enzymes Flashcards
what is an enzyme?
a protein molecule that acts as a biological catalyst and speeds up reactions
what type of protein is an enzyme
globular protein
how does an enzyme speed up reactions?
when a substrate fits into active site of an enzyme, it forms an enzyme-substrate complex (which is what lowers activation energy)
why does an enzyme speeding up reactions happen?
- if 2 substrate molecules need to join, being attached to the enzyme holds them closer together, reducing any repulsion between molecules so they join easier
- if enzyme is catalysing a breakdown, fitting into the active site puts a strain on the bonds so the substrate molecules break up more easily
why does an enzyme catalyse one specific reaction?
- the active site of any enzyme has a specific tertiary structure and is only complementary to the substrate
- only the substrate can bind to the active site
- to form an enzyme-substrate complex
what is the lock and key model?
substrate fits perfectly into the active site
what is the induced fit model?
active site conforms to its substrates shape
how does the induced fit model work?
- the substrate binds to the active site of the enzyme
- the active site of the enzyme then changes shape slightly to be completely complementary to the substrate as it binds
- this distorts/breaks/forms bonds as it causes bond strain in the substrate
- this decreases activation energy
What is a key property of enzymes regarding their specificity?
Enzymes are very specific and usually catalyze only one reaction.
Why do enzymes only catalyze one reaction?
Because only one substrate will fit into the active site, which is determined by the enzyme’s tertiary structure.
What determines the active site of an enzyme?
The active site is determined by the enzyme’s tertiary structure.
What happens if the tertiary structure of an enzyme is altered?
The shape of the active site will change, affecting enzyme function.
What factors can alter the tertiary structure of an enzyme?
Factors such as pH and temperature can alter the tertiary structure.
How is the primary structure of an enzyme determined?
The primary structure is determined by the gene encoding the enzyme.
What could be the consequence of a mutation in the gene encoding an enzyme?
A mutation could change the tertiary structure of the enzyme produced.
What are the main properties of enzymes?
- Very specific: usually catalyze only one reaction
- Active site shape determined by tertiary structure
- Alteration of tertiary structure affects function
- Primary structure determined by genes
What is the optimal temperature range for human enzymes?
0-37 degrees Celsius
How does an increase in temperature affect enzyme activity up to 37 degrees Celsius?
The rate of reaction increases due to higher kinetic energy of molecules
Why do substrate molecules collide more frequently with enzyme active sites as temperature increases?
Because higher temperature increases the kinetic energy of the molecules
What happens to the energy of collisions between enzyme and substrate as temperature increases?
The energy of the collisions increases, leading to more successful collisions
What occurs to the rate of reaction when the temperature exceeds 37 degrees Celsius?
The rate of reaction decreases
What happens to the kinetic energy of atoms in the enzyme as temperature increases beyond 37 degrees Celsius?
The kinetic energy continues to increase, causing more vigorous vibrations
How does increased kinetic energy affect the hydrogen bonds in an enzyme’s tertiary structure?
It breaks the hydrogen bonds, altering the enzyme’s shape
What is the consequence of the active site changing shape due to increased temperature?
The active site is no longer complementary to the substrate
What is the term used to describe an enzyme that has lost its functional shape?
Denatured
What are the factors affecting enzyme activity?
Temperature
pH levels
Substrate concentration
Enzyme concentration
What is the optimal pH for most humans?
pH 7 (neutral)
What is an exception to the optimal pH of 7 for humans?
Pepsin works best at pH 2 (acidic)
How does the rate of reaction change as pH increases from 6 to 8?
The rate of reaction increases from 0 to 100
What happens to the rate of reaction as pH increases from 8 to 10?
The rate of reaction decreases from 100 to 0
What occurs when pH deviates from the optimum level?
- Difference in concentration of H+ ions
- Breaks ionic/hydrogen bonds
- Changes tertiary structure of the enzyme
- Active site changes shape
- Substrate no longer complementary to active site
- Decrease in enzyme-substrate complexes
- Decrease in rate of reaction
What happens to the rate of reaction as substrate concentration increases to ‘x’ e.g. 2 mol dm^-3?
The rate of reaction increases
What occurs to the rate of reaction when substrate concentration increases beyond a certain point?
The rate of reaction remains constant
Why does the rate of reaction increase with substrate concentration initially?
More substrate molecules lead to more chances of successful collisions with the active site
What happens to the enzyme-substrate complexes as substrate concentration continues to increase?
All active sites become occupied
What becomes limiting when substrate concentration continues to increase and all active sites are occupied?
Enzyme concentration becomes limiting
What is the relationship between substrate concentration and the formation of enzyme-substrate complexes?
- As substrate concentration increases, more substrate molecules are available.
- This leads to a higher chance of successful collisions with the active site.
- More enzyme-substrate complexes are formed until all active sites are occupied.
Describe the phases of reaction rate in relation to substrate concentration.
- Rate increases as substrate concentration rises to a certain point (e.g., 2 mol dm^-3).
- Rate remains constant when all active sites are occupied.
- Enzyme concentration becomes limiting, leading to a plateau in the reaction rate.
What happens to the rate of reaction as enzyme concentration increases?
The rate of reaction increases
Why does the rate of reaction increase with enzyme concentration?
More available active sites lead to more successful collisions and enzyme-substrate complexes
What happens when substrate amount is limited and enzyme concentration increases?
An increase in enzyme concentration eventually has no further effect
what is an inhibitor
a molecule that binds somewhere on the enzyme and therefore prevents enzyme from functioning
competitive inhibitor
same shape as substrate and can bind to the active site (complementary) which creates an enzyme-inhibitor complex which prevents substrate from being able to bind and therefore no enzyme-substrate complexes are formed so reaction won’t occur and is much slower
what would a high conc. of substrate do to a competitive inhibitor?
flood out inhibitor out of active site therefore substrate can collide successfully producing an enzyme-substrate complex and rate of reaction goes back to normal
non competitive inhibitor
binds to enzyme away from active site (any location that isn’t the active site - the allosteric site)which changes the shape of the tertiary structure and the substrate is no longer complementary to the active site therefore - no enzyme-substrate complexes so decreases rate of reaction
what would a high conc. of substrate do to a non-competitive inhibitor?
non-competitive inhibitors don’t compete with the substrate molecules because they completely change shape of the active site so increasing substrate concentration won’t make a difference
