Chapter 4- Enzymes Flashcards
(31 cards)
Define an enzyme
A biological catalyst
What does anabolic mean?
Synthesis reactions (building up)
What is the opposite of anabolic?
Catabolic (breaking down)
What is the maximum rate of enzyme reactions called?
The vMax (maximum initial velocity)
Define enzyme specificity
Each enzyme catalyses a specific reaction
What is the activation energy?
The minimum amount of energy needed for a reaction to start- enzymes help molecules successfully collide and reduce activation energy
What are the two hypotheses about enzyme activity?
Lock and key- the substrate molecule is already the exact shape of the active site to form an enzyme substrate complex
Induced fit- although initial reaction is weak, changes are induced in the enzymes molecular structure that tightens the fit of the substrate
Give an example of an intercellular enzyme
Catalase breaks down hydrogen peroxide into oxygen and water
Give two examples of extracellular enzymes used in digestion
Amylase and trypsin
What is the purpose of extracellular enzymes in eukaryotes?
Extracellular enzymes break down organic molecules that are too large to enter the cell (proteins, polysaccharides)
Describe the breakdown of starch
1 Starch polymers are partially broken down into maltose (disaccharide) by amylase
2 Maltose is further broken down into glucose by maltose
3 Glucose is small enough to be absorbed into cells
Describe the digestion of proteins
Trypsin catalyses the digestion of proteins into smaller peptides
Peptides are further broken down into amino acids by other proteases
What does the temperature coefficient measure?
Measure of how much the rate of reaction increases with a 10 degree rise in temperature
Why does temperature increase the rate of reaction in enzymes?
Gives particles more kinetic energy, they move more and are more likely to successfully collide
How can temperature limit the rate of enzyme activity?
Because the bonds holding the protein together are affected and break, changing tertiary structure- this denatures the enzyme as it no longer fits to its specific active site
Define optimum temperature in enzyme activity
The temperature at which the enzyme has the highest rate of reaction increases
Why are enzymes affected by pH?
A change in pH refers to a change in the concentration of hydrogen ions (more in acidic, less in alkaline)
Hydrogen ions interact with the polar and charged R groups and change their relationship to eachothet, effecting the shape
What is the less obvious factor that has an effect on enzyme activity?
Substrate and enzyme concentration- if there is more enzymes than substrates the reaction will happen quickly but the opposite is also true. Rate of reaction increases up to the vMax
Define an inhibitor
A molecule that prevents enzymes from carrying out their normal function
What are the two types of inhibitor?
Competitive- blocks the active site to prevent substrates from joining
non competitive - joins the allosteric site and changes the tertiary structure so the substrate no longer fits the active site
Why are non competitive inhibitors normally irreversible? Give an example
They can’t be removed from their enzyme
Protein Pump Inhibitors treat indigestion, block enzyme systems responsible for producing hydrogen ions, reducing excess acid and preventing stomach ulcers
Define end product inhibition
When the product of an enzyme-substrate complex inhibits the enzyme and prevents it from catalysing any further reactions
What is end product inhibition an example of?
Negative feedback loops
How does ATP regulate its own production?
The addition of the second phosphate group during glycolysis is catalysed by phosphofructokinase (PFK), which is inhibited by ATP
When ATP levels are high more ATP bonds to PFK allostericly, preventing glycolysis from continuing
