Define what an enzyme is.

Enzymes are proteins that act as biological catalysts in cells and allow chemical reactions to occur at a suitable rate in the conditions found in living organisms.

What role do enzymes play in increasing rates of reactions in cells?

Enzymes ensure that substrate molecules are orientated correctly and close enough for a reaction to occur. Without the presence of enzymes, the rate of chemical reactions in organisms would be too slow to support life

Metabolism is the complex network of ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ and ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ chemical reactions occurring in living organisms.

Metabolism is the complex network of interdependent and interacting chemical reactions occurring in living organisms.

True or False? Only a few enzymes exist within organisms.

False . Many enzymes exist within organisms. This is because enzymes are specific to one or two substrate molecules; therefore cells require many different enzymes to ensure all the different metabolic reactions can be carried out.

Define what an anabolic reaction is.

An anabolic reaction is one that forms macromolecules from monomers by condensation reactions.

Define what a catabolic reaction is.

Catabolic reactions involve the formation of monomers from macromolecules.

What is an example of an anabolic reaction ?

An example of an anabolic reaction include: protein synthesis glycogen formation photosynthesis

What is an example of a catabolic reaction ?

Examples of catabolic reactions include hydrolysis of macromolecules into monomers in digestion and oxidation of substrates in respiration .

True or False? Enzymes are globular proteins.

True. Enzymes are globular proteins with a 3D shape including an active site where substrates bind.

What is an active site ?

The enzyme's active site is composed of only a few amino acids with a specific 3D shape to bind to a substrate molecule. The active site has the necessary properties for catalysis .

What is induced-fit binding ?

Induced-fit binding is where both substrate and enzymes change shape when binding occurs.

What role does movement play in enzyme-substrate complexes?

Movement is needed for a substrate molecule and an active site to come together. Movement is the result of the kinetic energy that the molecules have which allows an enzyme to collide with a substrate.

What happens during the denaturation of enzymes?

During denaturation, the bonds (e.g. hydrogen bonds) holding the enzyme molecule in its precise 3D shape start to break . This means the 3D shape of the enzyme changes. Therefore the shape of the active site is permanently changed, preventing the substrate from binding

What is meant by enzyme-substrate specificity ?

The specificity of an enzyme is a result of the complementary nature between the shape of the active site on the enzyme and its substrate(s). The active site of an enzyme has a specific shape to fit a specific substrate.

Explain the relationships between the structure of the active site , enzyme-substrate specificity and denaturation .

The active site is a precise 3D shape which ensures enzyme-substrate specificity . If an enzyme is denatured (due to high heat or extreme pH) then this specific shape is changed and a substrate can no longer bind with the enzyme.

What is a substrate ?

A substrate is a molecule that binds with an enzyme with the enzyme's active site. Substrates bind to enzymes , forming a temporary enzyme-substrate complex. Some enzymes have two substrates that must each collide with a separate active site at the same time

What happens to enzyme activity at low temperatures ?

At low temperatures, enzymes work slowly due to a lack of kinetic energy and collisions between the substrates and active sites.

How does increasing temperature towards the optimum temperature affect enzyme activity?

Increasing the temperature towards the optimum increases enzyme activity as the molecules have more kinetic energy , leading to more collisions with substrate molecules and a faster rate of reaction.

What is the effect of heating enzymes beyond the optimum temperature?

Heating enzymes beyond the optimum temperature will break the bonds that hold the enzyme together, causing it to lose its shape and become denatured .

Why does the rate of an enzyme-controlled reaction decrease as the pH level moves further from the enzyme's optimum pH ?

The rate of an enzyme-controlled reaction decreases as the pH level moves further from the enzyme's optimum because extremes of pH break the bonds that hold the amino acid chain together, denaturing the active site and reducing the rate of reaction.

True or False? All enzymes denature in acid.

False. Different enzymes function well at different pH levels, e.g. enzymes from the stomach have a low optimum pH (around pH 2) because the stomach is an acidic environment.

True or False? All enzymes have the same optimum pH.

False. Some enzymes that are produced in acidic conditions have a lower optimum pH , while those produced in alkaline conditions have a higher optimum pH .

What happens to the rate of enzyme activity when the concentration of substrate is increased?

When the concentration of substrate is increased the rate of enzyme activity increases. This is because there are more substrate molecules to collide with the enzyme and occupy the active site.

