Enzymes

Course Contents

• Importance of enzymes
• Enzyme as Protein
• Properties of Enzymes
• Enzyme Specificity
• Mechanism of Enzyme action
• Activators and inhibitors
• Factors affecting Enzymes activity
• o Concentration
• o Ph
• o Temperature
• o Time
• Co-Enzymes & its classification
• Enzymes in clinical medicines

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• 1. Discuss the importance of enzymes.
• 2. Explain the mode of enzyme activity.
• 3. Distinguish between apoenzymes, coenzymes & co factors.
• 4. Distinguish between activators and inhibitors
• 5. Understand inhibition of enzyme activity in
• o Competitive inhibitors
• o Non competitive inhibitors
• o Uncompetitive inhibition.
• 6. Describe with the classification of enzymes
• 7. Discuss the clinical significance of enzymes
• 8. Explain the factors affecting the enzyme activity.

Enzymes

• Enzymes are biological molecules that catalyze (i.e., increase the rates of) chemical reactions.
• In enzymatic reactions, substrates to products.
• enzymes are selective for their substrates and speed up only a few reactions from among many possibilities

Characteristics

• lowering the activation energy. As a result, products are formed faster and reactions reach their equilibrium state more rapidly.
• Most enzyme reaction rates are millions of times faster than those of comparable un-catalyzed reactions.
• As with all catalysts, enzymes are not consumed by the reactions they catalyze, nor do they alter the equilibrium of these reactions.
• highly specific for their substrates.
• A few RNA molecules called ribozymes also catalyze reactions

• Inhibitors: decrease enzyme activity;
• activators are molecules that increase activity.
• Many drugs and poisons are enzyme inhibitors.
• Activity is also affected by temperature, pressure, chemical environment (e.g., pH), and the concentration of substrate.

• Enzymes are in general globular proteins and range from just 62 amino acid residues in size, to over 2,500 residues
• A small number of RNA-based biological catalysts exist, with the most common being the ribosome; these are referred to as either RNA-enzymes or ribozymes.

• only a small portion of the enzyme (around 2–4 amino acids) is directly involved in catalysis.
• The region that contains these catalytic residues, binds the substrate, and then carries out the reaction is known as the active site.
• Enzymes can also contain sites that bind cofactors, which are needed for catalysis.

• enzymes are long, linear chains of amino acids that fold to produce a three-dimensional product.
• Individual protein chains may sometimes group together to form a protein complex.
• Most enzymes can be denatured—that is, unfolded and inactivated—by heating or chemical denaturants, which disrupt the three-dimensional structure of the protein.
• Depending on the enzyme, denaturation may be reversible or irreversible.

Lock and key model

• Enzymes are very specific,

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• Nobel laureate organic chemist Emil Fischer in 1894 suggested

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• both the enzyme and the substrate possess specific complementary geometric shapes that fit exactly into one another.

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• However, while this model explains enzyme specificity, it fails to explain the stabilization of the transition state that enzymes achieve.

Induced fit model

• In 1958, Daniel Koshland suggested a modification to the lock and key model:

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• since enzymes are rather flexible structures, the active site is continuously reshaped by interactions with the substrate as the substrate interacts with the enzyme.

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• As a result, the substrate does not simply bind to a rigid active site; the amino acid side-chains that make up the active site are molded into the precise positions that enable the enzyme to perform its catalytic function.

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• In some cases, such as glycosidase, the substrate molecule also changes shape slightly as it enters the active site

Allosteric sites

• Allosteric sites are sites other than active sites on the enzyme that bind to molecules in the cellular environment.

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• The sites form weak, noncovalent bonds with these molecules, causing a change in the conformation of the enzyme.

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• This change in conformation translates to the active site, which then affects the reaction rate of the enzyme.

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• Allosteric interactions can both inhibit and activate enzymes and are a common way that enzymes are controlled in the body.

Cofactors�

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• Cofactors: Some enzymes require non-protein molecules called cofactors to be bound for activity
• inorganic (e.g., metal ions and iron-sulfur clusters)
• organic compounds (e.g., flavin and heme).

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• prosthetic groups, which are tightly bound to an enzyme
• coenzymes, which are released from the enzyme's active site during the reaction. E.g. NADH, NADPH and adenosine triphosphate

• Aponzymes: Enzymes that require a cofactor but do not have one bound are called apoenzymes or apoproteins.
• Holoenzymes: An apoenzyme together with its cofactor(s) is called a holoenzyme (this is the active form).

