Enzymes 2.4 Flashcards
What is an enzyme?
A biological catalyst
What do enzymes do?
They reduce the activation energy for biochemical reactions
What is activation energy?
The energy needed to break the bonds to start the reactions
What is an intracellular enzyme?
An enzyme that works inside cells
What are the 2 examples of intracellular enzymes?
- catalase which breaks down hydrogen peroxide into water and oxygen
- lysozyme which is found in lysosomes and digests old organelles and foreign bodies
What is an extracellular enzyme?
An enzyme that works outside cells
What are the 2 examples of extracellular enzymes?
- amylase which is found in saliva to catalyse the hydrolysis of starch into maltose
- trypsine which is produced by the pancrease and released into the small intestine to catalyse the hydrolysis of peptide bonds of proteins into smaller polypeptides
What are the two enzymes which catalyse protein hydrolysis?
- trypsin turns proteins into amino acids from the pancrease
- pepsine turns proteins into amino acids from the stomach
- difference in PH causes a need for different enzymes
What are the two mechanisms of enzyme action?
- lock and key model
- induced fit model
What is the lock and key model?
Substrate is complimentary to the specific active site of the enzyme due to the tertiary structure of the enzymes active site and it slots into the active site to form an enzyme-substrate complex where it is then broken down into the products, forming an enzyme-product complex
What is the induced fit model?
- substrate fits into the active site of an enzyme as they have an aproximate complimentary shape and non-covalent forces (H bonds) bind the substrate to the active site
- once an enzyme-substrate complex has formed the enzyme slightly changes shape to fit the substrate better
- this applies pressure on the bonds of the substrate, breaking or making it
- then forms an enzyme-product complex and the products are released
What is a catalyst?
A substance that speeds up chemical reactions by lowering the activation energy without being used up
Why is the induced fit model considered better?
- it shows how other molecules can affect enzyme activity
- it shows how the activation energy is lowered
What are the factors affecting enzyme activity?
- PH
- temperature
- conc. of enzymes
- conc. of substrate
- inhibitors ( competitive and non)
What happenes to enzymes if the temperatures too hot?
The enzymes vibrate too much due to an increase in kinetic energy causing the bonds between the R groups to break, changing the tertiary structure therefore causing the enzymes to denature
What happenes to enzymes if the temperatures too cold?
The kinetic energy of the enzymes decreases so much that they no longer have enogh energy to have any successful collisions meaning that no reaction can happen as they can not reach the activation energy
What does Q10 stand for?
- temperature coefficient
- it shows how much the rate of reaction changes when the temperature is increased by 10 degrees celcius
What does a Q10 of 2 mean?
If you increase the temperature by 10 degrees celcius, the rate of reaction doubles
How does PH affect enzymes?
H+ ions and OH- ions found in acids and alkalis break the ionic and hydrogen bonds that hold the enzymes tertiary structure in place, changing the shape of the active site so it can no longer bind to the substrate
How does enzyme and substrate conc. affect rate of reaction?
It causes the rate of reaction to increase until it plateaus at the point of saturation where all the enzyme active sites have been filled as much as they can and there is another limiting factor stopping the rate of reaction from increasing any more
What do these represent in an enzyme/ substrate, rate of reaction graph?
- steeper line
- flat line
- 2 lines levelling out at the same point
- 2 lines levelling out at different points
- 1st line to level off first
- faster rate of reaction
- reaction has stopped
- all of the reactants have been used up
- they made a different mass of product so there was a different limiting factor
- enzymes have denatured
What does a competitive inhibitor do?
It has a similar shape to the substrate so it binds to the active site but no reaction takes place so the active site is blocked temporarily
What does a non competitive inhibitor do?
It binds to an allosteric site which causes the enzymes active site to change shape so that the substrate molecule no longer fits
What is reversible inhibition?
When the inhibitor binds with weaker bonds like hydrogen or ionic, so the inhibitor can be removed and the substrate can bind as normal
