enzyme

Examples of enzyme 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 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).

• 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.

• Types and Functions of Proteins

  • These enzymes are essential for chemical processes like digestion and cellular metabolism.
  • Because form determines function, each enzyme is specific to its substrates.
  • When the substrate binds to its active site at the enzyme, the enzyme may help in its breakdown, rearrangement, or synthesis .
  • There are two basic classes of enzymes:
  • Anabolic enzymes: enzymes that build more complex molecules from their substrates

• Control of Catabolic Pathways

  • The control of glycolysis begins with the first enzyme in the pathway, hexokinase .
  • This enzyme catalyzes the phosphorylation of glucose, which helps to prepare the compound for cleavage in a later step.
  • Phosphofructokinase is the main enzyme controlled in glycolysis.
  • If no more energy is needed and alanine is in adequate supply, the enzyme is inhibited.
  • These enzymes are isocitrate dehydrogenase and α-ketoglutarate dehydrogenase.

• Lysosomes

  • If no food is provided, the lysosome's enzymes digest other organelles within the cell in order to obtain the necessary nutrients.
  • Lysosomes also use their hydrolytic enzymes to destroy pathogens (disease-causing organisms) that might enter the cell.
  • The lysosome's hydrolytic enzymes then destroy the pathogen .
  • A lysosome is composed of lipids, which make up the membrane, and proteins, which make up the enzymes within the membrane.
  • The general structure of a lysosome consists of a collection of enzymes surrounded by a single-layer membrane.

• Peroxisomes

  • A type of organelle found in both animal cells and plant cells, a peroxisome is a membrane-bound cellular organelle that contains mostly enzymes .
  • In contrast to the digestive enzymes found in lysosomes, the enzymes within peroxisomes serve to transfer hydrogen atoms from various molecules to oxygen, producing hydrogen peroxide (H2O2).
  • They produce large amounts of the toxic H2O2 in the process, but contain enzymes that convert H2O2 into water and oxygen.
  • Peroxisomes are membrane-bound organelles that contain an abundance of enzymes for detoxifying harmful substances and lipid metabolism.

• Pancreas

  • The pancreas produces digestive enzymes and hormones, which are important in blood sugar regulation and other body functions.
  • It contains both exocrine cells that excrete digestive enzymes and endocrine cells that release hormones.
  • As a digestive organ, the pancreas secretes pancreatic juice containing digestive enzymes that assist the absorption of nutrients and the digestion in the small intestine.
  • These enzymes help to further break down the carbohydrates, proteins, and lipids in the chyme.

• Cell Signaling and Cellular Metabolism

  • Firstly, the regulation of an enzyme in a pathway is how its activity is increased and decreased in response to signals.
  • Secondly, the control exerted by this enzyme is the effect that these changes in its activity have on the overall rate of the pathway.
  • For example, an enzyme may show large changes in activity (i.e. it is highly regulated), but if these changes have little effect on the rate of a metabolic pathway, then this enzyme is not involved in the control of the pathway.
  • Cyclic AMP activates PKA (protein kinase A), which in turn phosphorylates two enzymes.
  • When energy is needed, glycogen is quickly reconverted to glucose. ) Phosphorylation of the second enzyme, glycogen synthase (GS), inhibits its ability to form glycogen from glucose.

• The Energy-Releasing Steps of Glycolysis

  • In the seventh step, catalyzed by phosphoglycerate kinase (an enzyme named for the reverse reaction), 1,3-bisphosphoglycerate donates a high-energy phosphate to ADP, forming one molecule of ATP.
  • The enzyme catalyzing this step is a mutase (isomerase).
  • This enzyme causes 2-phosphoglycerate to lose water from its structure; this is a dehydration reaction, resulting in the formation of a double bond that increases the potential energy in the remaining phosphate bond and produces phosphoenolpyruvate (PEP).
  • The last step in glycolysis is catalyzed by the enzyme pyruvate kinase (the enzyme in this case is named for the reverse reaction of pyruvate's conversion into PEP) and results in the production of a second ATP molecule by substrate-level phosphorylation and the compound pyruvic acid (or its salt form, pyruvate).
  • Many enzymes in enzymatic pathways are named for the reverse reactions since the enzyme can catalyze both forward and reverse reactions (these may have been described initially by the reverse reaction that takes place in vitro, under non-physiological conditions).