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Biological function

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• They are indispensable for signal transduction and cell regulation, often via kinases and phosphatases.
• They also generate movement, with myosin hydrolyzing ATP to generate muscle contraction
• moving cargo around the cell as part of the cytoskeleton.
• Other ATPases in the cell membrane are ion pumps involved in active transport.
• Enzymes are also involved in more exotic functions, such as luciferase generating light in fireflies.
• Viruses can also contain enzymes for infecting cells, such as the HIV integrase and reverse transcriptase, or for viral release from cells, like the influenza virus neuraminidase.
• amylases and proteases break down large molecules (starch or proteins, respectively) into smaller ones, so they can be absorbed by the intestines.

• Several enzymes can work together in a specific order, creating metabolic pathways.
• In a metabolic pathway, one enzyme takes the product of another enzyme as a substrate.
• After the catalytic reaction, the product is then passed on to another enzyme.

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• Without enzymes, metabolism would neither progress through the same steps nor be fast enough to serve the needs of the cell.
• Indeed, a metabolic pathway such as glycolysis could not exist independently of enzymes.

Factors affecting enzyme activity

• Concentration:
• Changing the concentration of a substance only affects the rate of reaction if it is the limiting factor: that is, it the factor that is stopping a reaction from preceding at a higher rate.
• If it is the limiting factor, increasing concentration will increase the rate of reaction up to a point, after which any increase will not affect the rate of reaction. This is because it will no longer be the limiting factor and another factor will be limiting the maximum rate of reaction.
• As a reaction proceeds, the rate of reaction will decrease, since the Substrate will get used up. The highest rate of reaction, known as the Initial Reaction Rate is the maximum reaction rate for an enzyme in an experimental situation.

http://alevelnotes.com/Factors-affecting-Enzyme-Activity/146?tree=

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Substrate Concentration

• Increasing Substrate Concentration increases the rate of reaction. This is because more substrate molecules will be colliding with enzyme molecules, so more product will be formed.
• However, after a certain concentration, any increase will have no effect on the rate of reaction, since Substrate Concentration will no longer be the limiting factor. The enzymes will effectively become saturated, and will be working at their maximum possible rate.

http://alevelnotes.com/Factors-affecting-Enzyme-Activity/146?tree=

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Enzyme Concentration

• Increasing Enzyme Concentration will increase the rate of reaction, as more enzymes will be colliding with substrate molecules.
• However, this too will only have an effect up to a certain concentration, where the Enzyme Concentration is no longer the limiting factor.

http://alevelnotes.com/Factors-affecting-Enzyme-Activity/146?tree=

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Temperature

• as temperature increases, initially the rate of reaction will increase, because of increased Kinetic Energy.
• However, the effect of bond breaking will become greater and greater, and the rate of reaction will begin to decrease.

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http://alevelnotes.com/Factors-affecting-Enzyme-Activity/146?tree=

November 18, 2015

pH

• Different enzymes have different Optimum pH values. This is the pH value at which the bonds within them are influenced by H+ and OH- Ions in such a way that the shape of their Active Site is the most Complementary to the shape of their Substrate. At the Optimum pH, the rate of reaction is at an optimum.
• Any change in pH above or below the Optimum will quickly cause a decrease in the rate of reaction, since more of the enzyme molecules will have Active Sites whose shapes are not (or at least are less) Complementary to the shape of their Substrate.
• Small changes in pH above or below the Optimum do not cause a permanent change to the enzyme, since the bonds can be reformed. However, extreme changes in pH can cause enzymes to Denature and permanently lose their function.
• Enzymes in different locations have different Optimum pH values since their environmental conditions may be different.

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Types of Enzyme inhibitors

http://www.wiley.com/legacy/college/boyer/0470003790/animations/enzyme_inhibition/enzyme_inhibition.htm

November 18, 2015

http://www.wiley.com/legacy/college/boyer/0470003790/animations/enzyme_inhibition/enzyme_inhibition.htm

November 18, 2015

Medical applications of enzymes

http://www1.lsbu.ac.uk/water/enztech/medical.html

November 18, 2015

Thank You