Where would you find an extracellular enzyme? Give an example.
Outside cells. Digestive enzymes
True or false? Catabolic reactions are where the enzymes catalyse reactions which breaks larger molecules into smaller molecules
Are enzymes globular proteins?
Are globular proteins (enzymes) water soluble?
What characteristic of an enzyme allows reactions to take place at a lower temperature?
The fact that it can reduce the activation energy
Where are intracellular enzymes found? Include examples.
Inside cells. DNA polymerase, RNA polymerase.
What are the two models that explain ways of thinking about enzymes?
Lock and key and induced fit model
What is meant by the term specificity?
The active site of an enzyme being only complementary in shape to one substrate
What is the name of an enzyme that breaks down ester bonds?
True or false? In induced fit, the shape of the active site of an enzyme is complementary to the shape of the substrate
False. Almost complementary
Define the term 'rate'
Rate is the amount of something produced per unit time
How would you calculate the initial rate of a reaction shown on a graph?
Draw a tangent on the graph. Difference in Y / difference in X
Give three factors that affect rate of reaction
pH, temperature and concentration of substrates
More ____________ form as the temperature moves towards the optimum.
Enzyme substrate complexes
What is saturation point?
When all active sites of enzymes are occupied by substrates.
Fill in the gaps in this basic description of enzymes. Enzymes are ________ _________. They are globular _________ that interact with the _________ molecules causing them to ________ at much faster rates without harsh environmental ________.
Biological catalysts, proteins, substrate, react, conditions.
True or false? Without enzymes many of the processes necessary to life would not be possible.
Living organisms need to be built and maintained. What does this involve?
The synthesis of large polymer-based components.
What is a word used to describe the chemical reactions required for growth?
What is the meaning of the word 'anabolic'?
What is a word used to describe reactions where energy is released from large organic molecules like glucose?
What is the meaning of the word 'catabolic'?
True or false? Only anabolic reactions involve enzymes.
False. Both anabolic and catabolic reactions involve enzymes.
Energy is constantly required for the majority of living processes including g_____.
Where are many of the large organic molecules involved in catabolic reactions obtained from?
Digestion of food.
What is metabolism and when can it happen?
Metabolism is the sum of all of the different reactions and reaction pathways happening in a cell or an organism and it can only happen as a result of the control and order imposed by enzymes.
True or false? Digestion is catalysed by enzymes.
Do reactions often occur in isolation?
No, they occur as part of multi-step pathways.
What is the speed at which different cellular reactions proceed affected by?
Different environmental conditions including: temperature, pressure and pH.
What is the name given to the point at which enzymes can increase the rates of reactions up to?
Vmax (maximum initial velocity or rate of the enzyme-catalysed reaction)
For a reaction to happen, what do the particles need to do?
Molecules need to collide in the right orientation.
In solution, how do molecules collide?
What are two factors that can increase the rate at which particles can collide?
Temperature and pressure.
How many different reactions can each enzyme catalyse?
Each enzyme catalyses one biochemical reaction.
What term is used to describe the fact that each enzyme can only catalyse one reaction?
What is the term used to describe the energy that needs to be supplied for most reactions to start?
True or false? Sometimes, the amount of energy needed to start a reaction is so large it prevents the reaction from happening under normal conditions.
Fill in the gaps. ________ help the molecules collide ________ and therefore _______ the activation energy required.
Enzymes, successfully, reduces.
How many enzyme hypotheses are there to explain how enzymes work and what are their names?
Two, the lock and key hypothesis and the induced fit hypothesis.
What is the active site of an enzyme?
An area within the tertiary structure of the enzyme that is complementary to the shape of a specific substrate molecule.
What is the lock and key hypothesis?
In the same way that only the right key will fit into a lock, only a specific substrate will 'fit' the active site of an enzyme.
In the Lock and Key hypothesis, what is formed when the substrate is bound to the active site?
An enzyme-substrate complex.
In the Lock and Key hypothesis, what happens when the substrate reacts in the active site?
Products are formed in an enzyme-product complex.
In the Lock and Key hypothesis, what happens once an enzyme-product complex has been formed?
The product or products are released
True or false? In the Lock and Key hypothesis, the enzyme remains unchanged and can take part in subsequent reactions.
