Enzymes And Biological Reactions 1.4 Flashcards
What are enzymes?
Biological catalysts that lower activation energy through the formation of enzyme-substrate complexes.
What is activation energy?
The minimum amount of energy needed to start a chemical reaction.
Describe the lock and key hypothesis
- active site is complementary in shape to the substrate
- the substrate is specific to the active site and fits into it.
- an enzyme-substrate complex is formed by temporary bonds
- products are released and enzyme remains unchanged and reusable.
Why can an enzyme only catalyse one type of chemical reaction?
The enzyme has a unique shape
How does the induced fit hypothesis differ to the lock and key model?
- the active site will change shape slightly to accommodate the substrate
- this puts a strain on the bonds in the substrate to lower its activation energy (as these bonds must be broken)
Give an example of an enzyme which supports the induced fit hypothesis
Lysozyme (an antibacterial enzyme found in human mucus saliva and tears.
What is metabolism?
All chemical reactions that occur in the body.
What are metabolic pathways?
The sequence of chemical reactions controlled by enzymes. This includes anabolic and catabolic reactions.
What is an anabolic reaction?
The building up of molecules
For example protein synthesis
What is a catabolic reaction?
Breaking down of molecules
For example digestion.
What are the properties of enzymes?
Biological catalysts so made of living cells.
Tertiary proteins with a globular structure
Soluble as it as the hydrophilic R-group in the outside.
Particular sequence of amino acids.
What are the three sites of enzyme action?
Extra cellular
Intercellular membrane bound
Intercellular in solution
Where do extracellular enzyme actions occur?
Outside the cell as they are secreted throughly exocytosis. For example amylase in digestion.
Where do intracellular /in solution enzymes work ?
I’m Inside the cell like in the stroma of chloroplasts catalyse the synthesis of glucose.
Where do intracellular /membrane bound enzymes work?
Inside the cell attached to a membrane. Like the cristae of mitochondria and grana of chloroplasts.
Why are enzymes soluble?
The hydrophilic R-group is on the outside of the enzyme
What bonds are present in enzymes.
- disulphide
- ionic
- hydrogen
- hydrophobic
- polypeptide
What factors affect the rate of enzymes reactions?
Substrate concentration
Temperature and PH
How does substrate concentration affect the rate of enzymes reactions?
Up to levelling off the higher the substrate concentration the higher the number of collisions between the enzyme and substrate so the rate increases.
Then it reaches saturation point and continues at a constant level as all active sites are occupied so maximum turn over rate has been reached for those conditions.
How does temperature affect the rate of enzyme action?
Rate increases as temperature increases until optimum temperature. This is because they have more kinetic energy so enzymes and substrate collide more frequently.
Above optimum temperature hydrogen bonds are broken so the shape of the active site changes cause inflation the enzyme to denature.
How does temperature affect the rate of enzyme action?
The rate of an enzyme catalysed reaction will vary with PH levels. Small changes in PH will cause small reversible changes in the enzymes structure causing inactivation. Extreme changes in PH will cause permanent changes to the enzyme structure causing it to denature.
How is enzyme action and enzyme concentration described as?
Directly proportional.
What is enzyme inhibition?
It is the decrease in the rate of an enzyme controlled reaction by an inhibitor.
What are the differences between competitive inhibition and noncompetitive inhibition?
Competitive inhibition is when the inhibitor goes into the active site and the active stays the same shape.
No competitive inhibition is when the inhibitor enters the allosteric site and changes the shape of the active site so that the substrate will no longer fit.