2.1.4 - Enzymes Flashcards
What are enzymes ?
Enzymes are biological catalysts that increase the rate of a chemical reaction, but are not consumed by that reaction
What type of proteins are enzymes ?
Globular proteins
What is meant by enzymes being specific ?
- Each enzyme is very selective, it catalyses specific reactions
- Each enzyme recognises a specific substrate, the active site fits to the substrate
What is the shape of the active site determined by ?
It is determined by the tertiary structure of the protein
What does an enzyme catalyst do ?
- Lowers the activation energy
- It is not used up during the reaction
- After the reaction, the enzyme is free to bind to a new substrate molecule.
What is activation energy ?
- It is the energy that must must be overcome in order for a reaction to occur
- The minimum amount of energy require for the reaction to begin
What are anabolic reactions ?
Chemical reactions required for growth
What catalyses anabolic reactions ?
Enzymes
What are catabolic reactions ?
Chemical reactions that break things down
What catalyses catabolic reactions ?
Enzymes
Define metabolism
Metabolism is all of the reactions happening in a cell or an organism at a given time
Define Vmax
- Vmax is the maximum possible rate of reaction
- Enzymes can only increase the rate of reaction until this point
Briefly explain how temperature increases the rate of reaction
When high temperatures and pressures are applied, the speed of the molecules will increase, therefore so will the number of successful collisions and the overall rate of reaction
What are the two hypothesis for enzymes ?
- Lock and key hypothesis
- Induced fit hypothesis
What is the lock and key hypothesis ?
- Only a specific substrate will fit the active site of an enzyme
- When the substrate is bound to the active site, an enzyme-substrate complex is formed
- The substrate then reacts and the products are formed in an enzyme product complex
What is the induced fit hypothesis ?
- The initial interaction between the enzyme and substrate is relatively weak
- These weak interactions rapidly induce changes in the enzymes tertiary structure which then strengthens the binding, putting strain on the substrate molecule
What are intracellular enzymes ?
Enzymes that act within cells
Give an example of an intracellular enzyme
Catalase breaks down hydrogen peroxide because it is a toxic product of many metabolic pathways
What are extracellular enzymes ?
Enzymes that are released from cells to break down large molecules into smaller molecules, done outside of the cell
Explain extracellular enzymes in single celled organisms
Single celled organisms, such as bacteria and yeast, release enzymes into their environment. The enzymes break down large molecules, which are then absorbed by the cells.
Explain extracellular enzymes in multicellular organisms
Large molecules are digested so smaller molecules can be absorbed into the bloodstream. They are then transported around the body to be used as substrates.
Explain the digestion of starch
- Starch is broken down into maltose, which is a disaccharide. The enzyme involved in this is called amylase
- Maltose then broken into glucose, which is a monosaccharide, the enzyme involved in this is maltase.
What is amylase ?
- Enzyme involved in the breakdown of starch into maltose
- It is present in the salivary glands and the pancreas.
- It is released in saliva into the mouth and in pancreatic juice into the small intestine
What is maltase ?
- Involved in the breakdown of maltose into glucose
- Present in the small intestine
What is trypsin ?
- Trypsin is a protease enzyme, an enzyme that catalyses the digestion of proteins
- It is produced in the pancreas and released with the pancreatic juice into the small intestine, where it acts on proteins
What is trypsin involved in ?
It is involved in the digestion of proteins into smaller peptides, which can then be broken into amino acids by other proteases
How are amino acids reabsorbed ?
They are absorbed by living cells of the digestive system and then absorbed into the bloodstream
What are the factors that affect enzyme activity ?
- Temperature
- pH
- Enzyme concentration
- Substrate concentration
What factors affect the structure of the enzyme ?
- Temperature
- pH
How can these factors be investigated ?
They can be investigated by measuring the rate of the reactions they catalyse
What does an increase in temperature do ?
Increased temperature increases the kinetic energy of the particles. As temperature increases, the particles move faster and collide more frequently
How does temperature affect an enzyme controlled reaction ?
