Enzymes

Enzymes

Enzymes are proteins that function as a biological catalyst. They are proteins in nature. A catalyst is a substance that speeds up a chemical reaction but isn’t changed by the reaction. Hydrogen peroxide (H2O2) is a substance that decomposes into Water (H2O) and Oxygen (O2) if it is left in room temperature for a period of time. This reaction could a long time, but it could be sped up if we add a catalyst. Each catalyst can catalyse a specific substance and nothing but it. The catalyst for Hydrogen peroxide is called Manganese4 oxide. If it is added we will get water and oxygen gas in a very short time, and the manganese4 oxide could be obtained again as it was, it remains unchanged.

How Do Enzymes Work?

Enzymes work the same way as catalysts do, they can work with only one substrate and they can be used more than once.

Enzymes have a structure that is called active site. Only one substance can fit into the active site to be digested, and it is the only substrate that this particular enzyme works with.

The figure above shows the function of enzymes:

• The substrate enters the active site of the enzyme.
• The reaction takes place.
• The substrate exits the enzyme as two simpler products.

You can also think of the way enzymes work as a key and a lock, the key is the substrate and the lock is the enzyme. The key should be exactly the right shape to fit in the lock, so does the substrate to fit in the active site of the enzyme. The key could only open only one lock, and the lock could be unlocked by only that key.

Enzymes are two types, Builders and Breakers. Builder enzymes do the opposite of breaker enzymes. Breakers break large molecules into smaller simpler ones, builders combine smaller ones to make large molecules.

Breaker enzymes are used in the digestive system to break down large insoluble molecules into simpler soluble ones to be used by the body. They are also present in cells that respire to break down sugars and oxygen into carbon dioxide, water and energy. Builder enzymes are present in plants to be used in photosynthesis, the opposite of respiration, in photosynthesis, oxygen and water are combined together to form carbon dioxide and sugars.

Naming enzymes depends on the substrate they work on. For example:
The sucrase enzyme works on sucrose.
The maltase enzyme works on maltose.

Enzymes are reusable and are only affected by the change in temperature and pH.

Affect of temperature on the enzyme’s activity:

Each enzyme has an optimum temperature, this is the temperature at which the enzyme is most active, below this temperature the activity of the enzyme decreases until it becomes inactive at low temperatures, above this optimum temperature the enzyme becomes denatured and can no longer work.

At low temperatures the enzyme is and the substrate are moving very slowly and collide weakly, the enzyme is said to be inactive and doesn’t work. As the temperature increases, the enzyme and substrate gain more kinetic energy and move faster colliding more, the enzyme becomes more active and the reaction takes place. When the enzyme reaches it’s optimum temperature, it is in its most active mood, if the temperature crosses the optimum the enzyme begins to die and become denatured. The enzymes become denatured when the shape of their active site changes as a result of high temperature, thus the substrate cannot fit into the active site and the enzyme is useless.

Each enzyme has its own optimum temperature, enzymes in humans have optimum temperatures of around 40 degrees. Plants have enzymes with optimum temperature of about 25 degrees.

The Effect of pH on the enzyme’s activity:

As in temperature, enzymes have an optimum pH. The pH is a scale  measuring the acidity or alkalinity of a substance or solution. The scale runs from 1 to 14. pH 7 is neutral, below that it is acidic and above that it is alkaline.

Each enzyme has an optimum pH, if this pH changes, the shape of the active site of the enzyme is changed, thus the substrate will not be able to fit in it, and the enzyme becomes useless.

Uses Of Enzymes In Seeds Germination:

Seeds grow into plants by germinating. Seed germination involves enzymes breaking the materials stored in the seed down to be used in growth, energy and building cells. The seed contains stored substances such as:

• Starch: Starch is broken down by amylase enzyme into maltose, maltose is then broken down by maltase enzyme into glucose which is used in respiration.
• Proteins: Proteins are broken down into amino acids by Protease enzyme, amino acids are used in building up cells and growth.
• Fats: Fats are broken down into fatty acids by lipase enzyme, they are used in making cell membranes.

In order for a seed to germinate, some conditions must be present:

• Water: To activate the enzymes.
• Oxygen: To be used for respiration.
• Warm Temperature: For providing the best conditions for enzymes to work and optimum temperature.

Uses Of Enzymes In Biological Washing Powders:

Washing powders contain detergents that help in cleaning clothes by dissolving stains in water. Some stains are made of insoluble substance, these cannot be removed by normal washing powders, instead, a biological washing powder is used. Biological washing powders contain enzymes that break down the insoluble stain into smaller soluble substances, which are then dissolved in the water. For example, if your shirt gets stained by egg yolk or blood, there is an enzyme called protease in the washing powder that will break down the insoluble protein into amino acids, which are dissolved in the water and sucked away. Thus the shirt becomes clean.

