.

C: Protein function is related to spatial structure, and protein degeneration is the destruction of spatial structure that leads to changes in biological function.

D is correct, insulin translates to produce a long chain, cut off the signal peptide, and then cut off the middle C peptide, forming two peptide chains A and B. Proteases are required for the post-translational processing of many proteins.

Option da DNA has only one strand that is the encoded strand.

b Just stretching and not breaking The last line of the new textbook on page 23 "Connecting with Life".

Term c is related to both spatial structure and amino acid sequence.

d Proteases play a modifying role.

The two polypeptide chains synthesized by ribosomes are formed into some proteins with specific spatial structures after being removed by proteases to remove some peptides!

Insulin is known by the subject analysis.

The nucleotide sequence of the gene, so it is more convenient to synthesize it directly by rubber More importantly, the insulin gene belongs to the eukaryotic gene, and the gene structure of eukaryotic cells includes coding and non-coding regions, which are composed of introns and exons as genetic engineering.

The target gene can only use its cDNA, and then modify and modify the beam, so it is necessary to extract mRNA first, use reverse transcription to obtain cDNA, synthesize it artificially by chemical methods, and then amplify it with PCR.

Therefore, a