An increase in temperature will result in more frequent successful collisions which would lead to an increase in the rate of reaction
What is the temperature coefficient ?
Q10, is a measure of how much the rate of reaction increases with a 10 degree increase in temperature
What is the temperature coefficient in enzyme controlled reactions ?
In enzyme controlled reactions, Q10 is 2
What does Q10 having a value of 2 mean ?
This means that the rate of reaction doubles with a 10 degree rise in temperature
What happens at extremely high temperatures ?
The bonds holding the protein together vibrate more until the bonds strain and then break
What does the breaking of bonds result in the structure of a protein ?
The breaking of bonds results in a change in the tertiary structure of the protein
What is the process where the temperature gets too high for the enzyme ?
Denaturing
What is optimum temperature ?
The temperature at which the enzyme has the highest rate of activity
What is the optimum temp in the human body ?
40 degrees
What are thermophiles ?
Thermophiles are organisms that live in extremely hot environments
What is the optimum temp in thermophiles ?
70 degrees
How are thermopiles adapted to their environment ?
- They are more stable than other enzymes due to the increased number of hydrogen bonds and disulphide bridges in their tertiary structure
- This makes them resistant to change as the temperature increases
What is a psychrophilic organism ?
Organisms that live in cold environments
What is the optimum temp in psychrophilic organisms ?
Below 5 degrees
How are psycrophilic organisms adapted to their environment ?
- They tend to have more flexible structures, making them less stable
- Smaller temperature changes will denature them
How are enzymes held in their 3D structure ?
-By hydrogen bonds and ionic bonds between amino acids and R - groups
What do these bonds result from ?
Interactions between the polar and charged R - groups present on the amino acids forming the primary structure
What determines pH ?
The amount of hydrogen ions present
What is a low pH ?
- More hydrogen ions
- Low pH
- Acidic environments
What is a high pH ?
- Fewer hydrogen ions
- High pH
- Alkaline environments
What is optimum pH ?
- The optimum pH is different for each enzyme
- The optimum pH is the pH where the active site is the right shape to catalyse the reaction
What happens when pH changes from its optimum ?
The structure of the enzyme and its active site is altered
What happens when the pH changes significantly ?
- The structure of the enzyme is altered and the active site is no longer complementary to the substrate
- Enzyme is denatured, reduces the rate of reaction
What is renaturation ?
When the pH returns to the optimum, the protein will resume catalysing reactions in its normal shape
What does changing the concentration of H+ ions cause ?
It changes the degree of the interactions between the H+ ions and the polar and charged groups
What does more/less H+ ions cause ?
- The R-groups are able to interact with each other more/less
- This leads to bonds breaking and the shape of the enzyme changing
- It is then unable to catalyse the same reaction
What does an increase in concentration of substrate mean ?
The substrate molecules in a particular volume increase
What does this lead to ?
- Higher collision rate with the active sites of enzymes and the formation of more enzyme-substrate complexes.
- The rate of reaction increases
What does an increase of the concentration of enzymes lead to ?
This will increase the number of available active sites in a particular area or volume, leading to the formation of enzyme-substrate complexes at a faster rate
What is the Vmax ?
The max point that the rate of reaction can reach
What happens at the Vmax point ?
At this point no more enzyme substrate complexes can be formed until products are released from active sites
How can you increase the rate of reaction when it is at its Vmax ?
Add more enzymes or increase the temperature
How are enzymes activated ?
Cofactors
How are enzymes inactivated ?
Inhibitors
What is an inhibitor ?
A molecules that prevents enzymes from catalysing reactions
What are the two types of inhibitors ?
- Competitive inhibitors
- Non competitive inhibitors
What is competitive inhibition ?
- A molecule that has a similar shape to the substrate of an enzyme can fit into the active site
- This blocks the substrate from entering the active site, preventing the enzyme from catalysing the reaction
- The enzyme can not carry out its function anymore and is now said to be inhibited
Why are they called competitive inhibitors ?