Fill in the gaps. In the Lock and Key hypothesis, the R-groups within the _______ site of the enzyme will _______ with the _______, forming temporary bonds. These put a ______ on the bonds within the substrate.
Active, interact, substrate, strain.
What is the name given to enzymes that act within cells?
What is the name given to enzymes that act outside of cells?
Why do the raw materials (substrates) need to be constantly supplied to cells?
To keep up with the constant demand.
What supplies the raw materials (substrates)?
Nutrients present in the diet or environment.
Nutrients are often in the form of polymers such as proteins and polysaccharides. Why can't these enter cells directly through the cell surface membrane?
Because they are too large.
What is the process by which enzymes break large polymers in to smaller components?
True or false? Only single-celled organisms rely on extracellular enzymes to make use of polymers for nutrition?
False. Both single-cellular and multicellular organisms do.
How do single-celled organisms make use of enzymes?
They release enzymes into their intermediate environment. The enzymes break down the larger molecules and then the smaller molecules are then absorbed by the cells.
Give two extracellular enzymes involved in digestion in humans.
Amylase and trypsin.
Where is starch digested?
In the mouth and in the small intestine
How many steps are there in the digestion of starch? How many enzymes are involved? Why?
Two steps. Two separate enzymes because there are two separate reactions and each enzyme only catalyses one specific reaction.
Describe the first step of the digestion of starch.
Starch polymers are partially broken down into maltose (disaccharide) by amylase.
The first enzyme involved in the digestion of starch is amylase. Where is this produced and released?
Amylase is produced by the salivary gland and the pancreas. It is released in saliva into the mouth and in the pancreatic juice into the small intestine.
Describe the second step of the digestion of starch.
Maltose is then broken down into glucose (monosaccharide) by maltase.
The second enzyme involved in the digestion of starch is maltase. Where is this found?
The small intestine
What type of enzyme is trypsin? What is its role?
Protease. It catalyses the digestion of proteins into smaller peptides.
Where is trypsin produced and released?
Produced in the pancreas and released with the pancreatic juice into the small intestine.
What happens to the amino acids that are produced by the action of proteases?
They are absorbed by the cells lining the digestive system and then absorbed into the bloodstream.
Describe the effect of temperature on enzymes in a reaction.
Increasing the temperature of a reaction environment increases the kinetic energy of the particles. The particles move faster and collide more frequently. There are more successful collisions between substrate and enzyme. This increases the rate of reaction.
What is the temperature coefficient Q10 of a reaction or process?
A measure of how much the rate of reaction increases with a 10ºC rise in temperature.
What happens to the bonds when an enzyme becomes denatured?
Enzymes are proteins and so their structure is affected by temperature. At higher temperatures, the bonds holding the protein together vibrate more. The vibrations increase until the bonds strain and then break. The breaking of these bonds results in a change in the precise tertiary structure of the protein.
Why does a denatured enzyme no longer function?
When an enzyme is denatured the active site changes shape and is no longer complementary to the substrate. The substrate can no longer fit into the active sites and the enzyme will no longer function as a catalyst.
What is the meaning of the term 'optimum temperature'?
The temperature at which the enzyme has the highest rate of activity.
What is the optimum temperature of most enzymes in the human body?
What is the optimum temperature of enzymes in thermophilic bacteria?
What is the optimum temperature of enzymes in psychrophilic organisms?
True or false? High and low temperatures can both denature enzymes.
False, only high temperatures.
Once the enzymes have denatured above the optimum temperature, the decrease in rate of reaction is rapid. Explain why.
There only needs to be a slight change in shape of an active site for it to no longer be complementary to its substrate. This happens to all of the enzyme molecules at about the same temperature so the loss of activity is relatively abrupt.
Give three examples of extremely cold environments.
- Deep oceans
- High altitudes
- Polar regions
How are some enzymes adapted to cold climates? How does this compare with ordinary enzymes?
Enzymes adapted to the cold tend to have more flexible structures, partcularly at the active site, making them less stable than enzymes that work at higher temperatures. Smaller temperature changes will denature them.
What is the name given to organisms that are adapted to living in very hot environments?
Why are enzymes in thermophiles more stable than other enzymes?
