enzymes activation and deactivation november 19 th, 2012
TRANSCRIPT
ENZYMES ACTIVATION AND DEACTIVATION
November 19th, 2012
Enzymes are Not Consumed in Reaction
https://www.youtube.com/watch?v=0XjyAkeQJag&feature=related
Factors Effecting Enzymes
Enzymes are not perfect They respond to environmental
conditions They work depending on various
factors which are? ________, ___________, _____________ Changing these factors
effects? _____________
Enzyme under Stress
pH
An decrease in pH, increases the [H+] ion concentration in solution
An increase in pH, increases the [OH-] ion concentration in solution
These ions interfere with hydrogen bonds and ionic bonds
Changing the conformation of the enzymes specifically the active site
Activity of enzyme is affected
Optimal pH
Different enzymes have different optimum pHs
At optimum pH the active site is the shape most complementary to the shape of their Substrate
At optimum pH, the rate of reaction is highest Large changes in pH can cause
enzymes to Denature and permanently loose their function
Temperature Effects Enzymes Generally, enzymes have a narrow
range of temperature they work in, Why?
At the optimal temperature enzymes are most active
Increase Temperature
What increases? energy Makes the substrate more active in
solution. So? More chances of substrate colliding with
active site. Makes the enzyme more flexible. Puts strain on weaker bonds. Pass a certain point enzymes denature.
What does it mean to denature? active site changes
Decrease Temperature
Makes the enzyme less flexible, Pass a certain point enzymes do not
function properly Not enough energy present
Taq Polymerase
Enzyme comes from Thermus Aquaticus, a species that thrive in hot springs and heat vents.
Functions at high temperature Used in Polymerase Chain Reaction (PCR) Can make multiple copies of a DNA sample
using only a small amount. PCR can be used for a forensic investigation,
genetic diseases, drug discovery and detection of pathogens
Temperature Curve
Various thermophillic organisms have their own type of DNA polymerase such as Pfu Polymerase (Pyrococcus furiosus) versus Taq Polymerase
Regulation of Temperature
Endotherms can maintain body temperature Heat is produced and
regulated by the body, How? Ectotherms do not maintain a body
temperature Less sensitive to changes in body temperature Endothermic organisms are mammals, birds
and some fish Most enzymes in the human body have an
optimal temperature of 37°C
Concentration
What is concentration?
Will the concentration of substrate the rate of reaction?
Will the concentration of enzyme effect the rate of reaction?
Substrate Concentration
Adding more substrate increases rate of the reaction
More substrate molecule collide with active site
At a certain point adding more substrate has no more effect. Enzyme active site is saturated
Enzyme Concentration
If an enzyme is saturated what can you do?
Increasing enzyme concentration, increases the rate of reaction
Why does the graph level off?
ENZYME REGULATION
November 20th & 21st, 2012
Biochemical Process
http://www.iubmb-nicholson.org/animaps.html
Enzyme Regulation
There are enzymes for each specific reaction of the human body
There is a need to control enzyme activity
Regulation is efficiency
Enzymes can be activated and inhibited
Road Map
Aspirin
Cyclooxygenase 2 (COX2) makes prostaglandins These chemical are involved in inflammation Inflammation is felt as pain and swelling in body Aspirin reacts with the amino acid serine irreversibly,
blocking the active site, substrate can not bind Other pain killers such as ibuprofen (Advil) bind less
strongly, are reversible bound
Inhibition
Enzyme inhibitors are substances that interfere with catalysis
Inhibitors slow down the rate of reaction Inhibitors can be reversible or irreversible Irreversible inhibition – halts enzymatic reaction
permanently Reversible inhibition – slows down the reaction
temporarily Inhibitors can act in a competitive or non
competitive form and interfere with the reaction
Competitive Inhibition
Competitive inhibition: Enzyme inhibitors prevent the formation of Enzyme-Substrate complexes because they have a similar shape to the substrate molecule.
Prevents enzyme from carrying out reaction it is suited for
Enzyme with Active Site Specific for Substrate
Substrate
Inhibitor
Inhibitor Competes with Substrate for the Active Site
Competitive Inhibition
Inhibitor has a different shape than the substrate but complements the active site
Inhibitor does not react since it has different structure than the substrate.
Reaction rate is decreased since fewer substrate molecules can bind to the enzyme
Inhibition is typically temporary, the inhibitor eventually leaves the active site
Inhibition depends on the relative concentrations of substrate and inhibitor, both compete for place in enzyme active site
Methanol Poisoning
Methanol if ingested is oxidized to formaldehyde and formic acid
Attack on the optic nerve causes blindness. Methanol found in engine fuel,
solvents, window cleaner, andantifreeze
Source: http://curriculum.toxicology.wikispaces.net/2.2.5.2.5+Methanol
Ethanol Competes with Methanol
Ethanol competitively inhibits the oxidation of methanol by Alcohol Dehydrogenase
Ethanol is oxidized in preference to methanol
Oxidation of methanol is slowed down
Toxic by-products do not have chance to accumulate.
