Enzymes Flashcards
What are enzymes ?
- Enzymes are biological catalysts made of proteins. They speed up reactions without being used up themselves by lowering the activation energy.
-Some of the essential reactions they catalyze include respiration, photosynthesis, protein synthesis, and digestion.
What is the structure of enzymes ?
- While enzymes are relatively large molecules, only a small part of the enzymes attaches to a substrate to catalyze a reaction. This site is known as the active site.
- The active site is specific and unique in shape due to the specific folding and bonding in the tertiary structure of the protein.
- Due to this specific active site, enzymes can only attach to substrates that are complementary in shape.
What are the mechanisms ?
- Induced fit
- Lock and key theory
What is the induced fit ?
Induced fit (remember glove) is when the enzyme active site is induced or slightly changes shape to mold around the substrate. When the enzyme-substrate complex occurs, due to the enzyme molding around the substrate, it puts strain on the bonds and therefore lowers the activation energy. The products are then removed, and the enzyme active site returns to its original shape.
What is the lock- key model ?
- This model suggests that the enzyme is like a lock and that the substrate is like a key that fits into it due to their complementarity in shape. This model suggests that the enzyme active site is a fixed shape and that due to random collision, the substrate can collide and attach to the enzyme. This forms an enzyme-substrate complex.
What are the types of enzymes?
- Intracellular
- Extracellular
What are intracellular enzymes ?
- Intracellular enzymes are within the cell
- For example catalase - breaks down hydrogen peroxide into water and oxygen (toxic) produced through metabolic reactions , would take too long if it was transported outside the cell.
What are extracellular enzymes ?
- Extracellular enzymes are realeased out of cell
- Two examples are Amylase and Tripsin
- Amylase - Starch to maltose , Tripsin - Proteins to nucleic acids
- Both must be released out due to digestion
What factors affect enzyme activity ?
- Temperature
- pH
- Enzyme/substrate concentration
How does temperature affect enzyme activity ?
- Enzymes have a specific optimum temperature
- This is the temperature at which they catalyse a reaction at the maximum rate
- Lower temperatures either prevent reactions from proceeding or slow them down because:
- Molecules move relatively slowly as they have less kinetic energy
- Less kinetic energy results in a lower frequency of successful collisions between substrate molecules and the active sites of the enzymes which leads to less frequent enzyme-substrate complex formation
- Substrates and enzymes also collide with less energy, making it less likely for bonds to be formed or broken (stopping the reaction from occurring)
- Higher temperatures cause reactions to speed up because:
- Molecules move more quickly as they have more kinetic energy
- Increased kinetic energy results in a higher frequency of successful collisions between substrate molecules and the active sites of the enzymes which leads to more frequent enzyme-substrate complex formation
- Substrates and enzymes also collide with more energy, making it more likely for bonds to be formed or broken (allowing the reaction to occur)
What is Denaturation ?
- If temperatures continue to increase past a certain point, the rate at which an enzyme catalyses a reaction drops sharply, as the enzyme begins to denature:
- The increased kinetic energy and vibration of the enzyme molecules puts a strain on them, eventually causing the weaker hydrogen and ionic bonds that hold the enzyme molecule in its precise shape to start to break
- The breaking of bonds causes the tertiary structure of the protein (i.e. the enzyme) to change
- The active site is permanently damaged and its shape is no longer complementary to the substrate, preventing the substrate from binding
- Denaturation has occurred if the substrate can no longer bind
What is the temperature coeffiecent ?
- The temperature coefficient for a biological reaction is the ratio between the rates of that reaction at two different temperatures
- For most enzyme-catalysed reactions the rate of the reaction doubles for every 10 °C increase in temperature
- The temperature coefficient (Q) for a reaction that follows this pattern is: Q₁₀ = 2
- The temperature coefficient can be calculated using the following equation:
- Temperature coefficient = (rate of reaction at (x + 10) °C) ÷ (rate of reaction at x °C)
How does pH affect enzyme activity ?
- pH = Partial concentration of ions
- higher pH (less H+) = alkaline
- lower pH (more H+) = acidic
- Protons can affect ionic and hydrogen bonds
- TOO much protons interact with polar and charged R groups of amino acids
- optimum pH changes due enzyme pepsin pH tripsin PH 8
How does substrate concentration affect enzyme activity ?
-The greater the substrate concentration, the higher the rate of reaction:
- As the number of substrate molecules increases, the likelihood of enzyme-substrate complex formation increases
- If the enzyme concentration remains fixed but the amount of substrate is increased past a certain point, however, all available active sites eventually become saturated and any further increase in substrate concentration will not increase the reaction rate
- When the active sites of the enzymes are all full, any substrate molecules that are added have nowhere to bind in order to form an enzyme-substrate complex
- For this reason, in the graph below there is a linear increase in reaction rate as substrate is added, which then plateaus when all active sites become occupied
How does enzyme concentration affect enzyme activity ?
- Enzyme concentration affects the rate of reaction
- The higher the enzyme concentration in a reaction mixture, the greater the number of active sites available and the greater the likelihood of enzyme-substrate complex formation
- As long as there is sufficient substrate available, the initial rate of reaction increases linearly with enzyme concentration
- If the amount of substrate is limited, at a certain point any further increase in enzyme concentration will not increase the reaction rate as the amount of substrate becomes a limiting factor