The best removal of stains is maintained by providing the optimum temperature for enzymes, presoaking to leave time for the enzymes to digest, putting the suitable amount of the powder.

Use Of Enzymes In Food Industry:

Enzymes are often used in the manufacturing of different foods

Diffusion and osmosis

Movement In And Out Of Cells

Substance move in and out of cells by three ways:

• Diffusion: The net movement of particles from a region of their higher concentration to a region of their lower concentration down a concentration gradient, as a result of random movement.
• Osmosis: The diffusion of water molecules from a region of their higher concentration (dilute solution) to a region of their lower concentration (concentrated solution) through a partially permeable membrane.
• Active Transport: The movement of ions, in and out of a cell, through a cell membrane, from a region of their lower concentration to a region of their higher concentration, against the concentration gradient, using the energy released by respiration.

Diffusion:

Diffusion is the process by which oxygen enters the blood from the lungs, and by which carbon dioxide enters the leaf from the atmosphere. There are many more examples of diffusion in biology.

Diffusion always takes place down a concentration gradient, that means that the particles that diffuse try to spread evenly in all spaces, so it moves from where it’s very concentrated to where it’s not concentrated.

There are some factors affecting the rate of diffusion, like the steepness of the concentration gradient. The steeper the gradient the faster the particles diffuse.

The surface area of the exchange membrane also affects the rate of diffusion. The larger the surface area of the exchange membrane the faster particles diffuse.

Thickness of exchange membrane too determines the diffusion rate, the thinner it is, the easier it will be for particles to go through it, the faster the diffusion rate.

Temperature is another factor affecting the diffusion rate, increasing the temperature will give particles more kinetic energy, making them move faster, thus increasing the rate of diffusion.

Osmosis:

Osmosis is the diffusion of water molecules. When we speak about osmosis, we don’t say water concentration; instead we use the term water potential. A dilute solution means it has lots of water molecules, and a high water potential. A concentrated solution has few water molecules and low water potential. Osmosis has to take place through a partially permeable membrane (or Semipermeable) this means that the Water molecules move from a place of their  high concentration to a place of their low concentration through a membrane with pores in it that lets some molecules through but not others.

The diagram shows two solutions, one dilute and one concentrated, separated by a semipermeable membrane. The solution on the right is diluted while the concentration on the left is concentrated. The water molecules will move from the right handside solution where they are very concentrated to the left handside solution where they are of a very low concentration, osmosis took place.

Osmosis happens all the time in cells. If you place an animal cell in distilled water. Osmosis will result in the water molecules moving from the distilled water where they are very concentrated to the Cell Where they are of low concentration Through the cell surface membrane. The cell becomes fat. As more Water molecules enter the cell, the cell will eventually burst and die.Osmosis happens all the time in cells. If you place an animal cell in distilled water. Osmosis will result in the water molecules moving from the distilled water where they are very concentrated to the Cell Where they are of low concentration Through the cell surface membrane. The cell becomes fat. As more Water molecules enter the cell, the cell will eventually burst and die.

Hypotonic Solution	Isotonic Solution	Hypertonic Solution
			Animal Cell
			Plant Cell

If we do the opposite, and place a red blood cell in a concentrated salt solution, the water in the cell has a higher water potential that the concentrated salt solution. Water molecules will move from the cell to the salt solution causing the cell to become shrunken and shrivel as in the diagram.

In plant cells, if a plant cell is placed in distilled water, water molecules will move from the distilled water to the cell, the cell swells up and becomes turgid but it will never burst because plant cells are surrounded by cell walls, which are made of cellulose and is elastic, it will stretch but never break, the cell becomes turgid.

If we place a plant cell in a concentrated salt solution whith low water potential, water will move from the cell to the solution causing the cell to become plasmolysed as in the diagram.

Active Transport:

Active transport occurs in cells, it is basically the movement of molecules or ions from a region of their low concentration to a region of their high concentration (against the concentration gradient) using energy of respiration. Active transport occurs in living, active cells only because it needs energy, these cells usually have a structure called mitochondria which respires producing energy to be used in active transport.

Active transport happens in roots to absorb mineral salts from the soil. It also occurs in the digestive system of mammals.

If oxygen is absent, respiration won’t take place, active transport will stop. Molecules are taken into the cell by protein carriers within the cell membrane.