BLY 205: INTRODUCTORY PHYSIOLOGY PURE AND APPLIED BIOLOGY
BOWEN UNIVERSITY, IWO
BACKGROUND
• Enzymes help speed up chemical reactions in the human body. They bind to molecules and alter them in specific ways. They are essential for respiration, digesting food, muscle and nerve function, among thousands of other roles.
• Enzymes can only function in a certain pH range (acidic/alkaline). Their preference depends on where they are found in the body
• Intestines- 7.5
• Stomach- 2.0
If the temperature is too high or if the environment is too acidic or alkaline, the enzyme changes shape; this alters the shape of the active site so that substrates cannot bind to it – the enzyme has become denatured.
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EXAMPLES OF SPECIFIC ENZYMES
• Lipases – a group of enzymes that help digest fats in the gut.
• Amylase – helps change starches into sugars. Amylase is found in saliva.
• Maltase – also found in saliva; breaks the sugar maltose into glucose. Maltose is found in foods such as potatoes, pasta, and beer.
• Trypsin – found in the small intestine, breaks proteins down into amino acids.
• Lactase – also found in the small intestine, breaks lactose, the sugar in milk, into glucose and galactose.
• Acetylcholinesterase – breaks down the neurotransmitter acetylcholine in nerves and muscles.
• Helicase – unravels DNA.
• DNA polymerase – synthesize DNA from deoxyribonucleotides.
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WHAT ARE ENZYMES?
• Enzymes can be defined as biological polymers that catalyze biochemical reactions.
• Enzymes are proteins that act as biological catalysts: Catalysts accelerate (or speed up the rate) chemical reaction
• Enzymes are known to catalyze more than 5,000 biochemical reaction types (Schomburg et al., 2013)
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WHAT DO ENZYMES DO?
• The digestive system – enzymes help the body break down larger complex
molecules into smaller molecules, such as glucose, so that the body can use them as fuel.
• DNA replication – each cell in your body contains DNA. Each time a cell divides, that DNA needs to be copied. Enzymes help in this process by unwinding the DNA coils and copying the information.
• Liver enzymes – the liver breaks down toxins in the body. To do this, it uses a range of enzymes.
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ENZYME STRUCTURE
• Enzymes are a linear chain of amino acids, which give rise to a three-dimensional structure.
• The sequence of amino acids specifies the structure, which in turn identifies the catalytic activity of the enzyme.
• Upon heating, enzyme’s structure denatures resulting in a loss of enzyme activity
• Compared to its substrates, enzymes are typically large with varying sizes, ranging from 62 amino acid residues to an average of 2500 residues found in fatty acid synthase. Only a small section of the
structure is involved in catalysis and is situated next to the binding sites.
• The catalytic site and binding site together constitute the enzyme’s active site.
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COFACTORS
• Cofactors are non-proteinous substances that associate with enzymes.
• A cofactor is essential for the functioning of an enzyme.
• An enzyme without a cofactor is called an apoenzyme.
• An enzyme and its cofactor together constitute the holoenzyme.
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KINDS OF COFACTORS PRESENT IN ENZYMES
• Prosthetic groups: These are cofactors tightly bound to an enzyme at all times. A fad is a prosthetic group present in many enzymes.
• Coenzyme: A coenzyme binds to an enzyme only during catalysis. At all other times, it is detached from the enzyme. NAD+ is a common coenzyme.
• Metal ions: For the catalysis of certain enzymes, a metal ion is required at the active site to form coordinate bonds. Zn2+ is a metal ion cofactor used by a number of enzymes.
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MECHANISM OF ENZYME REACTION
• Any two molecules have to collide for the reaction to occur along with the right orientation and a sufficient amount of energy.
• The energy between these molecules needs to overcome the barrier in the reaction. This energy is called activation energy.
• Enzymes are said to possess an active site.
• The active site is a part of the molecule that has a definite shape and the functional group for the binding of reactant molecules.
• The molecule that binds to the enzyme is referred to as the substrate group.
• The substrate and the enzyme form an intermediate reaction with low activation energy without any catalysts.
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ENZYME ACTION
• The enzyme action basically happens in two steps:
• Step1: Combining of enzyme and the reactant/substrate.
• E+S → [ES]
• Step 2: Disintegration of the complex molecule to give the product.
• [ES]→E+P
• Thus, the whole catalyst action of enzymes is summarized as:
• E + S → [ES] → [EP] → E + P
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FACTORS AFFECTING ENZYME ACTIVITY
As enzymes are made up of proteins, their actions are sensitive to change in many physio chemical factors such as:
• Active site
• Temperature
• pH
• Concentration and Type of Substrate
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TYPES OF ENZYMES
Oxidoreductases
• The enzyme Oxidoreductase catalyzes the oxidation reaction where the electrons tend to travel from one form of a molecule to the other.
• e.g. pyruvate dehydrogenase, catalysing the oxidation of pyruvate to acetyl coenzyme A.
Transferases
• The Transferases enzymes help in the transportation of the functional group among acceptors and donor molecules.
• An example is a transaminase, which transfers an amino group from one molecule to another.
