Chapter 4 - Enzymes Flashcards
Enzymes
➜ biological catalysts
➜ globular proteins - complex tertiary structures
➜ Metabolic pathways
➜ All enzymes are proteins that are produced via the process of protein synthesis inside cells
➼ intracellular and extracellular
Intracellular enzymes
➜ reactions inside cell
➜ could be part of a metabolic pathway (involve a series of small steps, each step involves a chemical change)
➜ e.g catalase
Catalase
➼ intracellular example
➼ hydrogen peroxide is the toxic by-product of several cellular reactions
➼ if left to build up, it can kill cells
➼ works inside cells to catalyse the breakdown of hydrogen peroxide to harmless oxygen and water
Extracellular enzymes
➜ reactions outside the cell
➜ where enzymes have been secreted outside cell
➜ amylase, trypsin
Amylase
➼ extracellular example - digestion
➼ work outside cells in digestive system
➼ macromolecules being digested are too large to enter cell
➼ amylase is found in saliva - secreted in the mouth by cells in the salivary glands - hydrolyses starch into simple sugar
-catalyses the hydrolysis of starch into maltose in the mouth
-produced by cells in pancreas and salivary glands and used for digestion of starch in mouth and small intestine
Trypsin
➼ extracellular example - digestion
➼ work outside cells in digestive system
➼ trypsin catalyses the hydrolysis of peptide bonds - turning proteins into peptides and amino acids
- secreted by the pancreas and enters the small intestine
Anabolic pathways
➜ energy is used to synthesise larger molecules from smaller ones
Catabolic pathways
➜ metabolites are broken down to smaller molecules and energy is released
Cofactors
some enzymes need a small non protein molecule to attach to them so that they can catalyse certain reactions
➼inorganic Ions
➼help to stabilise the structure of the enzyme or may actually take part in the reaction at the active site
➼ are not used up or changed in any way (don’t directly participate)
➼ CI- are cofactors for amylase
Coenzyme (carbon containing)
➜ organic non-protein cofactors
➜ some coenzymes are permanently bound to the enzyme and some coenzymes only bind temporarily during the reaction to assist in catalysing reaction
➜ vitamins = important source of coenzymes
➜ e.g pantothenic acid - key component for coenzyme A, Nicotinic acid, NAD & NADP, FAD
Cosubstrate
cofactor that works with the substrate to form the correct shape to bind to the active site
Prosthetic group
- non protein compound
➜ type of cofactor that is permanently covalently bonded to an enzymes active site
➜ essential to the enzyme functioning properly, as they help to form the final 3D shape
➼eg. Zn2+ are a prosthetic group for carbonic anhydrase
Competitive Inhibitor
➜ have similar shape to substrate
➜ fit into active site forming enzyme inhibitor complex - no reaction takes place
➜ no substrate molecules can fit in
Samiras part i dont understand a word:
➼ high conc of the inhibitor, it will take up nearly all the active sites and hardly any of the substrate will get to the enzyme
➼ higher conc of substrate, substrate chance of getting to active site before the inhibitor will increase
Non-competitive Inhibitor
➜ bind to enzyme away from active site
↳ this area is called the allosteric site
➜ causes active site shape to change
➜ substrate can no longer fit
➜ increasing conc of substrate makes no difference as non comp inhibitors don’t compete with substrate
Factors affecting enzyme activity
➼ temp
➼ pH
➼ substrate conc
➼ enzyme conc
Substrate Concentration
➜ ↑ substrate conc, then ROR ↑ so MORE collisions and more active sites used
➜ more enzyme-substrate complexes are formed.
