Enzymes Flashcards
What are enzymes
biological catalysts and globular proteins
What are the two forms of enzyme
Intracellular or Extracellular
What is an extracellular enzyme
enzymes active outside of the cell
What is an intracellular enzyme
enzymes active inside of the cell
Give an example of an intracellular enzyme
Catalase
Give an example of an extracellular enzyme
Amylase
What does catalase do
Converts hydrogen peroxide, which is harmful to cells and a by product of many processes, into water and oxygen - preventing damage to cells and tissues.
What does Amylase do
Hydrolyses starch into simple sugars. Digestion is usually carried out by extracellular enzymes, as macromolecules are too large to enter the cell.
What forms when an enzyme and substrate combine
An enzyme-substrate complex
What can denature enzymes
Heat and pH
What is the shape of the active site determined by
The complex tertiary structure of the protein that makes up the enzyme.
What determines the shape of an enzyme
the order of amino acids (if altered the 3D shape changes)
Is enzyme substrate complex temporary or fixed
Temporary
What two types of enzyme reactions are there
Catabolic or Anabolic
What is a catabolic reaction
When a single substrate is drawn into the active site and broken apart into two or more distinct molecules. E.g. Cellular respiration and hydrolysis
What is an anabolic reaction
When two or more substrates are drawn into the active site, forming bonds between them and releasing a single product. E.g. Protein synthesis and photosynthesis
What do enzymes do to activation energy
Lower it
What is activation energy
Amount of energy needed for a substrate to be unstable enough for a reaction to occur and products form
How do enzymes speed up chemical reactions
They influence the stability of bonds in reactants.
What does lock and key model suggest
Enzyme and substrates are a rigid shape that locked in together.
What does induced fit model suggest
Prior to binding substrate and active site aren’t completely complementary in shape. When substrate binds the active site alters shape and moulds around substrate.
What evidence is there to support induced fit model
X-ray diffraction techniques allow for 3D pictures of molecules to be formed. Can take pictures of enzyme before and after bond to see if it changes shape.
What are changes in shape known as
Conformational changes
How does a conformational change support the enzyme
It maximises the ability of the enzyme to catalyse the reaction
What do lower temperatures do to reactions
Prevent or slow them down
What do higher temperatures do to reactions
Speed them up
What happens if temperature is too high
Rate at which enzyme catalyses a reaction drops sharply. Enzymes starts to denature
How does pH affect enzymes
Below or Above optimum pH of enzyme, solutions with too much H+ ions (acidic) and OH- ions (alkaline) can cause bonds to break.
How can you estimate an enzymes optimum pH
Where an enzyme functions can be an indicator of its optimal pH.
How can you investigate the effect of pH on the rate of enzyme - catalysed reactions
Use buffer solutions of different pHs to measure the rate of reaction at different pH values. Buffer solutions will maintain their pH. Use same volume of each buffer solution when adding to reaction mixture.
How can you work out the pH of a solution if the hydrogen ion (H+) concentration is known
Put in calculator: -log(H+)
How does Enzyme concentration affect rate of reaction
If enzyme concentration is fixed but the concentration of substrate is increased past a certain point, all available active sites eventually become saturated and any further increase in substrates won’t increase rate of reaction. Substrates will begin to ‘queue up” for an active site instead.
What is it known as when substrates must queue up for an active site
Vmax (velocity = V)
What are the two types of reversible inhibitors
Competitive inhibitors and Non competitive inhibitors
What do competitive inhibitors do
Have a similar shape to that of the substrate molecules and therefore compete with substrate for active site.
What do non competitive inhibitors do
Bind to enzyme at an alternative site which alters the shape of the active site
What else other than reducing or stopping enzyme activity can reversible inhibitors do
Act as regulators in metabolic pathways so that no single enzyme can ‘run wild’ and continuously and uncontrollably generate more and more of a particular product.
How can metabolic reactions be controlled
Using the end - product of a particular sequence of metabolic reactions as a non - competitive, reversible inhibitor.
How is the process of enzymes converting substrates to products slowed down by itself
The end - product of the reaction chain binds to alternative sites of the original enzyme, changing the shape of the active site ad preventing the formation of more enzyme substrate complexes.It can then detach and be used elsewhere. Allows active site to reform.
What happens as you increase concentration of inhibitors
Rate of reaction decreases or can stop completely
How can you counter competitive inhibitors
Increase substrate concentration
Does increasing substrate concentration help counter non - competitive inhibitors
No
