TOPIC 4 : ENZYMES Flashcards
2.4.1 Action of Enzymes
What are enzymes?
Speeds up chemical reactions by acting as biological catalysts
A catalyst is a substance that speeds up a chemical reaction without being used up in the reaction itself
Globular protein
3D shape - and have a primary, secondary and tertiary structure
The 3D shape is due to the interactions between R-groups of the amino acids, that make uo the protein including H-bonds, ionic, covalent, hydrophobic/hydrophilic interactions
Each enzyme has an active site that is complimentary to the shape of a specific substrate molecule
2.4.1 Action of Enzymes
What is the structure of an enzyme?
They have an active site, and this is the part of the enzyme where the substrate molecule binds to
The active site has a specific shape, which is determined by the enzyme’s tertiary structure
For an enzyme to work, the substrate has to fit into the active site.
If the substrate shape doesn’t match the active site, the reaction won’t be catalysed
This means that enzymes are very specific and work with very few substrates - usually only one
When a substrate binds to an enzyme’s active site, an enzyme-substrate complex is formed
2.4.1 Action of Enzymes
How do enzymes work?
In order for a reaction to occur, reactant molecules must contain sufficient energy to cross a potential energy barrier, the activiation energy
All molecules possess varying amounts of energy (KINETIC ENERGY) but only a few have sufficent energy for a reaction to occur
The lower the potential energy barrier to reaction, the more reactant molecules will have sufficient energy and, hence, the faster the reaction will occur
All catalyst, including enzymes, function by forming a transistion state, with th reactants, of lower free energy than would be found in the incatalysed reaction
2.4.1 Action of Enzymes
Why are enzymes so important?
Living things have evolved to use enzymes to speed up their chemical reactions
However, the heat required for most reactions would damage the actual cells
An enzyme is a biological catalyst: biological meants they are made by living things and a catalyst is a chemical reaction that speeds up a chemical reaction without being used up itself
Enzymes work on chemiclas called substrates and produce products
Some enzymes are involved in anabolic reactions (building bigger molecules) and some are involved in catabolic reactions (breaking molecules down)
All chemical reactions inside a cell is called METABOLISM
Some enzymes work inside the cell –> INTRACELLULAR enzymes
While those that work outside the cell are called extracellular
2.4.1 Action of Enzymes
Explain the lock and key model?
This is where the substrate fits into the enzyme in the same way that a key fits into a lock - the active site and substrate have a complementary shape
Didn’t give the full story
The enzyme and substrate do have to fit together in the first place, but new evidence showed that the enzyme-substrate complex changed shape slightly to complete the fit
This locks the substrate even more tightly to the enzyme
Then came up with the induced model
2.4.1 Action of Enzymes
Explain the induced model?
Helps to explain why enzymes are so specific and only bond to one particular substrate
The substrate doesn’t only have to be the right shape to fit the active site, it has to make the active site change shape in the right way as well
2.4.2 Factors affecting enzyme activity
How does temperature affect enzyme activity?
The rate of an enzyme-controlled reaction increases when the temperature’s increased
Up to the optimum temperature, enzymes and substrate gain more kinetic energy so they move around more
Therefore, there is a greater chance of more successful collisions between the enzyme and the substrate
This leads to an increase in the rate of reaction
Optimum temperature at which the rate of reaction reaches a maximum
After the optimum, as temp increases the extra KE begins to break bonds in the tertiary structure of the enzyme
This will cause the enzyme to change shape, then the active site will change shape = denaturing
The active site will no longer have a complimentary shape to the substrate, so no ESCs form resulting the rate of reaction decreasing
2.4.2 Factors affecting enzyme activity
How pH affect enzyme activity?
Different enzymes have different optimum pH
As the environmental pH moves away from the optimum, the changing ratio of H+ and OH- interferes with the hydrogen and ionic bonds so they break, that holds the enzyme’s tertiary structure in place
This results in the enzyme’s active site changing shape (denaturation) so it is no longer complimentary to the substrate so no ESCs form resulting in the rate of reaction decreasing
2.4.2 Factors affecting enzyme activity
How does enzyme concentration affect enzyme activity?
The more enzyme molecules there are in a solution , the more likely a substrate molecule is to collide with one and form an ESC
Increasing the concentration of the enzyme increases the rate of reaction
If the amount of substrate is limited, there comes a point when there’s more than enough enzyme molecules to deal with all the available substrate, so adding more enzyme = no further effect
To maintain a high rate = add more substrate/increase (substrate)
2.4.2 Factors affecting enzyme activity
How does substrate concentration affect enzyme activity?
The higher the substrate concentration, the faster the reaction
More substrate molecues means a collision between substrate and enzyme is more likely, so more active sites will be occupied and more ESCs will be formed - only true until ‘saturation’ point
Aftr that, there is so many substrate molecules that the enzymes have about as much as they can cope with, and adding more makes no difference - enzyme concentration becomes the limiting factor
Because there are not enough enzymes present to act on the increasing number of substrate molecules - all active sites are saturated (Vmax)
To maintain a high rate = add more enzymes/increase (enzyme)
2.4.4 Co-factors, Co-enzymes and Inhibitors
What is a co-factor?