➜ substrate conc = limiting factor = saturation point where active sites are full
➜ certain point, rate of reaction plateaus
Enzyme Concentration
➜ higher the conc = greater number of active sites so higher chance of enzyme-substrate complex formed
➜ sufficient substrate available = initial rate of reaction increases linearly with enzyme concentration
➜ if substrate limited then = limiting factor
Temperature
- ↑ temp, up to optium, then rate of reaction ↑
↳ ↑ kinetic energy
➼ more successful collisions between the substrate and active site
➼ more successful collisions = more enzyme-substrate complex - ↑ temp above optimum, then rate of reaction ↓ sharply
➼ vibration breaks some of the bonds (hydrogen and ionic bonds)
➼ active site shape changes permanently (as tertiary structure changes)
➼ enzyme denatures - substrate can no longer bind - rate of reaction = 0 = when all enzymes denatured
Temperature coefficient
Temperature coefficient = (rate of reaction at (x + 10) °C) ÷ (rate of reaction at x °C)
Enzyme Substrate Complex
If a substrate successfully collides with enzyme
➼ formation of this enzyme substrate complex lowers activation energy
⤥ ↬ if the enzyme is catalysing a breakdown reaction, fitting into active site puts a strain on bonds in the substrate
↬ substrate molecule breaks up more easily
pH
- pH above or below optimum then rate of reaction ↓
- the H⁺ and OH⁻ ions found in acids and alkalis mess up ionic bonds and H bonds that hold the tertiary structure in place
↳ Enzymes denature and active site changes shape due to breaking of bonds - complementary substrate can no longer bind to active site
Buffer solutions
➼ each have specific pH
➜ maintain specific pH even when reaction is taking place (reactions can change pH)
➜ a measured vol of buffer solution is added to reaction mixture
➜ same vol (of each buffer) should be added for each pH val being investigated
Conc of Inhibitors
Competitive:
• ↑ substrate conc, then ↓ effect of inhibitor
• ↑ inhibitor conc, then ↓ effect of substrate
Non competitive:
• ↑ substrate conc has no effect on rate of reaction as there is a permanent change to active site
- and also inhibitor doesn’t bind to active site
Competitive inhibitors (reversible)
➜ a similar shape to that of the substrate molecules and therefore compete with the substrate for the active site
Non-competitive inhibitors (irreversible)
➜ bind to the enzyme at the allosteric site, which alters the shape of the active site and therefore prevents the substrate from binding to it
End product inhibition
➜ reversible inhibitors act as regulators in metabolic pathways
➜ metabolic reactions must be tightly controlled and balanced
➜ enzyme converts substrate to product so reaction slowed down as end product of reaction binds to an allosteric site on original shape
➜ this changes shape of active site = prevents formation of enzyme substrate complex
➜ end product detaches from enzyme and active site reforms so enzyme returns to active state
➜ this means as product levels fall, enzyme begins catalysing reactions again in a feedback loop
Non-reversible inhibitors
➜ some inhibitors form covalent bonds with enzymes, inhibiting them permanently
- known as non-reversible or irreversible inhibitors
➜ if occurs in a living cell or organism it will result in the complete inactivation of the enzyme
- dangerous: cause the biological reaction enzyme is catalysing will be stopped
➜ some non-reversible inhibitors are considered to be metabolic poisons
e.g cyanides, lead, mercury
➜ some inhibitors are beneficial in medical context like penicillin, aspirin
Enzyme Product Complex
substrate molecules are broken down or built up into the product
Lock and Key Hypothesis
➜ substrate only fit a specific enzyme
1890’s the first model of enzyme activity was described by Emil Fischer: suggested that both enzymes and substrates were rigid structures that locked into each other very precisely, much like a key going into a lock
* enzyme + substrate enter active site
* form enzyme substrate complex
* form enzyme product complex
* enzyme + product leave active site
Enzymes lowering Ae
➜ activation energy = minimum amount of energy needed for substrate to become unstable enough for reaction to occur
➜ enzymes speed up reactions = reduce stability of bonds in reactants = making it more reactive
Induced
➜ substrate can induce a change in the active site’s shape
* substrate entering active site of enzyme
* enzyme changes shape slightly as substrate binds (known as conformational changes) - ensures an ideal binding arrangement
* change in shape of active site weakens the bond in substrate
* form enzyme substrate complex
* form enzyme product complex
* products leave active site of enzyme