Due to the increased number of bonds, particually hydrogen bonds and sulfur bridges, in their tertiary structures. The shapes of these enzymes and their active sites are more resistant to change as the temperature rises.
A change in pH refers to a change in hydrogen ion concentration. Compare the concentration of hydrogen ions at a low pH and at a high pH.
More hydrogen ions are present in low pH (acid) environments and fewer hydrogen ions are present in high ph (alkaline) environments.
True or false? The active site will only be in the right shape at a certain hydrogen ion concentration which is the optimum pH for any particular enzyme.
What happens if the pH changes from the optimum?
The structure of the enzyme, and therefore the active site, is altered. The substrate will no longer fit.
What is a term used to describe the following. When the pH returns to the optimum then the protein will resume its normal shape and catalyse the reaction again.
What happens when the pH changes significantly?
The structure of the enzyme is irreversibly altered and the active site will no longer be complementary to the substrate. The enzyme is now denatured
How do hydrogen ions affect enzymes?
Hydrogen ions interact with polar and charged R-groups. Changing the concentration of hydrogen ions therefore changes the degree of this interaction. The more hydrogen ions present, the less the R-groups are able to interact with each other. This leads to bonds breaking and the shape of the enzyme changing. The reverse is true when fewer hydrogen ions are present.
What is the optimum pH of amylase and where is its site of action?
neutral (pH7-8), saliva
What is the optimum pH of lipase and where is its site of action?
Slightly alkaline (pH8), pancreatic juice
What is the optimum pH of pepsin and where is its site of action?
Acidic (pH1-2), gastric juice
What is the optimum pH of trypsin and where is its site of action?
Slightly alkaline (pH8), pancreatic juice.
When the concentration of substrate is increased the number of substrate molecules, atoms, or ions in a particular area or volume inceases. What does this lead to?
A higher collision rate with the active sites of enzymes and the formation of more enzyme-substrate complexes. The rate of reaction therefore increases.
What happens when the concentration of the enzyme increases?
The number of available active sites in a particular area or volume will increase, leading to the formation of enzyme-substrate complexes at a faster rate.
What happens once the rate of reaction reaches Vmax?
All of the active sites are occupied by substrate particles and no more enzyme-substrate complexes can be formed until the products are released from their active sites.
If a reaction had reached Vmax, what are the only two ways that the rate of reaction could be increased?
- Add more enzyme
- Increase the temperature
What happens if the concentration of the enzyme is increased?
More active sites are available so the reaction rate can rise towards a higher Vmax. The concentration of substrate becomes the limiting factor again.
Fill in the gaps. Enzymes can be activated with ________ or inactivated with _________
What are Inhibitors?
Inhibitors are molecules that prevent enzymes from carrying out their normal function of catalysis (or slow them down)
How many types of enzyme inhbitor are there and what are they called?
Two, competitive and non-competitive.
How does competive inhibition work?
- A molecule that has a similar shape to the substrate of an enzyme can fit into the active site of the enzyme
- This blocks the substrate from entering the active site preventing the enzyme from catalysing the reaction
- The enzyme can't carry out its function
Why is competitive inhibition called 'competitive'?
Substrate and inhibitor molecules present in a solution will compete with each other to bind to the active sites of the enzyme catalysing the reaction.
True or false? Most competitive inhibitors only bind temporarily to the active site of the enzyme so their effect is reversible.
True.....although aspirin is an exception.
What effect does a competitive inhibitor have on rate of reaction?
It reduces the rate of reaction but deos not change the Vmax
Statins are an example of a competitive inhibitor. Explain what they are used for.
They are used in the synthesis of cholesterol. Statins are regularly prescribed to help people reduce their blood cholesterol concentration. High blood cholesterol levels can results in heart disease.
Aspirin is a competitive inhibitor, how does it work?
Asprin irreversibly inhibits the active site of COX enzymes, preventing the synthesis of prostaglandins and thromboxane, the chemicals responsible for producing pain and fever.
How does non-competitive inibition work?
- The inhibitor binds to the enzyme on a location other than the active site (allosteric site)
- The tertiary structure changes, meaing that the active site shape changes
- This results in the active site no longer having a complementary shape to the substrate
- The enzyme can no longer carry out its function
How do non-competitive inhibitors effect the rate of reaction?
