Enzyme and substrate interaction

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DP Biology

Enzymes and Metabolism

On this page:

Introduction What Are Enzymes? Functioning of Enzymes Lock and Key vs Induced Fit Factors Affecting Enzyme Activity Metabolism ATP - Energy Currency Metabolic Pathways Enzyme Kinetics Coenzymes and Cofactors Enzyme Regulation in Metabolism Enzyme Metabolic Process Examples Conclusion

Enzymes and Metabolism

Enzyme and metabolism diagram

Chemical reactions are crucial for the survival of every living thing. Metabolic reactions, the reactions that include the building, breaking and providing of the energy storing and energy releasing molecules, happen constantly and are ongoing in cells. However, metabolic reactions can take an especially long time to complete if the chemical reactions are performed without help. At your normal body temperature, in fact, without help and without the presence of any enzymes, many of these reactions could take years to complete.

This problem is solved by the presence of enzymes in cells. Enzymes are biological catalysts, meaning that they speed up the rate of reactions, also without being used up in the reaction.

What Are Enzymes?

Enzymes are proteins that are biological catalysts, and some molecules of RNA also act as enzymes, and these are called ribozymes. Enzymes increase the rate of a reaction by lowering the activation energy (the minimum amount of energy that is needed for a reaction to occur).

Consider rolling a ball up a hill. Doing it on your own would be a lot of work. An enzyme is like a hill and makes it easier for the ball to roll over.

What You Need to Know About Enzymes

  • An enzyme's action is particular. Often, a unique complex will bind a substrate with an enzyme.
  • The place where the enzyme binds is termed an active site.
  • This temporary formation of an enzyme and substrate complex exists prior to the occurrence of the chemical reaction.
  • When an enzyme is used in a reaction, it is not consumed and remains unchanged.

Functioning of Enzymes

  1. The substrate attaches to the active site, and the complex is formed.
  2. Subsequently, there is a chemical transformation involving the substrate to yield a final product.
  3. When tightly bound to the complex, the products are set free. Enzymes remain available to carry out similar processes.

Interaction between an enzyme and a substrate is represented using two models.

Lock and Key Model vs Induced Fit Model

Lock and Key Model

In a similar way a key may fit into a lock, a substrate fits perfectly into an enzyme.

Induced Fit Model

When a substrate fits perfectly into an enzyme, it is easier to carry out the reaction. When an enzyme's activity is highest, the substrate is bound tightly.

Factors Affecting Enzyme Activity

Temperature

  • Most human enzymes work best at around 37°C. Each enzyme is said to possess an optimum temperature.
  • Precipitation will make proteins change shape and lose their activity.
  • Extreme temperature effects are precise.
  • Enzymes freeze are present.
  • Enzymes have an ideal temperature and at each temperature. While amylase has an ideal temperature of 37°C, pepsin's ideal temperature is 21°C.
  • Heat will denature proteins.
  • The time it takes to make products is referred to as the reaction time.

Substrate Concentration

The concentration of the substrate increases, the rate of reaction increases until all active sites are filled.

Enzyme Concentration

The amount of enzymes increases the rate of reaction if substrate is available.

At an active site, a substrate is bound to it, this is referred to as a bound substrate. A non-active site is a site on an enzyme other than the active site.

Enzymes are proteins that catalyze the metabolic pathways and enhance the rate of these reactions.

Metabolism

Anabolic Reactions

A process that involves the synthesis of more complex molecules from simpler ones.

Example: In protein synthesis, polypeptides are formed from amino acids.

Catabolic Reactions

A metabolic pathway that breaks down molecules into simpler ones and releases energy.

Example: During cellular respiration, glucose is transformed into CO₂ and H₂O, while simultaneously producing ATP.

All the enzymatic reactions that occur in an organism are termed as metabolism. Cellular respiration involves a series of metabolic reactions that convert nutrients into energy.

Metabolism consists of a series of chemical reactions. Enzymes regulate metabolism by controlling the timing, location, and speed of these reactions.

ATP - Energy Currency

To perform metabolic reactions, cell requires energy. This energy is stored and transported in the cells by a chemical called adenosine triphosphate (ATP). The chemical structure of ATP consists of the following:

  • Adenine
  • Ribose
  • Triphosphate (three phosphate groups)

When the terminal phosphate bond is cut, energy is released and ATP is converted to ADP and an inorganic phosphate, Pi.

