CH4: Enzymes Flashcards
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 sight where substrate(s) bind(s)
What is a substrate?
molecule which enzyme acts on
Why are enzymes specific to a molecule?
Due to the unique 3D shape of every enzyme, 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
> ^ speed of reactant molecules
> 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 > the substrate to enter the active site of the enzyme
- 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
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
- remain chemically unchanged after reactions > can be used over and over again
- are specific due to their specific 3D globular shapes
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 enzymes?
enzymes are inactive > rate of enzyme activities is low
How does temperature affect the rate of enzyme activity?
- ^ temperature > ^ k.e. of substrate and enzyme
- enzyme becomes more active
- enzyme and substrate collide more often > ^ formation of enzyme-substrate complexes
- ^ 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 ______.
remains constant
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
> active site is no longer complementary to substrate
> active site is unable to bind the substrate
> enzyme-substrate complex can no longer be formed
> rate of enzyme activity decreases
How does extreme pH affect enzymes?
enzyme loses its 3D globular shapes and active site is unable to bind to substrate
What happens to the rate of enzyme activity as the concentration of enzymes increase?
increased concentration of enzymes
> more active sites available to bind with substrate
> more effective collision occurs
> more formation of enzyme-substrate complexes
> more products formed
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 when to enzyme activity as substrate concentration increases?
increased concentration of substrates
> more effective collisions occur
> more formation of enzyme-substrate complexes
> more products formed
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
