Có 100+ tài liệu thuộc chủ đề "nguyên tắc của hóa sinh"
tailieu.vn Xem trực tuyến Tải xuống
Pregnenolone is transported from the mitochondria to the ER, where a hydroxyl oxidation and migration of the double bond yield progesterone. Pregnenolone syn- thesis in the adrenal cortex is activated by adrenocorticotropic hormone (ACTH), a peptide of 39 amino acid residues secreted by the anterior pituitary gland.. Progesterone is secreted from the corpus luteum during the latter half of the...
tailieu.vn Xem trực tuyến Tải xuống
Interestingly, nitrogenase reductase is a member of the G-protein family. As much as 5% of the cellular protein may be nitrogenase.. FIGURE 25.7 Ribbon diagram of nitrogenase reductase (the Fe-protein, blue. Nitrogenase reductase. ADP–ribosyl group ATP. FIGURE 25.8 Regulation of nitrogen fixation. 774 Chapter 25 Nitrogen Acquisition and Amino Acid Metabolism. the expression of the nif genes, the genes that...
tailieu.vn Xem trực tuyến Tải xuống
The ␣ -Ketoglutarate Family of Amino Acids Includes Glu, Gln, Pro, Arg, and Lys. Amino acids derived from -ketoglutarate include glutamate (Glu), glutamine (Gln), proline (Pro), arginine (Arg), and in fungi and protoctists such as Euglena, lysine (Lys). Proline is derived from glutamate via a series of four reactions involving activation, then reduction, of the -carboxyl group to an aldehyde...
tailieu.vn Xem trực tuyến Tải xuống
Nevertheless, four of the five enzymes necessary for isoleucine synthesis are common to the pathway for biosynthesis of valine, so discussion of isoleucine synthesis is pre- sented under the biosynthesis of the pyruvate family of amino acids.. The pathways of valine and isoleucine synthesis can be considered together because one set of four enzymes is common to the last four...
tailieu.vn Xem trực tuyến Tải xuống
FIGURE 25.40 The pathway of histidine biosynthesis. (Figure 25.40). Step 5 involves some novel chemistry: The substrate, phosphoribulosylformimino- 5-aminoimidazole-4-carboxamide ribonucleotide, picks up an amino group (from the amide of glutamine) in a reaction accompanied by cleavage and ring closure to yield two imidazole compounds—the histidine precursor, imidazole glycerol phosphate, and a purine nucleotide precursor, 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR). 25.5 How Does...
tailieu.vn Xem trực tuyến Tải xuống
Nucleotides are ubiquitous constituents of life, actively participating in the majority of biochemical reactions. Recall that ATP is the “energy currency” of the cell, that uracil nucleotide derivatives of carbohydrates are common intermediates in cellu- lar transformations of carbohydrates (see Chapter 22), and that biosynthesis of phospholipids proceeds via cytosine nucleotide derivatives (see Chapter 24). Many of the coenzymes (such...
tailieu.vn Xem trực tuyến Tải xuống
Deamination of AMP to IMP by AMP deaminase (Figure 26.8) followed by resyn- thesis of AMP from IMP by the de novo purine pathway enzymes, adenylosuccinate synthetase and adenylosuccinate lyase, constitutes a purine nucleoside cycle (Figure 26.9). Xanthine oxidase (Figure 26.8) is present in large amounts in liver, intestinal mu- cosa, and milk. It oxidizes hypoxanthine to xanthine and xanthine...
tailieu.vn Xem trực tuyến Tải xuống
As noted previ- ously, these two regulatory sites are designated the overall activity site and the sub- strate specificity site. ATP is an allosteric activator and dATP is an allosteric inhibitor, and they compete for the same site. The second regulatory site, the substrate specificity site, can bind either ATP, dTTP, dGTP, or dATP, and the substrate specificity of the...
tailieu.vn Xem trực tuyến Tải xuống
Kinetic controls over the rates of the catabolic path- ways are designed to ensure that the [ATP]/([ADP][P i. This is the role referred to when we call ATP the energy currency of the cell.. ATP also serves as an important allosteric effector in the kinetic regulation of me- tabolism. Its concentration (relative to those of ADP and AMP) is an...