True or False? Biological models in the form of sketch graphs can be evaluated using results from enzyme experiments. ( NOS )

True. Generalised sketches of relationships are examples of models in biology. These models can be evaluated using results from enzyme experiments.

How is rate of reaction of enzyme-controlled experiments determined?

The rate of reaction can be determined by measuring the rate of disappearance of a substrate or the rate of product accumulated in a given time period.

True or False? A reaction takes place in a short period of time; therefore it has a slow rate of reaction.

False. A reaction takes place in a short period of time; therefore it has a high rate of reaction. A high rate of reaction is when the reaction happens in less time i.e. it is faster. A low rate of reaction is when the reaction happens in more time i.e. it is slower

On a graph of time against the volume of product made, what does a steep line indicate?

A steep line on a graph of time against the product made indicates a high rate of reaction.

What are the units for rate of reaction where the volume of product is measured in cm 3 and time is measured in seconds?

The units for rate of reaction where the volume of product is measured in cm 3 and time is measured in seconds are: cm 3 per second (volume per second) cm 3 /sec cm 3 sec -1 These units all mean the same thing.

What is activation energ y?

Activation energy is the amount of energy needed by the substrate to become unstable enough for a reaction to occur and for new products to be formed.

What effect do enzymes have on activation energy?

Enzymes lower the activation energy required for a reaction to take place.

True or False? Energy is required to break bonds within the substrate.

True . Energy is required to break bonds within the substrate. Enzymes speed up chemical reactions because they reduce the stability of bonds in the substrate.

There is an energy when bonds are to form the products of an enzyme-catalysed reaction.

There is an energy yield when bonds are made to form the products of an enzyme-catalysed reaction.

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Enzymes & Metabolism (DP IB Biology)

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FrontMetabolism: Enzymes & Reactions
Define what an enzyme is.
FrontMetabolism: Enzymes & Reactions
Metabolism is the complex network of ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ and ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ chemical reactions occurring in living organisms.

