Factors Affecting Enzyme Activity Flashcards
Temperature
Increased temp=increased kinetic energy of particles. Particles move faster and collide more frequently. In an enzyme-controlled reaction an increase in temp will result in more successful collisions between substrate and enzyme. Increased rate of reaction.
The temperature coefficient, Q10, of a reaction is a measure of how much the rate of reaction increases with a 10 degree Celsius rise in temperature. For enzyme-controlled reactions this is usually taken as two, which means that the rate of reaction doubles with a 10 degree Celsius increase.
Denaturation from temperature
As enzymes are proteins their structure is affected by temperature, higher temperature, bonds holding the protein together will vibrate more. As temp increases the vibrations increase until the bonds strain and then break. Results in a change in the precise tertiary structure of the protein. Enzyme has denatured. When an enzyme is denatured active site changes shape and is no longer complementary to substrate. The substrate can no longer fit into the active sites and the enzyme will no longer function as a catalyst.
Optimum temperature
Optimum temp is highest rate of enzyme activity. Can vary. Around 40 degrees in human body, meanwhile thermophilic bacteria (found in hot springs) have enzymes with optimum temperatures of 70 degrees, and psychrophilic organisms (live in cold areas like Antarctic) have enzymes with optimum temp below 5 degrees.
Rapid decrease in rate of reaction after denaturation- temperature coefficient Q10 does no apply any more as enzymes have denatured.
Temperature extremes
Examples of extremely cold environments are deep oceans, high altitudes, and polar regions. The enzymes controlling the metabolic activities of organisms living in these environments need to be adapted to the cold. Enzymes adapted to the cold tend to have more flexible structures, particularly at the active site, making them less stable than enzymes that work at higher temperatures. Smaller temperature changes will denature them.
Thermophiles are organisms adapted to living in very hot environments such as hot springs and deep sea hydrothermal vents. Enzymes more stable due to the increased number of bonds, particularly hydrogen bonds and sulfur bridges, in their tertiary structure. The shapes of these enzymes, and their active sites, are more resistant to change as temperature rises.
pH
Hydrogen bonds and ionic bonds between amino acid R-groups hold proteins in their precise three dimensional shape. These bonds result from interactions between the polar and charged R-groups present on the amino acids forming the primary structure. A change in pH refers to a change in hydrogen ion concentration. More hydrogen ions are present in low pH (acid) environments and fewer are present in high pH (alkaline) environments.
The active site will only be in the right shape at a certain hydrogen concentration. This is optimum pH, altered active site if pH change. However if pH returns to optimum then protein will resume its normal shape- this is called renaturation.
What happens if pH changes more significantly
The structure of the enzyme is irreversibly altered and the active site will no longer be complementary to the substrate. The enzyme is now said to be denatured and substrates can no longer bind to the active sites. This will reduce the rate of reaction.
How do hydrogen ions interact with polar and charged R-groups
Changing concentration of hydrogen ions therefore changes degree of this interaction. The interaction of R-groups with hydrogen ions also affects the interaction of R-groups with each other.
The more hydrogen ions present (low pH) the less the R-groups are able to interact with each other. This leads to bonds breaking and the shape of the enzyme changing. The reverse is true when fewer hydrogen ions (high pH) are present. This means the shape of an enzyme will change as the pH changes and therefore it will function with a narrow pH.
Substrate and enzyme concentration
Higher collision rate with active sites. Formation of more enzyme-substrate complexes. Rate increases. Same for if conc of enzyme increases.
The rate of reaction increases up to its maximum V max. At this point all of the active sites are occupied by substrate particles and no more enzyme-substrate complexes can be formed until products are released from active sites.
