Enzymes Flashcards
What type of protein are enzymes?
Globular
What structure do enzymes have?
Tertiary - complex 3D shape held together by bond (ionic, hydrogen, disulphide bridges, hydrophobic interactions) determines shape of active site
What are enzymes?
Globular proteins which act as biological catalysts
What’s a biological catalyst?
Something made of living cells which helps speed up the rate of chemical reactions
What two types of metabolic reactions do enzymes control?
Anabolic
Catabolic
What’s an anabolic reaction?
Building up molecules (eg. Protein synthesis)
What’s a catabolic reaction?
Breaking down molecules (eg. Digestion )
When a substrate binds to an enzyme what forms?
Enzyme-substrate complex
What does complimentary shape mean?
Enzymes are specific to their substrate
How does an enzyme act on a substrate?
It makes temporary bonds at the active site forming an enzyme substrate complex
What does each enzyme do?
It catalyses one SPECIFIC reaction
Why do enzymes only catalyse one Specific reaction?
They have a specific 3D tertiary structure (active site is only specific to one substrate)
Why does Maltase only catalyse maltose in digestion? (3marks)
Maltase only catalyses maltose in a hydrolysis reaction because it has a specific 3D structure.
Therefore the active site will have a specific shape so only maltose (substrate) which has a complimentary shape will bind to the active site to form an enzyme substrate complex
How do reactions occur between enzymes and substrates?
Reactions occur due to collisions which have to be the right orientation and force
Where are enzymes made and where do they act?
Intracellular (inside cells)
Extracellular ( secreted outside cells)
What are the two different theories of how enzyme substrate complexes form?
Lock and Key Model
Induced Fit Model
What does the lock and key model suggest about E-S complexes?
It’s an earlier model which suggests enzyme active sites are rigid and permanent
Explain the lock and key model?
The active site of the enzyme acts as the specific lock whilst the substrate acts as the key due to its complimentary shape. When the substrate binds to the active site an anabolic or catabolic reaction occurs to achieve the products.
Explain the induce fit model?
Before the reaction, the active site is NOT complimentary to the substrate
As the substrate binds the active site changes shape to better fit/become complimentary to the substrate to form an enzyme-substrate complex
This stresses and distorts the bonds in the substrate causing the reaction to occur and products to be released
What do enzymes do to cause a high rate of reaction?
Lower activation energy
How is activation energy lowered and why is it useful?
The stress/ distorting of bonds in the substrate causes the activation energy to be lower
It reduces the minimum energy required to start a reaction
What needs to happen for a successful collision and what does it cause ?
It causes a reaction:
- collide with enough energy
- collide with suitable orientation
- substrate must be complimentary to active site
- come into physical contact with a substrate
Explain how the active site of an enzyme causes a high rate of reaction?
- Lowers activation energy
- Induced Fit = active site changes so E-S complex forms causing bonds to be stressed/distorted
What is an exergonic reaction?
Where energy is released
What is an endergonic reaction.?
Where energy is absorbed
What are the 5 factors affecting enzyme action?
Temperature
pH
Enzyme Concentration
Substrate Concentration
Inhibition
What is a buffer?
An aqueos solution that has a highly stable pH
What is the purpose of a buffer solution?
Resists changes in pH
How do you measure pH of a solution?
pH = - Log10 [H+]
How does substrate concentration affect enzyme action?
The higher the substrate concentration the faster the rate or reaction (due to more successful collisions) because more E-S complexes form. This is true until ‘saturation’ when all available active sites of complimentary enzymes are filled
When the substrate concentration has reached ‘saturation’ what does this mean’?
All available active sites are full so an increase in substrate concentration will have no further effect nd the rate of reaction plateaus.
How does enzyme concentration affect rate of reaction?
The more enzyme molecules there are the more likely a substrate molecule will collide and form a enzyme-substrate complex. Increasing enzyme concentration will increase the rate of reaction as more active sites are available.
What is the limiting factor when increasing substrate concentration has no further effect on rate of reaction?
Enzyme concentration
If the amount of substrates is limited what happens to the rate of reaction?
Enough enzyme molecules to deal with available substrate so adding more enzymes will have no further effect on rate of reaction
How does temperature effect enzyme activity?
Increase rate of reaction to provide enough kinetic energy for a successful collision
What happens if the temperature is too low (enzymes)?
There is not enough kinetic energy for a successful collision (to form an enzyme-substrate complex)
If the temperature is too high what happens to the enzyme?
The enzyme denatures - active site irreversibly changes - so enzyme substrate complexes don’t form
Why do enzymes denature at high temperature?
The energy (high temperatures) breaks the weak hydrogen bonds between nearby peptide bonds so alters tertiary structure and consequently active site
What is it called when enzymes reach there maximal rate of reaction?
Optimum
What do all enzymes have?
A unique optimum pH value
What happens if the pH is too high or low?
The OH- ions or H+ ions interfere with the charges in the peptide chains and disrupt the ionic/hydrogen bonds holding the tertiary structure together so active site is altered and less E-S complexes form
What are enzyme inhibitors?
Substances that directly or indirectly affect the functioning of the active site of a specific enzyme, and therefore prevent the substrate binding, preventing the formation of an enzyme substrate complex which leads to a decrease in the rate of reaction
What are the two types of enzyme inhibitors?
- Competitive
- Non-Competitive
What sort of structure do competitive inhibitors have?
Have a similar structure/shape to substrates so they can bind to occupy the active site of an enzyme
What do you competitive inhibitors do?
They compete with substrate for the active site
How do you reverse the binding of competitive inhibitors active sites?
Increase substrate concentration, which will overcome competitive inhibition as it is a reversible reaction
Where do competitive inhibitors bind?
On active site of an enzyme
What are competitive inhibitors.?
- Substances with a similar shape/structure to substrate so bond to and occupy active site of enzyme
- Compete with substrate
- Binding to active site is reversible and can be overcome by increasing substrate concentration
What a non-competitive inhibitors?
- Bind to enzyme at allosteric site
- Causes a change in the tertiary structure or enzyme so alters shape of active site
- Active site is no longer complimentary to the substrate so E-S complex can’t form
- Occurs permanently and can’t be overcome by increasing substrate concentration
Where do Noncompetitive inhibitor bind?
Allosteric site (other site than active site)
What do non-competitive inhibitors cause?
Cause a change in the tertiary structure of an enzyme therefore also change the shape of the active site
Can non-competitive inhibition be overcome?
No bind permanently changing the shape of the specific active site
Cells don’t want to make more or less product than required so use what?
End - Product Inhibition to control reaction pathways in negative feedback loop
What do inhibitors do?
Reduce binding of enzyme to substrate to form enzyme substrate complexes