Hydrolases
• Hydrolases are hydrolytic enzymes, which catalyze the hydrolysis reaction by adding water to cleave the bond and hydrolyze it.
• For example, the enzyme pepsin hydrolyzes peptide bonds in proteins.
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Lyases
• Adds water, carbon dioxide or ammonia across double bonds or eliminate these to create double bonds.
• e.g. aldolase (an enzyme in glycolysis) catalyzes the splitting of fructose-1, 6-bisphosphate to glyceraldehyde-3- phosphate and dihydroxyacetone phosphate.
Isomerases
• The Isomerases enzymes catalyze the structural shifts present in a molecule, thus causing the change in the shape of the molecule.
• Example: phosphoglucomutase catalyzes the conversion of glucose-1-phosphate to glucose-6-phosphate (phosphate group is transferred from one to another position in the same compound) in glycogenolysis (glycogen is converted to glucose for energy to be released quickly).
Ligases
• The Ligases enzymes are known to charge the catalysis of a ligation process.
• For example, DNA ligase catalyzes the joining of two fragments of DNA by forming a phosphodiester bond.
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• They break down large molecules into smaller substances that can be easily absorbed by the body.
• They help in generating energy in the body. ATP synthase is the enzymes involved in the synthesis of energy.
• Enzymes are responsible for the movement of ions across the plasma membrane.
• Enzymes perform a number of biochemical reactions, including oxidation, reduction, hydrolysis, etc.
to eliminate the non-nutritive substances from the body.
• They function to reorganize the internal structure of the cell to regulate cellular activities.
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• Dairy industry
• rennin and/or lipase
• used to hydrolyse protein in the manufacture of cheese.
• Food processing industry
• Amylase
• used to produce sugars from starch in making high –fructose corn syrup.
• Proteases
• used to lower protein level of flour in biscuit production
• Trypsin
• used In the manufacture of hypoallergenic baby foods
• As biological detergent
• Proteases, amylases, lipases
• used to remove protein, starch, and fat or oil stains from laundry and dishware.
• Mannanases
• used to remove food stains from the common food additive guar gum
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• Biofuel industry
• Cellulases
• used in the breakdown cellulose into sugars that can be fermented to produce ethanol ligninases used in pre treatment of biomas for biofuel production
• Brewing industry
• Amylase, glucanases, proteases
• Split polysaccharides and proteins in the malt
• Betaglucanases
• Improve the wort and beer filtration characteristics
• Amyloglucosidase and pullulanases
• Make low-calorie beer and adjust fermentability
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INHIBITION
• A situation where Enzyme reaction rates can be decreased/ halted by various types of enzyme inhibitors.
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COMPETITIVE INHIBITION
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TYPES OF INHIBITION
• Competitive
• A competitive inhibitor and substrate cannot bind to the enzyme at the same time.
• Often competitive inhibitors strongly resemble the real substrate of the enzyme.
• For example, the drug methotrexate is a competitive inhibitor of the enzyme dihydrofolate reductase, which catalyzes the reduction of dihydrofolate to tetrahydrofolate.
• This type of inhibition can be overcome with high substrate concentration.
• Non-competitive
• A non-competitive inhibitor binds to a site other than where the substrate binds.
• The substrate still binds with its usual affinity and hence Kmremains the same. However the inhibitor reduces the catalytic efficiency of the enzyme so that Vmax is reduced.
• This type of inhibition cannot be overcome with high substrate concentration.
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TYPES OF INHIBITION CONT’D
• Uncompetitive
• An uncompetitive inhibitor cannot bind to the free enzyme, only to the enzyme-substrate complex; hence, these types of inhibitors are most effective at high substrate concentration.
• In the presence of the inhibitor, the enzyme-substrate complex is inactive.
• This type of inhibition is rare.
• Mixed
• A mixed inhibitor binds to an allosteric site and the binding of the substrate and the inhibitor affect each other.
• The enzyme's function is reduced but not eliminated when bound to the inhibitor.
• Irreversible
• An irreversible inhibitor permanently inactivates the enzyme, usually by forming a covalent bond to the protein.
• Penicillin and aspirin are common drugs that act in this manner.
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FUNCTIONS OF INHIBITORS
• In many organisms, inhibitors may act as part of a feedback mechanism.
• If an enzyme produces too much of one substance in the organism, that substance may act as an inhibitor for the enzyme at the beginning of the pathway that produces it, causing production of the substance to slow down or stop
• Since inhibitors modulate the function of enzymes they are often used as drugs.
• Many such drugs are reversible competitive inhibitors that resemble the enzyme's native substrate.
• examples include statins used to treat high cholesterol
• protease inhibitors used to treat retroviral infections such as HIV.
• A common example of an irreversible inhibitor that is used as a drug is aspirin, which inhibits the COX- 1 and COX-2 enzymes that produce the inflammation messenger prostaglandin.
• Other enzyme inhibitors are poisons. For example, the poison cyanide is an irreversible enzyme inhibitor that combines with the copper and iron in the active site of the enzyme cytochrome c oxidase and blocks cellular respiration
