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Define the term 'Enzyme'

Enzymes are biological catalysts that interact with substrate molecules to facilitate chemical reactions. They are usually globular proteins.


Define the term 'substrate'

A substance which is used or acted on for or by another process or substance. For example, a reactant in an enzyme catalysed reaction.


Define the term 'product'

The result of a chemical reaction.


Explain why enzymes are necessary to life.

Because most processes necessary to life involve chemical reactions which need to happen very fast so they are catalysed by an enzyme.


Define the term 'anabolic reactions'.

Anabolism refers to chemical reactions in which simpler substances are combined to form more complex molecules.
Anabolic reactions build new molecules and/or store energy, and they normally require energy.


Define the term 'catabolic reactions'.

Catabolism refers to chemical reactions that result in the breakdown of more complex organic molecules into simpler substances.
Catabolic reactions usually release energy that is used to drive chemical reactions i.e anabolic reactions.


Explain how enzymes can affect both the structure and function of cells and whole organisms.

Enzymes can affect the structures in an organism because they are involved in the production of important proteins i.e. collagen. Enzymes are specific so they carry out a specific function on behalf of the cell/ organism. (bit dodge)


Define the terms 'digestion'.

The breakdown of large nutrient molecules into smaller molecules.


Define the term “metabolism”.

Metabolism is a term that is used to describe all chemical reactions involved in maintaining the living state of the cells and the organism.


Define the term “intracellular enzyme”. State where they can be found in the cell and give an example.

An enzyme which performs its function inside the cell that produces it. They can be found in the cytoplasm, chloroplasts or mitochondria. Catalase is an intracellular enzyme.


Define the term extracelluar enzyme. give two examppes.

Enzymes that perform their function outside of the cell. Amylase and trypsin (digestive enzymes).


State the substrates and products for the enzyme catalase.

Substrate: Hydrogen peroxide (H2O2)
Products: Water and oxygen
(Hydrogen peroxide is very toxic and it is the by-product of several celluar reactions and can kill cells if it builds up.)


State the substrates and products for the enzyme amylase.

Catalyses the hydrolysis of starch into maltose in the mouth.
It is found in salvia and secreted into the mouth by salivary glands.


State the substrates and products for the enzyme trypsin.

Trypsin catalyses the hydrolysis of peptide bonds, turning big polypeptides into smaller polypeptides. It is produced in the pancreas and secreted into the small intestine.


Explain the roles of extracellular enzymes in general.

Extracellular enzymes are released from cells to breakdown large nutrient molecules into smaller molecules. This is so the smaller molecules can enter the cell to meet its demand for nutrients.


Summarise the digestion of starch.

Starch polymers are partially broken down by amylase into maltose (a disaccharide).
Maltose is then broken down into glucose by maltase (a monosaccharide).


Define the term active site.

The area of an an enzyme with a shape complementary to a specific substrate, allowing the enzyme to bind to a substrate with specificity.


Define the term complementary shape.

It means that the shape of the Active Sites of Enzymes are exactly Complementary to the shape of the Substrate - they fit together perfectly. This is called lock and key hypothesis.


Define the term specific.

It means that the active site is only complementary to one type of substrate.


Explain why an enzyme only catalyses one type of reaction.

Because for an enzyme to work the substrate has to fit into the active site so its shape has to be complementary. If it the substrate shape doesn't match the active site the reaction won't be catalysed.


State the sequence of events in an enzyme-controlled reaction.

- A substrate binds to the active site forming an enzyme-substrate complex which lowers activation energy.
- Products are then produced


Describe the “lock and key” hypothesis of enzyme action.

The substrate fits into the enzyme in the same a key fits into a lock. The active site and substrate have a complementary shape, they are specific to eachother.


Describe the “induced-fit” hypothesis of enzyme action.

This helps to explain why a substrate might bind to an enzyme, but no reaction is catalysed.
The shape of active sites are not exactly complementary, but change shape in the presence of a specific substrate to become complementary. This happens because interactions between the substrate and enzyme induce changes in the enzymes tertiary structure.
However if the substrate is not the correct one for the enzyme no enzyme-substrate complex will form.


Suggest how the R-groups of amino acids are involved in catalysing reactions.

The R-groups contain the features which are responsible for the tertiary structure in proteins. The tertiary structure determines the active site's shape.


Define the term activation energy.

The energy required to initiate a reaction.


Define the term rate of reaction.

The speed of a reaction proceeds.


Draw an energy-level graph to show how a reaction progresses with and without an enzyme present (the transition state model).

With an enzyme the peak is lower and it declines faster because the reaction is completed faster.
Without an enzyme the peak is higher because the activation energy is higher.


State what the presence of an enzyme does to the activation energy for the reaction and explain why this increases the rate of reaction.

It lowers the activation energy because an enzyme substrate complex is formed. This lowers the activation energy because:
- If two substrate molecules need to be joined, attaching to the enzyme holds them close together reducing any repulsion between the molecules so they can bond more easily.
-If the enzyme is catalysing a breakdown reaction, fitting into the active site puts a strain on bonds in the substrate. This strain means the substrate molecule breaks up more easily.
A lower activation energy increases the rate of reaction because the reaction can happen at a lower temp than it could without the enzyme.


State 5 factors that affect the rate of an enzyme controlled reaction.

- Temperature
- Surface area of substrate
- Concentration of substrate
- Concentration of enzyme
- PH


Draw a graph showing how the total amount of product produced from an enzyme-controlled reaction changes over time following the start of an experiment. Explain the shape of the graph and explain the significance of the gradient of the line at any one point.

It has a steep incline initially due to a high concentration of substrate but starts to plateau as the substrate concentration decreases.