Bio Unit 1.4 - Enzymes and Biological Reactions Flashcards
What are metabolic pathways controlled by?
Enzymes
Anabolic Reaction
Building up of molecules (protein synthesis)
Catabolic Reactions
Breaking molecules down (digestion)
What are enzymes?
Globular proteins that acts as a biological catalyst - alters rate of chemical reactions without being used up by the reaction
What is the structure of an enzyme?
Tertiary structure - folded into globular shape, hydrophilic R groups on outside making enzymes soluble
What determines the bonds the amino acids make with each other in enzymes?
Elements in R groups
What bonds can form between amino acids in enzymes?
Hydrogen bonds, disulphide bridges, ionic bonds
Three sites where enzymes act
Extracellular, Intracellular in solution, Intracellular membrane bound
How do enzymes act extracellularly?
Some enzymes are secreted from cells by exocytosis and catalyse extracellular reactions
Examples of enzymes acting intracellular in solution?
Glucose breakdown in glycolisis
Example of enzymes acting intracellular membrane bound
Cristae of mitochondria, grant of chloroplasts (transfer electrons and hydrogen ions in ATP formation)
Induced Fit Model
Change in shape of the active site induced by the entry of the substrate so the enzyme and substrate can bond temporarily
Activation Energy
Minimum energy required for molecules to react, breaking existing bonds in reactants and making new ones in the products
How do you increase rate of reaction?
Increase kinetic energy to make successful collisions more likely
How do enzymes make sure reaction requires lower activation energy?
Modifying substrate allowing reaction to occur at lower temperatures
How do temperature and PH affect enzyme action?
Change three dimensional structure of enzymes, bonds are broken and configuration of active site altered
How does concentration affect enzyme activity?
Changes number of enzyme-substrate complexes formed
How does temperature above 40 degrees change enzyme activity?
Molecules have more kinetic energy but rate of reaction goes down, increasing vibration breaks hydrogen bonds changing tertiary structure, altering active site shape, enzyme denatured
At low temperatures the enzyme is…
Inactivated
How does PH affect enzyme activity?
Charges of amino acid side chains on active site affected by hydrogen ions/hydroxide ions
What happens to enzymes at low PH?
Excess hydrogen ions are attracted to negative charges and neutralises them
What happens to enzymes at high PH?
Excess hydroxide ions neutralise the positive charges
How does excess H+/OH- ions change active site?
Disrupts ionic and hydrogen bonds maintaining active site shape and shape changes, denatured
What happens at low substrate concentration?
Enzyme molecules only have a few substrate molecules to collide with, active sites not working to full capacity
Concentration of substrate controls rate of reaction and is therefore…
Limiting factor
As enzyme concentration increases…
more active sites available so rate of reaction increases
Inhibitor
Molecule/ion that binds to an enzyme and reduces the rate of the reaction the enzyme catalyses
What shape do competitive inhibitors have?
A shape complementary to the active site of the enzyme and similar shape to the substrate (competes for active site)
Where do non competitive inhibitors bind and what do they do?
Allosteric Site, affects bond within enzyme molecule and its overall shape including active site
If the concentration of substrate increases what happens to the affect of the competitive inhibitor?
Lesser effect, more substrate molecules, greater chance of binding to an active site leaving fewer available to inhibitor
Examples of non competitive inhibitors?
Heavy metal ions like lead, As3+,Pb2+
Immobilised Enzyme
Enzyme molecules bound to an inert material over which the substrate molecules move
What do immobilising enzymes do?
Allows reactions to occur at higher temperatures/more extreme PHs than normal as trapping an enzyme prevents denaturing of active site
Where are immobilised enzymes used?
Fermentation, column can be used repeatedly
Advantages of immobilised enzymes
increased stability and function over a wider range of temperatures and PHs, enzymes are easily recovered, enzymes can be easily added/removed, greater control over reaction, products not contaminated with enzyme
Examples of where Immobilised Enzymes are used?
Lactose free milk, Biosensors, HFCS
