For example, sucrase, 400 times the size of its substrate sucrose, splits the sucrose into its constituent sugars, which are glucose and fructose. The sucrase bends the sucrose, and strains the bond between the glucose and fructose. Water molecules join in and make the cleavage in a fraction of a second. Enzymes have these key features:
There are five main ways that enzyme activity is controlled in the cell.
Inhibitors can be used to stop an enzyme from binding to a substrate. This may be done to slow down an enzyme-controlled reaction. The inhibitors fit loosely or partially into the enzyme's active site. This prevents or slows down an enzyme-substrate complex being formed.
Denaturation is the "irreversible" alteration of an enzyme's active site, caused by an extreme change in temperature or pH. It will decrease the rate of reaction because the substrate molecule will not be able to fit into the active site, so products cannot be formed.
Cofactors, or coenzymes, are helper molecules which are needed to make an enzyme work. They are not proteins, and may be organic or inorganic molecules. Both types of molecules sometimes contain a metal ion at the centre, such as Mg, Cu, Mn or iron-sulphur clusters. This is because such ions may act as electron donors, and this is important in many reactions. The need of enzymes for various little helpers is the basic reason why animals, including ourselves, need trace elements and vitamins.
Enzymes have been classified by the "International Union of Biochemistry". Their Commission on Enzymes has grouped all known enzymes into six classes:
The individual enzymes are given a four-figure number which classifies them in the database.
Enzymes are used commercially for:
Mountain
A mountain is a large natural rise of the Earth's surface that usually has a "summit" (the name for a mountain's top, which can also be called a peak). It is usually steeper and taller than a hill. Mountains are often thought of as being a hill which is larger than 600 metres (about 2,000 feet). However, some definitions say a mountain is a hill larger than 300 meters (about 1,000 feet).
The forming of a mountain is called orogeny. Mountains are formed when rock layers in the ground are pushed from opposite sides, and by being pushed, they push the crust up. A mountain range is a large group of mountains beside each other. There are three main ways a mountain may be made:
Fold mountains occur when two plates collide. The less dense continental crust "floats" on the denser mantle rocks beneath. The continental crust is normally much thicker under mountains, compared to lower lying areas. Rock can fold either symmetrically or asymmetrically. The upfolds are anticlines and the downfolds are synclines. The Jura Mountains are an example of fold mountains.
Folded mountains make up some of the highest mountains in the world. Folded mountains commonly form along boundaries, where 2 continents meet. Some really complex folds are in parts of the Andes, Alps, Himalayas, Appalachians, and Russia's Ural Mountains. These long mountain chains also show lots of signs of folding.
Block mountains are caused by faults in the crust: a seam where rocks can move past each other. When rocks on one side of a fault rise relative to the other, it can form a mountain. The uplifted blocks are block mountains or "horsts". The dropped blocks are called "graben". They can form extensive rift valley systems. This form of landscape can be seen in East Africa, the Vosges, the Basin and Range province of Western North America and the Rhine valley. These areas often occur when the regional stress is extensional and the crust is thinned.
Volcanoes are formed in one of these ways:
Examples of volcanoes include Mount Fuji in Japan and Mount Pinatubo in the Philippines. The magma does not have to reach the surface in order to create a mountain: magma that solidifies below ground can still form dome mountains, such as Navajo Mountain in the states of Utah and Arizona, in the United States.
Volcanic mountains form when molten rock erupts onto the Earth's surface. They can either form on land or in the ocean. The Cascade Range in Washington, Oregon and northern California is made of volcanoes. Some of the largest volcanoes are on divergent boundaries, which form the mid-ocean ridges. The mid-ocean ridges have big volcanic mountain chains that run through the Atlantic, Pacific and Indian Oceans. The mountains in the mid-ocean ridges can grow tall enough to create islands such as Iceland or the Azores.
Other volcanic mountains form over hot spots, pockets of magma beneath the crust which erupt onto Earth's surface. The Hawaiian Islands are the tops of really high volcanic islands that have formed over a hot spot on the sea floor. The main Hawaiian island is a volcano about above the ocean floor. Its base is about wide. Almost of this island is above sea level.
Dome mountains, like those in the Black Hills of South Dakota and the Adirondack Mountains of New York, are an unusual domish type of mountain that is formed when molten rock rises through the crust and push up the rock layers above it. This creates a circular dome on the Earth's surface. The molten rock later cools off and forms hardened rock. When the pushed up rocks are worn away, the hardened rock is shown. This hardened rock then wears away in places. When it wears away, it leaves mountains, and they are called dome mountains.
Plateau mountains are formed a bit like folded mountains. They are large areas of flat topped rocks that have been lifted high above the crust by continental plates. Most plateaus are near folded mountains.
The height of a mountain is measured as distance above sea level.
The highest known mountain in the Solar System is the Olympus Mons (27 km high) on Mars. The highest mountain on earth is Mount Everest (8,848m) which is in Nepal and Tibet, in Asia.
The "tallest" mountain in the world is Mauna Loa, in Hawaii. The "height" of a mountain is measured from sea level, but the "tallness" of a mountain is measured from its base, even if under water. The highest mountain in North America is Mount McKinley (6,194m) in Alaska in the USA. The highest in South America is Aconcagua (6,962m) in Argentina. For Africa, it is Kilimanjaro (5,963m) of Tanzania. In Europe, the highest mountain is in Russia called Elbrus (5,633m). Antarctica's highest mountain is Vinsin Massiff (5,140m). In Oceania, a mountain called Puncak Jaya (5,030m) is the highest there. This particular mountain is in Papua New Guinea / Indonesia.
Machine code
Machine code is a computer program written in machine language. It uses the instruction set of a particular computer architecture. It is usually written in binary. Machine code is the lowest level of software. Other programming languages are translated into machine code so the computer can execute them.
An instruction tells the process what operation to perform. Each instruction is made up of an opcode (operation code) and operand(s). The operands are usually memory addresses or data. An instruction set is a list of the opcodes available for a computer. Machine code is what assembly code and other programming languages are compiled to or interpreted as.
Program builders turn code into another language or machine code.
Machine code is sometimes called native code. This is used when talking about things that work on only some computers.
Machine code can be written in different forms:
There are many kinds of instructions usually found in an instruction set:
Many modern processors use microcode for some of the commands. More complex commands tend to use it. This is often done with CISC architectures.
Every processor or processor family has its own instruction set. Instructions are patterns of bits that correspond to different commands that can be given to the machine. Thus, the instruction set is specific to a class of processors using (mostly) the same architecture.