Non-protein molecules which enables enzyme action
2.4.4 Co-factors, Co-enzymes and Inhibitors
What does the co-factor prosthetic groups do?
Non-protein, tightly&permanently bound groups to enzymes to enable ESCs to form - aren’t directly involved in the reaction
Known as a conjugate protein
EXAMPLE:
Zinc ions are a prosthetic group for carbonic anhydrase which breaks down CO2 in red blood cells
2.4.4 Co-factors, Co-enzymes and Inhibitors
What do the co-factor inorganic ions do?
Non-protein, inorganic molecules which loosely & temporarily bind to enzymes to enable ESCs to form - aren’t directly involved in the reaction. They are said to activate enzymes
Not used up or changed in any way
Obtained in the diet from minerals
EXAMPLES:
Chlorine ions (CL-) are cofactors for amylase - they bind in allosteric sites and can be called “allosteric activators”
2.4.4 Co-factors, Co-enzymes and Inhibitors
What do the co-factor coenzymes (organic molecules) do?
Non-protein, organic molecules - either vitaminis or derived from vitamins. They loosely & temporarily bind to enzymes often acting as carriers
Changed once released
EXAMPLE:
NAD is a cofactore for enzyme in respiration & other reactions such as the breakdown of alcohol - derived from Vit B3
2.4.4 Co-factors, Co-enzymes and Inhibitors
What are inhibitors?
Enzyme inhibitors are molecules that binds to enzymes and prevents enzyme action i.e they cannot catalyse reactions
2.4.4 Co-factors, Co-enzymes and Inhibitors
What are competive inhibitors?
Rate of reaction decreases
CI similar in shape to subrate therefore complementary to the active site
CI binds temporily to active site therefore less chance substrate binds therefore fewer ESCs formed therefore less product formed
To reduce inhibition = add more substrates than CIs/ increase (substrate) >(CI)
2.4.4 Co-factors, Co-enzymes and Inhibitors
What is non-competitve inhibitors?
Rate of reaction decreases even more
NCI binds to enzme at allosteric site NOT active site
Changes the shape of the active site
Substrate unable to bind to active site therefore far fewer substrate bind therefore far fewer ESCs formed therefore even less product is formed
To reduce inhibitation = add more enzymes than NCIs/increase (enzyme) > (CI)
2.4.2 Factors affecting enzyme activity
What is V(max)?
It is the rate of reaction when the enzyme is saturated with substrate - its the maximum rate of reaction
The maximal rate, Vmax reveals the turnover number of an enzyme i.e the number of substrate molecules being catalysed per second
2.4.4 Co-factors, Co-enzymes and Inhibitors
What are the prosthetic groups?
These are the co-factors which tightly and permanetly bind to the enzyme
The protein is then know as a cojugate protein
EXAMPLE: Zinc ions are a prosthetic group for carbonic anhydrase which breaks down CO2 in Red blood cells
2.4.4 Co-factors, Co-enzymes and Inhibitors
What are the inorganic co-factors?
These are inorganic molecules or ions that help the enzyme bind to the substrate
They are loosely bound and are not used up or changed in any way
Obtained in the diet from minerals
EXAMPLE:
Chlorine ions (CL-) are cofactors for amylase - they bind in allosteric sites and can be called ‘allosteric activators’
2.4.4 Co-factors, Co-enzymes and Inhibitors
What are co-enzyme (aka organic cofactors)?
These are organic molecules that participate in the reaction, by temporarily binding to the enzyme and are changed once released
Most commonly co-enzymes act as, carriers moving chemical groups between enzymes, and are continuously recylced
Obtained in the diet from minerals
EXAMPLE:
NAD cofactor for enzymes in respiration & other reactions such as the breakdown of alcohol - derived from Vit B3.
2.4.4 Co-factors, Co-enzymes and Inhibitors
What are reversible inhibitors?
Reversible inhibitation is when an inhibitor temporarily binds to the enzyme due to weak hydrogen / ionic bonds
2.4.4 Co-factors, Co-enzymes and Inhibitors
What is irreversible inhibitation?
Irreversible inhibitation is when an inhibitor permanently binds to the enzyme due to strong covalent bonds
2.4.4 Co-factors, Co-enzymes and Inhibitors
The role of metabolic poisons
Metabolic poisons interfere with metabolic reactions ( the reaction occurs in cells) causing damage, illness or death - they’re often enzyme inhibitors
EXAMPLE: How etheylene glycol (antifreeze) is metabolised by ethanol dehyfrogenase, to oxalic acid (poisonous)
Ethylene glycol is similar in shape to ethanol, which acts as a competitive inhibitor of the above reaction. Mixing large amounts of ethanol with ethylene glycol slows the above reaction
