To change hands. In football and basketball, a interception, or other method of giving the ball to the other side.
In the job market, the amount of activity of people quiting and being hired.
Turnover in biochemistry refers to the idea that organisms reuse and recycle their components continually. Everything is being regenerated in a cyclical process, degraded and resynthesized. Though the equilibrium remains fairly constant, the organism is nowhere near static. For example, in the average human body every single cell will have been replaced with a new one within seven years.

Turnover can speed up or slow down depending on environmental factors. Turnover will grind to a halt in bacteria if they are exposed to extreme cold temperatures, such as a collection hurtling through space or trapped deep beneath ice. As soon as the surroundings change: food becomes abundant or circumstances allow the initiation of biological processes again, turnover will reinitiate. Like a river, no organism remains exactly the same forever. Change is inherent in all composite things.

Turnover is especially important to metabolism, since a degraded part of a pathway must be replaced to ensure the stable continuation of chemical reactions.

In chemistry, "turnover" refers to the ability of a catalyst to, for lack of a better term, "turn over" after releasing a product molecule. Turnover leads to the regeneration of the "naked" catalyst, which can bind another molecule of starting material and restart the catalytic cycle.

All catalytic cycles operate on the same basic principle: a substrate (or multiple substrates) binds to the catalyst in some way, a chemical transformation of the substrate(s) takes place, and product is released with regeneration of the starting catalyst. A catalytic cycle is analogous to a conveyor belt: substrate goes on the conveyor belt, gets moved to a different position in "chemical space," and is released as the conveyor belt "turns over." Turnover is necessary in order for a process to be catalytic, and achieving catalyst turnover is often the most difficult part of turning a linear reaction into a catalytic cycle. One glaring problem is that the binding affinity of the product for the catalyst must be less than the binding affinity of the substrate for the catalyst. Otherwise, each molecule of catalyst would perform the catalytic cycle only once, then get stuck in the product-bound state. Such a system is missing turnover, and is stoichiometric rather than catalytic. The conveyor belt gets jammed up, in a sense.

Generalizing on this idea, we can say that in order to achieve turnover and avoid logjam, none of the active catalyst species should be too stable. For transition-metal catalysts this is rarely an issue, because transition metals can access a variety of oxidation states (i.e., possess a widely varying number of bonds) and easily bind and release organic molecules. Main-group catalysts are a different story. The common "organic atoms" (C, N, O, H, and the halogens) have oxidation states of widely varying energies, so falling into an unreactive thermodynamic sink along any reaction pathway involving these guys is likely. This problem is often circumvented by the inclusion of a reactive compound in stoichiometric quantities that "kicks up" the catalyst into its most reactive form. Iodine(III), for example, can catalyze C-O bond formation next to a carbonyl group...but to do so requires one full equivalent of mCPBA, in order to reoxidize iodine(I) back to iodine(III) and turn over the catalyst. Without the oxidant, iodine(I) forms upon release of the product and it gets stuck there. A full equivalent of oxidant is required because the catalyst must be reoxidized each time it runs the cycle.

Each run of the catalytic cycle is called a turnover. The number of times each molecule of a catalyst can perform the catalytic cycle before decomposition is called turnover number (TON). Higher TONs are good because they correspond to smaller catalyst loadings, the amount of catalyst required to transform a given amount of substrate. The number of turnovers a catalyst performs in a given time unit is called the turnover frequency (TOF). Higher TOFs are again good because they mean shorter reaction times. The turnover-limiting step of a cycle is the step with the slowest rate constant, which limits how often molecules of the catalyst turn over. You'll often hear people judge the quality of a catalytic cycle by these parameters.

In basketball, a turnover occurs when a team gives up possession of the ball before they have made an attempt at a shot. The turnover can occur because the ball is stolen, because someone attempts a basket that does not hit the rim or backboard, because the offensive team commits a foul that makes them give up the ball, or because of a violation of the shot clock.

For obvious reasons, turning over the ball is a negative thing to do, so statistics on turnovers are often looked at to see why a team is losing a game, or why a player might not be as good as their positive statistics reveal. However, like most statistics, turnovers can be deceptive. After all, the only real statistic that matters in basketball is the Win/Loss column. To show why turnovers can be deceptive, imagine a player who has the ball when the shot clock is about to run out, and who does not have a good shot available. They can make the shot, and miss; or they can not shoot and commit a turnover. In either case, they don't score, but in the second scenario, they earn a turnover. For this reason, although turnovers are not good, they don't tell the entire story, because there are many reasons an offense fails, and turning over the ball is just one of them.

In a human resources context, turnover, or labour turnover, is the rate at which an employer gains and loses employees. Put simply, it is how long employees tend to stay with a particular company. Turnover is measured for individual companies and for their industry as a whole. If an employer is said to have a high turnover relative to its competitors, it means that employees of said company have a shorter average tenure than those of other companies in the same industry.

Turnover can be defined as either internal or external. Internal turnover occurs when an employee leaves their current position for a different one within the same organization, either through promotion or demotion. External turnover, obviously, is when an employee leaves the company altogether. Both can either positively or negatively affect a company. In either case, the responsibility falls on HR to ensure the vacated position is filled promptly and adequately.

Turnover rates tend to be higher in unskilled fields. Though they still must eat the cost of training, the companies lose relatively less in terms of performance. Unskilled labour is easily replaced. Turnover in skilled labour fields, however, presents a problem. Individuals specialized in a certain field will surely be in high demand, so competition between companies in related industries comes into play. Replacing said individuals without sacrificing a certain level of skill can present a challenge.

High turnover rates often imply employee dissatisfaction and burnout, whether from unsafe or unfair working conditions or lack of support from management. A number of theories exist for this phenomenon, which I intend to address in future write-ups.


In a culinary context, turnover is a pastry-based food consisting of either a fully-enclosed (like a croissant) or semi-enclosed (like a sausage roll) filled pocket. Stewed fruit and/or jam are some possible contents for said pocket in the case of a sweet turnover, or meat and/or vegetables in savoury turnovers. Turnovers, also known as pasties or Cornish pasties in full, originated in Britain in the mid 1700s. They may be served hot or cold, and are a great easily-transportable food. There is a certain amount of controversy surrounding the "correct" size, shape and filling of turnovers, although the general idea is that the pastry is filled then "turned over".



Turn"o`ver (?), n.








© Webster 1913.

Turn"o`ver, a.



© Webster 1913.

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