Enzymes Flashcards
What are enzymes?
Globular proteins that alter the rate of metabolic reactions and are known as biological catalysts
What type of proteins are enzymes?
Globular
What does anabolic mean?
Building up
Chemical reactions required for growth
What does catabolic mean?
Breaking down
What is metabolism?
The sun of all chemical reactions happening in the body
What factors may have an effect on enzyme activity?
- Temperature
- pH
- Substrate concentration
- Enzyme concentration
How do enzymes catalyse reactions?
They reduce activation energy
What is Vmax?
Maximum initial velocity
Enzymes can only increase RoR up to this point
What is the lock and key theory?
- Active site = area within a tertiary structure of an enzyme that’s shape is complementary to the shape of a specific substrate
- Only a specific substrate will “fit”
- When the substrate is bound to the active site, an enzyme-substrate complex is formed
What is the induced-fit hypothesis?
- More recently, evidence suggests the active site actually changes shape slightly as the substrate enters
- The initial reaction between them is weak but they rapidly induce changes in the tertiary structure - strain on substrate
What are intracellular enzymes?
Enzymes that act within cells
What are extracellular enzymes?
Enzymes that act outside cells
Example of an enzyme that catalyses intracellular reactions?
Catalase
Example of an enzyme that catalyses extracellular reactions
Amylase and trypsin
How does temperature affect enzyme action?
- Increase in temp
- Increase in kinetic energy of particles
- Particles move faster
- Collide more frequently
- Bonds holding protein together vibrate more
- Vibrations increase until bonds strain and break
- Changes shape as it denatures
- Doesn’t form ESC
What is optimum temperature?
Where the enzyme has the highest rate of activity
Humans = 37°C
How does pH affect enzyme action?
- A change in the pH refers to a change in hydrogen ion concentration
- Hydrogen ions and ionic bonds between amino acid R-groups hold proteins in their precise 3D shape
- When the pH changes from optimum, the structure of the enzyme (active site) is altered
- However, if it returns back to optimum then it can return to it’s original shape - denaturalising
- No/fewer ESC formed
How does substrate concentration affect enzyme action?
- Increased collision rate with active sites
- More ESC
- Until all active sites are occupied
How does enzyme concentration affect enzyme action?
- Will increase number of available active site in a particular area
- More collisions
- Leads to more ESC
- If substrate runs out it will make no difference to rate
What are coenzymes?
Organic molecules but are not necessarily a protein - vitamins
What is Q10?
A measure of change in the rate of an enzyme controlled reaction if temperature is increased by 10°C
- The bigger the Q10 value, the bigger the difference in the rate
What is a cofactor?
A non-protein chemical compound or metallic ion that is required for an enzyme’s activity as a catalyst
What are inhibitors?
Molecules that prevent enzymes from carrying out their normal function
What is competitive inhibition?
- Competitive inhibitors gave a similar shape to the substrate
- They can also bind to the active site
- This stops the substrate forming an ESC
What is non-competitive inhibition?
- Non-competitive inhibitors bind to the allosteric site
- Changes tertiary structure of enzyme and shape of active site
- Active site no longer has complementary shape so substrate can’t bind
- No more ESC are formed
What is end-product inhibition?
- A form of negative feedback
- When the product of a reaction act as an inhibitor to the enzyme from an earlier step in the sequence
What are coenzymes?
- Small (non a.a) organic compounds
- Needed by some enzymes to work
- They’re recycled, not used up
How are coenzymes obtained?
From vitamins, e.g. vitamin B3
What are cofactors?
- Inorganic molecules
- Attached to same enzyme, needed for the enzyme to function
- Not used up
How are inorganic cofactors obtained?
Via the diet as minerals, e.g. calcium
What is a prosthetic group?
- Same as cofactors excepts they are chemically bonded onto the enzyme
- A non-protein group forming part of or combined with a protein
- E.g. Zinc ions (Zn2+)
What is precursor activation?
- Many enzymes are produced in an inactive form (inactive precursor enzymes). These often need to undergo a change in shape, particularly the active site, to be activated
- This can be achieved by the addition of a cofactor
What is activation energy?
The minimum energy require for a reaction to complete
What is Q10?
- The temperature coefficient
- Measures the amount of change to a biological reaction caused by increasing the temperature by 10°C
Describe reversible inhibitors
- Can be reversed
- Do not denature enzyme
- Weakly bind to enzyme, e.g. H bonds
- Could be temporary change/removal of: coenzyme or cofactors
Describe irreversible inhibitors
- Cannot be reversed
- Enzyme is permanently denatured
- Strongly bonded to enzyme, e.g. covalent bond
Describe metabolic poisons as a type of enzyme inhibition
- inhibit enzymes in essential metabolic pathways like respiration
- E.g. cyanide
- Normally non-reversible
Give 2 types of enzyme inhibition
1- Metabolic poisons
2- Medicines
Describe medicine as a type of enzyme inhibition
- Inhibit enzymes in essential processes unique to pathogens
- E.g. cell wall formation in bacteria (penicillin)
- Protein synthesis in viruses (reverse transcriptase)
Describe the role of product inhibition
- When the product of an enzyme catalysed reaction bonds to an enzyme and inhibits its activity
- Can be any type of inhibitor
- E.g. competitive/non-competitive
- They are always reversible
- Help to regulate how much product is made
How do you calculate Q10?
Rate of reaction X+10 / Rate of reaction X°C
