Enzymes Flashcards
(102 cards)
1
Q
What are enzymes? (definition)
A
Biological protein catalysts that increase the rate of reaction by lowering the activation energy.
most are proteins but can be ribosomes as well (ribozymes)
2
Q
Activation Energy
A
Amount of energy required to start a reaction.
Having a lower activation energy means that it’s easier for reactions to occur
3
Q
How do they make reactions faster?
A
- Provide an alternate reaction pathway, making it easier for reactants to come into contact
- This reduces activation energy and increases rate of reaction
4
Q
Catalyst
A
a substance that can increase the rate of reaction without being consumed in the reaction (reusable)
5
Q
Substrate
A
the molecules that bind to the active site of the enzyme to undergo chemical reaction, forming product
6
Q
Product
A
the molecules that are released from enzyme active site
7
Q
Enzymes have an __ and an __.
A
active site and an allosteric site
8
Q
Active Site
A
the region of the enzyme where the substrate molecules bind to and undergo a chemical reaction
9
Q
Allosteric site
A
an area of the enzyme that can bind to molecules other than the substrate.
10
Q
Enzyme- substrate complex
A
The temporary complex formed when the substrate is bound to the active site of the enzyme.
11
Q
Collision Theory
A
- Reactant particles must collide to react.
- Collisions need sufficient energy to overcome the activation energy.
- Particles must collide in the correct orientation to form products.
12
Q
Induced Fit Model
A
A model where the enzyme’s active site changes shape to fit the substrate snugly.
13
Q
How does the Induced Fit Model differ from the Lock and Key Model?
A
The active site is flexible, not rigid, allowing dynamic binding.
14
Q
What happens when the substrate binds to the enzyme in the Induced Fit Model?
A
The enzyme undergoes a conformational change, stabilizing the transition state.
15
Q
How does the Induced Fit Model affect activation energy?
A
It lowers the activation energy needed for the reaction.
16
Q
Give an example of an enzyme that follows the Induced Fit Model.
A
Hexokinase, which changes shape when binding to glucose.
17
Q
Conformational change
A
a change to the 3D shape of smth
18
Q
Complementary
A
means that they can fit together
(the active site is complementary to its specific substrate)
19
Q
Repercussions of conformational change
A
Substrate may not bind to the active site- problem- reaction won’t be as fast
(SHAPE = FUNCTION)
(shape changes- function changes)
20
Q
Features of enzymes
A
- reusable (not consumed in reactions)
- specific to a certain substrate (active site must be complimentary to the substrate)
- reversible (sometimes)
- only SPEED UP reactions NOT CREATE the reaction itself
- work together in biochemical pathways
- most enzymes end in -ase (exceptions like pepsin)
- written ABOVE the reaction arrow
-Can be affected by temperature, pH, and inhibitors
21
Q
What happens to reactant molecules in a normal reaction without enzymes?
A
The reactant molecules are floating around.
22
Q
How do reactant molecules interact in a reaction without enzymes?
A
By chance, they collide.
23
Q
What conditions must be met for a successful reaction without enzymes?
A
A collision needs to be in the right orientation and at the right speed (to give sufficient energy).
24
Q
Why do reactions without enzymes have a low success rate?
A
Because it is a tough set of criteria to meet consistently.
1. collision
2. orientation
3. energy
25
What is the key difference in how reactants behave in enzyme-catalyzed reactions compared to normal reactions?
Reactants float around alongside enzymes instead of relying on random collisions.
26
How do enzymes interact with reactant molecules?
Enzymes have complementary active sites that bind to specific reactant molecules (substrates).
27
How do reactants reach the correct position in enzyme-catalyzed reactions?
They are attracted to the active site and positioned correctly.
28
How can energy be supplied in enzyme-catalysed reactions?
Energy can be input via ATP instead of relying on collision speed.
29
Why are enzyme-catalyzed reactions more efficient than normal reactions?
The 'chance' component of collisions is removed, making the reactions more consistent and well-regulated.
30
Coenzymes
type of cofactors
31
Coenzymes and Cofactors
All coenzymes are a type of cofactor, but not all cofactors are coenzymes (some are metal ions).
32
Polypeptide chain
chains of amino acids linked together y pepetide bonds, which fold into a specific 3D structure to form proteins, inc. enzymes
33
What determines the specificity of an enzyme?
The specific amino acid residues in the active site, particularly the R groups, interact uniquely with the substrate.
34
R group
The variable side chain of an amino acid that makes each amino acid unique, influencing enzyme specificity.
35
Lock and Key Model
A model where the substrate fits perfectly into the enzyme's active site, like a key in a lock. This model is rare.
36
Why is the Lock and Key Model rare?
Most enzymes are flexible and undergo conformational changes to better fit the substrate, aligning more with the Induced Fit Model.
37
Why are enzymes reusable?
They are not consumed or altered in the reaction, allowing them to catalyse multiple reactions.
38
Why do most enzymes bind to only one substrate?
