4.1 - 4.4 - Enzyme Action, Inhibators, Factors Affecting Activity , Cofactors,coenzymes & Prosthetic Groups Flashcards
(53 cards)
What are enzymes?
proteins that act as biological catalysts for intra & extracellular reactions to determine structure and function
What type of proteins are enzymes?
They’re Globular proteins that interact with substrate molecules causing them to react at much faster rates without the need for harsh environmental conditions
What type of a structure do enzymes have ?
Tertiary structure
What are intracellular and extracellular enzymes and what are some examples?
Intracellular - produced and function inside the cell eg. Respiration, photosynthesis, glycogen and protein synthesis
Extracellular - secreted by cells and catalyse reactions outside the cells
Eg. Bacteria and fungi , decomposer organisms
What is the process of the intracellular enzyme catalase ?
• hydrogen peroxide is produced as a by product of many metabolic reactions
• harmful to cells
• catalase converts hydrogen peroxide into water and oxygen preventing any damage to cells or tissues
What is the process of the extracellular enzyme amylase ?
• digestion is usually carried out by extracellular enzymes
• due to the fact that the macromolecules being digested are too large to enter the cell
• amylase is involved in carbohydrate digestion it hydrolyses starch into simple sugars
• secreted by the salivary glands and pancreas for digestion of starch in the mouth and small intestine
Explain the induced fit model of enzyme action
• in this model the enzyme and substrate interact with each other
• the enzyme and it’s active site can change shape slightly as the substrate molecule enters the enzyme
• these changes in shape are called conformational changes
• conformational changes ensure an idea of ideal binding arrangement between the enzyme and substrate is achieved
• this maximises the ability of the enzyme to catalyse the reaction
• the initial interaction between the enzyme and substrate is relatively weak but these weak interactions rapidly induce changes in the enzymes in tertiary structure
• that strengthen binding puts a strain on the substrate molecule - weakens bonds in the substrate - lowering activation energy
Explain the lock and key model of enzyme action
• suggests that active site has a rigid shape determined by the tertiary structure
• thus is only complimentary to 1 substrate
• formation of ES complex lowers activation energy
• bonds in enzyme product complex are weak do product desorbs
Name 5 factors that affect the rate of enzyme-controlled reactions
• enzyme concentration
• substrate concentration
• concentration of inhibitors
• pH
• temperature
What is enzyme specificity?
The specificity of an enzyme is a result of the complimentary nature between the shape of the active site on the enzyme and it’s substrate
How does substrate concentration affect rate of reaction?
•Given that enzyme concentration is fixed = rate increases proportionally to substrate concentration
• the rate levels off when maximum number of ES complexes form at any given time
How does enzyme concentration affect rate of reaction?
•Given that substrate is in excess = rate increases proportionally to enzyme concentration
• rate levels off when maximum number of ES complexes form at any given time
How does temperature affect the rate of enzyme controlled reactions?
•Rate increases as kinetic energy increases & peaks at optimum temperature
• above optimum , ionic & H bonds in 3° structures break = active site is no longer complimentary to substrate (denaturation)
What is the temperature coefficient?
Q10 measures the change in rate of reactions per 10°c temperature increase
Q10 = R2/R1 ( wheee R represents Rate )
How does ph affect the rate of reaction?
Enzymes have a narrow optimum pH range
Outside range , H+/ OH- ions interact with H- bonds and ionic bonds in 3° structure = denaturation
What is activation energy?
Amount of energy required by the substrate to become just unstable enough for a reaction to occur and for products to be formed
What is denaturation?
• when temperatures are too high the increased kinetic energy and vibration of the enzyme molecules put a strain on them - causing the weaker hydrogen and ionic bonds that hold the enzyme molecule in its precise shape to start to break
• breaking of bonds = tertiary structure of protein to change = active site is permanently damaged = shape Is no longer complementary to the substrate = preventing the substrate from binding
How do competitive inhibitors work?
- Bind to active site since they have similar shape to substrate
- Temporarily prevent ES complexes from forming until released
- Increasing substrate concentration decreases their effect
How do non-competitive inhibitors work?
- Bond at allosteric binding site
- Trigger conformational change of active site
- Increasing substrate concentration has no impact on their effect
What is end-product inhibition ?
•One of the products of a reaction acts as a competitive or non competitive inhibitor for an enzyme involved in the pathway
• prevents further formation of products
What are irreversible inhibitors?
• permanently prevent formation of ES Complexes
• heavy metal ions eg. Mercury, silver cause disulphide bonds in tertiary structure to break
• bind to enzymes by strong covalent bonds eg. Cyanide binds to cytochrome
What are reversible inhibitors?
May be competitive or-non-competitive
• bond to enzyme temporarily eg. By H- bonds or a few ionic bonds
• ES complexes can firm after the inhibitor is released
Define metabolic Poison
Substance that damages cells by interfering with metabolic reactions , usually an inhibitor
Give some examples of metabolic poisons
Respiratory inhibitors include :
• cyanide- non competitive, irreversible, inhibits cytochrome c oxidase
• malonate - competitive, inhibits succinate dehydrogenase
• arsenic - competitive, inhibits pyruvate dehydrogenase
