4.1 - 4.4 - Enzyme Action, Inhibators, Factors Affecting Activity , Cofactors,coenzymes & Prosthetic Groups Flashcards
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
How do some medicinal drugs act as inhibitors?
Penicillin- non competitive inhibitor of transpeptidase to prevent formation of peptidoglycan cross-links in bacterial cell wall
Ritonavir - inhibits HIV protease to prevent assembly of new virions
What are inactive precursors in metabolic pathways?
•To prevent damage to cells, some enzymes in metabolic pathways are synthesised as inactive precursors eg. Proteases
• one part of the precursor acts an inhibitor
• ES complexes form when it is removed
What are coenzymes?
•Organic cofactors - do not bind permanently - often transport molecules or electrons between enzymes
• frequently derived from water- soluble vitamins
What are inorganic cofactors?
Facilitate temporary binding between substrate and enzyme
Often metal ions eg. Cl- is the cofactor for amylase
What are prosthetic groups?
Tightly bound cofactors act as permanent part of enzymes binding site
Give an example of a competitive inhibitor?
Statin
What is statin used in?
Synthesis of cholesterol
What is the alternative site that non-competitive inhibitors bind to?
Allosteric site
What is an example of an irreversible non- competitive inhibitor used in pesticides and herbicides?
Organophosphates
What is a inhibitor?
Molecules that prevent enzymes from carrying out their normal function of catalysis, it affects the binding of substrate to the enzymes
What is the process of competitive inhibition?
1 ) a molecule or part of a molecule that has a similar shape to the substrate of an enzyme can fit into the active site of the enzyme
2 ) this blocks the substrate from entering the active site , preventing the enzyme from catalysing the reaction
3 ) the enzyme cannot carry out its function and thus is said to be inhibited
4 ) the non substrate molecule that binds to the active site is a type of inhibitor
5 ) substrate and inhibitor molecules present in a solution will compete with each other to bind to the active sites of the enzymes catalysing the reaction
6 ) this will reduce the number of substrate molecules binding to the active sites in a given time and slows down the rate of reaction
What are competitive inhibitors?
Have a similar shape to that of the substrate molecules and there fore compete with the substrate for the active site
What are non-competitive inhibitors?
Bind to the enzyme at an alternative site, which alters the shape of the active site and therefore prevents the substrate from binding to it
What happens when you increase the concentration of an inhibitor?
Reduces the rate of reaction and if the inhibitor concentration continues to be increased the reaction will stop completely
In non competitive inhibition what happens when you increase the substrate concentration?
This cannot increase the rate of reaction once more as the shape of the active site of the enzyme remains changed and enzyme - substrate complexes are still unable to form
What do reversible inhibitors act as?
Regulators in metabolic pathways
How can metabolic reactions be controlled?
By using the end product of a particular sequence of metabolicreactions as a non-competitive, reversible inhibitor
How does non-competitive inhibition work?
1) the inhibitor binds to the enzyme at a location other than the active site
- this alternative site is called an allosteric site
2) the binding of the inhibitor causes the Tertiary structure of the enzyme to change - meaning the active site changes shape
3) this results in the active site no longer having a complementary shalt to the substrate so it is unable to bind to the enzyme
4 ) the enzyme cannot carry out its function and is said to be inhibited
What is PPIs ? and what do they do ?
-Proton pump inhibitors
- used to treat long term indigestion
- they irreversibly block an enzyme system responsible for secreting hydrogen ions into the stomach
What is end-product inhibition?
Occurs when the product of a reaction acts as an inhibitor to the enzyme that produces it
What is PFK?
Phosphofructokinase
Give 3 examples of non-reversible inhibitors as medicinal drugs
1) penicillin
2) Aspirin
3) eflornithine
What is a cofactor ?
A non protein that is obtained via the diet as minerals that transfer atoms or groups from one reaction to the other in a multi-step pathway or form part of the active site on the enzyme
What is precursor activation ?
Precursor enzymes need to undergo a process of change in order to be activated - this involve the addition of a cofactor
How are inorganic cofactors obtained ?
Via minerals
How are organic coenzymes obtained ?
Via vitamins
Are prosthetic groups cofactors or coenzymes ?
Cofactor
What is another name or a precursor protein ?
Apoenzyme
Explain what is meant by the term Vmax with respect to enzymes
The reaction is at a maximum rate and all active sites are occupied and enzyme activity is at a maximum
