Enzymes Flashcards
What are ENZYMES?
BIOLOGICAL CATALYSTS:
- Increase the rate of reactions
- Found in living organisms
CATALYSE BOTH:
Anabolic reactions ~ building up
Catabolic reactions ~ breaking down
The STRUCTURE of enzymes
- TERTIARY GLOBULAR proteins, where the protein chain is folded back on itself into a SPHERICAL shape.
- Each enzymes has its own sequence of AMINO ACIDS and is held in its tertiary structure by HYDROGEN, IONIC & DISULFIDE bonds.
- On the surface, the tertiary structure of the enzyme folds into a 3D shape called the ACTIVE SITE.
The PROPERTIES of enzymes
SOLUBLE IN WATER ~ have hydrophilic amino acids on their surface and the hydrophobic ones cluster together.
SPECIFIC ~ the tertiary structure of the active site is COMPLEMENTARY to the structure of the substrate.
HIGH TURN OVER NUMBER ~ can convert many molecules of substrate per unit time.
INTRACELLULAR enzymes
Found INSIDE cells.
CATALASE:
Binds to the toxic molecule HYDROGEN PEROXIDE and speeds up its break down in to the harmless products water and oxygen
hydrogen peroxide ———— water + oxygen
catalase
DNA REPLICATION:
- DNA polymerase
- DNA ligase
ON A MEMBRANE:
- The synthesis of ATP by ATPase during respiration
- occurs across the inner membrane of mitochondria.
EXTRACELLULAR enzymes
Found OUTSIDE of cells.
AMYLASE:
- Catalyses the break down of STARCH molecules into the disaccharide MALTOSE.
- Maltose is broken down further by other enzymes into GLUCOSE which can be absorbed into the bloodstream.
Starch ————- maltose
amylase
TRYSPIN:
- Produced by the pancreas and released in the digestive system.
- Catalyses the break down of PROTEIN molecules into PEPTIDES.
- Peptides are broken down into AMINO ACIDS.
Proteins ————————— Peptides
tryspin
How do enzymes work?
- On the surface of an enzyme is the ACTIVE SITE.
- Its role is attach to the SUBSTRATE molecule to form the ENZYME-SUBSTRATE COMPLEX.
- Each enzyme is SPECIFIC to the substrate it binds to.
- Once the substrate binds, the amino acids on the surface of the active site form TEMPORARY BONDS with the substrate molecule.
- The enzymes CATALYSES the reaction to form the ENZYME-PRODUCT COMPLEX.
- Now the products are RELEASED from the active site.
How do enzymes INCREASE THE RATE OF REACTION?
- Provide a PATHWAY for the reaction with a LOWER ACTIVATION ENERGY BARRIER.
- More substrate molecules now have enough energy to cross the activation energy barrier and react.
- Therefore the reaction rate increases.
LOCK & KEY HYPOTHESIS
Fisher 1894:
The substrate is EXACTLY complementary to the shape of the active site.
NATURE OF BINDING:
- Very strong as it does not form a transition state.
ACTIVE SITE PROPERTIES:
- Rigid
- Inflexible
- Static
EVIDENCE:
- Explains the specificity of some enzymes
- Example ~ amylase will only hydrolyse starch
INDUCED FIT HYPOTHESIS
Koshland 1959:
- Interaction of substrate at active site causes CONFORMATIONAL CHANGE .
- This causes the active site to MOULD itself tightly around the substrate.
- Ensures that the active site fits PERFECTLY to the substrate.
- This puts STRAIN on the substrate and weakens bonds.
- Involves a TRANSITIONAL STATE before bonds in the substrate are broken and products are released.
NATURE OF BINDING:
- Flexible, favouring the formation of a transition state.
ACTIVE SITE PROPERTIES:
- Flexible
- Not static
- Dynamic
EVIDENCE:
- Explains broader specificity of some enzymes.
- Example ~ proteins
SIMILARITIES between the two model of the enzyme
- Require an enzyme and a substrate.
- Explain substrate specificity of enzymes
What happens if molecules which are NOT substrate molecules try to bind to the active site?
- Molecules which are not the substrate cannot form the CORRECT BONDS to the correct amino acids int he active site.
- The tertiary structure of the enzyme DOES NOT CHANGE
- The shape of the active site DOES NOT ADJUST to fit the molecule.
Explain the shape of the graph showing the AMOUNT OF PRODUCT FORMED.
In terms of :
- Rate of reaction
- Number of successful collisions
Start:
- Line is STEEP
- LARGE amount of substrate molecules
- High FREQUENCY of successful collisions between the S & AS.
- RAPID initial rate
Middle:
- The line becomes LESS STEEP
- Some of the substrate is CONVERTED into product.
- The amount of substrate molecules FALLS.
- The chance of collision DECREASES
- Reactions SLOWS DOWN
End:
- Line is HORIZONTAL
- ALL of the substrate molecules have been converted into product.
- There are no more substrate molecules left to collide with the active site.
- Reaction has STOPPED
Measuring the rate of reaction at a CERTAIN POINT
- Draw a TANGENT to the curve
- This is a straight line which just touches the curve at the point we want to measure.
- Make the tangent line reasonably long as it makes it easier to read the number accurately.
GRADIENT OF THE TANGENT:
- make the tangent into a TRIANGLE
- measure the length of Y & X
Gradient ( rate ) = Y/X
TEMPERATURE ~ Beginning of reaction
- The rate INCREASES as we INCREASE the temperature.
- The KINETIC ENRGY of the enzyme and substrate INCREASES.
- They are moving more RAPIDLY
- This INCREASES the chance of S & AS colliding.
- The FREQUENCY of successful collisions INCREASE.
- The rate of reaction INCREASES
TEMPERATURE ~ At optimum temperature
- At a certain point, the reaction rate is at its MAXIMUM. (optimum temperature)
- Maximum frequency of collision between S & AS.
Human enzymes optimum temp ~ 40