The active site's shape and chemical properties are highly specific to the substrate's shape and chemical properties.
39
Can enzyme-catalysed reactions be reversed?
Yes, many are reversible, allowing enzymes to participate in both anabolic and catabolic pathways.
40
How do enzymes lower activation energy?
By bringing reactants closer to the transition state, reducing the amount of energy needed for the reaction.
41
Anabolic reactions
"building" smaller molecules to larger molecules (eg: amino acids- proteins)
42
Catabolic reactions
"breaking down" larger molecules from smaller molecules (eg: digestion of food)
43
How are enzymes different from other catalysts?
Enzymes are organic (protein or RNA) catalysts, while other catalysts can be inorganic, like metal ions.
44
How do enzymes influence biochemical pathways?
By catalysing each step, they regulate the rate and sequence of biochemical reactions.
45
How do enzymes affect the transition state?
They stabilise the transition state, making it easier for the reaction to occur.
46
Example of enzyme speeding up reaction
Carbonic anhydrase catalyses the reaction between CO₂ and water 10 million times faster than without the enzyme.
47
biochemical pathway?
A chain of enzyme-catalysed reactions where the product of one reaction becomes the substrate for the next.
48
How do coenzymes assist enzymes?
By altering the active site shape for activation or acting as electron carriers.
49
key characteristics of enzymes
Specific, reusable, can catalyse reactions in both directions, and work in catabolic or anabolic reactions.
50
The activity levels of an enzyme vary depending on:
Temperature
pH
Concentrations of the substrate and enzyme
Inhibition
Coenzymes
51
what happens when temp increases?
increase in temp- increase in kinetic energy of molecules- more movement- more frequent collisions- more reactions
52
How does temperature affect enzyme activity?
Enzymes have an optimal temperature at which their activity is greatest-- enzyme and substrate collisions are most frequent -- binding is more efficient.
53
What is the optimal temperature for an enzyme?
The temperature at which an enzyme works best, usually around 37°C for human enzymes. (60°C or higher for heat loving organisms like Thermophilic enzymes)
54
55
what happens when temp decreases?
Enzyme activity decreases as molecules move slower, leading to fewer collisions and less binding between the enzyme and substrate.
56
What happens when the temperature exceeds the optimal temperature?
The enzyme denatures, and the reaction rate decreases.
57
Enzyme denaturation?
It’s when high temperature alters the enzyme’s shape, preventing it from working.
58
What happens to enzyme activity when the temperature exceeds the optimal temperature?
The enzyme's 3D structure changes, causing the active site to lose its shape, preventing substrate binding, and reducing enzyme activity to zero.
59
Why is the relationship between enzyme activity and temperature asymmetrical?
High temperatures cause rapid denaturation, while low temperatures only reduce kinetic energy, making both extremes problematic, but not equally so for enzyme activity.
60
how does ph affect enzyme activity?
Enzymes have an optimal pH where they function best. Denaturation occurs equally above or below this pH, creating a symmetrical, bell-shaped curve when enzyme activity is plotted against pH.
61
What is the optimal pH range for different enzymes?
Pepsin (stomach): pH ~1.5-2
Pancreatic lipase (small intestine): pH ~8
Blood: pH ~7.4
Saliva: pH ~7.0
Bile: pH ~7.5
62
How does enzyme and substrate concentration affect reaction rate?
As concentration increases, the reaction rate increases until a plateau is reached when there’s no more substrate or enzyme available. It does not cause denaturation.
63
How does increasing substrate concentration affect enzyme activity?
If enzyme concentration is constant, increasing substrate concentration increases the reaction rate, as more reactants are available.
64
What is the saturation point?
The saturation point is reached when all enzyme active sites are occupied by substrate, and adding more substrate will no longer increase the reaction rate.
65
What happens at saturation point?
The reaction rate plateaus because all enzyme active sites are occupied.
66
What is a limiting factor?
A factor that prevents the reaction rate from increasing such as low substrate concentration before saturation is reached.
67
What happens when enzyme concentration is high?
High reaction rate – more active sites available for substrate to bind.
68
How does increasing enzyme concentration affect reaction rate?
It increases reaction rate, until enzymes are in excess.
69
What happens when enzyme concentration exceeds substrate availability?
Reaction rate plateaus, no further increase occurs.
70
What could happen with excessive enzyme concentration?
Reaction rate may decrease if all substrates are used up.
71
How does enzyme concentration relate to substrate in biological systems?
Substrate is usually more abundant, so increasing enzyme concentration typically increases the rate.
72
What are enzyme inhibitors?
Enzyme inhibitors are molecules that bind to an enzyme and prevent it from performing its function.
73
What happens when an enzyme inhibitor binds to an enzyme?
When an inhibitor is bound to an enzyme, the enzyme can either no longer catalyse its specific reaction or its functioning is greatly reduced.
74
Inhibitors can be __ and __.
Competitive and non-competitive inhibitors.
75
What is competitive inhibition?
