Chemistry for Biologists: Enzymes
Protein - Role of enzymes in metabolism: Some enzymes help to break down 2 , 3, and 4 are open, the water in A flows only to E, but, if valves 1, 2, 5, and 6 are. The concept of an enzyme active site will be introduced. 2 Enzyme structure They have a defined three-dimensional structure. They increase the speed of that reaction, typically by times What links here · Related changes · Special pages · Permanent link · Page information · Cite this page. Revise the molecules of life and the human digestive system for GCSE Combined Science, AQA.
Many amino acids in an enzyme molecule carry a charge. Within the enzyme molecule, positively and negatively charged amino acids will attract. This contributes to the folding of the enzyme molecule, its shape, and the shape of the active site.
Changing the pH will affect the charges on the amino acid molecules. Amino acids that attracted each other may no longer. Again, the shape of the enzyme, along with its active site, will change.
Extremes of pH also denature enzymes. The changes are usually permanent. Enzymes work inside and outside cells, for instance in the digestive system where cell pH is kept at 7. Cellular enzymes will work best within this pH range. Different parts of the digestive system produce different enzymes. These have different optimum pHs. The optimum pH in the stomach is produced by the secretion of hydrochloric acid. The optimum pH in the duodenum is produced by the secretion of sodium hydrogencarbonate.
Figure of unbonded molecules forming bonds To call something a catalyst for this reaction, two criteria have to be met: Figure of unbonded molecules using an enzyme catalyst to form bonds This second part of the catalyst definition is very important. If we imagine starting a camp-fire, which is essentially a chemical reaction between wood and oxygen, we could certainly speed the reaction up by dumping a huge bucket of gasoline on the fire.
The gasoline makes the reaction go faster as indicated by the charred eyebrows and singed hair of anybody trying this at home but it also gets used up. In other words, gasoline on a fire is not a catalyst.
Enzymes: principles and biotechnological applications
One of the best everyday examples of a catalyst is the emissions control system in your car. The main part of this system, unsurprisingly, is called a catalytic converter. This device is a container with a series of small screens coated in precious metals platinum, rhodium, etc. These metals are catalysts for the conversion of nitric oxide a nitrogen atom bonded to an oxygen atom into nitrogen and oxygen. Figure of a catalytic converter How do catalysts work?
Most catalysts including enzymes work the same basic way, because most chemical reactions including biochemical ones work the same basic way. As a good basic example, lets look at the nitric oxide reaction from the last section. What you have is the collision of two molecules of nitric oxide that results in the breakage of nitrogen-oxygen bonds and the creation of new nitrogen-nitrogen and oxygen-oxygen bonds.
Figure showing two molecules of nitric oxide gas colliding to form a molecule of nitrogen gas and a molecule of oxygen gas If we were to dump a whole bunch of nitric oxide molecules into a normal jar with no catalytic converterand we were able to get an extreme close-up of what was going on at the molecular level, we would see millions of N-O molecules spinning and tumbling in space, smashing into each other and ricocheting off the walls of the jar at incredible speeds.
Very, very few nitrogen or oxygen molecules would be created, whereas most ofthe nitric oxide molecules would just bounce off of each other. Why the nitric oxide molecules bounce off each other: You also know that if you try and align one pole of a magnet with the same pole of the other, the magnets will repel.
Nitrogen and oxygen atoms are like magnets in this sense.
Enzymes Make the World Go 'Round
Figure showing magnets attracting and repelling and a figure a nitrogen and oxygen atom attracting and repelling. The first rule is that there is a mutual attraction between red magnets and blue magnets. This means that if you stick the north pole of a red magnet to the south pole of a blue magnet, they will stick together, just like you would expect with two magnets. The second rule is that there is a stronger mutual attraction between magnets of the same color: What this means is that a red magnet will prefer to stick to another red magnet, and a blue magnet will prefer to stick to another blue magnet, if given the choice.
So those are the rules about how our magnets behave. If the poles of the colliding magnets are lined up in the correct way, so that the north pole of one red magnet is contacting the south pole of the other red magnet, with the same happening for the blue magnets, what would happen?
But only if the alignment is correct! Figure of nitrogen and oxygen atoms colliding then bonding. This magnet thought experiment is a good approximation of what happens with real-life molecules like nitric oxide.
BBC Bitesize - GCSE Combined Science - Animal organisation - digestion - AQA - Revision 5
But the alignment is key--nothing will happen without it. This is where catalysts come in. They help with alignment. The odds favor nothing happening. This is what happens with nitric oxide molecules in a jar, when no catalyst is present. Figure of nitric oxide molecules in a jar unable to correctly align. But now imagine that we add an extremely motivated and conscientious magic gnome to the inside of our jar, with the instructions that he is to grab a red-blue in each one of his hands, align them in the right way, and then smash them together.
Adding this helpful gnome assistant will increase the rate at which red-reds and blue-blues are made, because achieving the right alignment is no longer a matter of random chance. Figure of nitric oxide molecules in a jar correctly aligning in the presence of a catalyst.
Catalysts are the real-life versions of our imaginary magic gnomes. A platinum screen sits inside a catalytic converter attracting nitric oxide molecules to it and aligning them in just the right way, so that when they collide, the N and O switch places, and nitrogen gas and oxygen gas are created. Catalysts make reactions fast by aligning reactants so that successful reactions are more likely! Enzymes are biological catalysts Enzymes are the catalysts involved in biological chemical reactions.
Why enzymes are so important The big reason enzymes are important to life is because cellular energy is a precious resource.