Source: http://curriculum.toxicology.wikispaces.net/2.2.5.2.5+Methanol
Pennicillin
Pennicillin, an antibiotic, works against disease causing bacteria
Stops cell wall cross-linking permanently Inactivates transpeptidase, used to build cross-linked
peptidoglycan layer in the membrane The cross-linking peptide chains have repeats of D-Alanine Pennicillin also has a repeat of D-Alanine-D-Alanine
E.Coli cells can not grow and die
Succinate Dehydrogenase Inhibitor
Succinate Dehydrogenase catalyzes the conversion of succinate to fumerate, an important biochemical reaction in cellular respiration.
Malonate inhibits this reaction competitively Used to find
active sitechemistry
Used to study inborn errors of metabolism
Non-Competitive Inhibition
Non-competitive inhibition: enzyme inhibitors prevent the formation of Enzyme-Product Complexes.
Inhibitors prevent the substrate to react and form into product
Non-competitive inhibitors bind to a site other than the Active Site
Binding causes conformational changes that change the tertiary structure of the enzyme
Thus, enzyme can not catalyze reaction
Non-Competitive Inhibition
Substrate
Non-competitive Inhibitor
Enzyme Active Site Complementary to Substrate
Non-Competitive Reaction
Since they do not compete with substrate molecules, non-competitive inhibitors are not affected by substrate concentration.
Many non-competitive inhibitors are irreversible and permanent, and effectively denature the enzymes which they inhibit.
However, there are a lot of non-permanent and reversible non-competitive inhibitors that are vital in controlling metabolic functions in organisms.
Cyanide Poisoning
Another enzyme found in cellular respiration is cytochrome oxidase, one of the most important enzymes in the electron transport chain of reactions that occurs in the mitochondria inner membrane
Here oxygen is reduced and 34 ATP molecules are made.
Cyanide Poisoning
Cyanide acts as a non-competitive inhibitor for cytochrome oxidase complex
Cyanide does not compete for the active sites of the enzyme because it has no similarity to the substrate cytochrome
Cyanide attaches to another site on the enzyme and disrupts the enzyme's shape.
This brings the electron transport chain to a halt No energy can be derived out of respiration Hydrogen cyanide inhibits metal-containing enzymes
in the body, such as cytochrome c-oxidase, which contains iron
Irons in Enzymes
Chemical catalyst are usually metals Many enzymes get their ability to
catalyze reactions due to metals found in the active site
One common metal used is iron Fe2+ that is found in a protoporphyrin ring
Ferrochelatase
Ferrochetalase inserts iron into protoporphyrin rings
Lead forms covalent bonds with the sulphydryl side chains of the amino acid cysteine in the enzyme and prevents catalytic activity
The binding of the heavy metal shows non-competitive inhibition because the substrate still has access.
Chymotrypsin
Chymotrypsin is an enzyme which hydrolyzes peptides bonds
In its active site there are three amino acids Histidine57, Serine195 and Asparagine102 known.
Hydrogen Ion Inhibits Chymotrypsin These amino acids allow for the substrate
to be cleaved. By lowering pH, amino acids in the active
site no longer accept hydrogen proton since Asp102 becomes protonated (hydrogens added)
Hydrogen ion acts as a non-competitive inhibitor by preventing catalysis but do not prevent the substrate from binding to the active site.
Biochemical Pathway
A biochemical pathway is a series of step reactions leading to a product
Enzymes lie in biochemical pathways There are specific enzymes for each
reaction step Metabolism is a sum of biochemical
pathways and is made of anabolic and catabolic processes
Need to Regulate
There are so many pathways that are incorporated in the metabolic system of the human body
An efficient process is needed to regulate the use of resources and ensure that only what is required is being produced or broken down
Enzymes can be regulated by the ability to be activated and deactivated when needed
Allosteric Enzyme Regulation
An allosteric site, a site away from the active site,can bind molecules to change conformation of the enzyme.
At the allosteric site for an inhibitor, binding of an inhibitor causes a conformational change such that the active sites of an enzyme are non complementary to the substrate.
An activator can bind to its allosteric site to open or improve the fit between substrate and enzyme.
Feedback Inhibition
In a biochemical pathway, by controlling an earlier step, the next series of reaction steps can be controlled
Usually the end product in a chain of reactions is an inhibitor of an earlier enzyme in the chain to stop the creation of more product
Process is self-regulating and cell resources are not wasted by making more product than needed
Feedback Inhibition Using an Allosteric Site
Regulation of Glycolysis
Glycolysis is biochemical process where glucose is broken down to pyruvate
Pyruvate is used in mitochondria in the process of aerobic respiration to derive ATP
Pyruvate kinase is the enzyme that converts phosphenolpyruvate to pyruvate in glycolysis
This enzyme is the third regulated enzyme of glycolysis
ATP and alanine act as allosteric inhibitors of pyruvate kinase
Feedback Inhibition of Pyruvate