tailieu.vn Xem trực tuyến Tải xuống
Cholesterol is also synthesized in the liver from two-carbon units derived from acetyl-CoA.. The amino group is excreted after incorporation into urea in the urea cycle. The liver is also the principal detoxification organ in the body. 27.6 What Regulates Our Eating Behavior?. Obesity is the single most important cause of type 2 (adult-onset insulin-independent) diabetes. Appetite and weight regulation...
tailieu.vn Xem trực tuyến Tải xuống
Replication Requires Unwinding of the DNA Helix. coli proceeds at a rate approaching 1000 nucleotides per second and there are about 10 bp per helical turn, the chromosome would accumulate 100 positive supercoils per second! In effect, the DNA would be- come too tightly supercoiled to allow unwinding of the strands.. The enzyme that carries out DNA replication is DNA...
tailieu.vn Xem trực tuyến Tải xuống
of proteins that interact with Dbp11, leads to the recruitment of DNA polymerase to the replication origins. Proteins of the Prereplication Complex Are AAA ⴙ ATPase Family Members. Cdc6, the Orc proteins, and MCM proteins are members of the AAAⴙ ATPase family, a group of proteins characterized by sequence and structural homology, ATPase activity, and a general function as molecular...
tailieu.vn Xem trực tuyến Tải xuống
The DNA strand dis- placed by the invading 3-terminal ssDNA is free to anneal with the 5-terminal strand in the original DNA, a step that is also mediated by RecA protein and SSB (Figure 28.21c). An RuvA tetramer (Figure 28.22a) fits precisely within the junction point (Figure 28.22b), which has a square-planar geometry, and this RuvA tetramer mediates the assembly...
tailieu.vn Xem trực tuyến Tải xuống
(Figure 28.30). However, 2-AP can form a single H bond of suf- ficient stability with cytosine (Figure 28.31) that occasionally C replaces T in DNA replicating in the presence of 2-AP. Hypoxanthine (Figure 28.32) is an adenine ana- log that arises in situ in DNA through oxidative deamination of A. Oxidative deamination of cytosine yields uracil, which base-pairs the way...
tailieu.vn Xem trực tuyến Tải xuống
The propensity of the PrP sc conformational form to polymerize into cell-destructive ag- gregates is thought to be the basis of prion diseases.. On the basis of Figure 28.2, draw a simple diagram illustrating replication of the circular E. Why doesn’t the mismatch repair system of E. Hexameric helicases, such as DnaB, the MCM proteins, and papil- loma virus E1...
tailieu.vn Xem trực tuyến Tải xuống
This sequence is termed the operator (Figure 29.8). Interaction of a regulatory protein with the operator controls transcription of the gene cluster by con- trolling access of RNA polymerase to the promoter. In prokaryotes, gene expression is often responsive to small molecules serving as sig- nals of the nutritional or environmental conditions confronting the cell. RNA polymerase. FIGURE 29.7 The...
tailieu.vn Xem trực tuyến Tải xuống
We see this latter feature in the activation of RNA polymerase by CAP–(cAMP) 2 , for example. Proteins That Activate Transcription Work Through Protein ⬊ Protein Contacts with RNA Polymerase. Generally speaking, a nucleotide sequence that provides a binding site for a DNA-binding protein can serve as an activator site if the DNA-binding protein bound there can interact with promoter-bound...
tailieu.vn Xem trực tuyến Tải xuống
Initial events in transcriptional activation include acetyl-CoA–dependent acetylation of -amino groups on lysine residues in histone tails by histone acetyltransferases (HATs) (Figure 29.30). Phosphorylation of Ser residues and methylation of Lys residues in histone tails also contribute to transcription regulation (Figure 29.30). Covalent Modification of Histones Forms the Basis of the Histone Code. FIGURE 29.30 A schematic diagram of the...
tailieu.vn Xem trực tuyến Tải xuống
Some of the different proteins form a “core” set common to all snRNPs, whereas others are unique to a specific snRNP. The 5-end of U1 snRNA is complementary to the consensus sequence at the 5-splice junction of the pre-mRNA (Figure 29.43), as is a region at the 5-end of U6 snRNA. Assembly of the spliceosome begins with the binding of...
tailieu.vn Xem trực tuyến Tải xuống
The complete translation of the genetic code is presented in Table 30.1. Of the 64 codons, 61 specify particular amino acids.. “stop” signals indicating that the end of the protein has been reached.. Each of the 61 “sense” codons encodes only one amino acid.. The degeneracy of the code is evolution’s buffer against mutational disruption.. The genetic code is “universal.”...