Enzymes Flashcards
What are enzymes called?
Biological catalysts because they speed up metabolic reactions in living organisms.
What do catalysts do?
Catalysts speed up chemical reactions and remain unchanged at the end of the reaction, able to be used again.
Define ‘turnover number’
The number of reactions that an enzyme can catalyse per second.
Why are enzymes better than chemical catalysts?
- Chemical catalysts need high temperatures, increased pressure and extremes of pH
- Enzymes speed up reactions by up to 10^12 times at lower temperatures, at neutral pH, normal pressures
- More specific, do not produce unwanted by-products and rarely make mistakes
What does the active site consist of?
6-10 amino acids
What are intracellular enzymes?
Enzymes that work inside the cell
Define catabolic and anabolic pathways.
Catabolic= metabolites are broken down to smaller molecules and release energy
Anabolic= energy is used to synthesise larger molecules from smaller molecules
What does the enzyme Catalase do?
It protects cells from damage by reactive oxygen by quickly breaking down hydrogen peroxide to water and oxygen.
Desrcibe some structural features and functional features of catalase.
- Has 4 pp chains and a haem group with iron
- Fastest acting enzyme with highest turnover number
- Found in vesicles called peroxisomes in eukaryotic cells
- WBC’s use catalase to help kill invading mircobes
- Optimum pH is around 7 for humans, 4-11 for other organisms
- Optimum human temp is 45C, others is 90C
What are extracellular enzymes?
Enzymes that work outside of the cell
Name an example of extracellular enzymes.
The bread mould Mucor
- Releases hydrolytic enzymes from thread like hyphae
- Enzymes digest carbohydrates, proteins and lipids in the bread, products of digestion (glucose, amino acids, glycerol) are absorbed into hyphae for respiration
What is activation energy?
The minimum amount of energy needed to start a chemical reaction
Describe the lock and key model
- Enzyme and substrate collide successfully
- Substrate enters complementary active site, forming an enzyme-substrate complex and then the enzyme-product complex.
- Product leaves the active site
- Enzyme is available and unchanged.
Desrcibe the induced fit model
- The active site is not FULLY complementary, the active site is flexible.
- The substrate induces the fit and interacts with the R groups in the active site which causes a temporary conformational change of shape.
- This causes bond strain
- Enzyme substrate and enzyme product complex are formed
- Active site returns to normal shape.
Describe the effect of changing pH on the rate of enzyme activity
- Changes in pH can disrupt H and ionic bonds in tertiary structure, causing enzymes to lose shape of active site
- Affects R groups and can be temporary or permanent
Describe the shape of the pH graph
- When pH is outside the optimum range bonds are disrupted and tertiary structure is lost.
- Active site is denatured so substrates cannot bind
- High H+ ion concentration means the pH is lower
- H+ ions are positive and attract negative ions.
- H and ionic bonds hold the tertiary shape of enzyme and active site together
- these are oppositely charge amino groups
- Differences in pH will affect tertiary structure
Describe the effect of temperature on enzyme activity
- Increasing temperature increases kinetic energy which causes more successful collisions
- Increased E/S complexes and an increase in the mass/ volume of products formed
- Further increase means that H bonds holding tertiary structure will break, causing the active site to change shape and no longer be complementary
Explain the shape of the temperature graph
- Low temperature means there is not enough kinetic energy to create successful collisions
- Decrease in mass/ volume of products, bonds not affected
- Above optimum, more kinetic energy and successful collisions
- H bonds break, enzyme denatures, substrate cannot fit
How does substrate concentration affect rate of reaction?
- As it increases, collisions between enzymes and substrate increase
- More complexes formed and product
- Rate of reaction increases
- occurs up to a certain point where the enzyme molecules are forming the enzyme substrate complexes
- all of the active sites are occupied
- Further increase = no effect
- Enzyme concentration is the limiting factor
Why do enzymes need cofactors?
- Enzymes may need help
- They might transfer groups from one reaction to another in a multistep pathway
- May form part of the active site
What is a prosthetic group?
- A cofactor that is permanently covalently bonded to the enzyme
- contains a zinc ion permanently bonded to its active site
- vital to enable CO2 to be taken away from respiring cells
What is a cofactor?
- Inorganic
- Some enzymes work better in the presence of ions that are not permanently bound
- act as co-substrates- they and the substrate form the correct shape to bind to the active site
- Change in the charge distribution in the AS or substrate make bonds in E/S complex easier to form
- Amylase works better in the presence of chloride ions
What is a coenzyme?
- organic, small, non-protein
- Can be slightly chemically changed by reaction and need to be recycled to the original state before reused
- many are derived from vitamins so vitamin deficiency indicates a lack of coenzymes.
- NAD, FAD, COA= respiration
- NADP= photosynthesis
What is competitive inhibition?
- A molecule of similar shape to substrate
- It fits into active site, forming an inhibitor complex preventing substrate from binding
