enzymes

Examples of enzymes in the following topics:

• Control of Metabolism Through Enzyme Regulation

  • It "competes" with the substrate to bind to the enzyme.
  • The substrate can still bind to the enzyme, but the inhibitor changes the shape of the enzyme so it is no longer in optimal position to catalyze the reaction.
  • The availability of various cofactors and coenzymes regulates enzyme function.
  • Cells have evolved to use feedback inhibition to regulate enzyme activity in metabolism, by using the products of the enzymatic reactions to inhibit further enzyme activity.
  • Metabolic pathways are a series of reactions catalyzed by multiple enzymes.

• Enzyme Catalysis

  • However, catalysts are also found in nature in the form of enzymes.
  • One model of enzyme mechanism is called the induced fit model.
  • This model proposes that the binding of the reactant, or substrate, to the enzyme active site results in a conformational change to the enzyme.
  • An enzyme catalyzes a biochemical reaction by binding a substrate at the active site.
  • List the five typical mechanisms used by enzymes to catalyze biological reactions

• Enzyme Active Site and Substrate Specificity

  • Dramatic changes to the temperature and pH will eventually cause enzymes to denature.
  • As the enzyme and substrate come together, their interaction causes a mild shift in the enzyme's structure that confirms an ideal binding arrangement between the enzyme and the substrate.
  • When an enzyme binds its substrate, it forms an enzyme-substrate complex.
  • The enzyme will always return to its original state at the completion of the reaction.
  • After an enzyme is done catalyzing a reaction, it releases its products (substrates).

• Enzymes Used in Industry

  • Synthetic molecules, called artificial enzymes, also display enzyme-like catalysis.
  • Inhibitors can decrease enzyme activity; activators can increase activity.
  • Many drugs and poisons are enzyme inhibitors.
  • In addition, some household products use enzymes to speed up biochemical reactions (e.g., enzymes in biological washing powders break down protein or fat stains on clothes; enzymes in meat tenderizers break down proteins into smaller molecules, making the meat easier to chew).
  • Industrially-produced barley enzymes are widely used in the brewing process to substitute for the natural enzymes found in barley.

• Nonsteroidal Anti-Inflammatory Drugs

  • They prevent a particular enzyme from working in the body.
  • These enzymes are called cox 1 and cox 2 enzyme.
  • It is not selective and inhibit both enzymes, but vary at the levels it blocks the enzymes.
  • There are some NSAIDs that block the COX-2 enzyme more than the COX-1 enzyme, which prevents the cause of ulcers.
  • Depending on the NSAID, the inhibition of the COX enzymes varies.

• Regulatory Mechanisms for Cellular Respiration

  • Reactions that are catalyzed by only one enzyme can go to equilibrium, stalling the reaction.
  • A number of enzymes involved in each of the pathways (in particular, the enzyme catalyzing the first committed reaction of the pathway) are controlled by attachment of a molecule to an allosteric (non-active) site on the protein.
  • These regulators, known as allosteric effectors, may increase or decrease enzyme activity, depending on the prevailing conditions, altering the steric structure of the enzyme, usually affecting the configuration of the active site.
  • The attachment of a molecule to the allosteric site serves to send a signal to the enzyme, providing feedback.
  • This feedback type of control is effective as long as the chemical affecting it is bound to the enzyme.

• Molecular Products from Microbes

  • Taq polymerase is an enzyme that was first isolated from the microbe Thermus aquaticus.
  • Restriction enzymes are a specific class of enzymes isolated from various bacteria and archaea, in which they grow naturally as a means of protection against viral infection.
  • The enzymes have the ability to recognize foreign DNA and cut it up.
  • The bacteria and archaea from which these enzymes are isolated from have innate mechanisms to protect their own DNA sequences from these enzymes, such as methylation.
  • Describe how Taq polymerase, restriction enzymes and DNA ligase are used in molecular biology

• Pancreatic Juice

  • Pancreatic fluid contains digestive enzymes that help to further break down the carbohydrates, proteins, and lipids in the chyme.
  • These enzymes help to further break down the carbohydrates, proteins, and lipids in the chyme.
  • Pancreatic fluid or juice contains digestive enzymes that pass to the small intestine where they help to further break down the carbohydrates, proteins, and lipids (fats) in the chyme.
  • This is useful in neutralizing the acidic gastric acid, allowing for effective enzymic action.
  • Because the pancreas is a sort of storage depot for digestive enzymes, injury to the pancreas is potentially fatal.

• Carboxysomes

  • Carboxysomes are intracellular structures that contain enzymes involved in carbon fixation and found in many autotrophic bacteria.
  • They are proteinaceous structures resembling phage heads in their morphology; they contain the enzymes of carbon dioxide fixation in these organisms.
  • Similar structures are known to harbor the B12-containing coenzyme glycerol dehydratase, the key enzyme of glycerol fermentation to 1,3-propanediol, in some Enterobacteriaceae, such as Salmonella.
  • Carboxysomes are bacterial microcompartments that contain enzymes involved in carbon fixation.
  • These compartments are thought to concentrate carbon dioxide to overcome the inefficiency of RuBisCo (ribulose bisphosphate carboxylase/oxygenase) - the predominant enzyme in carbon fixation and the rate limiting enzyme in the Calvin cycle.

• Chemical Digestion of Carbohydrates, Proteins, Lipids, and Nucleic Acids

  • Chemical breakdown of macromolecules contained in food is completed by various enzymes produced in the digestive system.
  • These enzymes break down food proteins into polypeptides, which are then broken down by various exopeptidases and dipeptidases into amino acids.
  • The digestive enzymes, however, are secreted mainly as their inactive precursors, the zymogens.
  • Sucrase is an enzyme that breaks down disaccharide sucrose, commonly known as table sugar, cane sugar, or beet sugar.
  • Lactase is an enzyme that breaks down the disaccharide lactose into its component parts, glucose and galactose, which can also be absorbed by the small intestine.