proteins are enzymes Flashcards
3.1.4.2
Why do different proteins have different structures?
- different proteins have a different order and number of amino acids in the polypeptide chain
- this means the R groups are in different places
- so the hydrogen, ionic and disulphide bonds will form in different places
- so the tertiary structure will be different and fold into a different 3D shape
How can proteins become denatured?
- bonds in the tertiary structure are broken with heat and if the pH is too low or too high
- which changed the shape of the tertiary structure
- since the structure of proteins are fundamental for carrying out its function, any change in shape means it can no longer carry it out
What is an enzyme?
- Enzymes are globular proteins
- they are biological catalysts and work by lowering the activation energy
- the globular shape includes an active site where a reaction takes place
- each enzyme is specific for one substrate
Why are enzymes beneficial for biological reactions in cells?
- act as catalysts - speed up reactions
- by reducing activation energy - reactions can occur fast enough to substation functioning of the cell at a lower temperature than otherwise necessary
- not used up in the reaction
- effective in small quantities
What are the two models for how enzymes work?
- lock and key model
- the induced fit model
Describe the lock and key model
Enzyme active site = lock
Substrate = key
The active site is a fixed shape, exactly complementary to the substrate shape and specific to that one substrate
When the substrate and enzyme collide, an enzyme-substrate complex forms
Describe induced fit model
- active site isn’t fixed, it is flexible
- as the substrate binds to the active site, the active site folds around substrate, becoming complementary to the substrate, forming an enzyme-substrate complex
- as the active site folds round, weakens bonds in substrate, therefore lowering activation energy for reaction
Describe how enzymes are specific
- each enzyme has a different primary structure
- which would mean the R groups would be in different places
- so the ionic, disulphide and hydrogen bonds would form in different places
- producing a different tertiary structure
- so a different shaped active site which would only become complementary to one substrate/reaction
What are some factors affecting the rate of enzyme-controlled reactions?
- temperature
- pH
- enzyme concentration
- enzyme volume
- substrate concentration
- substrate volume
- inhibitors
Effect of enzyme concentration?
- increasing the enzyme concentration increases the rate of reaction
- there are more active sites available to the substrates so more successful collisions and more enzyme-substrate complexes
Effect of substrate concentration?
- initially, increasing substrate concentration increases the rate of reaction, so more successful collisions and more enzyme-substrate complexes
- then it levels off at a certain point because all the active sites are full, max number of enzyme-substrate complexes have formed
- enzyme concentration is a limiting factor
What are enzyme inhibitors?
Reduce enzyme activity by preventing formation of enzyme substrate complexes
There are two types
What are the two types of enzyme inhibitors?
- competitive
- non-competitive
Describe competitive inhibitors
- similar shape to the substrate
- compete with the substrate molecules
- bind to the active site and block it
- prevents the substrate from binding
- inhibition can be overcome by more substrate
Describe non-competitive inhibitors
- binds at a site that is not the active site (allosteric)
- causing a change in the shape of the active site
- therefore the substrate is no longer able to bind to the active site
- prevents the formation of an enzyme substrate complex
- cannot be overcome by addition of more substrate