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Define what an enzyme is.
Enzymes are proteins that act as biological catalysts in cells and allow chemical reactions to occur at a suitable rate in the conditions found in living organisms.
What role do enzymes play in increasing rates of reactions in cells?
Enzymes ensure that substrate molecules are orientated correctly and close enough for a reaction to occur. Without the presence of enzymes, the rate of chemical reactions in organisms would be too slow to support life
Metabolism is the complex network of ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ and ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ chemical reactions occurring in living organisms.
Metabolism is the complex network of interdependent and interacting chemical reactions occurring in living organisms.
True or False?
Only a few enzymes exist within organisms.
False.
Many enzymes exist within organisms. This is because enzymes are specific to one or two substrate molecules; therefore cells require many different enzymes to ensure all the different metabolic reactions can be carried out.
Define what an anabolic reaction is.
An anabolic reaction is one that forms macromolecules from monomers by condensation reactions.
Define what a catabolic reaction is.
Catabolic reactions involve the formation of monomers from macromolecules.
What is an example of an anabolic reaction?
An example of an anabolic reaction include:
- protein synthesis
- glycogen formation
- photosynthesis
What is an example of a catabolic reaction?
Examples of catabolic reactions include hydrolysis of macromolecules into monomers in digestion and oxidation of substrates in respiration.
True or False?
Enzymes are globular proteins.
True.
Enzymes are globular proteins with a 3D shape including an active site where substrates bind.
What is an active site?
The enzyme's active site is composed of only a few amino acids with a specific 3D shape to bind to a substrate molecule. The active site has the necessary properties for catalysis.
Label the active site on the image.
The active is labeled as follows:
What is induced-fit binding?
Induced-fit binding is where both substrate and enzymes change shape when binding occurs.
What role does movement play in enzyme-substrate complexes?
Movement is needed for a substrate molecule and an active site to come together. Movement is the result of the kinetic energy that the molecules have which allows an enzyme to collide with a substrate.
What happens during the denaturation of enzymes?
During denaturation, the bonds (e.g. hydrogen bonds) holding the enzyme molecule in its precise 3D shape start to break. This means the 3D shape of the enzyme changes. Therefore the shape of the active site is permanently changed, preventing the substrate from binding
What is meant by enzyme-substrate specificity?
The specificity of an enzyme is a result of the complementary nature between the shape of the active site on the enzyme and its substrate(s). The active site of an enzyme has a specific shape to fit a specific substrate.
Explain the relationships between the structure of the active site, enzyme-substrate specificity and denaturation.
The active site is a precise 3D shape which ensures enzyme-substrate specificity. If an enzyme is denatured (due to high heat or extreme pH) then this specific shape is changed and a substrate can no longer bind with the enzyme.
What is a substrate?
A substrate is a molecule that binds with an enzyme with the enzyme's active site. Substrates bind to enzymes, forming a temporary enzyme-substrate complex. Some enzymes have two substrates that must each collide with a separate active site at the same time
What happens to enzyme activity at low temperatures?
At low temperatures, enzymes work slowly due to a lack of kinetic energy and collisions between the substrates and active sites.
How does increasing temperature towards the optimum temperature affect enzyme activity?
Increasing the temperature towards the optimum increases enzyme activity as the molecules have more kinetic energy, leading to more collisions with substrate molecules and a faster rate of reaction.
What is the effect of heating enzymes beyond the optimum temperature?
Heating enzymes beyond the optimum temperature will break the bonds that hold the enzyme together, causing it to lose its shape and become denatured.
Describe what is depicted by the blue lines in the graph. (Application of Skills)
The blue lines show the optimum temperature (approximately 34 ^oC). The rate of reaction is at its maximum at the optimum temperature. After this point, the enzyme begins to become denatured and the rate of reaction decreases.
Why does the rate of an enzyme-controlled reaction decrease as the pH level moves further from the enzyme's optimum pH?
The rate of an enzyme-controlled reaction decreases as the pH level moves further from the enzyme's optimum because extremes of pH break the bonds that hold the amino acid chain together, denaturing the active site and reducing the rate of reaction.
True or False?
All enzymes denature in acid.
False.
Different enzymes function well at different pH levels, e.g. enzymes from the stomach have a low optimum pH (around pH 2) because the stomach is an acidic environment.
True or False?
All enzymes have the same optimum pH.
False.
Some enzymes that are produced in acidic conditions have a lower optimum pH, while those produced in alkaline conditions have a higher optimum pH.
Describe what is shown in the graph.
The graph shows an increase in enzyme activity rate as pH increases, up to pH 8.5. This is the optimum pH. After this pH the enzyme begins to denature.
What happens to the rate of enzyme activity when the concentration of substrate is increased?
When the concentration of substrate is increased the rate of enzyme activity increases. This is because there are more substrate molecules to collide with the enzyme and occupy the active site.
Explain what happens in the graph after point X.
At point X on the graph:
- Active sites are saturated with substrates
- The rate of reaction has plateaued/stopped
- Any further increase of substrate concentration will not alter the rate of reaction
True or False?
Biological models in the form of sketch graphs can be evaluated using results from enzyme experiments. (NOS)
True.
Generalised sketches of relationships are examples of models in biology. These models can be evaluated using results from enzyme experiments.
How is rate of reaction of enzyme-controlled experiments determined?
The rate of reaction can be determined by measuring the rate of disappearance of a substrate or the rate of product accumulated in a given time period.
True or False?
A reaction takes place in a short period of time; therefore it has a slow rate of reaction.
False.
A reaction takes place in a short period of time; therefore it has a high rate of reaction.
A high rate of reaction is when the reaction happens in less time i.e. it is faster.
A low rate of reaction is when the reaction happens in more time i.e. it is slower
On a graph of time against the volume of product made, what does a steep line indicate?
A steep line on a graph of time against the product made indicates a high rate of reaction.
What are the units for rate of reaction where the volume of product is measured in cm³ and time is measured in seconds?
The units for rate of reaction where the volume of product is measured in cm³ and time is measured in seconds are:
- cm³ per second (volume per second)
- cm³/sec
- cm³ sec^-1
These units all mean the same thing.
What is activation energy?
Activation energy is the amount of energy needed by the substrate to become unstable enough for a reaction to occur and for new products to be formed.
What effect do enzymes have on activation energy?
Enzymes lower the activation energy required for a reaction to take place.
True or False?
Energy is required to break bonds within the substrate.
True.
Energy is required to break bonds within the substrate. Enzymes speed up chemical reactions because they reduce the stability of bonds in the substrate.
There is an energy when bonds are to form the products of an enzyme-catalysed reaction.
There is an energy yield when bonds are made to form the products of an enzyme-catalysed reaction.
Label the following on the graph:
- Substrate
- Products
- Activation energy with enzyme
- Activation energy without enzyme
The graph is labelled as follows:

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