Translocation speed

Dillingham, M. S., Wigley, D. B., and Webb, M. R. Demonstration of unidirectional single-stranded DNA translocation by PcrA helicase measurement of step size and translocation speed. Biochemistry 2000, 39, 205-12. 

The charging of the tRNA molecule with the aminoacyl moiety requires the hydrolysis of an ATP to an AMP, equivalent to the hydrolysis of two ATPs to two ADPs and phosphates. The entry of the aminoacyl-tRNA into the A site results in the hydrolysis of one GTP to GDP. Translocation of the newly formed pep-tidyl-tRNA in the A site into the P site by EF2 similarly results in hydrolysis of GTP to GDP and phosphate. Thus, the energy requirements for the formation of one peptide bond include the equivalent of the hydrolysis of two ATP molecules to ADP and of two GTP molecules to GDP, or the hydrolysis of four high-energy phosphate bonds. A eukaryotic ribosome can incorporate as many as six amino acids per second prokaryotic ribosomes incorporate as many as 18 per second. Thus, the process of peptide synthesis occurs with great speed and accuracy until a termination codon is reached. 

Systemic Acquired Resistance. SAR is the induction of a transient long-distance (translocated) defence response to fungal attack that is distinct from the local production of phytoalexins. The transient nature of SAR is important and has likely been selected in the course of evolution as a corollary to the energy demands that are made on the plant by the permanent mobilisation of resistance mechanisms. However, plants challenged by fungi are sensitised to subsequent attack and the speed of their SAR response is increased. 

Mineralization often has the initial effect (e.g., immediately after leaffall) of immobilizing N (36). In ecosystems where plant growth is limited by the availability of N, mineralization is also limited by N in the sense that addition of N to the leaflitter speeds decay and increases the rate at which N is immobilized by decomposers (37, 38). This initial immobilization period is marked by a net increase in the N content of leaflitter. Nitrogen limitation of decomposition follows in part from the low N content typical of litter, which arises from the translocation of N out of leaves during senescence. The immobilization phase of mineralization is followed by a period of slow release of inorganic N from the soil microbial pool (36). 

Rather than the solute speed in the phloem, we are sometimes more interested in how much matter is translocated. For example, if the sieve elements contain 0.5 m (500 mol m-3) sucrose moving at an average speed of 0.6 m hour-1, what is the transfer rate of sucrose in kg m-2 hour-1 By Equation 3.7 (Jj = vjcj), the flux density of sucrose is... 

In higher eukaryotes messenger RNAs for chloroplast and mitochondrial proteins have been localized exclusively to free and not membrane-bound polysomes [4,68]. In yeast, the situation is not as clear a portion of the polysomes for some of the proteins is found to be bound to mitochondria [69,70], This may only reflect the speed at which the import process occurs in the different organisms. Most of the cytoplasmically-synthesized precursors have amino terminal extensions varying in size and nature. The size variation goes from no extension (cytochrome c and ATP-ADP translocator) to approximately 12000 Da (proteolipid of the proton... 

Cytocentrifuge at 1000 rpm (115g) for 6 min. The speed and time of centrifugation may be extended (to 1500 rpm (173g) and 10 min, respectively) to additionally flatten the cells for their more favorable geometry that may be useful to detect variation in local density of fluorochrome, e.g., when studying translocation of certain some molecules. 

Fromm and Bauer [36] found that action potentials in maize sieve tubes change phloem translocation. Using macro- and microautoradiography in mature leaves of maize, Fromm and Bauer [36] studied the inhibition of phloem translocation caused by electric and cold shock. They stimulated the leaf tip with ice water and found that the velocity of signal transmission was 3-5cm/s. Upon stimulation, the microelectrode recorded a basipetally propagating action potential with a depolarizing amplitude of 80 mV in the sieve tubes (Fig. 2). During electrical stimulation, the action potential was measured in the sieve-tube system with a speed of 5cm/s. 

The transport speed of the transporter is equivalent to the ion flux of the ion channel. However, the ion flux of channels does not exhibit saturation with an increase of the ion concentration and it is larger by orders of magnitude than the transport speed of transporters. The ion flux is directly proportional to the ion stream. The basis of the function of translocators is membrane-enclosed compartments cells, organelles, vesicles, or proteoliposomes (prolis). Prolis and liposomes play a role in purification and reconstitution of translocators. The following sections are dedicated to them. 

Finally, since the moleeule/surface interaction also affects the speed of translocation, the same approaeh can be used to modulate the translocation time, e.g. for DNA [47]. This could be very useful in nanopore-based DNA sequencing, where the very high speed of translocation is one of the factors preventing single base resolution. 

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