Each enzyme has an "active site". The active site of each enzyme is unique in terms of 3D structure. Each unique active site can be thought of as a 3D surface that is able to bind only a single unique substrate or set of substrates, and it is the shape of the active site that is responsible for each enzyme's substrate selectivity. Most enzymes actually use the same or nearly the same, mechanisms of action; most commonly simple acid-base chemistry is used to catalyse reactions.
It may be difficult to understand, but enzyme active sites are actually thought to bind the "transition state" of the substrate. The transition state may be thought of as a state where the structure of the substrate is literally stretched to be somewhere between the orginal substrate structure, and the structure of the product of the enzyme catalyzed reaction. In other words, the enzyme can be thought of as "pulling" the substrate into a product. In this way, the enzyme lowers the energy required to pass the "transition" state, and accelerates the reaction of substrate to product.
Thus, the structure of the enzyme imparts both its substrate specificity (because only certain substrates will fit into the active site), and its activity (because in binding the substrate, the enzyme lowers the transition energy required for the substrate to form product).
Hope this helped, despite my rambling.
it was more time than he expected then
A, a class system. The feudal system itself was a system that separated and distinguished certain people by putting certain people above others. At the bottom were the the serfs. These were the servants. They worked for a lord, in exchange for food and protection from rival lords. Several lords reported to a king. In exchange for fighting for him, a king would pay lords by giving them portions of his land.
The correct answer to this open question is the following.
It seems that there is no question here, just a statement. You forgot to include the question and the options of the question.
What is needed here is the following.
The Columbian exchange resulted in population booms in parts of Europe and Asia due to the introduction of new staple subsistence crops from the Americas.
According to Alfred W. Crosby in "The Columbian Exchange,” it resulted in population booms in parts of Europe and Asia due to the introduction of new staple subsistence crops from the Americas.
The Columbian Exchange impacted most regions of the planet with the constant exchange of goods and raw materials and the development of new cash crops that were exported. Livestock also was introduced which was an important part of the farms.
However, the negative side of the Columbian Exchange was that it almost wiped out entire Native American Indian populations due to the introduction of European diseases such as smallpox, Malaria, chickenpox, Colera, Influenza, or measles.
Answer:
Explanation:
PRO : (1) Current federal contribution limits have not been adjusted for inflation in more than 20 years. The maximum individual contribution -- set at $1,000 in 1974 -- is worth approximately $300 in 1996 dollars. Candidates need to raise more than 3 times what they did 22 years ago to achieve the same result.
CON : (1) Only a small percentage of citizens can afford to give $1,000 or more to a candidates. Increasing the contribution limit or abolishing it altogethermight magnify the influence that wealthy individuals and groups have over elected officials.
PRO : (2) Studies show that PACs and related organizations prefer to give money to incumbent candidates, not challengers. Raising contribution limits might help challengers raise enough money to get their campaigns off the ground.
CON : (2) Because PACs and wealthy individual contributors favor incumbents, there is no reason to believe that challengers will have an easier time raising money from those same sources if limits are lifted.
PRO : (3) Candidates would spend less time fundraising, and more time meeting citizens and tending to their official duties.
CON : (3) Campaign finance problems would not be resolved by adding more money to the current system or doing nothing at all. We are much more likely to succeed if we build on what works in our current system.
PRO : (4) Given the escalating cost of political communications, especially the cost of TV advertising, candidates need more money than ever to communicate effectively with voters.
CON : (4) People who are wealthy enough to spend lots of money on political activities that are not limited by current campaign finance laws (like soft money, independent expenditures) will continue to do so, making higher limits as easy to evade legally as current limits.