CH4: Enzymes Flashcards
(26 cards)
Define ‘enzymes’
- proteins that are folded to take on 3D globular shapes
- function as biological catalysts that speed up the rate of chemical reactions
- without themselves being chemically changed at the end of the chemical reactions.
How are enzymes shaped?
folded into three-dimensional globular shapes that have an active site complementary to substrate that binds to it
What is a substrate?
molecule which enzyme acts on
Why are enzymes specific to a molecule?
- Due to the unique 3D shape of their active site
- The shape of each active site is complementary to the shape of a specific substrate
- Hence, each active site only allows specific substance(s) to fit in
What are catabolic reactions?
reactions that BREAK UP complex molecules into simple molecules (e.g. hydrolysis)
What are anabolic reaction?
The process of SYNTHESISING macromolecules from monomers or simpler molecules.
What is activation energy?
Energy supplied to the reactant molecules for them to chemically react
How does the supply of activation energy to reactant molecules allow them to react chemically?
- Activation energy is usually supplied in the form of HEAT
- Absorption of thermal energy
> ^ k.e. of reactant molecules
> vibrate more vigorously
> collide ^ frequently and forcefully
> in the correct orientation for chemical reaction to occur - Thermal agitation of the atoms
> bonds more likely to break
Why is using heat to speed up a chemical reaction inappropriate for a biological system?
In high temperatures,
1. proteins denature and cells are killed
2. other chemical reactions will also be sped up
How do enzymes lower activation energy?
- the active site has a 3D shape complementary to the substrate, it provides a template which the substrates can come together in the correct orientation for a chemical reaction to occur
- When the enzyme binds to the active site of the enzyme, the enzyme-substrate complex is formed, lowering activation energy
Describe the process of an enzymatic reaction
- substrate collides with the enzyme at the correct orientation
- substrate binds to the active site of the enzyme and forms the enzyme-substrate complex
- formation of enzyme-substrate complex lowers the activation energy
- chemical reaction occurs and products are formed
- enzyme-substrate complex releases the products and the chemically unchanged enzyme
What are the 2 models used to explain enzyme reaction?
- Lock and key
- Induced fit model
How does the lock and key hypothesis explain enzyme reaction?
substrate > key, enzyme >lock
shape of active site in enzyme is COMPLEMENTARY to the shape of substrate > substrate fits EXACTLY
substrate binds to the active site of the enzyme, forming enzyme-substrate complex > lowers activation energy > speeding up the rate of chemical reactions
How does the induced fit model explain enzyme reaction?
active site of the enzyme is complementary but not a perfect fit to the substrate it catalyses
when the substrate binds to the active site of the enzyme, the shape of the active site changes
allows substrate to fit more tightly into the active site, forming enzyme-substrate complex
Characteristics of enzymes:
- speed up chemical reaction by lowering activation energy (biological catalysts)
- remain chemically unchanged after reactions
- are specific due to the specific 3D globular shape of their active site that is complementary to their substrate
- needed in minute amounts
- are affected by temperature and pH
What factors affect the rate of enzyme-catalysed reactions?
- temperature
- pH
- enzyme concentration
- substrate concentration
How do low temperatures (near or below 0°C) affect the rate of enzyme activity?
- enzymes and substrates posses low K.E.
- they move slowly
- less effective collisions occur
- fewer enzyme-substrate complexes are formed
- rate of enzyme activity is very low
How does the increase in temperature affect the rate of enzyme activity?
- ^ temperature > ^ k.e. of substrate and enzyme
- enzyme and substrate vibrate more vigorously > enzyme and substrate collide more frequently
- ^ formation of enzyme-substrate complexes > lower activation energy
- ^ rate of enzyme activity
The rate of reactions doubles every ___ increase in temperature
The rate of reactions doubles every 10°C increase in temperature
At the enzyme’s optimum temperature, the rate of reaction ______.
plateaus
What happens to the rate of enzyme activity when the temperature increases beyond optimum temperature?
enzyme is denatured
> loses its 3D globular shape of its active site
> as bonds within the enzyme are broken
> active site is no longer complementary to substrate
> substrate is unable to bind to the active site
> enzyme-substrate complex can no longer be formed
> rate of enzyme activity decreases
How does extreme pH affect rate of enzyme activity?
Rate of enzyme activity decreases when pH increases or decreases beyond its optimum pH
changes in pH cause
> enzyme to denature and lose its 3D globular shapes
> as bonds within the enzyme are broken
> active site is unable to bind to substrate as its shape is no longer complementary to its substrate
> enzyme-substrate complex cannot form
What happens to enzyme activity as enzyme concentration increases?
increased concentration of enzymes
> more active sites available to bind with substrate
> more effective collision occurs
> more formation of enzyme-substrate complexes
> lower activation energy
> increase enzyme activity
At high enzyme concentrations,
- rate enzymatic reactions plateaus
- all substrates are bound to an enzyme’s active site
- there is an excess of enzyme molecules present
- substarte concentration becomes the limiting factor
What happens to enzyme activity as substrate concentration increases?
increased concentration of substrates
> more effective collisions occur
> more formation of enzyme-substrate complexes
> lower activation energy
> rate of enzyme activity increases
At high substrate concentrations,
- rate of enzyme activity plateaus
- all active sites available are occupied
- there is an excess of substrates present
- enzyme concentration is now the limiting factor