During cell respiration, ATP is regenerated.

ATP operates similarly to a rechargeable battery. It stores energy in its chemical bonds which are used by the cell as needed.

Metabolic Pathways

Metabolic reactions typically occur as multiple steps. These steps are called:

Linear Pathway
Glycolysis is an example.
Branched Pathway
In the synthesis of amino acids, a single substrate may result in the synthesis of multiple products.
Cyclic Pathway
During cellular respiration, the Krebs cycle is an example. The last substrate in the cycle is the same as the first substrate.

For the maintenance of an internal stable (physiological) environment, metabolism is controlled.

  • Feedback inhibition occurs when the end product of a metabolic pathway inhibits an enzyme that acts at an early step in the pathway.
  • Allosteric regulation = the enhancement or suppression of enzyme activity by binding to sites other than the active site.

Enzyme Kinetics

Enzyme activity can be measured by using the Michaelis-Menten kinetics.

Vmax = The rate of reaction when all active sites are occupied.

Km = Michaelis constant. The substrate concentration when the reaction rate is half of the Vmax. This indicates the affinity of the enzyme for the substrate.

  • Low Km = high affinity → Substrate binds easily.
  • High Km = low affinity → More substrate is needed to reach half of the Vmax.

Scientists can understand how enzymes work along with the effect of inhibitors by plotting enzyme activity against substrate concentration.

Coenzymes and Cofactors

These are some of the other molecules that some enzymes need to work properly:

Cofactors

These are non-protein, inorganic molecules, such as ions of Mg²⁺, Zn²⁺.

Coenzymes

These are organic molecules, often derived from vitamins, that are involved with the enzyme's activity, such as NAD⁺ and FAD in cellular respiration.

These molecules play an important role in the stabilization of substrates or the transfer of groups or electrons.

Enzyme Regulation in Metabolism

Enzymes are of different types, and the cell regulates them to conserve energy and resources. The major ways in which enzymes have been regulated are described below:

  • Gene Regulation: This is when enzymes are synthesized only when required.
  • Allosteric Regulation: This is when molecules bind to an inactive site of the enzyme to change the enzyme's activity.
  • Covalent Modification: This is when enzymes are activated or inactivated through the addition or removal of certain chemical groups like phosphate.
  • Compartmentalization: This is when certain reactions are restricted to certain organelles to avoid interference from other reactions.

Enzyme Metabolic Process Examples

Photosynthesis

Enzymes turn water and carbon dioxide into glucose.

Example: Rubisco does the catalyzing of the CO2 fixation during the Calvin Cycle.

Cellular Respiration

  • End products of glycolysis are pyruvate and glucose.
  • During the Krebs cycle, pyruvate is converted to carbon dioxide and ATP.
  • The final process of cellular respiration involves the electron transport chain, in which, ATP is produced from the energy molecules, NADH and FADH2.

Digestion

  • Amylase enzyme turns starch into maltose.
  • Lipase breaks down lipids into fatty acids and glycerol.
  • Protease enzyme catalyzes the breakdown of proteins into amino acids.

CONCLUSION

  • Enzymes are biological catalysts.
  • Enzymes speed up reactions by lowering the energy needed to get the reaction started.
  • Each enzyme only works for one specific reaction.
  • Enzymes work at their own optimum temperature and optimum pH.
  • Enzymes can be inhibited or turned off.
  • Your metabolism is all the chemical reactions that take place in your body.
  • Catabolic reactions release energy.
  • Anabolic reactions use energy.
  • ATP is your body's energy currency.
  • Metabolic pathways can be: Linear, Branched, Cyclic.
  • Metabolic pathways are precisely regulated by the cells to provide for the needs of the organism.
  • The speed and direction of chemical reactions during metabolism is controlled by a combination of factors: enzyme kinetics, cofactors, coenzymes, inhibitors.
  • Fundamental to an understanding of life processes and living systems is the study of metabolism and enzymes. Study of metabolism and enzymes help us understand how energy is obtained by the cells, how are molecules constructed by the cells, and how life is sustained.