3.1.4:2 Enzymes Flashcards Preview

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What is an enzymes function?

To catalyse reactions


How do enzymes speed up reactions?

Lower the activation energy of the reaction it’s catalysing


What are the two models of enzyme function?

Lock and key


What do the properties of an enzyme depend on?

The tertiary structure of the active site
Ability to combine with complementary substrates


What is formed in a catalysing processes?

Enzyme-substrate complex


What is specificity?

Each enzyme can only combine with one substrate because of their complementary shapes


What is activation energy?

The least amount of energy required to activate atoms of molecules to a state in which they can undergo a chemical reaction


What is it the functional part of the enzyme called?

Active site


What are enzymes made from?

Amino acids


Describe the structure of an enzyme?

Globular protein
Tertiary structure
Depression in the side (active site)
Specific as each active site fits one substrate


Why are enzymes needed in living things?

The activation energy in living things is too high as the temperature is too low so the enzymes lower the activation energy


Define activation energy?

The energy needed to activate atoms or molecules to a state in which gang can undergo a chemical reaction


What happens to the enzyme when the temperature or pH is too high or low in the reaction?

It denatures


What happens when an enzyme denatures?

When the temperature is too high there is enough energy to break hydrogen bonds in the tertiary structure so the active size changes shape. It’s no longer complementary to the substrate so enzyme-substrate complexes can’t be formed. No products are formed.


What is the difference between an anabolic and catabolic reaction?

Anabolic builds bonds
Catabolic breaks bonds


What is wrong with the lock and key theory?

It suggests that enzymes are rigid but they’re not
They can alter their shape


What factors affect the rate of an enzyme controlled reaction?

Concentration of substrate
Concentration of enzyme


How do we express the rate of an enzyme controlled reaction

Turnover number
The number of substrate molecules which one molecule of enzyme can turn into product per minute
(usually 100,000’s)


How can rate of reaction be measured?

Increase in product over time
Decrease in substrate over time
(Tangent on graph)


Why does rate on reaction in an enzyme controlled reaction tend to decrease over time?

Substrate is converted into product
Less and less substrate molecules for enzymes to act upon
Less enzyme-substrate complexes formed


What conditions must be satisfied for a reaction to take place naturally?

Substrates must combine with enough energy to alter the arrangement f their atoms to form products
The free energy of the products must be less than that of the substrates
Activation energy


What is the induced fit model?

The proximity of the substrate leads to a change in the enzyme that forms the functional active site
As the shape changes, the enzyme puts statin on the substrate molecule
The strain distorts a particular bond or bonds in the substrate
This lowers the activation energy needed to break the bond


What is the effect of rise in temperature on enzyme action?

Increases the kinetic energy of molecules
The molecules move around more rapidly and so collide with each other more often
More enzyme substrate complexes are formed in a given time
Rate of reaction increases


What happens to enzyme activity when the temperature is too high?

Hydrogen (and other) bonds in the enzyme break
The polypeptide chains become unravelled as the tertiary structure changes
The active site changes shape so the substrates are no longer complementary
Fewer enzyme substrate complexes formed
Enzymes denatured
Rate of reaction decreases


Why is our body temperature 37*C when the optimum for many human enzymes is 40*C?

Additional energy would be needed to maintain higher temperatures
Other proteins may be denatured at a higher temperature
If the temperatures were higher and a further rise in temperature occurred, due to illness for example, enzymes might denature


What would be the pH number of a solution with a hydrogen ion concentration of 1x10^-9?



Why are pH changes in organisms likes to reduce an enzyme’s action that to denature it?

pH fluctuations in organisms are usually small


What happens to rate of reaction at low enzyme concentration?

Too few enzyme molecules for all substrate molecules to find an active site at one time
Rate of reaction is half the maximum possible for the number of substrate molecules


What happens to rate of reaction at intermediate enzyme concentration?

With more molecules available, all substrate molecules can occupy an active site at the same time
Rate of reaction increases to its maximum


What happens to rate of reaction at high enzyme concentration?

Addition of further enzyme molecules has so effect
All substrates have an active site already
Rate of reaction is at a constant level


What enzyme inhibition?

Directly or indirectly interfering with the functioning of the active site to reduce its activity


What are the two main types of enzyme inhibitors?



How do competitive inhibitors slow enzyme function?

They have a similar molecular shape to the substrate
They can occupy the site of an enzyme
They are not permanently bound to the active site so substrates can eventually take their place
This makes the rate slower


What determines the effect of competitive inhibitors?

The difference in concentration of the inhibitor and substrate
More inhibitor will slow the reaction more


How do non-competitive inhibitors work?

Attach to a binding site on the enzyme that is not the active site
This affects hydrogen bonding and disulphides bridges, altering the tertiary structure and 3D shape
The active site changes shape so is no longer complementary
The enzymes function is blocked no matter how much substrate is present
Rate of reaction is reduced