When an inhibitor binds to the enzyme’s active site, blocking the substrate from binding.
76
How does a competitive inhibitor block the active site?
The inhibitor must have a shape similar to the substrate, allowing it to occupy the active site without triggering a reaction.
77
Why is it called "competitive" inhibition?
Because both the substrate and inhibitor compete for the same active site.
78
Non-competitive inhibition
- Inhibitor binds to a site other than the active site (allosteric site).
- Causes a conformational change in the enzyme’s active site.
- Substrate can no longer bind, preventing the reaction.
79
What is a biochemical pathway?
A series of connected enzyme-catalyzed reactions where the product of one reaction becomes the substrate of the next.
80
What is the role of enzymes in biochemical pathways?
Enzymes speed up reactions in biochemical pathways by lowering the activation energy required for the reaction to occur.
81
What is feedback inhibition in a biochemical pathway?
- A form of regulation where the end product of a pathway inhibits an early enzyme in the pathway.
- Prevents overproduction of the final product.
- Ensures that resources are not wasted.
82
What is the function of a substrate in a biochemical pathway?
- A molecule that an enzyme acts upon in a biochemical reaction.
- The substrate binds to the enzyme’s active site to form an enzyme-substrate complex.
- After the reaction, the substrate is transformed into a product.
83
How does product inhibition regulate metabolic pathways?
- The product of a reaction inhibits the enzyme that produces it.
- This prevents the pathway from continuing once enough product has been made.
- Helps maintain homeostasis by regulating production rates.
84
What is non-competitive inhibition?
- Inhibitor binds to an allosteric site (different from the active site).
- Causes a conformational change in the enzyme, preventing substrate binding.
- Does not compete directly with the substrate.
85
What happens if enzyme 1 is inhibited in a pathway?
- The entire pathway is affected as the subsequent enzymes have reduced substrates.
- Results in lower production of products in the pathway.
- Can cause a buildup of earlier substrates, affecting other processes.
86
How does substrate concentration affect enzyme activity?
- At low substrate concentrations, the reaction rate increases with more substrate.
- At high concentrations, enzymes become saturated, and the reaction rate plateaus.
- The reaction rate becomes independent of substrate concentration once all enzyme active sites are occupied.
87
What’s the difference between competitive and non-competitive inhibition?
Competitive inhibition: Inhibitor competes with the substrate for the active site, preventing the substrate from binding.
Non-competitive inhibition: Inhibitor binds to an allosteric site, altering the enzyme's shape and preventing substrate binding.
88
Why is enzyme concentration important in metabolic pathways?
- Higher enzyme concentration increases the reaction rate, up to a point.
- Once all substrate molecules are bound to enzymes, the reaction rate plateaus.
- Enzyme concentration is often much lower than substrate concentration in biological systems, so changes in enzyme concentration can significantly impact reaction speed.
89
What is a cofactor?
- A molecule that assists enzyme functioning.
- Can be inorganic (e.g., metal ions) or organic (coenzymes).
90
What are coenzymes?
- A type of cofactor that is organic and non-protein.
- Assist enzymes in catalyzing reactions by binding to the active site.
91
What happens to the enzyme and coenzyme during the reaction?
- The enzyme remains unchanged.
- The coenzyme’s structure is altered.
92
How do coenzymes assist in enzymatic reactions?
- Coenzymes donate energy or molecules to the reaction.
- After the reaction, they leave the enzyme and are recycled.
93
What is the cycling of coenzymes?
- The process where coenzymes are reused after each reaction.
- Coenzymes are recycled by accepting energy, allowing them to assist in more reactions.
94
What is the most well-known coenzyme?
Adenosine triphosphate (ATP) and its partner, adenosine diphosphate (ADP).
95
What is the role of ATP in enzymatic reactions?
- ATP donates energy to catalyse reactions.
- It loses a phosphate group and becomes ADP.
96
How is ADP converted back to ATP?
- ADP gains a phosphate group through phosphorylation.
- This recycling allows ATP to catalyse more reactions.
97
What are phosphorylation and dephosphorylation?
- Phosphorylation: Adding a phosphate group (ADP → ATP).
- Dephosphorylation: Removing a phosphate group (ATP → ADP).
98
What is coenzyme cycling?
- The continuous conversion of ATP to ADP and back.
- ATP is the 'loaded' form, and ADP is the 'unloaded' form.
99
How frequently is ATP cycled in the body?
The same ATP molecule can cycle to ADP and back over 1,000 times daily.
100
What are enzyme optimal conditions?
- Enzymes have specific optimal temperatures and pH levels.
- Extreme conditions can cause denaturation.
101
How do substrate and enzyme concentrations affect reaction rate?
Increasing substrate or enzyme concentration increases reaction rate until a saturation point is reached.
102
How do coenzymes differ from inhibitors?
- Coenzymes assist enzyme functioning and are recycled.
- Inhibitors block enzyme activity, either competitively or non-competitively.