Substrate and inhibitor molecules compete with each other to bind to the active site of the enzyme
What does the degree of inhibition depend on ?
The relative concentration of substrate, inhibitor and enzyme
How long do competitive inhibitors bind for ?
- They only bind temporarily
- Their effect is reversible, apart from aspirin
How does competitive inhibition affect the rate of reaction ?
- It reduces the rate of reaction for a given concentration of substrate
- But, it does not change the Vmax of the ezyme
What are some examples of competitive inhibition ?
- Statins, they are used in the synthesis of cholesterol and given to people to help reduce blood cholesterol levels
- Aspirin irreversibly inhibits the active site of COX enzymes, preventing the synthesis of the chemicals responsible for producing pain and fever
What is Non-competitive inhibition ?
- The binding of the inhibitor to an allosteric site causes the tertiary structure of the enzyme to change, active site shape changes
- This results in the active site no longer being complementary to the substrate and unable to bind to the enzyme
What is an allosteric site ?
An alternative site that the inhibitor binds to on the enzyme
How long do non competitive inhibitors bind for ?
- They can not be removed from the enzyme
- They are irreversible
Why is it called a non-competitive inhibitor ?
The inhibitor does not compete with the substrate for the active site
How does non-competitive inhibition affect the rate of reaction ?
- Decreases the rate of reaction
- Increasing the concentration of the enzyme or substrate will not overcome the effect of the inhibitor
- Increasing the concentration of the inhibitor will decrease the rate of reaction as more active sites become unavailable
What are some examples of non-competitive inhibition ?
- Organophosphates irreversibly inhibit the enzyme acetyl cholinesterase, an enzyme necessary for nerve impulse transmission. This can lead to muscle cramps, paralysis and even death if ingested
- Proton Pump Inhibitors are used to treat indigestion. They irreversibly block an enzyme responsible for secreting hydrogen ions into the stomach. They prevent the production of excess acid which can form stomach ulcers.
What is end product inhibition ?
It is the term used for inhibition that occurs when the product of a reaction acts as an inhibitor to an enzyme that produces it
What does end product inhibition serve as ?
- A negative feedback control mechanism
- Excess products are not made and resources are not wasted
What are cofactors ?
They are non protein helper components that help an enzyme carry out its function of catalysis
What do cofactors do ?
- They can transfer atoms from one reaction to another in a multistep pathway
- They may form part of the active site of an enzyme
How are cofactors obtained ?
- They are obtained via minerals
Give an example of a cofactor
Amylase, it contains a chloride ion which is necessary for the formation a correctly shaped active site
What are coenzymes ?
A coenzyme is an organic molecule that helps an enzyme to carry out its function
How are coenzymes obtained ?
Via Vitamins
Give some examples of coenzymes
- B3 is used to synthesise NAB
- B5 is used to make coenzyme A which is involved in the breakdown of fatty acids and carbohydrates in respiration
What is a prosthetic group ?
Prosthetic groups are cofactors, they are required by certain enzymes to carry out their catalytic functions
How are prosthetic groups bound to the enzyme ?
They are tightly bound to the enzyme and form a permanent feature of the protein
Give an example of a prosthetic group
Zn 2+ ions in carbonic anhydrase in the metabolism of CO2
What are some enzymes originally produced as ?
Inactive precursor enzymes
Which types of enzymes are produced as inactive precursor enzymes ?
- Enzymes that can damage cells or tissues
- Enzymes whose actions need to be controlled and activated under certain conditions
How can inactive precursor enzymes be activated ?
By a change in the tertiary structure and ultimately a change in the active site
What needs to be added to activate inactive precursor enzymes ?
A cofactor
What is it called before adding the cofactor ?
An apoenzme
What is it called after adding the cofactor ?
A haloenzyme
What are zymogens ?
Precursor enzymes that are activated by a change in conditions, not a cofactor, which results in a change in their tertiary structure
