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Enzymes
Harriet, Lauren and Eliza
What is an enzyme?
‘A substance produced by a living organism
which acts as a catalyst to bring about a
specific biochemical reaction’
Enzymes continued…
Enzyme –
Enzymes are large molecules that speed up the chemical reactions inside cells.
Each type of enzyme does one specific job.
Biological catalysts Due to enzymes being a biological catalyst, they speed up the rate of reaction
without being used up.
The reaction Due to its interaction with the substrate, it means that the reaction where the
substrate becomes the products can take place without harsh environmental
conditions, therefore the cell is not damaged.
Lock and Key
Enzymes are also proteins that are folded into complex shapes that
allows smaller molecules to fit into them.
Enzymes can be used to break
down food into nutrients.
What is the structure of an enzyme?
Enzymes are proteins that consist of chains of amino acids connected
together by peptide bonds. The sequence of amino acids within is
distinct in each enzyme and this is what determines the unique three
dimensional shape in which the chains are folded.
This 3D shape is what determines the activities of the enzyme.
An enzyme is a globular protein.
Many enzymes also contain an extra non-protein component called a
cofactor or coenzyme, this may be an organic molecule or a metal ion.
Why is an enzyme specific for one substrate?
How is this achieved?
An enzyme is specific for one substrate because the active site has to
be the right shape for the substrate molecules to fit into. This means
that enzymes have a high specificity for their substrate.
This is achieved because the amino acid chains are unique so the way
that they bond and fold will always be different meaning that the active
site will be specific.
a substance produced by a living organism which acts as a biological
catalyst which interacts with substrate molecules to facilitate chemical
reactions.
• Enzymes are made up of amino acids which are linked together via peptide
bonds in a chain. The resulting amino acid chain is called a polypeptide or
protein. The specific order of amino acids in the protein is encoded by the DNA
sequence of the corresponding gene
• Because of the hydrogen in the amino group and the oxygen in the carboxyl
group, each amino acid can hydrogen bond with each other and this means that
the amino acids in the same chain can interact. Polypeptide chains are folded or
pleated into different shapes, called their Secondary Structure. Two common
examples of secondary structures are Alpha Helices and Beta Pleated Sheets.
Secondary structure is held together by many Hydrogen bonds, overall giving the
shape great stability.
• As a consequence of the folding-up of the 2D linear chain in the secondary
structure, the protein can fold up further and in doing so gains a threedimensional structure. This is its tertiary structure
Tertiary structure is held together by four different
bonds and interactions:
• Disulphide Bonds
• Ionic Bonds
• Hydrogen Bonds
• Hydrophobic and Hydrophilic Interactions
• The enzyme's active site binds to the substrate. Since enzymes are
proteins, this site is composed of a unique combination of amino
acids. Each amino acid can be large or small; weakly acidic or basic;
hydrophilic or hydrophobic; and positively-charged, negativelycharged, or neutral. The positions, sequences, structures, and
properties of create a very specific chemical environment within the
active site. A specific chemical substrate matches this site like a jigsaw
puzzle piece and makes the enzyme specific to its substrate
Metabolism
What is metabolism?

Types of metabolism:

Metabolism is the rate of chemical reactions in cells

Vmax – Maximum rate of reaction

Catabolic

This is the breaking down of molecules into smaller units +
energy

Anabolic

Construct molecules from smaller units

Needs energy from the hydrolysis of ATP
Role of enzymes

What are enzymes?

Enzymes are biological catalysts

What is a catalyst:

A catalyst provides an alternate reaction pathway that has a lower activation
energy
Factors Affecting
Temperature
Denatured
pH
Breaks the hydrogen
and Ionic Bonds
Concentration
Enzyme-Substrate
complexes
Inhibitors
Non competitive inhibitor – An inhibitor
that binds to an enzyme at an allosteric
site
Competitive inhibitor - An inhibitor that competes
with substrate to bind to active site on an enzyme
LOCK AND KEY HYPOTHESIS
ACTIVE SITE AND SUBSTRATE
- The active site is an area within the tertiary structure of an enzyme
- It has a complementary shape to the specific substrate molecule
- The active site never changes its shape to fit a substrate – there is a specific substrate shape
for each active site
THE PROCESS
Active site + substrate = enzyme-substrate complex = enzyme + products
- The substrate binds to the active site where an enzyme-substrate complex is formed
- The substrate then reacts because it is held in such a way by the enzyme that the right atom groups are close
enough to react. The active site contains R-groups that also interact with the substrate, forming temporary bonds.
These bonds put strain on the bonds within the substrate which helps the reaction along
- Due to this reaction products are formed in an enzyme-product complex
- The products are released from the active site – leaving the enzyme unchanged and able to take part in other
reactions
What is the Induced Fit
Hypothesis?
By Eva & Neve
Induced Fit Hypothesis:

More recently, evidence from research into
enzyme action suggests the active site of
the enzyme actually changes shape slightly
as the substrate enters. This is called the
induced- fit hypothesis and is a modified
version of the lock and key hypothesis.
Induced Fit Hypothesis:

The initial interaction between the enzyme and
substrate is relatively weak, but these weak
interactions rapidly induce changes in the
enzymes tertiary structure that strengthen binding,
putting strain on the substrate molecule. This can
weaken a particular bond or bonds in the
substrate, therefore lowering the activation energy
for the reaction.
Induced Fit Model
Intracellular Enzymes
By Mr Bullock & Archie Brydon OBE
What is an intracellular enzyme???
• An enzyme that functions within the cell in which it was produced.
• Majority of enzymes fall within this category.
• Intracellular enzymes are not as effective as extracellular.
(Extracellular enzymes are up to 25% more efficient in breaking down
the substrate)
Catalase
• Catalase is a common intracellular enzyme found in nearly all living
organisms exposed to oxygen (such as bacteria, plants, and animals).
• Breaks Hydrogen Peroxide down into water and oxygen.
About catalase:
• Catalase is a natural enzyme found primarily in the liver of animals.
• It is the fastest acting enzyme known.
• It is an important part in the bodies antioxidant
defences.
The reaction.
• Hydrogen peroxide is toxic to cells because it reacts with the metal
ions found in proteins, causing considerable damage to the structure
of the protein in the process.
• This is where catalase is useful to the cell, since it decomposes
hydrogen peroxide
• 2H2O2→2H2O+O2
• Catalase is a tetramer of four polypeptide chains, each approximately
500 amino acids long. One molecule of catalase can decompose
millions of hydrogen peroxide molecules each second.
Extracellular Enzymes
What are extracellular enzymes? Why are
they needed?
• Enzymes that work outside of the cell
• The enzymes are released to break down large nutrient molecules
into smaller molecules. This is because the larger molecules cannot
enter the cells through the cell surface membrane.
• The enzyme breaks down proteins that are too big to enter the cell,
into glucose and amino acids that are small enough to be absorbed.
Amylase
• The enzyme involved in digestion, where
starch is broken down into maltose.
• It is produced in the salivary glands and
pancreas and is released in saliva in the
mouth to break down food.
Trypsin
• It is a protease- an enzyme that catalyses the
digestion of proteins into smaller peptide.
• It is produced in the pancreas and released in
pancreatic juice into the small intestine.
• These can then be broken down into amino
acids by other protease that can then be
absorbed by cells or into the blood stream.
Cofactors and Coenzymes
Jess & Poppy
Some enzymes need a nonprotein ‘helper’ component in
order to carry out the function as
a biological catalyst.
Cofactors
• Inorganic ions
• Can transfer atoms or groups from one reaction to another
or form part of the enzymes active site
• Obtained via the diet as minerals including… iron, calcium,
chloride, and zinc ions. For example, the enzyme amylase
which catalyses the breakdown of starch – contains a
chloride ion which is necessary for the formation of a
correct active site.
Coenzymes
Alcohol dehydrogenase
• Organic molecule
• Usually derived from vitamins B3 - a class of organic
molecule found in the diet.
• For example, vitamin B3, is used to synthesise NAD
(nicontinamide adenine dinucleotide) which is a
coenzyme responsible for the transfer of hydrogen
atoms between molecules involved in respiration.
• NADP also derived from vitamin B3.
H+
Ethanol, H+, and NADH are
released from the active site
Prosthetic Groups
What is a prosthetic group?

A non-protein component of a conjugated protein.

They are required by certain enzymes to carry out their catalytic
functions. The prosthetic group makes them ‘active’.

They are tightly bound to form a permanent feature of the protein.
This is what makes them a prosthetic group, not a cofactor.

In an enzyme, prosthetic groups are often involved in the active site.

Vitamins are a common prosthetic group, which is why they are
important in the human diet. Inorganic prosthetic groups, however,
are usually transition metals.
Examples:

Haemoglobin has a prosthetic group of iron (Fe) ions. The iron helps to
transfer oxygen and carbon dioxide.

Carbonic Anhydrase has zinc (Zn2+ ) ions. This is used for the metabolism of
carbon dioxide.
Precursor activation
This is the term used when certain enzymes are produced in an inactive form.
Bry + Ella
Why does this happen?
• This is particularly useful for enzymes that might cause damage to a
cell in its active state
• It is also the case for any enzyme where their action needs to be
controlled and can only be activated in certain conditions
What happens
• Enzymes often need to undergo a change in shape (particularly in the
active site to allow a reaction to occur) to activate
• This is regulated by the cofactor – a molecule that is not the substrate
• Before: inactive apoenzyme
• After: complete and catalytically active holoenzyme
Zymogens and Proenzymes
• Sometimes, the change of shape of an enzyme is brought about by the
action of another enzyme
• Example
• Protease breaks down the bonds in a molecule
Or
• Change in condition – pH or temperature
• Example
• Inactive pepsinogen is released into the stomach to digest proteins the acid pH
transforms the enzyme into pepsin - an active enzyme
• This protects the body tissues against the digest action of the enzyme
The importance of precursor activation
• Blood clotting
• Clotting factor X relies on the cofactor vitamin K for activation
• Factor X cleaves certain bonds in prothrombin to transform it into thrombin
• Thrombin catalyses the conversion of soluble fibrinogen into soluble fibrin
fibres which with platelets form a blood clot