ENZYMES Flashcards
Enzymes definition
-Biological catalysts that speed up metabolic reactions
-They are globular proteins
The lock and key model
-The enzyme site is exactly complimentary to the substrate
-The substrate fits into the enzymes active site, to form an enzyme-substrate complex
-The enzyme then breaks down the substrate to form an enzyme-product complex
-The product no longer fits into the active site so it is released
The induced fit model
-Rather than being an exact fit, the active site of the enzyme very closesly matches the shape of the substrate
-The enzyme’s active site can mould itself around the substrate, forming a precise fit.
-Since the active site is flexible, the enzyme is able to put pressure on the substrate, and break particular bonds :. lowering the activation energy
-Once the products are released, the enzyme’s active site returns to it’s original shape
Coenzymes
-Type of cofactor
-Non-protein, organic molecules necessary for enzyme action
-They are not permenantly attached
-Important in the biochemistry of respiration and photosynthesis
-Conezymes NAD and FAD act as hydrogen acceptors in respiration
The effect of substrate concentration on the rate of reaction
-Rate of reaction increases as substate concentration increases. Substrate molecules all occupy active sites and substrate availability limits the rate of reaction with some active sites unused
-The addition of more substrate molecules has no effect as all of the active sites are in use. Number of enzyme active sites limits the rate of reaction
The effect of enxyme concentration on the rate of reaction
-As more enzymes and active sites become available more enzyme-substrate complexes can form and reactions take place
-Enzyme activity levels off as the number of substrate molecules becomes limiting
-Normally in living systems, acitvity continues to increase as substrate is seldom limiting
The effect of temperature on the rate of reaction
-Increasing temperature gives both the enzume and the substrate more kinetic energy (molecules are moving faster :. higher chance of collision)
-Once the temperature reaches above the optimum, this causes some bonds to break, as temperature increases, more and more bonds get broken and the shape of the enzyme’s active site changes
-Around 60’ the damage is so great that the enzyme is denatured
The effect of pH on the rate of reaction
-At either side of the optimum pH, changes in pH wil reduce activity (chnages in the pH disrupting the bonds that determine the shape of the enzyme’s active site)
-Ionic bonds in particular are subject to disruption at non-optimal pH’s
-The further the pH is from the optimum, the greater the degree of disruption is, until eventually denaturatin results
Competitive inhibitors
-The inhibitor substance competes with the usual substrate for the active site
-If the amount of inhibitors is low, it will have little to no effect, but if it is high, it can significantly affect enzyme activity
Non-competitive inhibitors
-Inhibitor attaches itself to a part of the enzyme other than the active site
-The presence of the non-competitive inhibitor leads to the active site changing shape so that it is no longer complimentary to the substrate
-Increase of subtrate concentration does not reduce the effect of the inhibitor, but the number of functioning enzymes has been reduced
Enzymes as biomarkers of disease
ELASTASE
-Enzyme released by white blood cells as a consequence of lung infection (breaks down the protein elastin, an important component of lung tissue which helps the lung tissue strech and recoil.
Elastase-induced emphysema
-Normally elastin is not broken down as the elastate inhibitor (alpha-1-antitrypsin) prevents elastate activity once the infection has been cleared.
-However cigarette smoke causes too much elastase to be released in the lungs and there is not enough inhibitor present to control the elastase
-Therefore the elastin in the alveoli is broken down eventually resulting in elastase-induced emphysema
For enzyme inhibitors to be effective as therapeutic drugs they need to be…
-Specific in that they will only target an enzyme involved in disease progression
-Able to work well at low doses (to prevent a buildup of the inhibitor to levels which may be toxic)
ACE inhibitors
-Angiotensin converting enzymes can be used to treat high blood pressure
-They work by inhibiting an enzyme that leads to the constriction of blood vessels
Penicillin
-Work by inhibiting enzymes involved in cell wall formation in bacteria
-Some antiviral drugs inhibit the DNA/RNA polymerases essential in viral replication
