Enzymes Flashcards
look back through notes for equations and graphs.
What are enzymes?
Biological catalysts
Increase rate of reaction by lowering Ea.
Globular proteins. Hydrophilic amino acids on outside and hydrophobic amino acids on the inside. Therefore, soluble in water.
How do enzymes catalyse?
Substrate matches active site.
enzyme substrate complex.
substrate binds, amino acids on surface form temporary bonds.
Enzyme then catalyses to form enzyme product complex.
Product is then released.
Co factors, co enzymes and prosthetic groups
co factors - small inorganic molecules which help the enzymes catalyse.
co enzymes - large organic molecules which help the enzyme catalyse. Can move between different enzymes. it is loosely bound.
prosthetic groups - tightly bound. Cofactor permanent part of the enzyme structure.
The complete catalytically active enzyme bound to its cofactor/coenzyme is known as the Haloenzyme.
Lock and Key model
E.fisher 1890
weak chemical bonds form between enzyme and substrate
lock and key
Induced fit model
D.E Koshland, 1958
more accurate model
substrate binding causes enzyme to change (known as conformational change).
Anabolism
Catalysed by anabolic enzymes.
-requires energy
-Biosynthetic
-involves formation of bonds between molecules.
-involves dehydration synthesis
-endogernic, takes up more energy than it releases.
Catabolism
catalysed by catabolic enzymes
-doesn’t require energy -degradative
-breaking of bonds between molecules.
-involves hydrolytic reactions, uses water to break bonds. e.g. digestion of carbs
exergonic, produces more energy than it consumes.
cellular metabolism
consume food: proteins, carbs, fats, nucleic acids
these are broken into simpler molecules respectively; amino acids, glucose, fatty acids, nucleotides.
broken down molecules use anabolism to build molecule.
Anabolism requires ATP, which is released when ATP breaks down to ADP.
ADP is then restored back to ATP through the smaller molecules breaking down even more to provide energy for it to build back up.
enzyme kinetics
study of rates of chemical reactions that are catalysed by enzymes.
what does the michealis menten equation (1913) show?
- how enzymes can increase the rate of metabolic reactions
- how reaction rate depends on concentration of enzyme and substrate.
saturation effect of enzymes
decrease in [S], rate/velocity, is proportional to [s].
As [s] increases, reaction rate decreases. further increase in [s], reaction rate becomes constant and independent, enzyme is now fully saturated. (imagine graph where reaction rate is affected by [s].
why is michealis menten constant (kM) significant?
- same unit of the substrate
- km = [S] at 1/2 vmax meaning when [s] is at half maximal velocity in the reaction.
-measure of enzymes affinity; higher km lower affinity
-strength of binding; lower km stronger the binding
-indicates enzyme can recognise lowest concentration of substrate before catalysis.
-describes substrate concentration saturation level at which half the enzymes active site is occupied.
significance of vmax
- gives us an idea of how fast reaction can occur under certain circumstances.
-turnover number of enzyme: how many number of substrates being catalysed per second.
competitive inhibitor
-reduces chances of substrate binding to enzyme.
-due to inhibitors similar structure to substrate.
-tries to fit he active site but fails, therefore decreasing frequency of substrate binding to enzyme.
-can be overcome by increasing substrate concentration.
-km increases no change in vmax.
non competitive inhibitor
-does not bind to active site but to allosteric site.
-affects the product formation but not the substrate binding.
-effect cannot be overcome by increasing substrate concentration
-may bind to free enzyme or ES complex.
-no change with km, however decrease in vmax.