It will decrease the rate of reaction as the active sites become unavailable
Fill in the blanks. Irreversible inhibitors are often very _______ but not always. Organophosphates used as _________ and herbicides irreversibly inhibit the _________ acetyl cholinesterase, neccessary for nerve impulse transmission. This can lead to muscle cramps, paralysis and even ______.
toxic, insecticides, enzyme, death.
Proton pump inhibitors (PPI's) are used to treat long-term indigestion. How do they work?
They irreversibly block an enzyme system responsible for secreting hydrogen ions into the stomach. This makes PPI's very effective in reducing the production of excess acid which has the potential to form stomach ulcers.
What is end product inhibition?
Enzyme inhibition that occurs when the product of a reaction acts as a inhibitor to the enzyme that produces it.
What are the benefits of end product inhibition?
- Excess products are not made
- Resources are not wasted
True or false? Respiration is a metabolic pathway resulting in the production of ATP.
Describe how glucose is broken down.
The first step involves the addition of two phosphate groups to the glucose molecule. The addition of the second phosphate group, which results in the initial breakdown of the glucose molecule, is catalysed by the enzyme phosphofructokinase (PFK). This enzyme is completely inhibited by ATP therefore ATP regulates its own production.
How does ATP regulate its own production?
When the levels of ATP are high, more ATP binds to the allosteric site on PFK preventing the addition of the second phosphate group to glucose. As ATP is used up, less binds to PFK and the enzyme is able to catalyse the addition of a second phosphate group to glucose.
What is a cofactor?
Something which may transfer atoms or groups from one reaction to another in a multi-step pathway or may actually form part of the active site of an enzyme
When would you use the term coenzyme as oppose to cofactor?
If the cofactor is an organic molecule, it is called a coenzyme.
How are inorganic cofactors obtained? GIve some examples.
Inorganic cofactors are obtained via the diet as minerals.
- Iron ions
- Calcium ions
- Chloride ions
- Zinc ions
Amylase, which catalyses the breakdown of starch, contains a cofactor. Which mineral is this and what does it do?
A chloride ion that is neccessary for the formation of a correctly shaped active site.
What is a vitamin?
A class of organic molecules found in the diet
What is the use of vitamin B3?
It is used to synthesise NAD (nicotinamide adenine dinucleotide), a coenzyme responsible for the transfer of hydrogen atoms between molecules involved in respiration. NADP which plays a similar role in photosynthesis is also derived from vitamin B3
What is vitamin B5 used for?
It is used to make coenzyme A. Coenzyme A is essential in the breakdown of fatty acids and carbohydrates in respiration.
What is one similarity and one difference between a cofactor and a prosthetic group?
One similarity is that they are both required by certain enzymes to carry out their catalytic function. A difference is that cofactors bind loosely to proteins in order to activate them whilst prosthetic groups are tightly bound and form a permanent feature of the protein.
Which metal ion forms an important part of the structure of carbonic anhydrase, an enzyme necessary for the metabolism of carbon dioxide.
Zinc ions (Zn2+)
What are inactive precursor enzymes?
Enzymes produced in an inactive form.
What types of enzyme are most often inactive precursor enzymes?
Enzymes that can cause damage within the cells producing them or to tissues where they are released, or enzymes whose action needs to be controlled and only activated under certain conditions.
How can precursor enzymes be activated?
They must undergo a change in shape of the active site which can be achieved by the addition of a cofactor.
Before the cofactor is added, the precursor protein is called a __________. When the cofactor is added and the enzyme is activated it is called a __________.
Before the cofactor is added, the precursor protein is called an apoenzyme. When the cofactor is added and the enzyme is activated it is called a holoenzyme.
What can result in a change in tertiary structure of the precursor enzyme?
Either the action of another enzyme such as a protease which can cleave certain bonds in the molecule or a change in condition such as pH or temperature
What are zymogens or proenzymes?
Precursor enzymes which require a biochemical change to make them active.
What happens when inactive pepsinogen is released in to the stomach to digest proteins?
The acid pH brings about the transformationinto the active enzyme pepsin. This adaptation protects the body tissues against the digestive action of pepsin